If I charge my phone in my car is it “free”?
Posted by S_mawds@reddit | AskUK | View on Reddit | 280 comments
Ok first off I know no energy is free it come from somewhere, but in the scenario proposed when I charge my phone in the car is it free
The power is coming from the battery that in turn will be recharged via the alternator that’s powered by the engine using the accessory belt
This belt is spinning with the engine so wound be moving even if the phone isn’t plugged in so surly this charge would have been regenerated by the car anyway so I must be charging for “free”
Can some expert put me in my place and tell me why I’m wrong and this is making a difference and if your even smarter can you tell me the cost of this charging
Rh-27@reddit
Technically, no it isn't free.
What runs your alternator?
The combustion engine.
What runs the combustion engine?
Fuel.
nevynxxx@reddit
The question here is, what happens when the battery is full? Does the alternator stop turning? If the answer is yes, then you’re correct. If the answer is no, then what you are doing by charging is using energy that otherwise would be lost to heat. So it’s effectively free, because you’re wasting it either way.
Mikes1992@reddit
The alternator powers everything when the car is running (charging and electricals), because it's providing 14v and a car battery settles to 12.6-13v once the alternator stops so no current can flow out of the battery when the alternator is running, There's always a small amount of current trickling into the battery. The majority of the batteries life its close to 100% charge (ideally), car batteries aren't designed to be deep discharged and discharging below 80% reduces the lifespan and performance. There's a reason they usually need replacing if you leave something on and the battery goes flat. The battery serves one purpose - to start the engine. It can run a few auxiliaries without the engine running but it doesn't take allot to make the battery struggle to start the engine.
What allot of people don't realise is that alternator load (the resistance to turn it) varies based on the power it is providing. Get a basic dynamo motor, short the leads together and try turning it, because the leads are a dead short its extremely difficult to turn. Alternator/dynamo power isn't free.
StereoMushroom@reddit
The mechanical resistance of the alternator increases when you pull more current from it, making the engine have to work harder and burn more fuel. It doesn't turn more energy to heat if the electrical load is lower.
HankKwak@reddit
The alternator will continue to spin but power output is directly proportional to resistance on the belt so more power taken, more fuel needed to spin the belt.
Low load (fully charged battery), low resistance, high load (charging the battery or auxiliary systems), high resistance.
No free lunch here.
Loose_Reputation_356@reddit
The alternator never stops turning, that’s true, but It requires more engine power (fuel) to turn it under ‘load’. So plugging a device into the cigarette lighter demands more of the alternator, creating more load on the engine to turn it - and therefore increased fuel consumption.
You’d be surprised how your home energy bill is effected by leaving things like phones and tablets on constant ‘trickle’ charge - and although the difference in a car under way would be minimal, (more wasted energy through the drive train / subsidiary electrical circuits running full time) it still won’t be ‘free’.
VOODOO285@reddit
My god, read a book! Or was that a joke? It may still be turning but there’s less load on it so it takes less fuel to turn it, ergo…. Not free.
Rh-27@reddit
It won't stop turning.
The alternator will keep spinning because other systems also require power.
Your water pump and cooling system is just one of many examples.
nevynxxx@reddit
Yeah, let’s assume other loads are the same either way. There’s a point where your engine is doing the same work, either your phone is taking the juice, or it’s becoming heat/noise.
Probably negligible either way.
Rh-27@reddit
The alternator is simply not designed to stop turning.
The V belt/drive belt loops around it which is powered by the crankshaft spinning. Hypothetically speaking, if the battery was at 100%, the belt doesn't suddenly detach itself from the alternator so this is impossible.
A quick Google search says the alternator will regulate its own output and if there isn't a heavy load required to charge the battery, it lowers to trickle charge to supply just enough energy to keep things maintained.
But as I say, there are many systems in a modern ICE car that constantly require power to run.
elbapo@reddit
Does this voltage regulation therefore reduce magnetic resistance needed to turn the alternator (when power unneeded)? In which case its not free. Or does it convert to other forms of energy I.e heat - meaning its nearly free?
Rh-27@reddit
The former. The voltage regulator controls how much current flows to the rotor within the alternator that produces the magnetic field to produce electricity.
Therefore, charging your phone is not free. There is a minute cost but it's almost impossible to measure.
danieljamesgillen@reddit
So converse to the original answer it is actually free.
Rh-27@reddit
No. It costs. It's not free.
Phone plugged in to 12v = more current required = voltage regulator in alternator tells the alternator to produce more current = generates more electricity = more fuel.
danieljamesgillen@reddit
Does it mean more fuel use? Or does it mean when you press the pedal, less of the energy from the fuel burned goes to propulsion than otherwise? So you're still using the same fuel, just going a little slower?
Rh-27@reddit
More load on the alternator = more load on the engine = more fuel use.
SlackersClub@reddit
Correct me if I'm wrong but the fuel use will be the same. The gas pedal directly determines how much fuel is used (barring any modern computer interference).
If the load on the engine is higher because the alternator's magnetic resistance has increased, a higher proportion of the engine's energy output will flow to the alternator instead of propulsion. You would need to step on the pedal more by a hair to keep the same speed.
Ambiguous_comment@reddit
Think about driving up a hill, you'll need to depress the pedal more to maintain the same speed as you would on the flat.
This is because the engine is also having to output energy to raise the cars potential energy, as well as the standard energy required to offset air and rolling resistance.
The load of charging (transferring energy) to something via the alternator will act in the same way as the hill, the engine will be outputting extra power offset the load.
It's not normally noticeable because engines can produce a lot of power compared to standard device charging speeds. (100kW vs 100w), or ~1%.
You'll sometimes hear the idle revs change when turning on headlights or heater fans. This is the alternator placing extra load on the engine and the idle control taking a second to catch-up and feed in more air and fuel to keep the engine idling.
SlackersClub@reddit
Exactly so how does that contradict what I said? If you plug your phone charger in, everything else remaining equal, the revs will slightly decrease but the fuel consumption will stay the same.
Ambiguous_comment@reddit
That wasn't what I said. The revs at idle can decrease under an electical load, which requires the control system to open the throttle more to maintain the idle revs.
Focusing on what happens at idle makes this confusing as basically everything at idle is wasted (hence why stop-start exists).
I would focus on the driving up the hill scenario. If you're driving along and the road gets steeper, what happens if you don't increase throttle input? The car slows and stops. You have to command more fuel to keep the car moving and the engine turning.
The same goes for electrical load. When you plug a phone into charge, the increased torque required to turn the alternator to generate that energy requires a change in engine power output, which requires a change in fuel input.
SlackersClub@reddit
...to maintain the same the same revs.
The original question was whether a car would slow down and use the same amount of fuel, or keep the same speed and use more fuel when a charger is plugged in. To use your analogy it would be like asking, "if I go up this hill, will my car slow down or will it keep the same speed and use more fuel?" Everything else being equal, the correct answer is that it will slow down, because to keep the same speed you would need to depress the gas pedal and THEREFORE use more fuel.
Ambiguous_comment@reddit
In the fixed throttle up a hill scenario, less revs means less power, so without throttle input changes the car will eventually come to a stop as the load climbs and the revs continue to.
I think it's maybe confusing to think about revs in this situation. At part-throttle crusing conditions the fuel usage is mostly dependent on throttle opening. It's easier to consider the engine as a machine that turns chemical energy into kinetic energy at a fixed(ish) efficiency, with the power output controlled by the throttle. This allows you to think about the energy production and consumption in this system.
In your fixed throttle/power output scenario:
SlackersClub@reddit
That's a lot of words to just repeat what I said in the first place.
Ambiguous_comment@reddit
Confidently wrong, I love it. Have a good evening.
Rh-27@reddit
This.
elbapo@reddit
Yes but you go less far for same fuel so hence not free. Pretty cheap but not free
lerjj@reddit
But charging a phone at home is also a fraction of a penny per hour. Phones don't take that much energy to charge.
The question is would it be cheaper to charge your phone in the car, than to buy petrol from a petrol station, burn it in a reasonably efficient engine, driving a turbine to create a current that charges your phone
nevynxxx@reddit
Yeah, so there’s constant energy flow in, but different energy flow out electrically based on load. The difference will be heat.
So for OP’s q, no, it doesn’t cost you to charge your phone. You just heat your surroundings a little bit less.
Rh-27@reddit
Not quite.
We have two conditions here.
Condition 1 = alternator energy converts to heat = TRUE
Condition 2 = car battery is at 100% = never, because it's not designed to be = FALSE.
Therefore, it does cost to charge your phone.
I'm no engineer, I'm happy for someone to prove me wrong if I am.
nevynxxx@reddit
Yeah, that all makes sense. I’d be very surprised if 1 isn’t true. Seems like a lot of extra engineering for little gain?
FredFarms@reddit
It's rather a lot of gain actually. An alternator can have a maximum power output of a couple of kw, mainly so it can recharge the battery quickly from the huge load of turning the starter motor when you start the engine.
Having all of that power dumped to heat constantly would be a massive waste, equivalent to boiling a kettle constantly for no reason.
Rh-27@reddit
So condition 1 is TRUE, however, there is no excess heat waste which further disproves the point made above about free charging and reducing heat to the environment.
This is because the current the alternator provides to the battery when it's full is simply much lower than when it requires more current to charge the battery to "100%" (no such thing).
Therefore, the alternators voltage regulator determines how much heat is generated as a byproduct of converting mechanical energy to electronic energy proportionally.
JoeyJoeC@reddit
The alternator doesn't convert electricity to heat when it's at maximum, it simply has less load and thus less resistance. It spins more freely.
There's a voltage regulator which controls the load on the alternator to keep the battery at a nominal voltage. When it drops too much, it engages the alternator, when it's at the right voltage, it disengages it.
It absolutely does cost fuel to charge your phone since phone will cause the voltage to drop faster, and thus engage the alternator more, more resistance = more fuel.
devils_advokat_@reddit
The real answer
Throbbing-Missile@reddit
This is correct. Simple charging systems like those found on older motorcycles would just dump excess energy to a heat sink but for decades car alternators have a regulator that varies the current in the field windings to maintain a steady output voltage. Since the current generated in a conductor moving relative to a magnetic field is proportional to the strength of the magnetic field, and the strength of a magnetic field generated by current flowing through a winding is proportional to the current in the winding, by varying the field winding current you can vary the output current. Some simple solid state electronics can be used to monitor the charge voltage (determined by the current generated and the impedance of the load) and constantly adjust the field current to maintain a setpoint. This will constantly compensate for changes in electrical load (phone charging, headlights etc) and changes in engine speed (the other factor in the equation giving current in a conductor moving through a magnetic field is the speed of the conductor)
CatBroiler@reddit
A lot of modern alternators have a clutched pulley as well, so the alternator can be disengaged when suitable. Same goes for other accessories as well, like water pumps.
Rh-27@reddit
Thanks, I did some reading and my other comment on the same comment thread concludes this.
OmegaPoint6@reddit
Energy flow into the alternator isn’t constant. The larger the load on the alternator from all the electrical bits the more energy is required to turn the alternator.
dogdogj@reddit
This is the crucial bit that everyone is missing. If you've ever used a power tool plugged into a petrol generator, you can tell the increased electrical load results in the generator being harder to turn.
51onions@reddit
When the battery is fully charged, the battery will be taking less power from the alternator. This will mean that the overall load on the alternator is smaller, and the engine will have an easier time turning the alternator. In other words, the alternator therefore saps less power from the engine, and the engine can use less fuel to keep on turning at the same speed.
Fantastic_Welcome761@reddit
No. When the battery is full the alternator is easier to spin. So it requires less power from the engine.
SensitivePotato44@reddit
This is wrong, the energy being used to charge your phone comes from burning fuel that would otherwise be being used to move the vehicle. Charging the phone increases fuel consumption. Not noticeable for a phone but significant if you’re running aircon for example.
AutoPanda1096@reddit
A quick Google suggests this is not the case.
crankyandhangry@reddit
You are correct that charging your phone is negligible on the car battery and fuel consumption. The same is true of charging a phone in a home. Phone charge is pretty small relative to air conditioning or a washing machine or moving a car.
AutoPanda1096@reddit
Indeed it isn't noticeable. But neither is it free
AutoPanda1096@reddit
When more charge is needed there is more resistance so it has to work harder.
It is generally not noticeable indeed.
However, it is not "free"
Cam2910@reddit
Most newer vehicles will keep the battery less than full, so that it maxxing out and energy that could have been recycled getting lost is less likely.
Jimbob136925@reddit
Not necessarily. Many vehicle alternators are now fitted with a "Freewheeling Clutch Pulley"
Imagine a conventional clutch in a gearbox to some extent, it disengages the gearbox so that you can change the gear. The clutch pulley can disengage the alternator. So although the belt will continuously spin whilst the engine is running, the alternator itself does not turn, so does not generate any power, and reduces the load on the engine.
Itchy_Notice9639@reddit
Quick mention here, i think on Vw’s Bluemotion range the alternator has a electromagnetic clutch and disengages when battery is charged sufficiently, which puts less stress on the engines and therefore has a better consumption. I might be wrong, but from my measurements, with the engine on, the battery doesn’t always show 14.8 V (as in charging) but more like 12.3V, and if i put AC on, then it shoots up to 14.5-14.8 V to account for power usage
CarrowCanary@reddit
The alternator will keep spinning because it's attached by a belt to the engine's crankshaft. If one is going round, so is the other.
Rh-27@reddit
Yes, I also mentioned this on another comment thread last night.
Other users also pointed out that if the alternator doesn't have a heavy load, it will spin with lower resistance and therefore more freely.
So despite it being physically attached to the drive belt spinning it, the output of the alternator will still vary based on its voltage regulator .
iZian@reddit
On my car, I can see the 12V battery load, and I can see that, if it’s full and I’ve just used engine braking to cone to a stop where it’s put a load of amps to the battery, as I stop it actually draws amps from the battery for a short while (engine still running).
The alternator is still spinning but it’s providing less than the car needs, the battery picks up the slack because it’s full and then after a short time it goes to zero in or out of the battery, and then lift off engine brakes will put a load of amps to the battery again.
It seems to use the 12V battery as an energy recovery to let the car use less fuel afterwards for a short while.
I don’t like it because in imagining it’s putting a load of extra strain on the cell.
hellothere56734182@reddit
Most of the time yes.
But our 2 year old Audi shuts off the alternator when it decides for increased fuel efficiency/power
matthew47ak@reddit
Pretty sure the water pump is belt driven on most cars
Rh-27@reddit
It is.
Cooling system indirectly referred to the fan.
TheZZ9@reddit
When an alternator isn't producing power it needs less energy to turn it.
Think of it like a hand winch that you are using. As you turn the hand crank to take up the loose slack in the cable it is easy to turn. As soon as you take up all the slack and are actually lifting something it takes much more effort to turn it.
An alternator is the same. With no load it is easy to turn. Plug your phone in to charge and it gets slightly harder to turn, thus using slightly more petrol.
ZeroMocha@reddit
When a car screeches it’s usually because the battery or alternator is weak, the car is cold and with lots of electric things on and so the load on the alternator makes it so difficult to turn it overcomes the friction created between the belt and the pulley and screeches.
FunPie4305@reddit
Turn your high beams and fan and anything else electrical in your car to the max and you will see the revs increase slightly from idle. This is because the engine has to compensate for higher energy consumption in the car, the same thing will happen when charging your phone, albeit on a smaller scale.
ZeroMocha@reddit
Small cars with electric assisted steering dim the lights and/or the revs when you turn the steering wheel when stationary
ZeroMocha@reddit
From A level chemistry I remember that lead acid batteries are designed to need constantly charging. When the battery isn’t being charged, the lead creates a salt which is lead sulphate that begins to coat the lead plates (usually from the bottom) and when it collects enough to touch the lead sulphate being formed on an adjacent plate, this will cause a short. There are videos of people reconditioning batteries by taking them apart cleaning and adding the lead that was changed into a salt then put into the battery with fresh sulphuric acid. This is what I vaguely remember so some of it could be inaccurate. I just remember my chemistry teacher did a phd on something to do with car batteries or something
silentv0ices@reddit
The load on the alternator changes as the load on the alternator goes up the load on the engine goes up. It's never free unless you have a electric car on regeneration going downhill.
Whisky-Toad@reddit
No it’s not lol
You don’t get free energy
HardlyAnyGravitas@reddit
You do in my car. My car's alternator only charges the battery on the overrun - for example when you're braking and when there is no fuel being burned. In normal driving, the alternator doesn't put any load on the engine, so the battery is effectively charged for free.
Whisky-Toad@reddit
It’s still not free, that energy is a byproduct of inefficient driving.
You can argue all you want but you still had to use fuel to build that momentum. Ideally you should be driving without ever having to brake as that is truly wasting fuel.
Of course in the real works that isn’t really possible, so the system is just taking advantage of
HardlyAnyGravitas@reddit
Lol. It's not inefficient driving - it's normal driving. If you use the brakes you're wasting energy as heat. My car wastes less energy as heat and uses some if that to charge the battery
Obviously. If you didn't use fuel you wouldn't move. What a stupid thing to say.
Ok. This is even more stupid.
Some of us actually live in the real world - not in a world where cars can accelerate but never need to slow down.
I'm sort of glad you didn't finish that thought, because I know it was going to even more dumb...
613663141@reddit
Nobody is trying to break the laws of physics. They quite clearly were referring to energy which would have been spent anyway, but expended as heat rather than usable electricity.
FredFarms@reddit
That's not quite how it works. The alternator will be turning either way, but the force required to turn it will depend on what load is connected to it. So the engine will be working harder.
I remember finding an experiment showing this in a science museum at one point. You hand turn a small generator and have a light bulb you can turn on and off. It's really easy to get the system to spin with the bulb off, but as soon as you connect it you have to put much more effort in to keep it going.
Large-Fruit-2121@reddit
Right but the alternator load will be higher. Eg provide a higher resistance to turn for the engine
Snoot_Booper_101@reddit
The energy for isn't going to come from waste heat though - the system doesn't suddenly become more thermodynamically efficient just because you're charging your phone. The change in load on the alternator will make it slightly more resistant to turning, and therefore require a bit more power from the engine to maintain the same idle (or driving) speed that it would be running at anyway. That means a little bit more fuel being burnt; a negligible amount, for sure, but ultimately the phone charge is going on the car's fuel bill.
handtoglandwombat@reddit
Completely backwards. Gibberish.
It’s only free if you can charge without the alternator turning.
simiesky@reddit
The amount of electricity the alternator produces depends of the strength of current through its field windings, when it needs to produce more it ramps up the field current which increases the strength of the magnetic field, this makes it harder to turn so more mechanical energy and ultimately fuel is required. The opposite happens when there is less demand on it.
A car will always be using electricity for its onboard systems so it will always be generating. Plugging your phone in will increase the demand on it so it will use more fuel. A measurable amount? Probably not, but I would imagine electricity from your home to charge it would be cheaper if you were to calculate it.
Possible-Ad-2682@reddit
The battery is there to start the engine. Once the engine is running, the alternator supplies electrical power to the vehicle and charges the battery.
Alternators have controllable output, and are capable of pretty much maximum output at idle speeds. They just match the demand of the vehicle.
Prediterx@reddit
To be honest, if the electrical system isn't pulling power, then the alternator won't produce it.
Rather than any energy being additionally wasted, the engine will just use less fuel.
Take a diesel generator, if you run it at 90% it may only last 4 hours on a small tank, whereas at 10% it may run 10 because it's not burning that fuel to make electricity.
richdrich@reddit
So if you get an alternator don't connect it to anything, and turn it by hand it turns quite easily. Now put a load (or short) across it and try and turn it, you get much more resistance.
This should be (or is) a demo / experiment in school science.
wotsit_sandwich@reddit
This is a great explanation, and is also demonstrable with a wind up flashlight. It's easy to wind when you are just feeding the battery, but turn on the light and the effort required to turn the handle increases (by quite a lot)
Specimen_E-351@reddit
Some alternators do have clutched pulleys so that they do stop turning.
New_Line4049@reddit
The alternator doesn't stop turning, but what it does do is de-power its excitation field. An alternator or generator works by reletive motion between a magnetic field and conductor. You spin one inside the other. To get the magnetic field they pass an electric current through windings, this is known as excitation current, more current means stronger field, and a stronger field means more electricity is generated. Wait.... we're creating a magnetic field by passing current through a conductor, to induce current in another conductor..... but doesnt that mean that you'd get a second magnetic field from the generated current? BINGO! Yes it does. And more than that, that 2nd field is directly in opposition to the field you're deliberately creating, and the interaction of the 2 fields resists the spinning of the generator.
OK, so given all this we can control how much electricity a generator or alternator produces by varying the excitation current, that varies the current output but also how much resistance the alternator feels to spin. When there is no draw at all you don't provide any excitation and all the magnetic fields collapse. The alternator can keep spinning with only its mechanical resistance (bearings and such) but won't produce power.
Sorry-Programmer9826@reddit
It will keep turning but it will have less load on it. The battery is trying to slow the belt down while charging. Once charged it no longer applies that load so the belt runs freely
Classic_Mammoth_9379@reddit
The common response is one like yours, I'm half on board but half unconvinced. You say the battery is up to 100% and my understanding is that this is common, most vehicles driven for long distances regularly should see their batteries up around 100% which would suggest that there is excess power here. Nobody is syaing it's 'free' in the sense that it comes from nowhere or costs nothing to produce, the money is being spent on the fuel but it's got nowhere to go.
If I have solar panel sat in the sunshine exposed to a fuel source (the sun) but have nothing connected it produces no amps, if I connect a load, then it will consume the amps, so the difference in cost between nothing connected and a load is zero, nobody is claiming it's a magic energy source.
That said, I've had a small engined car where you hear the engine dip when you turn the AC on at idle. What I'm not seeing anyone here get to is the physics of it. In simple terms I'm expecting a coil spinning through a magnetic field, so I guess the load may change that magnetic field essentially adding resistance that's fed back via the belt to the engine? Even with that in mind, I still can't help but think that if I've been driving for 3 hours, battery is up at 100% and my engine is doing 4K RPM that there isn't already some 'excess' in the system? Or are we saying that combustion engine car with a 100% full battery goes faster/more efficiently than one that's having to charge a battery because it's only at 10%?!
Bladeslap@reddit
The output of the alternator is controlled by the voltage regulator (it's the reason for using an alternator rather than a dynamo, as earlier cars did, but why is a bit much for a Reddit post). That means the alternator only generates as much power as is required to charge the battery and run the electrical loads of the car*. Charging a phone will, technically, draw a little more power from the alternator and thus the engine but it's such an insignificant amount it's really not worth worrying about.
Air conditioning is different. In a car the AC compressor is generally driven by the same belt as the alternator, but unlike the alternator the AC pulley has an electromagnetic clutch so it can be engaged or disengaged from the engine. That's why you see the revs change.
*As you want the physics, the voltage regulator works by varying the current in the field coil of the alternator. As the field current increases, so does the output current. By matching the output to the electrical draw of the car the voltage is maintained.
Classic_Mammoth_9379@reddit
The AC point is interesting, thanks, it was mentioned a lot here but it always seemed to be a bit too noticable just to be 'another' electrical load.
I understand that the voltage needs to be regulated else it will be all over the shop when you change speeds and that's not going to be good for anything connected, still murky on the whole amps piece though and how there is never any excess available...
Bladeslap@reddit
On almost all internal combustion engines air conditioning is a mechanical load, not electrical. The fan is electrical but it's a relatively trivial amount. The compressor is the bit that needs lots of power and that's driven by the engine rather than the alternator, it's more efficient that way.
You can think of the voltage regulator like cruise control, but for voltage rather than speed. When you've got lights, heated seats, windscreen heaters etc. on that's like going uphill, so the voltage regulator increases the field current (like pressing the accelerator pedal). When the battery's charged and most things are turned off it's like going slightly downhill, there's not much power so the voltage regulator can ease off and reduce the field current. More current is available, it's just not needed. There's always some electrical load so the alternator is putting some power out whenever the engine is running.
(I've used current and power interchangeably, with voltage staying constant they're proportional)
rtuck99@reddit
It definitely isn't on mine because in the past I've managed to get a flat battery by leaving the A/C on while the engine was off.
Bladeslap@reddit
It's extremely unlikely that you've got electric air conditioning on an ICE car. Even on electric vehicles it's not driven by the 12V battery, it requires too much power.
rtuck99@reddit
Well, for what it's worth, before I had the flat battery, that's what I thought. However during the \~20 minute phone call which I had on a hot day in the parcel depot car park, the ignition was in accessory mode, the interior fan was blowing, the condenser fan was kicking in and out (it does this every \~20 seconds in a Honda Jazz if you leave the climate control in auto mode), and I was kept relatively cool. At the end of the phone call the car battery was flat as a pancake and the engine wouldn't even turn over.
Also I was driving my car to work every day a good 20 mile round trip, and the alternator is good so the battery should have been good for more than that IMO.
So even if the compressor isn't running, whatever else is happening, evidently that draw is apparently sufficient to drain the battery. Admittedly, if I had known the phone call was going to last as long as it did (which TBH I should have, given who was on the other end) I probably would have had second thoughts about having the A/C on, but honestly it didn't cross my mind and it was only after I tried to start the car that I twigged what had happened.
Ever since I have made sure that when I am e.g. stuck in traffic with the engine off, I take it out of A/C mode and I have not had any repeat of the problem.
Bladeslap@reddit
Ah, we may have had a bit of a misunderstanding. Air conditioning is part of the HVAC (Heating, Ventilation, Air Conditioning) system in a car, its job is to cool the air and it does that using a refrigerant system. To do that it needs a compressor, and that takes a lot of power and is driven by the engine via a clutch. There are other bits of the HVAC system (such as the fans) which are indeed electrical. I guess when you were talking about AC you meant the whole climate control system, I was just referring to the coolant part.
Obviously with the ignition on there are various other electrical systems on as well. Like you, I would have expected the battery to last longer than 20 minutes!
konwiddak@reddit
Hybrids have an electric motor for the compressor.
rtuck99@reddit
Mine isn't a hybrid and after u/Bladeslap's comment I did have a look and seems like compressor for my model are driven off the accessory belt. However even if the compressor doesn't run, seems like there is enough load to drain a standard 12v battery PDQ.
TBH what with electric motors being so ubiquitous these days it wouldn't surprise me if non-hyprid ICE cars also had an electric compressor.
Rh-27@reddit
As I say, the battery is never at a true 100% which is why it's illogical that charging the phone is free.
The battery reading may say 100% when it's removed from that car, in which case that's true.
But when it's in a running engine, it's in a constant flow or charge and discharge based on the demand of various systems that always consuming power via the battery.
Meaning, the alternator is constantly spinning and required to charge the battery... Which costs fuel.
OPs post was written as if the energy required to charge their phone was coming from a magic source lol and they wanted disproving.
Classic_Mammoth_9379@reddit
I'm not claiming expertise here on cars but I have some electronics knowledge, built my current DC solar setup myself so struggling to understand what the differences are, if any.
I don't understand this idea of the battery never being a true 100% and magically filling with electricity only when removed?! If I have a battery in a circuit, alternator spinning and able to generate 10A and a 5A load, then as far as I'm concerned, 5A is going from the alternator to the load, and 5A is going into the battery. Those electrons aren't simultaneously flowing in two directions at once (in and out) of the battery. When the battery is full then that alternator is powering the loads directly and (in my mind) has capacity for higher loads.
JoeyJoeC@reddit
There's a voltage regulator which keeps the voltage within a range, drops too low it will pull a load from the alternator which charges the battery, too high and it stops pulling a load from the alternator. The load is actually variable on most cars I believe.
When there's a load applied to the alternator, the alternator is harder to turn, the engine wants to slow down, to maintain the revs, it needs more fuel. When the battery is at a sufficient voltage and the alternator isn't providing power, plugging in a phone will discharge the battery faster, and so the alternator will turn on sooner to bring the voltage back up.
It's not free power, the power being used is ultimately putting a load on the engine so it needs more fuel.
Classic_Mammoth_9379@reddit
Where is this in the circuit? I get the idea that an alterantor rotating at different speeds will generate different voltages so the output voltage will need to be regulated. You seem to be talking about it in the context of charging though? Lead acid batteries really want to be charged with constant current for the bulk charging phase with the voltage slowly rising to target. When they hit the target voltage you want to switch to constant voltage (variable current) to help the internal cells balance and then maintain the charge Are you referencing that or something else?
By definition that surely the case, less load if the battery is already charged, more load if I've got the lights on and my stero on full blast.
Why though? Even when there is no load, the belt is still connected and turning the alternators rotor though a magnetic field isn't it?
gundog48@reddit
Think of an alternator like a reverse synchronous motor. The shaft is always spinning, that cannot change. But when there is a load of any kind connected across the coils, the shaft becomes harder to spin, almost like backpressure.
If there's no load, it spins freely, with losses only from friction. There is no magnetic field. But when a load is applied, it acts like a magnetic brake.
It's the same thing turbines in power stations are pushing against. There, if fuel consumption remains static while load increases, the frequency drops, they'd need to burn more to push harder and maintain frequency, only that is spread across the whole grid, because one underperformong generator adds more load to the whole network, and the generator will be 'held up' by the grid, effectively driven like a motor.
Shitelark@reddit
You Sir, are a knight of physics. Join me in my eternal battle with Lord Entropy! I will fight him to the very Heat Death of the Universe.
DippyDragon@reddit
Let's walk it back.
Let's say the phone battery is 3500 mAh, it's 3.7 volts (assuming it's lithium) so 3.5 Ah x 3.7 V = 12.95 Wh.
Our phone more than likely is 5 volts. The charger is 90% efficient working from a 12 V suplly. 12.95 Wh ÷ 0.9 = 14.39 Wh.
Some energy is also lost in the voltage control of the lighter socket (or usb supply) the battery and alternator (or equivalent depending on the powertrain type) runs at approximately 12V, but could be higher 14.6V is common alternator output. So let's call it 15 Wh required.
Now I'm going to skip the mechanical losses of the connection between the engine and the alternator but only because it's dwarfed by the inefficiency of the stem as a whole. As a very rough guide 65% of the fuel energy is lost as heat so only 35% is mechanical power. The connection to the alternator is part of that mechanical power output. So 15 ÷ 0.35 = about 43 Wh.
So that's 43 Wh of fuel to charge about 13 Wh of phone battery.
For petrol the energy content is approximately 9.7 kWh per litre. 43 ÷ 9700 = 0.0044 litres or about a teaspoon.
A teaspoon of petrol in the UK at 138 p/litre is about 0.7 pence.
Burning that much petrol would generate around 12g of CO2 which is easily within the measurement capability of a modern emissions dynamometer.
Ok cool. More than i was expecting, maybe ive done something wrong in sure the internet will correct me but not done yet...
The WLTP cycle has an average speed of 46.5 km/h. A phone typically charges at 15 W, 15 ÷ 12.95 = 1.16 hours. At 46.5 km/h thats 54 km. So the phone charging is 12 g over 54 km for 0.22 g/km.
In the EU the average over the WLTP cycle is 107.8 g/km.
0.22 ÷ 107.8 = 0.2%
Charging your phone in your car increases your fuel consumption by 0.2%.
Other random bits just for fun. 43 Wh is about 37 kcal, apparently a standard mars bar is 228 kcal. So it takes less than a bite of a mars bar to charge your phone in your car.
Somebody please out pedantic me by checking my math 😅 have a good evening.
tameroftrees@reddit
Thank you. I did A-level physics and gcse technology and was just scrolling and thinking “it isn’t terribly difficult to have a stab at actual maths on this”. But also I left school a few decades ago and I really just want to drink a cold beer and scroll idly through Reddit. So I’m not going to be checking your working - it all sounds like sensible assumptions and that good enough sometimes. Cheers
Ody_Odinsson@reddit
My only pedantry is directed at your use of "math". It's maths.
Scienceboy7_uk@reddit
But if the battery is full then the power being generated has nowhere to go other than as heat, ie waste.
konwiddak@reddit
The torque required to spin an alternator is proportional to the current you try to draw. As in, if you don't connect an alternator to anything it's much easier to spin than if you connect a heavy electrical load.
If you draw zero current then the torque to spin the alternator just drops to be the friction in the bearings, belt and maybe a small amount of electrical & magnetic losses if the controller keeps the windings energised.
Scienceboy7_uk@reddit
Why Is It difficult to turn an alternator when there’s no load? Using the logic describe it should have no resistance, or are you referring to subsequent/additional resistance due to inductive load?
konwiddak@reddit
I'm a bit confused at this comment! The alternator is easy to spin when there's no load.
S_mawds@reddit (OP)
Yes I get that but my point is does charging the phone use and extra fuel or reduce efficiency of the car
Djinjja-Ninja@reddit
Yes, a miniscule amount, but still yes.
Some beer mat maths incoming:
A 3000mAh battery is about 40,000 joules of energy.
A litre of petrol is about 32,000,000 joules.
To fully charge a phone battery it would take 12.5ml of petrol assuming 100% efficiency.
A petrol engine is between 20 and 40% efficient.
An alternator is between 50 and 75% efficient.
A phone charger is between 50% and 90% efficient.
Stack all of those losses up, let take the middle ground, so 1 x .3 x .6 x .7 that's about 12.5% total efficiency.
So to charge your phone it would be approx 100ml of fuel, or two large (doubles) shot glasses worth.
If your car does 40mpg, that's about 17km/l, so charging your phone is the equivalent of about 1700m, or just over a mile of range.
Nzuk@reddit
I’m curious, I have one incredibly inefficient car. It’s a lot of fun, but I typically only see 18-20mph (UK).
How would this differ with a 3l engine like this?
deathmetalbestmetal@reddit
Only 18-20mpg from a 3l? What is it?
Nzuk@reddit
Audi S5 2015 model, super charger probably helping those numbers! Along with a heavy right foot
ultraboomkin@reddit
My car has a 3.5L engine and I get about 20mpg
deathmetalbestmetal@reddit
18-20 from only 3 seemed low. My daily drivers are 4.6 and 4.3 and both of those can average 18-20 in mixed driving.
National_Ad7292@reddit
20mpg is half of 40mpg, so it costs you twice as much.
Somethingrandom787@reddit
*1.25mL, so your out an order of magnitude
Djinjja-Ninja@reddit
Shit, yeah you're right. I'll edit.
_Nefarium@reddit
Putting an electrical load on the alternator increases how much energy is required to turn it (plugging your phone in makes the alternator harder to turn), therefore more load is applied to the engine and more fuel is used.
scoschooo@reddit
more fuel is not used because you use the exact same amount of fuel needed to move your care to your destination. There is excess electricity being created and you are using that excess to charge your phone. In no way are you using more fuel with your phone plugged in than with it not plugged in. You complete your trip using the same amount of fuel.
dkech@reddit
Yes, charging the phone uses more fuel. The alternator will resist spinning more when it is charging your car battery so your motor will use more fuel to maintain the same speed. The difference will obviously be too small to detect, but the fuel cost will likely be more than your electricity cost at home for the same charge.
Visible_Account7767@reddit
Yes, using the AC also uses more fuel, the ac or phone when on charge requires more energy to turn the AC compressor or alternator.
Have you ever used a petrol generator? When you connect things like drills etc, when you switch stuff on you can hear the noise of the generator charging as its doing more work to generate the power
Wild-Individual6876@reddit
Yes, same as putting your radio on, lights on etc
louwyatt@reddit
Despite a lot of people putting a lot of effort into their answers, they are wrong. The answer is it depends on how much electricity you are using in your car and the minimum your alternator can put out.
So, given the right circumstances, it's possible that it would be free. However it's incredibly likely that it will cost a negligible amount
Rh-27@reddit
Yes, it does.
Logically speaking, the possibility of it not costing you is illogical based on my comment above.
It'd be nigh impossible to even calculate the true cost to you as the owner of the vehicle.
wasdice@reddit
Yes it does
TheRisingPandas@reddit
Damn, I was hoping you would slam this down with a kwh vs MPG full analysis.
Rh-27@reddit
Haha. I think at least two people have tried to show the true cost way down in the comment threads I read last night.
Both have so much room for error due to too many uncontrollable factors, mainly around efficiency of engines, alternators etc.
Simply nigh impossible to calculate.
Haggath@reddit
Nailed it!
RichBristol@reddit
But almost free
Rh-27@reddit
It's only marginally more expensive than charging via wall socket. We're taking decimal point differences probably.
Theobliviouslizard42@reddit
r/theydidthemath
BrotoriousNIG@reddit
What is the mechanics of this, in terms of how the increased load requirement is met by the mechanical turning of the engine? We can observe that the revs increase when increasing the electrical by doing things like turn the airconditioning on and your engine needs to work harder to do its main job of propelling the car. The effect is so pronounced that a friend of mine refers to turning the AC off in his 1.0L Fiesta as “sport mode”. Without the complication of feeding an alternator, an increase in revs results in an increase of wheel speed, but that doesn’t happen when we need to feed the alternator—the opposite happens. Is there some sort of diff in play that directs the required amount of mechanical energy to the alternator?
elbapo@reddit
I'm asking a question/clarification on this as opposed to be all akshually.
But- in the scenario where the battery has a capacity of fully charged it can reach - does the alternator still spin when it's at 100%? My point being, should the phone charge take the battery down to 95% of capacity- the alternator would then top it up using its spin. So without the phone being charged, this potential energy is simply wasted. Or does the alternator turn off at full charge?
If it stays operating and just diverts the energy (i dunno where) when battery is fully charged this would make the phone charge much closer to being 'free' (albeit not fully). So the phone being charged provides an opportunity to store the energy produced versus it being wasted. Or does it switch off its magnetic resistance when full charge is reached.
I don't know I'm just thinking out loud.
konwiddak@reddit
The effort to spin an alternator changes based on electric power demand.
The alternator is easy to spin when little or no electrical power is being drawn from it, and it's hard to spin when a lot of power is drawn.
It doesn't need to divert the power, it simply doesn't produce any excess power.
Rh-27@reddit
The alternator has a voltage regulator which controls how much current it supplies the car based on load. The alternator powers the car and charges the battery simultaneously, if required. Until the battery reaches 100%, the alternators reduces the current it supplies the battery to a trickle charge to prevent overcharging or damaging it but it still powers everything else electronic in the car.
The alternator is always running so long as the engine is running. The voltage regulator controls how much current flows in to the rotor.
The more rotor current = stronger magnetic field = more electricty = power fuel consumption.
There is no excess waste. The alternator will generate as much current as the load is required from the car.
dadaddy@reddit
This is the right answer - but I can have a slight go at some of the maths to give you an idea of how terribly batshit bad it is (and I'll say - your phone uses so little power it's not worth thinking about)
Petrol in this case is the primary energy source - the best purpose built generators that I've been able to research for a recent project were able to extract about 3kwh/litre of fuel
Assuming a cost of £1.20 per litre - that gives you a cost of about £0.40/kwh
More interestingly an iPhone 16 has a battery capacity of 13.84wh - 0.01384kwh - so that's like 0.5p to charge your phone in the car (negligible) at absolute best case scenario
Buuuuut without even thinking about loses from the engine doing a bunch of other work - we know that energy from the wall is like £0.3/kWh - so it's going to be cheaper to charge at home
But more importantly how can we charge our phones for free - get a solar panel power bank
Energy cannot be created or destroyed - only converted. In this way we know that no matter how we charge our phone it's going to cost something but generating energy in a 0 cost way (ignoring capital cost) is the only way we can get it for "free"
However, assuming a worst case scenario of 1p/day - given an average cost of £25 for a solar power bank it would take almost 7 years to break even charging your phone from empty to full twice per day.
TLDR: you're overthinking this, charging your phone costs fuck all
ShortGuitar7207@reddit
It’s utterly negligible, compared with the fuel used to move the car, power the windscreen wipers, heaters etc. So it’s effectively free as you’d have a great deal of difficulty measuring the actual increase in fuel as it’s likely to be a few millilitres in a 50l tank.
Rh-27@reddit
Your statement is technically incorrect. Even if it's negligible, which I agree it is and stated so, it is still costing you something.
endo55@reddit
Some cars can indicate fuel use of heated seats, Aircon, demisters etc . It shows it as liters per hour under convenience costs.
DefinitelyARealHorse@reddit
“In this house we obey the laws of thermodynamics!!”
CarrowCanary@reddit
Anyone who says you should shut the door/window because it "lets the cold in" is instantly thrown outside.
MonkeyboyGWW@reddit
Turn the aircon on when using an older car and you will know your engine needs to work harded
w3woody@reddit
To fully charge your iPhone you probably use around 13 milliliters of gasoline, a little less than 3 teaspoons. You're probably losing that much gasoline (or even more) if you leave your car parked outside on a hot afternoon due to evaporation and vapor loss.
Trifusi0n@reddit
While this is true, it also means that it’s more expensive to charge your phone from your car than at home. Even so, the cost is basically negligible.
highstreethellcat@reddit
Depends….
My 15 yo bmw that I sold 2 years ago converts kinetic energy to battery charging (start stop) so depending on how much start stop driving you do and the battery requirements. If the battery requirements are exceeded by the energy conversion the phone charging could be free and even reduced breaking maintenance costs.
Bladeslap@reddit
The battery isn't constantly charging and discharging. Once the engine is running the alternator supplies the current required to power the car's electrical systems and charge the battery. Once the battery's charged there's no more current in or out of it unless the alternator is unable to cope with the electrical load.
Rh-27@reddit
I thought the same, however the alternator regulates its voltage to continue a supply of current to the battery. A car battery is never full for long, so it's a balance of regulating the voltage of the alternator to prevent overcharging and damaging the battery.
Bladeslap@reddit
I'm afraid your understanding is wrong. Once the battery voltage reaches the alternator's output voltage there's no potential difference and therefore no current flow. I operate vehicles that have an ammeter to show what the current flow in or out of the batteries is. It's a cause for concern if the current isn't 0 within a couple of minutes of starting the engines. (They actually trickle charge at <3 amps for a while longer, but that's just down to how batteries charge. There's no current drain from them until the engines are shut down)
Rh-27@reddit
Thank you
S_mawds@reddit (OP)
Didn’t see the end of your comment that’s what I thought I was just curious
Firm_Environment_808@reddit
Only answer.
Alarming_Repeat_4016@reddit
IMHO, it’s practically free, but because the engine in cars with alternators is combustion, it means it’s not free because you have to pay for fuel. But, that’s also like saying a hand crank dynamo isn’t free because you have to eat… (it’s a free gym)
Surasonac@reddit
No. Take the car battery out of the equation because it's not actually doing anything when the engine is turned on. The alternator is what's powering everything in the car, like the ECU, lights, ignition coils etc. If you increase the electrical demand on the alternator, it will be harder to spin adding addition load to the engine. As a result, the engine uses more fuel.
Thr0witallmyway@reddit
'At no extra cost' might be the correct term.
EEPY-BABY-102@reddit
An electrical generator (such as an alternator) generates electricity by slowing down the spinning shaft that is powering it. The increase in electrical energy that the generator is producing is caused by a decrease in mechanical energy of the generator shaft.
I'm not familiar with engine architecture details, but if the alternator's "generator shaft" is spun by a belt, the alternator will not slow down the accessory belt as much when it is not charging the battery (i.e. if generator is not in use) compared to if it's not charging - because the generation process specifically slows down the engine, it's not just the mechanical losses in the gear/pulley systems.
If you use more electrical power you'll therefore be using more fuel to speed the engine back up as the increased use of the generator is slowing the engine down more than if you used less power.
beavertownneckoil@reddit
I would want to assume it's cheaper to charge your phone in your house. Because otherwise why don't we all have car engines stuck to the side of the house powering it rather than it be hooked up to the grid if it's not cheaper? But I seriously don't know and I'm not the type to work it out
StereoMushroom@reddit
Yep you're exactly right. Petrol is a relatively expensive energy source, and cars are very inefficient electricity generators
beavertownneckoil@reddit
Aye, thought so hanks for confirming
lxgrf@reddit
No energy is free.
But some energy is small enough not to matter.
StereoMushroom@reddit
Heating in a car is free
VanderBrit@reddit
There’s no such thing as free energy. That would break the laws of physics.
StereoMushroom@reddit
But some energy is there whether or not you use it, like the engine waste heat which you can use to warm the inside of the car at no additional cost. Yes you've paid for it, but you have to pay for it if you don't use it too, so the heating is effectively free.
OP is asking whether electricity in a vehicle is like that, the answer to which is no. Using more electricity will mean more fuel is used. You pay for it directly.
VanderBrit@reddit
Yes, I understand how vehicles generate and consume electricity
HardlyAnyGravitas@reddit
Free energy doesn't break the laws of physics. Energy from the sun is free.
VanderBrit@reddit
Well obviously I wasn’t referring to monetary cost. I mean you can’t get energy from nowhere or from nothing. Any energy you consume comes from a source. It can’t be magicked out of nothing.
HardlyAnyGravitas@reddit
How does that relate to OP's question? Nobody is claiming the energy is coming from nowhere. The question is whether it costs you anything.
If you roll your car down a hill, the alternator is generating free energy. It's coming from gravitational potential, but it's still free.
ItsDominare@reddit
Sure, but unless that car was built in a factory at the top of said hill, all you're doing is reclaiming some of the energy you spent getting the car up there in the first place.
HardlyAnyGravitas@reddit
Yes. That reclaimed energy is free because you had to get the car up there in the first place. You can choose to reclaim the free energy on the way down or waste it as heat, for example.
ItsDominare@reddit
If you have an apple which I steal from you, then the next day I return it to you, have you just received a free apple? No, you're just back in the same position you were in before we started.
...except of course since no conversion is perfectly efficient, what you're getting back is more like a quarter of an apple.
HardlyAnyGravitas@reddit
The analogy is wrong.
If I sold you an apple and you gave it back, then I would have a free apple.
doctorgibson@reddit
HMS_Hexapuma@reddit
There was an episode of Top Gear where they were curious if the always-on LED running lights on Volvos used more fuel to compensate for the additional electrical drain. So they got in touch with Volvo who did a whole bunch of mathematics and said that the amount of extra fuel used to run the lights was so tiny it was lost within normal driving style variations. Those are high power LEDs and so may not use as much power as a phone charging but the numbers won't be too far distant.
Minor additional point, you don't draw power from the battery to charge your phone unless you charge with the engine off. You only use the battery to start your car and run anything that runs while the car is off. The moment you start the car, the alternator becomes a generator and amongst its jobs is charging the battery. You're drawing power from the alternator.
Tl;dr: charging your phone in the car will make you use more petrol, but so little extra petrol that you wouldn't be able to tell.
StereoMushroom@reddit
This answer doesn't check out to me. You will have driving style variations on top of the effect of the lights; it's not like the two will cancel out. An economic driver and aggressive driver would each have slightly lower fuel economy with the lights.
dolce-ragazzo@reddit
A little extra petrol, yes, and therefore a little extra cost.
However, charging your phone at home is cheaper.
The cost to charge in your car is difficult to quantify. The cost of charging your phone at home is less than a penny: 0.02kWh battery @ 50p per kWh (these numbers are rounded up for simplicity)
In summary: charging your phone is always free if, like me, you consider <1p to be effectively zero.
UnhappyAttempt129@reddit
If there was no load on the electrical system the alternator would provide less resistance to the engine thus costing less fuel. When there is a high electrical load the engine has to work a little bit harder and use more fuel. For example if you sit still in your car and turn the steering wheel you might hear a slight change in engine sound or more commonly you might notice a slight change in engine sound when you put the aircon on. Put simply its too small an amount of energy to make a difference.
StereoMushroom@reddit
Power steering and air con are often driven mechanically by the engine, rather than running on electricity btw. Though newer cars have been moving more towards those functions being electric
tzrr125@reddit
It is ‘free’ if you don’t keep the engine running just to charge the phone. Alternators don’t have clutches, excess current generated is lost as heat via the voltage regulator
bob-starr@reddit
After @rh-27 ‘s comment,
Here’s a very very rough estimation of how much fuel per hour charging a phone may use;
Let’s use an assumption of; It’s a 30whr providing charger, The charger is 90% efficient at power delivery Losses from the alternator, to the battery, to your fuse board, to your 12v 120w socket is 12%, Your engine is a modern efficient turbo charged petrol engine @ 30% efficient.
So the charger will be pulling approximately 33whrs, that’s because the charger is giving your phone 30whrs of electricity. The additional 3w is wasted heat from the electronics inside the charger.
This is pulling about 2.8 amps from the socket. Providing a 9v ~3amp charge to the phone, assuming your phone is charging at 9volts.
So the alternator may be putting about 37~38watts of extra “strain” on the engine. After the efficiency calc of “petrol to electric”, this now at almost 50whrs of petrol.
One litre of petrol contains aprox 8~10kwhrs, depending on the quality of the fuel, but I’ll assume it’s the “worst” In theory, you should be able to provide at least 160hrs of charge to a phone, on one litre of petrol.
However, your phone if it is sapping 30whrs from the charger, it will be sapping about 6.25mls of petrol per hour from the engine. Call it a teaspoon 🤷🏼♂️
Every day if your commute is an hour long, that’s about 2.3L of petrol a year, ~£3.01 @ £1.309 per litre.
Charging your phone for an hour every day, sapping 33whrs from the socket at home though at the current July price cap, costs about £3.10 a year. So it may actually be more cost effective to charge your phone in the car.
Due-Entertainer-2812@reddit
Fill your tank up and drive till it’s empty. Fill it up again to drive home and charge your phone.
The distance you’ve got left to walk is your “cost”.
If you get home with fuel then your car is paying you to charge your phone but this experiment has cost a tank of fuel.
Embarrassed-Whole989@reddit
I charge it in works lorry it's free then at (at least for me) the cost is probably less than 2p an hour I'm sure my work would rather they'd be able to contact me and use a satnav ok my phone lol.
Tinbum89@reddit
Free? No, it costs money to put fuel in the car….the engine runs on that fuel, the engine that is required to charge the battery…so no, it’s not “free”
stevononline@reddit
If it is free, don't let the government find out. They'll find a way to tax us
BrightFleece@reddit
You're paying for it in your petrol bill not your electricity bill
If you're using energy to charge your phone, you're loosing some which would otherwise have moved your car
GrapefruitHuge6732@reddit
Have you ever had an older car where you put on your lights windscreen wipers and radio all at once and your revs dip a little bit then recover? That’s the drain on the battery and alternator being compensated for and the current being drawn then requires more fuel to maintain those revs. As you’ve said no energy is free. The extra energy it takes is approximately the capacity of the battery you’re charging plus a little extra for heat loss etc.
Old_Fant-9074@reddit
I agree with what you have said but it’s not the whole picture as, 1) the energy input obtained from motion (eg free wheeling down hill) will still likely have the engine running even if idle, 2) the engine is required to pull the car up the hill in the first place. The battery is a store and not a generator of electricity, likewise the down hill is the release of stored energy obtained from the work done to get up the hill the power has all come from the fuel. If you turn on the radio the energy has to have come from the fuel even if via the battery as a store or from the alternator outputting, I also think the alternator needs some battery power to engage its clutch if it has one or operate its circuits to know how much load to put out this again has to come from the battery and so fuel. Now if you had a solar charge, or plug in hybrid okay, but a fuel only car, well that’s where the power comes from. (Well it call comes from the sun really right )
Pircster38@reddit
Charge it at home it only costs about £0.05 🤔
Flat_News_2000@reddit
Only if you're charging specifically while driving somewhere you already planned on going. Otherwise it's more expensive than just electricity in your home.
makebeansgreatagain@reddit
It puts a tiny extra load on the alternator, which means the engine has to work minutely harder to turn said alternator, using a fractional amount more fuel. That's where the energy comes from, but that said, it's so little that it's completely negligible.
VodkaMargarine@reddit
A good example of this is air conditioning. You might think that since the air con in your car also runs off the engine it is also "free" but that's much more obviously not the case. If you have a car that tells you the MPG then try turning air con on and watch that number.
one-man-circlejerk@reddit
Whereas heating actually is pretty close to free, since it pumps what would have been waste heat from the engine into the cabin
tsunx4@reddit
Is it though? The heat is byproduct of combustion which is biggest inefficiency of ICE (This is the reason why turbocharged engines are classed as more efficient compared to the NA ones). Also the engine must drive the water pump to circulate the liquid and alternator to turn the blower fan inside the cab.
I know I'm nitpicking here, but technically nothing is free, even opening your windows because it will create enough drag at certain speeds to put more load to the engine.
Appropriate-South314@reddit
Yes it is basically free. You will notice no difference in the MPG in an ICE powered car with heating on vs heating off.
The mi/kWh on an EV is absolutely decimated by using the heating.
wimpires@reddit
An iPhone 16 Pro Max has an 18.17Wh battery. If you managed to fully deplete it 2 times a day that's 13 kWh per year or about £3.30 a year in charging costs on home electricity.
anchoredtogether@reddit
A litre of petrol has about 9kWh of raw energy, which will be about 4kWh of engine energy, so maybe 3kWh of energy into the phone.
So 6 litre of petrol will cost you £1.33, making about £8 to charge in the car.
m---------4@reddit
More like £4.50, charging batteries isn't 100% efficient
quite_acceptable_man@reddit
Everything that draws power puts extra load on the alternator, which in turn puts extra load on the engine. Things like air-con, or heated seats etc. put quite a load on and increase fuel consumption. Charging your phone will put extra load on the alternator, and in turn extra load on the engine, but such a negligible amount, it would be pretty much impossible to measure the extra fuel consumption.
So while not technically free, it's as good as.
nova75@reddit
Load on the alternator increases load on the engine. So, not free. But minimal. Very minimal due to the energy requirements to change.
hypercrypt@reddit
The electricity comes from the petrol. The alternator spins anyway but it takes more energy when there is a load (or a higher load) to spin it. But, the amount of energy in a phone battery is very small, an iPhone 16 Pro has a ~14Wh battery, so charging it at home (~30p/kWh) costs less than a penny, so while the petrol usage will go up a tiny bit by plugging your phone in, it’s not a lot of energy it’s using.
Annual-Cookie1866@reddit
r/theydidthemath
hallerz87@reddit
Where does the energy to power your car come from? The petrol/diesel/electricity you put into it. The car can't create energy, it can only spend what we put into it. Simply put, if you're paying for petrol/diesel/electricity, your phone isn't being charged for free.
josh50051@reddit
Basically but ask yourself what the cost of charging a phone is . Also already negligible. £0.002 yes that's 5 full charges per 1p
I'm almost certain it costs less to charge at home when you consider the draining on the car battery.
fantasticmrsmurf@reddit
Unless you get your fuel for free, no, technically not.
UHM-7@reddit
Cannot believe that people like this are walking around freely, breathing the same air as me
Admast79@reddit
If you want free charge you need to charge your phone at work or at friend house :)
Old_Fant-9074@reddit
It costs fuel to turn on the radio. As the only source of power is from the fuel.
HardlyAnyGravitas@reddit
Not true for all cars.
The source of electrical power in a car is the battery. The battery is charged from the alternator. The alternator doesn't need fuel to turn - it just needs motion.
In my car, the alternator is (normally) only engaged when the car isn't using fuel, such as when you're braking, decelerating or 'coasting' downhill, for example.
Hoopyloopy111@reddit
I charge mine in a work van. Therefore definitely free. Only have to charge once a week at home
EVRider81@reddit
Compared to the amount of money/energy being wasted by a petrol engine as heat, you could say charging your phone is free..
eelam_garek@reddit
If you own an EV and you charge the car overnight on a cheap tariff, then charging your phone in the car after that is not far off free. You're talking pennies.
The traction battery still charges the 12v battery which then charges your phone and does the various other electrical things in the car (lights, wipers etc) but because it's cost you a few quid to charge the car up, that cost filtering down to you're phone will be tiny.
It's not exactly costly in an ICE vehicle either - I would say for either it's not going to hurt you much financially...
teeeeeeeeem37@reddit
Charing your phone is as good as free anyway on a day to day basis. Electricity in the UK costs about 25p/kWh. The biggest laptop battery is 0.99kWh (due to rules about barriers on planes. Charging your laptop costs about 2.5p. A phone battery is closer to 0.1-0.2Wh or 0.25-0.5p. That’s less than £2 to charge your phone once a day for a year.
Theoretically if you were freewheeling down a hill with the engine off but in gear and the alternator was generating electricity it would be free in terms of fuel usage, but a phone drawing 40w from a car that is likely producing minimum 10-20kW when maintaining speed, and 50KW or more then accelerating, it’s negligible.
Teaofthetime@reddit
No, but the cost would be very small as it would be from a mains outlet too.
sssstttteeee@reddit
When I go downhill in my electric car it is free as the drive motor recharges the battery 😊
sammy_conn@reddit
No, but if you connect a small wind turbine outside the car then it can charge stuff up for free as it generates its own electricity independent of the vehicle.
JohnCasey3306@reddit
If somehow you're getting sufficient motion from your car without paying to power it then maybe yes, but please let me know the physics cheat code you've found.
Winter-Ad-8701@reddit
Whenever you charge the phone, it adds a small extra load to the engine, so no, definitely not free. It's harder to turn a generator that has a load than one with an open circuit.
Watch this, the generator is easy to spin when the bulb is disconnected" https://youtu.be/fttNmcWNFFQ?t=130
Paulsowner@reddit
If you did not buy the fuel it's free, but even when charged at home the cost is miniscule, less than a penny.
If you done this every day for a year, you would save less than £3, 2 years you may be able to afford a coffee
10b0b@reddit
In this sub we obey the laws of thermodynamics.
Go to your room.
ChickenKnd@reddit
I mean technically by using it you burn more fuel, but like you’ll never notice it
Available-Ear7374@reddit
As other's have said, no it's not free Here's some rough maths:
It's not that difficult to measure the cost.
say we're delivering 1kW, and lets say we charge something for an hour (this high rate is so we get kWHr which means we can compare to domestic electricity)
Now lets be generous and say the incremental efficiency in the alternator is 75%, that's about as good as you can get today
So now the engine needs to produce an additional 1.33kW.
A modern car engine will be operating at about 30\~35% efficiency if it's petrol, a little better if it's diesel, yes engines can peak at higher efficiency but tend not to during steady driving, which is the typical case.
So we need roughly 4kW of power into the engine
4kW for an hour is 14Mjoules
14Mjoules of petrol is about 0.42 litres at 34MJ/litre.
Our petrol is in the region of £1:35 a litre so that's about 57 pence.
which should be more than double what you'll pay per kWHr at home.
Equally given the low energy requirements of a phone battery it's doubtful it would be noticeable even if you did this every day.
Bulky_Dog_2954@reddit
I think its time for bed for me....
kettle_of_f1sh@reddit
If you could make free energy, trust me, you’d be a very rich person.
DifficultConcept9832@reddit
No, it's not free, yes the engine is spinning, battery charging etc but the more you draw from the battery by using power the harder the alternator works and the more load it puts on the engine therefore using more fuel.
ARobertNotABob@reddit
Lots of perspectives here, but only one matters, yours. Yes, the charge is free because you already have the engine running for another reason (transporting you A to B), and that task is not impacted by the energy going elsewhere, like your phone.
MyAccidentalAccount@reddit
No your car is using extra fuel to drive the belt which charges the battery.
It's negligible though.
welsty2003@reddit
The cost is pretty much negligible, but no, it isn't free.
The engine will work a tiny tiny bit harder to power your phone charger but compared to the energy needed to move the car and all it's other power consuming things like AC, de-misters and the stereo etc. The power used to charge a phone isn't even worth considering.
Being a total geek and having studied physics at uni, (I wanted to know for myself too!) I thought I'd try to quantify it for you.
I used Google's Gemini to get some rough figures for energy used by a car on a 1 hour journey (roughly the time to fast charge a phone), and also the energy stored in a phone battery. It worked out that the phone used 1/10000 of the energy that the car did. Cost wise it worked out at about 0.08 pence in UK money.
Yay!
Unhappy-Research7407@reddit
A solar panel on your car would be essentially free after the initial. Investment
Spacecowboy947@reddit
Bro next post is going to be about his perpetual motion machine
Cynis_Ganan@reddit
No, but also, yes.
The alternator always turns. And the more it has to power, the greater the resistance on the engine.
If your battery is fully charged or you are going downhill, that power is wasted (mostly as heat). Charging your phone is free.
If your battery is running other things (lights, radio, AC, heated seats), then you are burning more fuel. Charging your phone costs gas.
I'd say that all in it probably approximates to being free. The drain is so small that you won't notice it.
That said, if you have a smart meter, go to your circuit breaker and turn off all power to your house one switch at a time. Take your smart meter reading. Turn on one room, and make sure all your other devices are off. Fast charge your phone from flat in that one room. Take your smart meter reading. Charging your phone off your mains power also approximates to free.
Daveddozey@reddit
A typical phone has a 10Wh capacity. A lite of petrol will generate about 10,000Wh.
Electricity at home is about 25p per kWh, or about 0.25p to charge a phone. Efficiency is near enough 100% for a magnitude calculation (phones vary, some are upto 15W)
The engine stack is about 30% efficient and altemrator about 50%. 1 litre will generate 10kWh and cost £1.30. After efficiency that’s £1.30 for about 1.5kWh so £1/kWh, so charging a phone costs about 1p of fuel.
myxcatsxonxfire22@reddit
Charge it at work. It's free then 😉
Annual_History_796@reddit
If you don't pay for petrol or any car maintenance then yes, it is free.
Otherwise no.
Visual_Stable3692@reddit
No, you place a miniscule extra load on the alternator making it harder to turn so use a miniscule amount of extra fuel - but you got me thinking.
The thing that you do get "for free" in a petrol or diesel car, is masses of waste heat - absolutely buckets of it. Some of it gets just vented out of the exhaust as hot gas, some used to heat the cabin air, and the rest heats up the air moving over the radiator and is completely lost.
This extra heat costs a whole load of fuel to generate.
Why not try to recover this lost energy and use it to power electrical systems / charge a battery (in the case of hybrids) ? does any car manufacturer do this?
Waste_Vegetable8974@reddit
Once the battery is fully charged the power is effectively delivered directly to the devices using it. The battery sits at the same voltage as the alternator (alternator voltage needs to be higher than the battery voltage for charging) in a condition called 'floating'.
buckwurst@reddit
ICE or EV?
grekster@reddit
Awesome, problem solved
No, as you "already know"
Yes but, to put simply, the more electricity the alternator is trying to supply the harder it is to physically turn. This means the engine itself has to work harder to turn it and so consumes more fuel.
This is the same reason why say running your aircon or your lights isn't free either. The engine has to do more work when it is on and so uses more fuel.
This principle is also how regenerative brakes work. It's harder to turn the motor shaft when the motor is recharging an EVs battery and so this slows down a rolling car.
Weirfish@reddit
For what it's worth, charging your phone is probably close to free anyway. The average phone needs 5 to 10 watts for 2 hours, so 0.01 to 0.02 kWh, which is ~0.25p to ~0.5p. Note, that's fractions of a penny.
BarNo3385@reddit
No, but it's very close to it.
Assuming you aren't driving an electric car but an ICE one, the engine is already suffering the friction/energy loss that would power the electrics of the car. If you have everything turned off (no lights, no air con, no heated seats, no phone charged etc), its just inefficient.
As you turn things on more of that energy loss is converted to electricity rather than just heat and therefore the efficiency goes up.
The other way to see this is from the car's perspective you are already driving round with all the electrics on maximum, so it doesnt get worse when you actually turn things on.
To your question therefore, its not that charging a phone is "free" is more like you are already paying the cost whether you do it or not.
International-You-13@reddit
Technically, no, it isn't free, but the power consumed is so small that it will be masked by other inefficiencies in the combustion engine and charging system.
AdCharacter1715@reddit
Is it free ? Jeez. What makes the battery charge ? The alternator. What makes that move? The engine. How does the engine move ? Fuel. Is fuel free? NO !!
anoamas321@reddit
I mean the cost of charging a phone is pretty negligible so why care?
DazzlingClassic185@reddit
Nothing’s ever free, but you could calculate the cost of charging, and it would come up as bugger all squared, so it might as well be considered free. Especially if you’re charging in someone else’s car!
stabdarich161@reddit
Wow, what a silly question
Educational_Pin_1455@reddit
Cmon bro.
Fuel
ArithonUK@reddit
Internal combustion engines are hopelessly inefficient, so the "loss" of charging your phone is relatively little, as around 30-40% of the energy from your fuel is lost in heat & noise anyway.
But no, it's not free. You're paying (I assume) for the petrol and charging your phone will require more to be consumed. Laws of physics require the energy comes from someone. It's not magic.
North-Village3968@reddit
Education has failed in the UK
Rattarang@reddit
financially , yes, charging a phone battery has a negligible expense.
Physically, these other comments address it.
imtheorangeycenter@reddit
If you are driving from A to B anyway, then essentially, measurabley, yes it would come at no real cost to you. A headwind for a quarter mile of your journey would be more expensive.
If you sit idling in your car to charge it up, I can't think of a less free way of doing it!
scoschooo@reddit
I would argue there is no extra cost in fuel to move the car. You use the same amount of fuel - but the phone is using excess electricity generated.
StuartHunt@reddit
There are two ways of looking at it,
You are using fuel to create the "free" electricity.
If you are already using the car for another purpose, ie; your journey to work, then the electricity is a by-product of you travelling to work, therefore you have no additional expenses from utilising this power to charge your phone.
One-Cardiologist-462@reddit
When you draw more current from an alternator, you increase the resistance it subjects the engine to.
Essentially, your engine will have to add a tiny bit more fuel to keep the RPM the same.
A bigger scale system which utilizes the same principal is actually used in trains to slow down, called dynamic braking.
When the train needs to slow down over long downhill runs, the power is no longer applied to the traction motors. Instead, they're used as dynamos, which dissipate the power generated by the rolling train across a bank of resistors.
The momentum of the train is converted to heat electrically, instead of by friction.
michael-65536@reddit
An alternator works by forcing two magentic fields against each other to push electricity through a wire (electromagnetic induction).
The more electricity being pushed, the stronger the magnetic fields are, the harder it is to move the fields against each other. If an alternator had a hand-crank on it, you would be able to feel this difference in the amount of strength it takes to turn it between a large electrical load and a small one.
Have you heard of regenerative braking? Whereby the movement of an electric car is slowed by converting that movement into electricity and putting it back into the battery? It works on the same principle. Your alternator is basically braking the engine to make electricity.
Of course, a car engine generates an immense amount of power compared to how much charging a phone needs, so it isn't detectable. If you were charging a giant bank of RV batteries it would be detectable - RVs have especially large alternators for this reason - and the extra power would noticeably affect fuel consumption.
divdiv23@reddit
Infinite energy glitch lol
Naja42@reddit
The energy is paid for at the fuel station
Panda_hat@reddit
No but if you charge it at work it is.
Peppy_Tomato@reddit
The math is straightforward. Add up how much you pay for the car monthly and the fuel and maintenance. Divide by the amount of energy you used to charge your phone. Let's day £400 a month in total. Now, your phone needs say 50W a day, times 30 days equals 1.5kWh a month.
400 divided by 1.5 equals £268 per unit. The good thing is, you can drive a few hundred miles for "free" each month.
jake_burger@reddit
Bear in mind that phones use a tiny amount of power, £5-10 worth of mains electricity in a year.
I think it’s a moot point personally
TenderfootGungi@reddit
No. Your logic breaks down where you assume the alternator is always putting out energy that somehow is not used if not needed. The alternator in fact turns off and on to produce energy when the battery needs it.
noodlesvonsoup@reddit
no, the fuel you put in your car pays for it.
painful_butterflies@reddit
As others have said, no, alternator, battery, recharge blah!
But my logic is, cars already running, fuel already being burnt, so therefore, nothing extra happening to charge phone. And no amount of well reasoned science will change my mind.
I apply the same logic to charging my battery pack when I'm using my PC, computers already on, therefore no extra effort to charge battery, nonsense, but shush, I'm happy.
audigex@reddit
No, the alternator puts an additional load on the engine due to the additional force required to rotate the alternator’s little shaft against the magnets
It’s not a LOT of extra load, but it is an extra load
That extra load slows the engine itself down a little. The ECU detects this and adds a little extra fuel into the cylinder
So you do use extra fuel for the extra ~10-20W of power being drawn
Visible_Account7767@reddit
No it's not free even though the alternator belt is spinning already.
The resistance of how hard it is to spin the alternator depends on the load/work it's doing.
A good experiment to demonstrate this is to get a dc electric motor (a dc motor also works as generator)
Spin the motor with your hand with nothing connected to the motor wires and you will feel it spins freely and easily, now short together the wires for the motor and try to spin it, it suddenly becomes very hard to turn and will not spin freely.
This is because you have shorted the circuit so now it is trying to generate the maximum power possible, that power has to come from somewhere so more work is required to turn it.
Steppy20@reddit
Technically it isn't free, but the amount of extra fuel usage due to the increased load required by the alternator is minimal compared to say a 1% increase in gradient or a 1mph wind speed increase.
Running your tyres slightly flat would have more of an effect than charging your phone.
spaceshipcommander@reddit
It's not free in a perfect world, but we don't live in a perfect world.
Essentially, a car powered by a combustion engine is somewhere around 40% efficient. 60% of the fuel you pay for is wasted. If you can capture some of that wasted energy and turn it into useful energy then you have a legitimate claim that it's "free" energy.
An example is a hybrid which we commonly accept are 20%+ more efficient than a pure combustion powered vehicle. What that actually means, in terms of physics, is that they are just wasting less energy.
So whether charging your phone is free in practise really depends on the driving you are doing. If you are sat at a constant speed on the motorway, charging your phone isn't free because you're not recovering any wasted energy. If you're in town, you are recovering wasted energy every time you stop so there's an argument that the cost of charging your phone is reduced.
A lot of modern cars do a lot of clever trickery to try and recover wasted energy. A perfect example of this is something Audi has been doing for a long time, which is increasing the voltage of the electrical system under braking to recover some wasted energy via the alternator. Then they can essentially allow the battery to not charge or discharge under normal driving, knowing that they can make up for it under the conditions I just stated.
TLDR; you've got a legitimate claim that charging your phone in the car costs less than at home, but not exactly for the reason you are thinking.
New_Line4049@reddit
No, its not free.
The reason is.... a little complicated, but basically comes down to this, as you try to draw more and more power from the alternator by turning things on or plugging things in it becomes harder and harder to turn the alternator. That resistance is transferred via the belt to the engine, it therefore takes more fuel to keep the engine spinning at the same speed. The difference when charging a phone will be miniscule though as the power draw isn't really all that much.
CapriSonnet@reddit
It's free if you drive for a living. Ie: someone else's vehicle.
LordAnchemis@reddit
You would marginally have worse mpg - but unless you're powering something ridiculous 20W is nothing compared with what the engine can output etc.
DeadBallDescendant@reddit
This is an usually good thread. Well done everyone.
GordonLivingstone@reddit
No. It isn't free. Though you won't notice the extra cost as a percentage of your petrol bill (or electric car charging bill).
The electricity to charge your phone comes from the car alternator (a rotating generator)- which is turned by the engine which in turn is powered by burning petrol.
Any extra electricity used in your car means that it becomes harder to turn the alternator and thus more petrol has to be burned to keep it moving at the same speed.
You can see this effect if you sit with the car at idle then turn on something that uses a lot of current - like a heated window. The engine speed will at least briefly slow down.
That small amount of extra petrol will cost more than the mains electricity that you would use if you charged at home.
Phones however don't use a lot of power. Something like 4 Ah is a full charge. So a fifty percent charge over an hour will need 2A at five volts and an efficient charger would only need 1A at 12V to supply that. A pair of halogen headlamp bulbs would take 9A.
The other way of looking at it is that 4 Ah at 5V requires 20W of power from the car. Even a small car engine can produce 50kW flat out. Even if you are only using a tenth of that to cruise, 20W is an insignificant load for the engine.
Essentially the same considerations will apply to an electric car. The cost will however be even lower as the electric car doesn't use an innefficient combustion engine to turn an alternator. It simply stores electricity supplied via the mains - unless you are using a very expensive fast charger.
No_Refrigerator3947@reddit
Analogy for you.. Your legs are spinning on the pedals of a bike because the wind is behind you helping you along, now apply the brakes a little.. (plug your phone in) your legs are still spinning but now they have to do work to maintain speed... Is that energy free.
No_Refrigerator3947@reddit
You have to pay for fuel to turn the engine.
If the alternator has to do work it uses fuel.
No it is not free.
Tall_Working_2942@reddit
For one phone the difference will be imperceptible. But it is using some power from the car. Would a million phones charging in your car be imperceptible - no. And also practically impossible, but you get the concept.
FWIW the cost per kWh of electricity generated in a petrol car will be a lot higher than the cost of electricity at home:
Martipar@reddit
The power is coming from the fuel, so petrol or diesel (unless you drive an electric car and then it's a bit more complex but we shall say your power supplier). It's not free energy as such but it's a very small amount of what your car uses.
Mail-Malone@reddit
Anything you use electrical wise on your car uses petrol/diesel. Watch your revs blip when you put on the air con for example. But it’s minimum.
Basically your car battery doesn’t stay charged with no cost, if it did that be the holy grail of energy supply.
Weary_Bat2456@reddit
However, are you plugging your phone in and leaving the engine running / draining your battery just for the sake of the phone running, or are you just doing it as a secondary effect of the fact your engine is producing energy?
Personally my car charges my phone so slowly that I'm better off wasting a tiny portion of my electricity bill to charge my phone than to waste my fuel for it to say '6 hours until battery is full' whilst at 50%.
S_mawds@reddit (OP)
I drove 8/9 hours a day and to be fair my phone charges in about an hour in the car
Master-Leopard-7830@reddit
If someone else paid for the petrol, yes.
Charging your phone will use fuel because the engine is being used to keep the car battery charged which is also charging your phone. But it will be a negligible amount and nothing to worry about in the grand scheme of things.
srm79@reddit
Sort of but not totally - it'd be incredibly difficult to calculate because of the number of factors at play, but fair to say the cost of changing your phone in your car is negligible, especially if you were only going to drive the car anyway
used_bathwater@reddit
No.
Charging uses electric, this requires the alternator to (only very very slightly) produce more current, this in turn puts more strain against the engine via the alternator belt, which in turn uses more fuel. Not that it will be noticeable. Same with running your air conditioning vs not running it.
Unlikely_Concept5107@reddit
The engine has to work harder to do all its other jobs plus charge phone, than it would if the phone wasn’t charging.
This uses more fuel.
Fuel costs money.
So, no.
r1ch@reddit
The phone will slightly increase the load on the alternator which will in turn slightly increase the load on the engine which will cause it to use slighlty more fuel, so it’s not free but too small to be noticed.
SeniorPea8614@reddit
It's only free if you do it in someone else's car.
But really, I think by drawing current from the battery, and in turn the alternator to recharge it, there is a tiny amount of extra force "pushing back" against the engine, which will increase your fuel consumption.
HampshireTurtle@reddit
Charging the phone or running the AC or using the lights puts more load on the alternator which will put more load on the engine so you'll use more fuel.
However the cost of charging the phone this way (or at home) is virtually nothing in comparison to the cost of electricity used to boil kettles, heat the oven, heat your water etc.
Expensive-Estate-851@reddit
It's energy your car would probably use but in the grand scheme of things a phone battery isn't big enough to make any noticeable difference to an engine propelling 2 tonne of steel around. So not free but not noticeable either.
MeenaBeti@reddit
Yes I’d say so.
SituationIcy5938@reddit
No. But yes.
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