I have an old generator. Is there something I can plug in to make it output a pure sine wave?
Posted by funkmon@reddit | preppers | View on Reddit | 50 comments
I have a 1970s Kohler generator. It works but it doesn't output pure sine wave so I can't charge my Jackery units from it. Is there something I can plug in that that will output a pure sine wave?
I hear UPSes don't do this.
I'm considering just giving it away.
Paranormal_Lemon@reddit
Why not get a new generator? The whole point of an inverter generator is they let the engine rev down, so they are much more efficient when the load is not 100%. Keep your old one for a backup. You already have an older less efficient generator and you are going to add stuff to cause even more losses. Remember in a regional outage gas stations will be closed. You want efficiency with your setup.
TTdriver@reddit
Couldn't you just plug a ups into it and your devices into the ups?
vaikedon@reddit
Just a guess: some big fat capacitors???
Longjumping-Army-172@reddit
So, my earlier searches on the Jackery units showed that they weren't cheap. And you used the plural.
A Predator 3500 inverter generator will run you between $8-900 at Harbor Freight. Just last weekend, I fired up one that had been sitting up unused for several years...not only did it run (not great) but produced plenty of power.
If it were me...I'd get one of the Predator generators (big enough to also use for critical appliances such as fridge/freezer), and use that to charge the Jackery units. They'll charge faster than using 12-24 volt options, and you'll have it for other applications as well.
Don't get me wrong I'd consider using the Kohler unit on less-picky devices until it dies (I doubt you'll get much for it on the used market)...but it will eventually die. And Mr. Murphy tells us it will happen at the worst possible time.
engineerogthings@reddit
Um how does a generator not produce a pure sine wave? I’m confused. If you put on an AC to DC rectifier then add an inverter you are creating a square wave, complete with losses. The only way to get true sine wave is through a rotational generator, which you have.
funkmon@reddit (OP)
I'm not sure. I jumped to a conclusion which I probably shouldn't have. Maybe harmonic distortion? I don't know. But my Jackery thing wouldn't charge. I'll test it this afternoon.
Jaicobb@reddit
Not 100%, but I believe the reason you don't get a pure sine wave from a gas engine is because it revs up and down, very quickly so you can't hear it, it just sounds like a normal hum of the engine. It's this change in RPMs that slightly alters the current produced. Engines have constant oxygen and fuel moving through them. The RPMs really fluctuate on extremely small scales that are unnoticeable.
engineerogthings@reddit
You are almost there but not quite, the generator has a AVR (automatic voltage regulator) and a governer. Basically if the generator needs to give more power (ie more current) the governer gives the engine more fuel and the AVR controls the voltage of then gen at the correct amount. The frequency and is controlled by the rotational speed of the generator. The wave form coming out of the gen is a pure sine wave because its alternating current, its only the frequency of the wave that changes dependent on speed. Most gens have also have a pair of slip rings to act as exciters but on older gens can also be used as a dc power supply. Usually to charge their own starting batteries
Jaicobb@reddit
Is it the frequency change that makes it hard for some electronics?
engineerogthings@reddit
Yes exactly, as soon as you put a load on the gen it slows the engine dropping the rpm/ frequency, the AVR and governer kick in and give it more fuel to get it back to the revs required. This obviously causes frequency fluctuations.
wwglen@reddit
You get a "Pure Sine Wave", just a lot of them (harmonica), and noise added to it as well as variable frequency of that sine wave.
PrisonerV@reddit
What I'm buying for my Ecoflow....
https://www.amazon.com/gp/product/B0DSFNJM8K?smid=ANOY66NTC7AH8&psc=1
https://www.amazon.com/gp/product/B0CBM5SSWH?smid=A2Z5G0Z476BAVE&psc=1
This should allow me to charge from my non-sine wave generator at 12v 500 watts into the solar charging port on the Ecoflow.
wwglen@reddit
You will only get about 200 with that and melt the car adaptor.
This is because the EcoFlow limits the DC 13-15 Amps max.
OnTheEdgeOfFreedom@reddit
Your generator is almost certainly generating a sine wave. If it works by spinning magnets, that's the output. If it's not an exact sine wave it's because the generator isn't good at maintaining frequency, which is pretty likely given how they have mechanical regulators for speed, or isn't good at keeping the voltage constant, due to wear, overload, etc.
In short, I don't blame the generator for not outputting sine. I blame the jackery for demanding really clean power. That's a terrible design. I have run into UPSes - which is basically what the Jackery is - that were fussy like that and I returned them. They should be able to charge the battery using anything up to a square wave, just less efficiently; and even if they can't improve on the line voltage they should at least pass it through without complaint.
Power conditioners that will generate pure sine power from crappy input do exist. Internally they simply convert to DC and then generate a proper AC waveform, and by simply I mean a lot of expensive components and some amount of inefficiency. It doesn't come cheap.
It's probably best to contact Jackery and ask them what they heck they are expecting, and then get a generator that can hit those specs. But be careful because a lot of modern generators are inverting and output modified sine wave, which might not be good enough.
funkmon@reddit (OP)
You're probably right. That's interesting. So it's not a modified sine wave problem, it's a pure sine wave that is wonky from an old ass generator and restrictive power input from the Jackery.
I wonder if I can tune this thing up well enough for the Jackery to like it.
Theoretically, these small inverter generators that are advertised as being good for electronics should allow the Jackery to charge though, as they output clean power?
OnTheEdgeOfFreedom@reddit
In theory, yes. It might not only be harmonic distortion that's the problem, though. THD is what happens when what's supposed to be a sine wave isn't, but frequency drift can cause the output to still look a lot like a sine wave but devices still might not like lit. Same with voltage sags and spikes - it can still be close to a sine wave, but devices can object.
Why they object, I don't know. You can feed a square wave to a transformer and it will buzz and get hot and maybe shorten the life, and efficiency goes down, but it still works. You can rectify an AC square wave and filter it with big capacitors and dump overvoltage away as heat, and get closer to a sine wave that way. So it's always possible to build a power supply that will handle crap. Why people don't, I don't know.
Sweet-Leadership-290@reddit
Strange as hell!!!
These usually put out a pure sine wave !
Why do you say it is not? Are you sure this isn't a frequency issue instead???
funkmon@reddit (OP)
Why would a 2 stroke generator from the 1970s output pure sine wave?
I haven't tested it in a while but iirc I plugged in my Jackery and it wouldn't charge. It doesn't charge from modified sine wave, only pure.
Sweet-Leadership-290@reddit
Because a sine wave is output from ALL of the old AC generators. It is easy to get a sine wave because if you spin a coil past a field at a set rate, the natural voltage output is a sine wave due to the analog nature of a generator.
By comparison, synthesizing it from DC is difficult because it technically requires infinite sampling to create. This is why cheap inverters have a "modified sine wave" for an output. To synthesize this only requires the addition of the first two odd harmonics of the Fourier series. In this case 60hz & 180hz square waves.
funkmon@reddit (OP)
Interesting. I wonder if it is the wrong voltage then.
ToddRossDIY@reddit
I haven’t read all the comments yet so maybe someone else said this already but the keyword you’re looking for is Total Harmonic Distortion, or THD. My Bluetti can’t charge off my expensive 10kw generator either because its THD is something like 12-14%, but the Bluetti requires less than a couple percent. Basically it’s how far off it is from a perfect 60hz sine wave, same reason you’re not supposed to plug sensitive electronics into generators, sometimes they’re only putting out 58hz, or some other factor that messes with the shape of the sine wave
qbg@reddit
My guess is that the frequency is varying too much for it.
shikkonin@reddit
Because physics, as long as the load's power factor is reasonably close to unity without huge switching spikes.
Anything rotating at a constant speed produces a sine wave, as that's simply what a sine wave is.
RedOctobyr@reddit
What's the output voltage from the generator? That could also be wrong.
It's not going to be a "perfect" sine wave, you'd need a modern inverter generator to get that. But given that the Jackery is just basically just trying to turn it into DC and charge a battery, I'm surprised it would be THAT sensitive to the waveform. I would hope the output looks better than the rounded-corners square wave of a cheap "modified sine wave" inverter.
Forgive my lack of familiarity with them, can the Jackery charge from USB-C or something like that? Something besides AC power? A USB-C power adapter would be pretty cheap, and straightforward.
funkmon@reddit (OP)
I was also surprised how sensitive it was. I have tried to charge the Jackery with modified sine wave inverters before and it simply doesn't work.
I picked up a pure sine wave inverter as an experiment and it charged just fine from that.
The Jackery takes DC, but limits it to 400 watts. I have 3000 watts to fill. I do know the Jackery WILL charge from my 12v trickle charger at 1 amp.
So if I get a 24v 15+ amp charger, will it run off the generator? I'm not sure.
At what point does the sketchiness of the system and using an ancient 2 stroke outweigh spending $500 on a new propane generator that just does it all for me?
RedOctobyr@reddit
Oof, I forgot this is a 2 stroke as well :) If you have access to a Kill A Watt meter, it will show you AC voltage, but also AC frequency. I think some WiFi smart switches can also show this sort of info. Some multimeters can also measure AC frequency. Or use a $10-15 induction hour meter/tachometer to measure RPM, and divide by 3600.
Frequency is easy to adjust if it's not 60Hz, that's just a tweak to the governor.
It quickly sounds like this is not a great solution, to me. A 2-stroke is loud, requires mixing oil, and is likely not fuel-efficient. Plus it's old.
If this is to charge the Jackery once every 5 years when you lose power for 8 hours, no big deal. If you want this as a longer-term solution during longer outages, you're investing time and money (and failure points if adding DC power supplies, etc) into what, to me, is a "sub-optimal" starting point :)
Used generators have gotten cheap. New ones are pretty cheap too. If you found a good used listing nearby, you could even bring the Jackery and confirm that the used generator will charge it before buying.
I paid $500 each (10 years ago) for my used Honda EU2000i units. They are awesome. Quiet, light weight, reliable, fuel-efficient, and very clean sine wave output. Parts are available, I have the service manuals, loads of online support, etc. Quite certain there are propane conversion kits available. They will basically last me as long as I want to keep them.
They have gotten us through multiple power outages, while running quietly in the driveway (nice for sleeping, as well as not advertising having a generator), and sipping gas. They run 4-10 hours on the 1 gallon tank, depending on load, and I made an external 5 gallon supply using an outboard marine tank, which could run us for the weekend without ever touching it.
Investing in a modern inverter generator would be my choice 5 times over, before continuing to put time and $ into trying to force this to work, just personally. If the Jackery doesn't like the output, other things may not as well, if you needed to run something else. And a modern inverter offers a bunch of benefits beyond just being able to easily plug in the Jackery to charge.
funkmon@reddit (OP)
I'll scope it out with my multimeter this afternoon and my knock off kill a watt. I wonder if you are right and it's the voltage and frequency being gone.
RedOctobyr@reddit
I hope it's an easy fix! I'm curious to learn what you find, it would be cool if this could be sorted out for free.
Ryan_e3p@reddit
This is incorrect; generators, unless they are specifically inverter generators, do not put out pure sine wave. It is often modified sine.
shikkonin@reddit
Generators cannot produce modified sine waves.
TacTurtle@reddit
What you are basically asking for is sold commercially as a Variable Frequency Drive (VFD) - they take AC input, rectify to DC, then output an AC sine wave at whatever frequency you specify. This is most commonly used to control 3-phase motor speed, but can also be used to provide very clean power.
However, good VFDs are fairly expensive and will likely run more $ than a new generator.
Possible alternate - does your Jackery have a DC input? You may be able to just convert the noisy 120V AC down to 12 or 24VDC, then charge the Jackery with that (after all, the Jackery already has to internally convert the 120V AC into DC to charge the battery packs).
funkmon@reddit (OP)
Oh shit yeah. It DOES have DC input. I also have a big boy Schumacher wheeled battery charger. Only charges 12 volts though, and a battery tender but it's only 1 amp.
Now the Jackery limits 12v DC to 8 amps, that's how it checks if it's coming from a car so as to not blow a fuse, but above 15 volts it will take 400 watts.
400 watts is plenty for me. Do you know a 24 volt battery charger that can output 15 amps?
I'll do a bit of searching.
qbg@reddit
Transformers are an AC thing, not DC.
How much do you want to spend? You could get a variable power supply; this one will do up to 30V and 30A. That's a comfortable margin on the amp output.
TacTurtle@reddit
You should be able to find a 350-400W 24DC power supply for LEDs or PCs for under $60
KeithJamesB@reddit
Solar battery chargers have some pretty good output and have 24 volt models. I use one to charge my battery bank if I have to run my generator at night.
States_Rights@reddit
Will you post a picture of the data plate on the generator head? It will look something like this.
funkmon@reddit (OP)
I can't get to it but here is the model someone has pictures of on Offer up. The plate with the model number is legible.
https://offerup.com/item/detail/47024dcc-b814-3c4a-a0bf-a9d4de92d80e
xashen@reddit
Is your Jackery trying to charge at higher than the 800 watts your generator can put out? I have an Ecoflow battery that charges at 1500 watts, but I can drop that down in the app.
funkmon@reddit (OP)
No, the Jackerys are set to quiet mode which has them charge at like 400 watts.
Frundle@reddit
What is the output of the generator? Sine wave inverters turn DC into AC but they're typically used when you're taking power from a battery or solar panel.
funkmon@reddit (OP)
800 watts. And that's right. I could get an AC to DC thing then slap on an inverter, which I have, but I'm not sure how practical that is.
roberttheiii@reddit
Sure could. Some battery packs even charge direct from DC. Could also get a pretty inexpensive 2000 ish watt suitcase generator that would sip fuel.
funkmon@reddit (OP)
That's still $400 for a new one (propane or bust)
livestrong2109@reddit
Yeah, but the new one is going to be pure sinewave dual, fuel, have a brand new carb, and no internal wear. Better ground fault protection. Its such a pivotal component to a prep.
funkmon@reddit (OP)
While it's pivotal...I've largely sidestepped it.
The Jackerys have solar panels. Those will work some of the time. If they don't, I have contingencies.
In the winter, the batteries alone can run the furnace for 40 hours, which is 4 days comfortably, 5 days uncomfortably or with a bit of solar. During the day I have about 4 days of kerosene heat and 12 days of propane heat.
In the summer, I can run the fridge and freezer for about 3 days as well fairly safely just on battery power by my reckoning.
So assuming I never get solar power, what do I do if the outage lasts more than 3 days in the summer or 5 days in the winter (both of which I haven't seen in 20 years)? I turn on the car and charge the big batteries for about 10 hours at around 300 watts. I've tested this and it uses less than a half a gallon per hour, which is inefficient but it works. I have 3 cars, and assuming they're all half full, that's 4-5 cycles of battery recharging, putting me at worst case scenario 15 days without even touching a generator. That's a SHTF event. And more than likely I'll get enough sun that I don't have to do it more than once or twice.
Anyway, getting a generator would leapfrog the car step of course, but I'm not hurting for it.
So it's hard for me to kinda throw this away and get a $500 one that I don't really need anyway.
But I have put it on my registry. Lol let's see if anyone buys it
Frundle@reddit
Seems like it would work, but that does seem like a lot of gadgetry.
Another component you could look into is a power conditioner. I've only used them with audio equipment, but they are made to provide "cleaner" power. At 800W you might be able to find one that can handle your generator. Amperage and voltage will be a factor for using a power conditioner.
funkmon@reddit (OP)
I understand they don't really help the squareness of the waves. Shrug
davidm2232@reddit
Throw the 2 stroke generator in the trash. Bad on fuel and not designed to run for long periods. Get a newer Honda 4 stroke
silasmoeckel@reddit
Yes but it's another inverter/battery.
Most likely the frequency is off (generators make a sign wave as a function of spinning and coils so that's not the issue). An inverter with generator assist and push it to be on frequency. But at that point you have something far better than the jackery.
It's not cost effective as that ineter/battery to do it would be more than a compact suitcase inverter generator.
Virtual-Feature-9747@reddit
I was thinking a power line conditioner would do this but looks like maybe not. A "double conversion UPS" is the textbook answer.