Expected range of 48v 17.5aH?

Posted by lawyerz88@reddit | ebikes | View on Reddit | 26 comments

I'm having some range issues with a brand new 48v ebike with 2.2" MTB tyres.

The battery is a 17.5aH 48v Reetion Dorado battery. With mixed terrain, mostly flat, no throttle use and a rider weight around 90kg, I'm only seemingly getting 35km of range which seems low.

I've also noticed if I leave the battery charged up to the minute I am using the bike, range is a further than if I charged to full and turn off the charger and only pick it up again a few days later.

Need some advice, have I got a faulty battery? Should I ask for a replacement battery, or is there something I'm doing wrong?

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Educational_Ad_3922@reddit

No 35Km on that size of battery is about normal. Usually half of what the claimed range is is the max you can expect.

The easiest way to figure this out is to calculate the rated wattage of the motor based on the top speed you can achieve while riding.

So 48v x 17.5Ah = 840 watts.

So lets say you have a 500W rated motor, thats 840 ÷ 500 which = 1.68 hours of continuous usage at 500w. However its worth noting that peak wattage of a 500w motor is usually around 750W or roughly 25% more than its rated wattage.

For arguments sake here, lets assume the peak and continuous wattage is the same, at 500W.

So if we find that we reach a max speed of 32kph, we can simply multiply 32 by 1.68 to find out maximum possible range. (32 x 1.68 = 53.76Km)

However given that peka usage is higher and we calculate by that instead (840w ÷ 750W = 1.12) which amounts to 33 x 1.12 = 35Km max range.

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Educational_Ad_3922@reddit

As for why your battery may have less range when fresh off the charger is because of how the cells don't all charge at the same rate due to variances in their fabrication. To compensate for this a battery will use a BMS (Battery Management System) to balance the voltage between all cells to be as close to the same as possible. In doing this, after charging the cells with higher voltage will help to charge the lower voltage cells until they are balanced again.

Typically this shouldn't result in more than a total of a 5% loss in overall charge level. If you leave a battery plugged in for longer the BMS will balance the cells after the charge is complete than top off all cells with additional power from the wall.

So in short, no your battery is not likely faulty but rather within spec for a battery of its size and chemical composition.

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lawyerz88@reddit (OP)

Thank you, this has been insanely helpful and knowledgeable!

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Educational_Ad_3922@reddit

You're very welcome :)

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kennydsl@reddit

What is the power of the motor? If this is not a 250W motor, it changes everything.

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lawyerz88@reddit (OP)

Thanks all for replying, I think I've gotten my answer as it's roughly in the ballpark based on ride. I'll keep an eye on the watts used when riding and do some quick mental calcs in the near future.

Another question! Is it possible to tune bafang rear hub motor to be less aggressive in terms of the ramp up and ramp down of the selected PAS level?

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Bagel42@reddit

How many watts is your motor?

You have an 840wh motor. If you were to draw 840w the entire time, you would be out of battery in an hour. If that gets you to say, 20mph, then you would get 20 miles of range or about 33km

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lawyerz88@reddit (OP)

Ooo this is a useful visualisation. I've got a 500w rear hub bafang motor, which peaks just over 800w according to my screen. My commutes about 1 hr 15 mins, for simplicity let's say I ride at 800w for half the journey and 400w for the other half.

That works out to be 500wh + 250wh used so 750wh used so it's close.. maybe it's correct.

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Bagel42@reddit

Welcome to why I prefer watt hours over amp hours. Unless you know what you’re doing, it makes more sense. 840w for an hour or 420w for 2 hours, etc.

I think that with aggressive motor usage like you have, you’re getting pretty much exactly the amount of range I would expect you to get. If you went a little slower you might get more range, though.

See if you can get an average of 5-600 watts over the whole ride, might get a little farther. Personally, I would invest in a second battery. My bike peaks at 3200w so I only get about 10 miles of (pleasant) range on an 18ah battery, so I have 2. It can usually go another mile but the acceleration is lacking and top speed goes way down.

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lawyerz88@reddit (OP)

Yeah it's super helpful because my display shows my current live wattage usage so I can visualise this. Thanks!

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V65Pilot@reddit

Unfortunately, that's kind of a "how long is a piece of string?" question.

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Intermittent-canabis@reddit

Dual 48v 18.5ah setup here with 56kph top speed running mostly flat out gets me around 48km so u sound in the right ballpark For fellow freedom lovers that's 37mph and 30 miles

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plorraine@reddit

In my 4000lb Tesla Model 3, I would get about 3 miles. My e-scooter would get 20-30 miles depending on the speed (most highly) and tire pressure. My e-bike using PAS 2 out of 9, will get about 40-50 miles.

If you are struggling with range, first check your tire pressure. Then conduct your range experiment at 10-12 mph - your range will soar. Energy consumption over a given distance roughly doubles every time you double your speed - you get there in half the time but you need to input 4x the kinetic energy. The lighter the bike and the lighter the rider, the longer the range will be as well. Also, don't blast up hills - you may be able to cruise up hills at 10 mph while at 20 mph you will max out the current from your battery and things will heat and become less efficient.

So decrease rolling resistance, lower weight where possible, decrease speed - all will put you closer to what the manufacturer lists as the nominal range.

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TenMilePt@reddit

https://reallygoodebikes.com/pages/electric-bike-ebike-range-calculator

2 things I generally find -- the battery either has a faulty cell (or bank of cells) or the cells are not properly balanced -- not all BMS' balance cells. Its also possible it has a loose/wet/damaged connector as those Dorado style batteries tend to get wet inside.

If you have a multimeter (or your bike display shows voltage) -- when it's fully charged it should be at 54.6V when unplugged from the charger. The BMS and/or your bike will likely shut the motor down when the voltage reads 41V. It is useful to take a voltage reading when its fully charged and when it shuts down -- note that when you put the battery under load (e.g. while you are riding) the battery voltage will drop by 2-3V so it's quite possible to see 43-44V on the battery after the bike has shut down. If you find the fully charged voltage is less than 54.6V you probably have a bad cell or cell bank.

Of note, if this is a new bike -- that battery was built in June of 2022 so might be old stock.

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lawyerz88@reddit (OP)

I'll look at getting a multimeter if it isn't too costly. Is having the battery being old stock a problem per se on this new bike? It's new and hasn't gotten into any wet riding at all.

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TenMilePt@reddit

You can usually grab a MM for $10-20.

Cell balancing is something the BMS (circuit board) on the battery is supposed to do. Sometimes the manufacturers install BMS modules thar won't balance the cells. It's supposed to happen each time the battery is charged over 90%. What it does is ensures each cell is charged to the same voltage so that they drain and wear at the same level.

Older cells aren't really a terrible issue. It depends how they were stored -- charge level and temperature can degrade them.

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chuckwolf@reddit

Depends on the wattage of your bike and the speed you ride at on average. But with that battery on a 750 watt bike at class 2 speeds, 20 mph it should last about an hour or slightly over. So 20 miles range at the highest PAS level, further if you go slower and use less actual motor power.

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_ToxicBanana@reddit

17.5Ah should be around 70km with low-ish assist in flat ground.

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Total_Coffee358@reddit

Probably low-quality cells.

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lawyerz88@reddit (OP)

Supposedly 'samsung' cells in there. I've really no way to verify these claims.

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Total_Coffee358@reddit

How much did you pay? That will likely tell you all that you need to know. A battery that size should start at $500.00.

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lawyerz88@reddit (OP)

Came with the new bike.. the whole bike is USD 1300, bafang 500w rear hub.

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lawyerz88@reddit (OP)

Like to add it's a bafang 500w rear hub. MTB tyres are non knobby continental tyres

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