Idea for a high capacity e-bike using LiFePO4 12 volt batteries. Good idea or nuts?

lakeyboi12

10 µW
Joined
Jan 6, 2024
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5
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British Columbia
Hi all. I have 4 of these off-the-shelf 12 volt LiFePO4 box batteries previously used on a boat.

61w55sK8H6L._AC_UF1000,1000_QL80_.jpg

They are 100 Ah "mini" batteries. Each one is about 10 x 5 inches and weighs 19 lbs. I don't take the boat out so often anymore so I had an idea to build an e-bike using the spare batteries. My plan is to wire the 4 batteries in series to create a 48 volt bank to power the motor rather than the small in-frame batteries that typically come on e-bikes. Since the batteries are quite heavy, they will be in a plastic or wood battery box and secured onto a cargo bike or trike such as:

81hS75u6aKL._AC_UF894,1000_QL80_.jpgcargo-rear-rack-facing-left-1030x687.jpg
I will go for a bike with at least 100 lbs rated capacity on the rear rack for safety margin. It may already be an electric bike or may need a conversion kit put onto it. I weigh about 140 lbs, batteries might total to 90 lbs and some of the bikes I'm looking at are about 50-70 lbs. Let's assume a total weight of 300 lbs.

Questions:

What motor would power this bicycle sufficiently? I don't need to go fast, 40 km/h top speed is more than enough for me. At least a 750W mid drive or 1kW hub motor seems appropriate. The bicycle will need a lot of torque to move 300 lbs especially uphill, so I am leaning towards the mid drive.

Does this setup seem like it will give solid range? 100km throttle only?

Is there anything I am overlooking for this build idea? I have built 2 e-bikes before but they were both plug and play kits. Would this be difficult or impractical?
 
On my 20"x4" 750W motor fat tire bike with geared rear hub, I have to pump more like 1600W in to go 30mph and I don't have a super heavy battery to pull like that.
 
On my 20"x4" 750W motor fat tire bike with geared rear hub, I have to pump more like 1600W in to go 30mph and I don't have a super heavy battery to pull like that.
I see. Maybe the 1kW Bafang BBSHD is a good choice then? 15-20mph (24-32km/h) cruising is fine, just need good torque to pull up the hills.
 
What motor would power this bicycle sufficiently? I don't need to go fast, 40 km/h top speed is more than enough for me. At least a 750W mid drive or 1kW hub motor seems appropriate. The bicycle will need a lot of torque to move 300 lbs especially uphill, so I am leaning towards the mid drive.
I highly recommend you explore the motor simulator at ebikes.ca to estimate the power requirements for your specific riding conditions, style, terrain, speed, weight, etc. This will give you some numbers to base your hardware needs on. You must find out what the actual slope of the hills is, worst case, to estimate actual power required.

Basic simulation for 300lbs, preset 48v battery, 40A controller, default hubmotor, 10% slope, full throttle, gets you almost 23kph for 5 minutes before overheating the system to >250C, 79Wh/km.

Same but 20% slope gets you less than 1kph, "instant" overheat.

You can input the parameters for your actual battery, and various other things, or pick from the dropdown lists, to guesstimate different setups' capabilities under your specific conditions.

Does this setup seem like it will give solid range? 100km throttle only?
To answer this, you need to answer for yourself some questions:

What Wh/km do you expect the system to use up under your specific riding conditions, including the hills?

How many Wh are actually available in your batteries? (it will be less than the labelled amount, or the amount calculated by nominal voltage x Ah, both because of age and because you never get the full amount for various reasons).

Another question you must answer is: Can your batteries supply the current (A) required by whatever system you end up using (under the worst case loads on those hills, etc)? (if not, you'll need different batteries that *can* do that)

You should also check with the manufacturer of the batteries to make sure it is safe to series them. Many batteries have a BMS in them that can be damaged by seriesing too high a voltage (when one of them tries to shut off due to whatever limit is exceeded, the FETs in the BMS see full pack voltage (much higher than the single-battery they were meant for) and fail, often shorted...so then they can no longer ever shut off the input/output and protect the cells against damage that can lead to a fire)).
 
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You would have insane range with 48v 100ah. That's >6x the range of most bikes.
Any 1kw motor would do.. and help support the added weight.

I would go for 36v instead to cut down the weight. Many 'fast winding' hub motors exist that can make pretty good speed on 36v using more amps than volts.

You may be unhappy with how ~60lbs @ 36v affects the handling though. Rear racks aren't the best place for batteries because of how up high they are.
 
Any 1kw motor would do.. and help support the added weight.
To haul 300lbs up hills? Maybe...depends on the hill, speed, motor winding / gearing etc.
 
I dunno, his top speed is 25mph.
Does depend on the hills. If over 5% grade for long periods of time, a leafbike 1.5kw 5T or RH212 would be a better choice, depending on wheel size.

ebikes.ca motor simulator will help us find the ideal configuration (y)
 
What do you want the bike for? No interest in solar storage, portable sound systems, go carts, quads, snowmobiles, maybe even hovercrafts? I’d broaden the considered set, because it’ll be a challenge to find any vehicle that resembles a bicycle able to maintain acceptable handling and stability with that battery load on board. You could, however, tow a battery, even one twice that weight.
 
, because it’ll be a challenge to find any vehicle that resembles a bicycle able to maintain acceptable handling and stability with that battery load on board.
CrazyBike2 could. Other similar cargo longbikes probably could too; there's a number of heavy-cargo longjohns for instance.
 
What do you want the bike for? No interest in solar storage, portable sound systems, go carts, quads, snowmobiles, maybe even hovercrafts? I’d broaden the considered set, because it’ll be a challenge to find any vehicle that resembles a bicycle able to maintain acceptable handling and stability with that battery load on board. You could, however, tow a battery, even one twice that weight.
Electricity is cheap in my area (7-8 US cents per kWh) and the sky is gray half the year so a solar system doesn't seem worth it. I was considering a go kart or mini bike but would like the ability to pedal with assist (also the HOA and local cops may get involved at some point if I'm driving a go kart down the street). I had never even considered a bike trailer, has anyone here tried putting batteries on a bike trailer? I'm just worried about the thing decoupling and ripping off.
 
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Basic simulation for 300lbs, preset 48v battery, 40A controller, default hubmotor, 10% slope, full throttle, gets you almost 23kph for 5 minutes before overheating the system to >250C, 79Wh/km.

Same but 20% slope gets you less than 1kph, "instant" overheat.
Interesting. Had never considered motor overheating. Perhaps some kind of forced cooling system (fan ziptied next to the motor :ROFLMAO:) or amp limit on the controller would be a solution.

On the simulation I can see hub motors really hate any sort of grade. I'm leaning towards the BBSHD and slapping it onto a kit bike then. It has good torque and large fins for heat dissipation. 20% grades are not too common but there are a few 10%ers.

How many Wh are actually available in your batteries? (it will be less than the labelled amount, or the amount calculated by nominal voltage x Ah, both because of age and because you never get the full amount for various reasons).
The batteries are pretty new and only have a few cycles so I assume there's at least 5 kWh left in there.

Another question you must answer is: Can your batteries supply the current (A) required by whatever system you end up using (under the worst case loads on those hills, etc)? (if not, you'll need different batteries that *can* do that)

You should also check with the manufacturer of the batteries to make sure it is safe to series them. Many batteries have a BMS in them that can be damaged by seriesing too high a voltage (when one of them tries to shut off due to whatever limit is exceeded, the FETs in the BMS see full pack voltage (much higher than the single-battery they were meant for) and fail, often shorted...so then they can no longer ever shut off the input/output and protect the cells against damage that can lead to a fire)).

The batteries state 100A continuous discharge and maximum of 4P4S on the manufacturer website. It is a white label Chinese battery so I don't know whether to trust it or not but the specs seem to be standard for this type of battery
 
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CrazyBike2 could. Other similar cargo longbikes probably could too; there's a number of heavy-cargo longjohns for instance.
Yeah, with the load low and between the axles. Expensive bikes though. To spend that type of money and allocate the required shed space for it, you’d want to be regularly hauling cargo with it. Buying one for the purpose of repurposing a heavy battery is a stretch. Personally I’d use whatever bike I had, with a trailer.
 
Electricity is cheap in my area (7-8 US cents per kWh) and the sky is gray half the year so a solar system doesn't seem worth it. I was considering a go kart or mini bike but would like the ability to pedal with assist (also the HOA and local cops may get involved at some point if I'm driving a go kart down the street). I had never even considered a bike trailer, has anyone here tried putting batteries on a bike trailer? I'm just worried about the thing decoupling and ripping off.
I’m sure they have, but It’s uncommon. The hitches are proven designs. It’s no different to towing kids or dogs. If you’d entrust your kids to it, you’d entrust a battery.
 
Interesting. Had never considered motor overheating. Perhaps some kind of forced cooling system (fan ziptied next to the motor :ROFLMAO:)

There are a number of motor-cooling threads including testing of assorted methods...but you can't cool the parts that need it with just a fan from outside unless you cut it open to reach the inside and leave it exposed to the elements. :/

The 'easiest" option is statorade plus hubsinks for a hubmotor. YOu'll find several motors in the simulator have the option to test out all three--plain, just statorade, and that plus hubsinks, and some conditions will show a dramatic difference in results between these.


But the best thing is using a motor setup capable of handling the conditions. ;)


I used two (mismatched) MXUS 450x (one 4, one 5) motors and controllers (one ancient Grinfineon, one generic) on my SB Cruiser heavy-cargo trike, one in each rear wheel, and could easily ride up the steep hill of 7th street at north mountain, and CrazyBike2 before that could easily handle Cave Creek Road which is very similar, in the same area, at 20MPH, with only about 70-80A current on a 52v battery. (might've been less, that was a few years back). No overheating in the several minutes it takes to reach the top, after riding at the same speed to get there.

I still use one of those motors and controllers on the left side of SBC, and a smaller motor (Ultramotor off an A2B) but better (and higher current) controller (Phaserunner v6) on the right; haven't tested this combination out on those slopes though I expect similar results.


or amp limit on the controller would be a solution.

Then you limit the torque the motor can create, and thus the speed you can go up the hill and the amount of weight it can push up the hill...but if you keep trying to push the higher amount of weight then the motor overheats because it's going to slow and internal current rises too much making too much waste heat.

On the simulation I can see hub motors really hate any sort of grade. I'm leaning towards the BBSHD and slapping it onto a kit bike then. It has good torque and large fins for heat dissipation. 20% grades are not too common but there are a few 10%ers.

Hubs vs grade results depend on the specific winding of the motor (kV) vs voltage used vs wheelsize they're in vs speed you go and grade. Set it up right for the expected conditions and it'll work fine...but it's all a compromise between those worst-case conditions and the rest of your ride requirements. :/

Non hubs include a gearing ratio between the motor and wheel as well as those things, so any of them that use the pedal drivetrain (or other shiftable gear ratio) to get the motor power to the wheel allow you to shift gears as needed for the conditions of the moment, just like you do when pedalling, to keep the load as low as possible while maintaining the speed you're after.

The batteries are pretty new and only have a few cycles so I assume there's at least 5 kWh left in there.
What kind of Wh/km did you get in your simulations? (you can also use the trip simulator to test out entire routes, etc, and get a better idea of usage).

Using the Wh/km average you can divide your capacity by that to get a range guesstimate.

FWIW, 48v (4x12v) x 100Ah is only 4800Wh, but if yours had more capacity than they were "rated" for then you might get your assumption amount.

If you have 5kWh available, and need 100km range, you need to keep the average Wh/km usage down to 5000 / 100 = 50Wh/km.
 
What kind of Wh/km did you get in your simulations? (you can also use the trip simulator to test out entire routes, etc, and get a better idea of usage).

Wasn't exactly sure what to use for some of the parameters but assuming 50% average throttle and a 3% average grade using a Bafang G01 hub motor and 100 W pedal input, I got an average of about 26 Wh/km which suggests a 187 km range

It does overheat after 16 minutes but adding 100 W of pedal input fixed that and dropped the Wh/km to 20

Still figuring the simulator out and I have to do more learning, seems like a lot of considerations for what I thought was a free time project over a few weekends :oop:

FWIW, 48v (4x12v) x 100Ah is only 4800Wh, but if yours had more capacity than they were "rated" for then you might get your assumption amount.

The 4 batteries combine to be 51.2 volts and some capacity testing online suggests they deliver a bit over their rated capacity. Maybe 5 kWh is a bit optimistic though
 
Normally you use the nominal voltage to calculate capacity, so 12v x 4 is 48v, because you don't get that full voltage thru the entire capacity...if you instead use the average (nominal) voltage then it's a decent guesstimate of actual usable capacity in Wh.

If yours are 51.2v in hte middle of their charge/discharge curve (when only half full), then you can use that voltage, otherwise use whatever they are at when half full.



I've spent about a decade and a half getting to where I am now, with a fairly reliable heavy cargo trike that is also my daily commuter.

It can be done much quicker depending on your budget and whatnot, of course--I started out with negative budget and using just recycled parts; most of what I have now is still recycled parts but I had a bit more choice in what I used and knew more about what *to* use. :lol: I also knew elecronics but not motors and batteries, those and all the other systems I've learned a fair bit about over the years here, and that has also helped.

Most of what I did was by guess and by gosh and I would have been better off figuring out what it would actually take to do what I wanted..but I may have learned more by doing it the hard way. :oops:
 
My rule of thumb for mid drive vs a hub motor: mid drives are better than hub motors (especially direct drive) for hauling heavy loads under 1500w, then once you start getting into the bigger hub motors like a qs 205 they stop caring about grades. I currently run a qs 205 in a 20 inch wheel (a small wheel will do a LOT for keeping heat generation down) at 2.5kw, it hauls me and a generator up mountains and barely gets warm (maybe 20-30c above ambient) without statorade. I had a bbshd for a while too and up until I got the big hub motor it had way more torque than any of my hub bikes in first gear.

If I were you (and I’m not), I would get a big direct drive hub motor in a small 16 inch moped wheel and haul butt with all the current you have available in those big batteries (you could probably comfortably dump 4-5 kW from them). Think climbing steep grades at 30 mph. But I know you don’t want to go fast, so likely the only benefit you would get from a big hub is the near zero maintenance. You also aren’t required to go fast with a big hub, they just happen to be really good at it. If you get a hub, make sure to get a clamping torque arm so you can use regen.

A mid drive is going to require you to frequently lubricate your chain, change your chain about every 1500 miles, replace your brake pads super frequently since you can’t use regen (another big benefit of the hub, I haven’t replaced my pads for over 2,000 miles and they are still basically new), and grease the internal gears every so often, as well as replacing the cassette and chainring every so often. If this is fine, go ahead and get a mid drive, you won’t regret it. But if you want to just set it and forget it, get a big hub motor in a smaller wheel size and enjoy the headroom.

If you decide on getting a hub motor, I highly recommend getting a programmable FOC controller that can dump a fair amount of current into your motor, specifically any VESC. You will be able to use variable regen, which is awesome. You also get a torque throttle, which is almost necessary on an ebike with high torque. Use the motor simulator to determine how many phase amps you need. The controllers that mid drives come with are usually fine.
 
Hi all. I have 4 of these off-the-shelf 12 volt LiFePO4 box batteries previously used on a boat.

View attachment 345652

They are 100 Ah "mini" batteries. Each one is about 10 x 5 inches and weighs 19 lbs. I don't take the boat out so often anymore so I had an idea to build an e-bike using the spare batteries. My plan is to wire the 4 batteries in series to create a 48 volt bank to power the motor rather than the small in-frame batteries that typically come on e-bikes. Since the batteries are quite heavy, they will be in a plastic or wood battery box and secured onto a cargo bike or trike such as:

View attachment 345655View attachment 345656
I will go for a bike with at least 100 lbs rated capacity on the rear rack for safety margin. It may already be an electric bike or may need a conversion kit put onto it. I weigh about 140 lbs, batteries might total to 90 lbs and some of the bikes I'm looking at are about 50-70 lbs. Let's assume a total weight of 300 lbs.

Questions:

What motor would power this bicycle sufficiently? I don't need to go fast, 40 km/h top speed is more than enough for me. At least a 750W mid drive or 1kW hub motor seems appropriate. The bicycle will need a lot of torque to move 300 lbs especially uphill, so I am leaning towards the mid drive.

Does this setup seem like it will give solid range? 100km throttle only?

Is there anything I am overlooking for this build idea? I have built 2 e-bikes before but they were both plug and play kits. Would this be difficult or impractical?


Been there. My experience is on EValbum. Complex. Now..this..
 

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