Risks of buying an incomplete e-bike

[JonasBauer]

Hello,

Since I've ridden an e-(fat)bike on my vacation in Livorno, Italy, I'm hooked. Overall it was such a great experience. Now, back home in Holland, I'm exploring my options of buying an e-bike.

There's this one bike for sale that looks aesthetically pleasing, with a 750w 8fun motor, 16 headway 12Ah cells, but without a BMS, and without a battery pack cover. The seller marketeers it as a hobby project. I'm already in love with this particular build and the seller lives close by. However, I have absolutely no electrical engineering skills. I did work on mopeds like the Gilera DNA and Aprilia RS 50 from my 16th-20th, which worked out perfectly fine when I did my research on Google and Youtube before I opened up the engines.

If you are experienced with e-bike builds, can you explain to me what risks I'm undertaking if I want to purchase this bike? If installing a BMS is very simple, why didn't the seller do it himself yet? Does this indicate that likely something is wrong with the battery pack? And can I test this with e.g. a multimeter?

And, as a follow up question; did some of you start working on e-bikes without prior knowledge? Can it work out when you're not afraid to do some learning, or is it doomed to fail?

 

[JonasBauer]

 

[brightonebikes]

If the price of the bike as is, allows for you to buy a new 48V battery within your budget, I'd be tempted to write off the headway cell battery and replace with better quality cells, Samsung, Panasonic or alike.

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[mike killay]

If someone is selling something incomplete, there is almost certainly something wrong with it that they cannot put right.
That is why they are selling it.

 

[Deleted member 4366]

Headway cells are about the best you can get as far as performance and life are concerned. Their main disadvantage is that they're very heavy. That battery will weigh 7kg and is rather large, so it's always a bit tricky to find a place to mount it. On a rack. it spoils the handling of the bike.

It needs a 16S LiFePO4 BMS with a rating of at least 30 amps. 40A is probably ideal. To fit one is fairly straight forward if you know how, but you do need a bit of kbowledge, good soldering skills and a heavy-duty soldering iron.

I suspect that the guy bought the battery, but then couldn't find a suitable way to mount it, which is why he didn't take the project any further. If he has a charger, he could have charged and used the battery without a BMS for test purposes as long as he knew what he was doing; however, it's dangerous to carry on like that.

Your pictures don't show.

 

[Wicky]

Here are the earlier images from Jonas:

 

[brightonebikes]

Headway cells are about the best you can get as far as performance and life are concerned. Their main disadvantage is that they're very heavy. That battery will weigh 7kg and is rather large, so it's always a bit tricky to find a place to mount it. On a rack. it spoils the handling of the bike.

It needs a 16S LiFePO4 BMS with a rating of at least 30 amps. 40A is probably ideal. To fit one is fairly straight forward if you know how, but you do need a bit of kbowledge, good soldering skills and a heavy-duty soldering iron.

I suspect that the guy bought the battery, but then couldn't find a suitable way to mount it, which is why he didn't take the project any further. If he has a charger, he could have charged and used the battery without a BMS for test purposes as long as he knew what he was doing; however, it's dangerous to carry on like that.

Your pictures don't show.

Hmmm, must be different Headway to the ones I tried (perhaps cheap fakes), because the sag I experienced was very poor, and the capacity dropped rapidly within about 250 cycles..

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[IR772]

Here are the earlier images from Jonas:

That bike really is a looker!

 

[JonasBauer]

Thanks for sharing all your insights; this helps. I'm evaluating if the 750w Bafang 8fun engine + bike alone together are worth the price. Does anyone have an idea what bike forms the foundation of this build?

I also found a link for these headway cells on Aliexpress, they sell for 80USD per 4 cells, rated at 3.2V. All headways on Aliexpress are rated at 10Ah, not 12Ah as the seller states. The battery pack is 16S1P. Doing the math, this build should be rated at: 16x3.2V = 51.2V with 10Ah. Weight of the battery pack: 5.5kg. Weight of the engine: 3.9kg. Total: ~10kg.

I'm now considering buying the bike and if the battery is faulty, swapping the battery for a homemade pack of 13S4P Samsung 18650, to get 48V with 10.4Ah. That pack will cost me ~180 USD and some time. But it will be a nice project. The weight of the new battery pack is 2.34kg for the batteries, so ~3kg total.

When that works out, I'll then create a battery mount so that the battery is swappable. Then I can travel with 2 fully loaded packs (one in my backpack).

I'm aware that the engine can also be faulty. But if the price is decent with respect to just the engine + bike, I think I'll take on that risk.

 

[Deleted member 4366]

This is the same battery, but with a BMS. Check out the specification:

https://bmsbattery.com/ebike-battery/153-48v-12ah-38140-lifepo4-battery-16-cells-ebike-battery-pack-battery.html

These are the cells:

https://bmsbattery.com/ebike-battery/89-headway-38140s-12ah-10c-lifepo4-cylindrical-battery-cell-with-screw-battery.html

The bike is very interesting. It has the perfect design for the rear suspension, where the line from the axle to the pivot should go to the steering head. I've never seen it on a bike before. I assumed that you would need an additional idler sprocket on the swinging arm pivot, otherwise the chain tension will vary a lot as the swinging arm goes up and down, but your one seems to use the derailleur spring to deal with that. I guess that you'd have to be careful about changing the front gears to a smaller chainwheel before you select the lowest gears at the back to avoid running out of chain length; however, with only a single chainwheel on the crank-motor, I've got a feeling that it's not going to work.

It's a shame. I may be wrong, but I think it's another case where someone has got a really nice bike to convert, and then they've tried to fit a kit to it, instead of deciding what kit they want, and then finding an appropriate donor bike.