Ebike battery question

W1r3d
Posts: 1
Joined: Wed Jan 20, 2016 6:36 pm

Ebike battery question

Postby W1r3d » Thu Jan 28, 2016 9:29 am

Hi guys,
Has anyone made their own battery pack to suit their motors voltage?
I am considering making my own 48volt battery pack. I will be using 4 x 12volt li-ion 20 mah rechargeable batteries. I would the connect the batteries in a series to obtain my voltage. Then once its time to recharge them i would disconnect them and recharge then one at a time.
Does this sound doable?

cj7hawk
Posts: 1143
Joined: Sun Jan 18, 2015 9:00 pm

Re: Ebike battery question

Postby cj7hawk » Thu Jan 28, 2016 11:33 am

No, it sounds like a terrible idea - Spending a day charging each battery one at a time would be painfully slow and it's a pain removing them from the bike each time too - and you can buy battery chargers for that configuration anyway.

Also, you didn't really specify the battery, but a combination of "12v" and "Lithium ion" makes me think you might be using particularly low-current capability batteries, that will not put out enough for your bicycle. I won't even ask the wattage of the wheel if it's 48v, but I'm assuming that you're going for around 10A Minimum? Many 12v lithiums ( except the ones in car starters ) won't put out that kind of current and often have smaller wires intended for lower currents - usually around 2A.

So please be careful, as there is a little engineering to go into the mix before you start.

Anyway, the best forums for that kind of work if you want to read them are the endless-sphere forums on electric bicycles - That's where all the homebrew batteries show up - :)

But there's also a lot of knowledge here if you want to post more information and solicit ideas - :)

Regards
David

eldavo
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Joined: Tue Sep 01, 2009 12:21 am
Location: Perth, Western Australia
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Re: Ebike battery question

Postby eldavo » Thu Jan 28, 2016 12:18 pm

You can get 2 x 22-25V 6S 20Ah in series to give what you want (44V discharged, 50V off charger) with a series harness, and a single charger that balance charges 2 independent batteries automatically or programmable to charge voltage you want (90% extends cycle life for a cycles/capacity benefit, 80% further extends cycle life but dropping capacity depth of discharge decreases life to avoid).
You need to be present when charging in case of fire so only doing it once a day/night it would be as convenient as any other setup.
There are also smaller lighter individual chargers that are not programmable but auto balance 100% charge, much cheaper so can run one per battery to charge 2 at the same time.

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