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First Batterypack build, some beginner questions
#11
(05-16-2018, 01:49 PM)thanar Wrote: A 350w nominal e-bike would draw a nominal 10A current. However, it could easily ramp up to 20A draw. That said, since laptop batteries are low discharge rate batteries, I only use new power cells for e-bike packs. Unless you have a way to fit 200 cells on the bike, which would make a 10s20p battery that would easily handle 20A of current.

Also, as an added bonus to the high-amp draw of e-bikes, you almost definitely should use a BMS, even one of the $10 ones.

I don't use a BMS on any of my batteries, I construct my packs to be electrically two 7S8P battery pack with two main ports and two balance connectors coming off of one single battery pack. When I plug the pack into my ebike, I take the two 7S packs and connect them in series. For charging, I connect both batteries in parallel. 

I would suggest OP does the same for his battery pack. Your pack is only 36v, so build two 5S battery packs and connect them in series for discharging. Then connect them back into a single larger 5S pack for charging with something like an ebay imax b6. 

The reason I don't use a BMS on any of my packs is because I use salvaged power tool cells or lipo batteries. Both these types of batteries are very easy to go out of balance, and a standard BMS will not be able to balance the pack back after a high discharge cycle like an ebike. 

To make sure your pack doesn't get over discharged, connect one of these to each balance port and they beep really loudly when one cell goes below 3v:

https://www.ebay.com/itm/2pcs-RC-Lipo-Ba...SwDGhazwAk

If OP wants to use laptop cells, for his load they absolutely can. Older laptop cells don't handle high current very well, but most newer laptop cells can actually discharge saftely without too much sag at about 1C.

I would suggest OP goes for a 36v, 20AH ebike battery if they want to go the laptop cells route. This will require 10 cells in parallel and 10 in series for a 100 cell pack. If OP assembles their packs like I do in an offset triangular pattern, it shouldn't be that big. Currently I have plans to build a 168 cell 24S8P 84v 14AH battery pack made of hoverboard or power tool cells to power a 3000w hub motor, so I need power. 

I will be pulling about 50 amps form this pack continuously, so I need 18650 cells that can do 20 amps each to keep the heat down. 

It has been very hard to find good cells like that, but for ebikes under 500w, laptop cells can work totally okay. For my situation where I may be asking 7-10 amps per cell, I need high drain cells.
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