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Old 04-13-2014, 04:22 PM   #4 (permalink)
P-hack
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A couple issues with the bms node:
BL20 Cell Balancer for GBS 20Ah - BATTERIES - EV Parts Store

It uses a shunt, which is ok for bottom balancing occasionally, but they are using it to top balance, which can kill one of your cells since some reach the bottom before the others, but the pack voltage is still fairly high.

They make heat instead of moving charge from cell to cell, possibly not an issue on a bike.

The bolt-through-pcb is an issue, different rates of expansion for pcb and steel.

The bolt pattern probably doesn't fit leaf cells.

But perhaps most importantly is they are designed for a different chemistry than is in the leaf:
- Nominal Cell Voltage: 3.20V
- Load Turn On Voltage: 3.55V
recall the leaf "cells" are 2.5v min, 3.75 nominal, 4.2v max (32ah) and each leaf module is 7.5v 65ah (2s2p).


I wouldn't worry about bms for starters, you can test 18 cells with a vom pretty easily and a simple circuit will tell you if it is obviously out of wack and needs a bottom balance.

9 "leaf" modules will get you to 67.5v nominal fyi.

Last edited by P-hack; 04-13-2014 at 04:32 PM..
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