GXMnow
Solar Wizard
- Joined
- Jul 17, 2020
- Messages
- 2,842
I totally agree that any series string of lithium cells needs some sort of BMS to protect against a single cell event. It is true that brand new cells can stay well balanced, but all it takes is one cell drifting out a few mv each cycle and it won't take long for it to go over or under safe voltage limits.
I built a small test pack of 18650's for an e-bike project. They were new Samsung 25R cells. It worked just fine with no BMS for a few rides. But my son let his friend try it, and he went up a few steep hills and came back saying it lost all torque. One of the cells measured 1 volt reverse polarity and was so hot the shrink wrap was tearing. All the other cells were still over 3 volts. Luckily we got the pack apart and cooled before it went into chain reaction thermal run away. A cheapo BMS would have saved it and eliminated the chance of a bad fire.
I built a small test pack of 18650's for an e-bike project. They were new Samsung 25R cells. It worked just fine with no BMS for a few rides. But my son let his friend try it, and he went up a few steep hills and came back saying it lost all torque. One of the cells measured 1 volt reverse polarity and was so hot the shrink wrap was tearing. All the other cells were still over 3 volts. Luckily we got the pack apart and cooled before it went into chain reaction thermal run away. A cheapo BMS would have saved it and eliminated the chance of a bad fire.