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Old 03-25-2020, 11:58 AM   #7
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Join Date: Oct 2012
Location: Southwestern Pa.
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Default Re: Couple lithium questions.

Originally Posted by panteramatt View Post
Any reason this wouldnt work without a bms?
Yes, as Bronsonj stated that kind of setup only controls "Pack" voltage. Not individual cell voltage.

So...unless your going to manually check the cells charged voltage on a regular.....very regular basis you could run into big trouble.

A good BMS will "take from the rich and give to the poor" in terms of battery charge. So....if you set an upper limit of say 4.1 for each cell....and one or two cells are at 4.2 and you have a few at say 4.05, the BMS will reduce the higher cells and give that power to the lower cells.

The big reason for that is when your dealing with Lithium....if you overcharge or undercharge ONE cell, that cell is now damaged forever and if you continue to charge a damaged will likely experience "Thermal Runaway" or essentially....that battery will start a very hot.....very fast fire.

See the sticky post on the fellow (teenager) who did just that and he may still have the photos still there. His cart ended up a small pile of melted plastic....and melted metal.

Hence the "insurance factor" of a BMS.

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