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Forum Index : Solar : Lithium Ion/LiFePo4/LFP BMS

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bob.steel
Senior Member

Joined: 27/02/2020
Location: Australia
Posts: 188

Posted: 02:38am 16 Feb 2022

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Lithium Ion/LiFePo4/LFP/LTO and others BMS

Seems members are not well up on these and how they work so just a brief intro here and perhaps it helps.Not all BMS's are the same but most .

The BMS is basically a circuit with two switches in it . Both of those switches must be on for current to pass along the negative rail. A control chip reads the data it needs from the cells and switches off one of the switches if what it reads is outside of its set parameters.

Often another part of the chip can attempt in a small way to balance cells whose voltage might be out by more than 100mV. It does this only up near top charge voltage and it puts a resistor to earth to bleed off the higher cell ,usually under half an amp or so) and continue to allow the other cells to charge up.

Thats how I see it anyhow and there are other approaches but they are not yet common .Here is a schematic and the control chips can be purchased in a mulltitude of values for settings depending on what the designer wants.

The MOSFET switches are bottom left in parralel.

Edited 2022-02-16 12:54 by bob.steel

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