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Forum Index : Electronics : Another Active Cell Balancer, BMS

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Solar Mike
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Joined: 08/02/2015
Location: New Zealand
Posts: 1150

Posted: 02:10am 17 May 2025

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I have been toying with the idea of another active cell balancer design, using a forward converter for each battery cell and a mechanism to read the individual cell voltages by transformer action.

If all coils are wound on the same 65mm ferrite core and drive signals are synchronous, then any cell with a higher voltage than the others will pump current into lower voltage cells, by simple transformer action of voltage difference, at the inverter switching frequency, 60Khz in this case. In order to perform core reset, the pwm on period must be 50% or less.

To measure the individual cell voltages, we have a voltage reference winding and a precision full wave active rectifier. If individual cell converters are switched on, then the voltage at the reference winding is representitive of that cell and as this is a common volt meter, easilly calibrated; thats the theory anyway.

Here is a partial schematic for each cell, it uses an inexpensive mosfet isolated driver (Pai8211A) and 12-12v 1w isolated psu from LCSC. A shift register is used to turn off\on the cell inverters as required; they can be easilly linked to control another bank of 8 cells.

As each cell electronics is duplicated, I might approach this by placing those components on small pcbs, then soldered or plugged into a common carrier board that has the battery cell connections and a cpu controller of some sort.

Here is the base schematic:

Cheers
Mike

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