[chbot] BMS - How they work?

[Helmut Walle]

 From reading the description and looking at the PCB at the first URL below I am speculating 
that it just applies a constant voltage of 4.2 V per cell, and then there is a resistor network 
for cell balancing. Not sure what the small transistors are doing, but these 6-pin components 
next to them might be something PWM (maybe based on OpAmps?)? Or are there any 6-pin PWM chips? 
Not quite my area of expertise - but 555 timers are 8-pin, and then there are dedicated PWM 
components in packages with somewhat higher pin counts.

Easiest way to find out at this price might be to buy one, take a close look, then set up with 
batteries and measure.

Kind regards,

Helmut.

On 07/12/2022 12:36, Marshland Engineering wrote:
> Aliexpress has many 2 3 and 4 cell BMS boards.
> 
> I'm struggling to find out what exactly do they do ?
> 
> See here https://www.aliexpress.com/item/33031988423.html
> 
>  From what I have read, Li-ion batteries have a very specific charging method.
> I cant see this board doing anything like this.
> 
> I have a 12 Li-ion motorcycle battery with a very similar board in the
> housing.  It uses 4 cells. Does it only charge each cell to 3.6 volts or so
> and not 4.2 ?
> 
>  From what I think, car and bike batteries use direct connections to the cells
> for the high starting currents required but should have a completely separate
> charging system. This can easily be done as the alternators can be isolated
> from ground therefore providing a independent charging circuit that can
> monitor each cell.
> 
> Something like this.
> 
> https://www.aliexpress.com/item/32800729065.html
> 
> 
> Any thoughts?
> 
> 
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