[chbot] BMS - How they work?

[Martin Towers]

There's a description of the board here:-
https://circuitdigest.com/electronic-circuits/lithium-ion-battery-management-and-protection-module-bms-teardown-schematics-parts-list-and-working
scroll down for the exact version.

and a data sheet for some of the chips here:-
https://www.hycontek.com/wp-content/uploads/DS-HY2213_EN.pdf
Martin

-----Original Message-----
From: Helmut Walle <helmut.walle at gmail.com>
Reply-To: Christchurch Robotics <chchrobotics at lists.ourshack.com>
To: chchrobotics at lists.ourshack.com
Subject: Re: [chbot] BMS - How they work?
Date: Wed, 7 Dec 2022 21:33:18 +1300

 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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