Hacking DW01 as a cell balancer

[aruna1]

HI All,
I'm working on a project that has a 2 cell lithium ion battery pack. Currently I'm designing the BMS circuit which has a cell balancer.
IC I chose for the purpose of cell balancing is HY2213 which is pretty cheap.



Unfortunately my component sourcing vendor has ran out of stocks of HY2213 and I couldn't find a replacement IC which is in same price range.

And then this thought came to my mind since HY2213 is infact a voltage monitor that generates an output when it sees a predefined voltage, and this behavior is similar to what li cell protection chips do during over charge, can I hack a cheap protection chip like DW01 in to a balancer?

So basically my idea is like below



since I connected CS pin to battery GND, I believe overcurrent / short circuit functionality will be disabled, and whenever it sees cell voltage above 4.25, OC pin will go low, turning on P-MOSFET which then will drain the battery until DW01 sees the release voltage.

Now I have no way to try this out in a test circuit as I don't have a DW01 at hand and ordering couple of chips will take lot of time to deliver (plus huge cost in shipping due to covid situation)

I would like to know your expert idea on this. will this work ? on better do you know any replacement for HY2213?

[NiHaoMike]

It will work if you're using cells rated for more than 4.25V charging voltage, a standard one designed for 4.2V maximum will degrade very quickly above that.

[aruna1]

It will work if you're using cells rated for more than 4.25V charging voltage, a standard one designed for 4.2V maximum will degrade very quickly above that.

Ya you are correct. but I'm running out of options.
but same will happen in battery protection circuits right? I'm not expecting to see cell in balance frequently, and I have a 2S charger IC already setup so things should not over charge

[NiHaoMike]

How about an opamp based rail splitter, with a pair of MOSFETs to only connect it when charging?

[thm_w]

You don't want to use a premade board right?
https://www.aliexpress.com/item/1005001636432977.html

Or build the IC into your circuit and use the premade board as a temporary solution.

[aruna1]

How about an opamp based rail splitter, with a pair of MOSFETs to only connect it when charging?

I tried the DW01 trick and it worked 

[magic]

It seems you are looking for a low power so-called "voltage detector" IC.

I tried the DW01 trick and it worked 

Report back after the cell has spent a few years on float charge like that

[Miyuki]

Is some cheap micro too expensive or too complicated for you?
You need just one for multiple cells
It is a common solution in bigger bms

[Marco]

What's wrong with the humble TL431?

[magic]

It's a big power hog as soon as Vref exceeds 1V - check out the datasheet.
Its input current is 2µA, which necessitates even higher standing current in the divider to avoid error - more power wasted.

You may find some luck with those improved xx431 chips, dunno.