Hacking DW01 as a cell balancer - Page 1
Forum section: electronics / projects

author: aruna1
author_rank: Regular Contributor
timestamp: September 10, 2021, 02:33:32 am
content: 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 belowsince 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?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 10, 2021, 03:31:29 am
content: 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.

author: aruna1
author_rank: Regular Contributor
timestamp: September 10, 2021, 03:50:21 am
content: Quote from: NiHaoMike on September 10, 2021, 03:31:29 amYa 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

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 10, 2021, 04:29:19 am
content: How about an opamp based rail splitter, with a pair of MOSFETs to only connect it when charging?

author: thm_w
author_rank: Super Contributor
timestamp: September 10, 2021, 09:23:19 pm
content: You don't want to use a premade board right?https://www.aliexpress.com/item/1005001636432977.htmlOr build the IC into your circuit and use the premade board as a temporary solution.

author: aruna1
author_rank: Regular Contributor
timestamp: September 11, 2021, 06:43:39 am
content: Quote from: NiHaoMike on September 10, 2021, 04:29:19 amI tried the DW01 trick and it worked

author: magic
author_rank: Super Contributor
timestamp: September 11, 2021, 07:13:41 am
content: It seems you are looking for a low power so-called "voltage detector" IC.Quote from: aruna1 on September 11, 2021, 06:43:39 amReport back after the cell has spent a few years on float charge like that

author: Miyuki
author_rank: Frequent Contributor
timestamp: September 12, 2021, 10:49:50 am
content: Is some cheap micro too expensive or too complicated for you?You need just one for multiple cellsIt is a common solution in bigger bms

author: Marco
author_rank: Super Contributor
timestamp: September 12, 2021, 06:04:01 pm
content: What's wrong with the humble TL431?

author: magic
author_rank: Super Contributor
timestamp: September 12, 2021, 06:25:40 pm
content: 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.