BMS 3S 4S 6S 7S 8S 9S 13S 16S which one to buy???

[jdevera1972]

wow.. what a great video on the Active BMS. really cool but it got me thinking. which one should I get? 4S or 6s? would it be better to get the 6S and use it on a 4S? will it balance the 4s batteries?

ref:

 

[svetz]

I believe Will recanted on the active balancers...

I'm not convinced it's actively balancing by charging a lower voltage cell using the higher voltage cells. I watched the lowest voltage cells in your demo and they didn't go up in voltage. It looks to me like it's discharging the highest cells through the big 1R0 (1 Ohm) resistor on the board by measuring which of two neighbouring cells is higher, and is probably why it gets warm. I think the IC on the board is something like a TI BQ29209 that you can specify an external balance resistor for. TI call this "Automatic Cell Balance"

REPLY
https://www.youtube.com/channel/UCoj6RxIAQq8kmJme-5dnN0Q

https://www.analog.com/en/technical-articles/active-battery-cell-balancing.html

And none of the resistors are large enough to pull that. They are teeny tiny

REPLY
Craig Overend3 months ago
@DIY Solar Power with Will Prowse They aren't inductors on the board you have. Those three large 1R0 passive devices are wire wound resistors. I've seen the the Analog Devices link and videos about the devices years ago when it was Linear Technologies, it is a totally different device that only come in much higher pin counts, and uses transformers and integrated switching FETs to charge from one cell to the next while maintaining isolation.

REPLY
cruiser97eric13 months ago
@DIY Solar Power with Will Prowse Every inductor is also a resistor and every resistor is also an inductor. So you are both right and wrong.


REPLY
DIY Solar Power with Will Prowse
@cruiser97eric1 oh sure, but craig is saying its being used to dissipate 1.2 amps. And I doubt that. Ill just get my meter on this thing and see whats actually going on.


REPLY
DIY Solar Power with Will Prowse
@Craig Overend I think you are right. Been doing some tests today. Damn it.


REPLY
DIY Solar Power with Will Prowse
after more thinking and testing it seems Craig is totally correct

 

[b.james]

Well I use it on a small 50Ah pack I have that has a very weak low capacity cell in it just to make up the 12V . It seems to get all the cells to within 30mv really well and does not get excessively hot , in fact I don't feel any heat at all while its got any leds turned on. I'm fairly sure its not draining the higher cells down because at 50Ah capacity that would take weeks.

Those guys above can't be right . Can there be some other reason for the posts. Do they make an active balancer themselves maybe? I'm sceptical and a few posts like that can destroy a project quickly. Maybe both apparent users are the same person?

Ill see if I can find a circuit and have a look at the chip they mention and see what I can find but as I said it seems to be bringing my bad cell up not pulling the other 3 good ones down.

 

[b.james]

First thing I see is that the chip mentioned is for 2 cells only and the min voltage in is 4 volts . So that chip is not the right one . Ill delve into the board.
Thats a good link Svetz

 

[b.james]

Grizzzman just posted this enlightening page on investigation into active cell balancers.
https://www.beyondlogic.org/review-...ive-equalizer-balancer-energy-transfer-board/

 

[jobu01]

I bought an 8S 1.2A one and it appears to work. It balanced my 8x120AH LiFePO4's much faster than the ISDT BattGo BG-8S. So, now I just use the BG-8S as a monitor.