Smallest 3-cell Li-ion battery protection circuit?

[eccerr0r]

Curious if anyone has come across a small 3-cell li-ion battery protection circuit. It only needs to pass a maximum of 2A or so, but needs to be small...say, smaller than 1.5" x 2" x 0.3" or so, if there's something close it's worth entertaining!

BTW: If it's the width of 3 18650's, that's too long in that dimension most likely... don't have much room for this application - it uses prismatic pouch cells.

[sam_sam_sam]

Re: Smallest 3-cell Li-ion battery protection circuit?

Could you please post the photo of the cells you are going to use thanks

[eccerr0r]

Re: Smallest 3-cell Li-ion battery protection circuit?

As the box is made of plastic and has those plastic clasps I hesitate to open it more than needed. Anyway it's a small battery pack. I'm sort of retrofitting someone else's "hack" so it's a hack of a hack which isn't pretty - the pack originally was 7 pcs ½AA retrofitted with 3pcs pouch Li-ion cells. The inside dimensions of the box is approximately 55mm x 30mm x 33mm, of which most of it is occupied by the cells.

I was worried before but perhaps the longer 55mm dimension might actually be long enough to accommodate an 18650x3 board as long as it's thin enough - I don't think I have more than 3 mm to spare in in the 30mm direction and 5mm in the 55mm dimension due to the rectangular pouch cells (the three cells bound together would be around 50mm x 27mm x 33mm).

It would be a tight fit no matter what.

[sam_sam_sam]

Re: Smallest 3-cell Li-ion battery protection circuit?

Is the voltage 4.2 or is it 12 volts you are using

[eccerr0r]

Re: Smallest 3-cell Li-ion battery protection circuit?

Using the "12" volts. Note I "quoted" it because it's way too many volts, alas it does work... just won't charge it all the way to 12V to limit damage. Hopefully the cells will last more cycles since they won't be fully charged -- though the risk of overdischarging is a big problem.

[eccerr0r]

Re: Smallest 3-cell Li-ion battery protection circuit?

Speaking of overvoltage protection, can the voltage limits typically be easily reduced lower, to, say, 11.7 volts charge cut off (3.9V x 3) instead of 12.6V (4.2V x 3)? Maybe an even 4.0V would be fine. I suppose SMT rework would be inevitable but that's what it is...

[sam_sam_sam]

Re: Smallest 3-cell Li-ion battery protection circuit?

Curious if anyone has come across a small 3-cell li-ion battery protection circuit. It only needs to pass a maximum of 2A or so, but needs to be small...say, smaller than 1.5" x 2" x 0.3" or so, if there's something close it's worth entertaining!

BTW: If it's the width of 3 18650's, that's too long in that dimension most likely... don't have much room for this application - it uses prismatic pouch cells.

This is about as close as you are going to get for what you are looking for


https://www.ebay.com/itm/3A-4A-3S-12...4AAOSwHMJYDCrd

Or

https://www.ebay.com/itm/Battery-BMS....c100005.m1851

[sam_sam_sam]

Re: Smallest 3-cell Li-ion battery protection circuit?

Speaking of overvoltage protection, can the voltage limits typically be easily reduced lower, to, say, 11.7 volts charge cut off (3.9V x 3) instead of 12.6V (4.2V x 3)? Maybe an even 4.0V would be fine. I suppose SMT rework would be inevitable but that's what it is...

I have wondered what you have to change in order to change the voltage

[eccerr0r]

Re: Smallest 3-cell Li-ion battery protection circuit?

Looking at possible reference designs for the protection circuits, I think it's not possible to change the voltages as it typically depends on internal references within the ICs.

Now the question is which ones are balancing and which one are simply protection. I think the simple protection is sufficient though balancing would be better.

[sam_sam_sam]

Re: Smallest 3-cell Li-ion battery protection circuit?

In two links that I posted the first one is only a protection board
The second one says that it is a BSM board but I do not see the specks for the balancing so I am not sure that it is a BSM board

[eccerr0r]

Re: Smallest 3-cell Li-ion battery protection circuit?

Some balancing boards use i2c to program voltages, that may be good, though a lot of boards I can't read the balancing IC... If it were done by an external voltage divider...

... it would consume so much power that the idle battery life would be severely impacted...