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Lithium pouch cell protection circuit? (imgur.com)

submitted 1 month ago by tuff_wizard@aussie.zone to c/askelectronics@discuss.tchncs.de

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Trying to trouble shoot a cheaper wireless meat thermometer. It was working find when put away last year.

Now won't turn on or respond when put on charge.

The lithium pouch cell looks fine and reads 3.5v at the battery tabs. No voltage read on the output of the small circuit board attached to the pouch cell. A bit of googling has lead me to believe it is some kind of "battery protection circuit" or possibly a BMS or charge controller. I have found many similar ones but no exact match on AliExpress. It reads QLD-3036.

If anyone is familiar with those little boards can they let me know

If there would be any reason it would be stopping power getting from the battery to the main unit?

If there is some easy way to reset the board?

If the small board modifies the voltage of the battery at all and if not would it be ok to bypass the small board and supply dc to the main board where the red and black wires connect for testing purposes? I have a variable power supply and would have no issue with converting this unit to run connected to a power supply permanently.

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[–] g5pw@feddit.it 4 points 1 month ago (1 children)

That looks like a battery protection PCB, yeah. It usually does three things:

over voltage protection
undervoltage protection
overcurrent protection
reverse polarity protection

Bypassing it would be a bad idea, but it’s also pretty rare they fail. Maybe it’s just in undervoltage protection mode. Try to hook up your variable power supply with 4.2V and a 50-100mA current limit to the battery tabs (check polarity!) and see if the cell takes current. Above 3.6V the battery protection should lift and you should see voltage on the battery output terminals.

[–] tuff_wizard@aussie.zone 2 points 1 month ago (1 children)

Awesome, thanks. that is exactly the kind of info I was looking for, I'll give that a go.

[–] g5pw@feddit.it 3 points 1 month ago (1 children)

Keep a sand bucket nearby, just in case :)

[–] tuff_wizard@aussie.zone 1 points 1 month ago (1 children)

Sooo I accidentally caused a short (just a teeny tiny one, hardly any smoke!) and it’s blown a trace on that little board.

Considering the battery has no indication of size is it possible to recommend a battery protection board To replace it with? Before the short the device had switched on.

I am also open to just wiring a 240vac to 4.2vdc charger straight to the board where the battery was. It is used for long smoking sessions so I am happy to run an extension lead. It would run when flat off a Samsung phone charger so probably needs less than 1a.

[–] g5pw@feddit.it 1 points 1 month ago* (last edited 1 month ago)

Uh that is unfortunate :/ battery protection circuits do not usually care about capacity directly, but just about max currents (which is usually related to capacity), so… unless you need a lot of current, get a 2A limiter and you should be good.

Try not to short anything else, like the battery terminals though! It may weld stuff into a continuous short and start a fire.