Battery protection board needs to have voltage applied to output before turning on.

Thread Starter

noweare

Joined Jun 30, 2017
115
Hello

I have a Lithium ion battery pack that uses a small protection board
that protects the battery pack from short circuits and under voltage.
I am using 2 lithium ion cells in series for a nominal 7.4 volt output.

The wierd thing is the protection board has to be first initialized
by applying a voltage across the P-,P+ outputs. It will only turn on by doing that.

Here is a link to the board:
Link to board

The board has 3 inputs that are used to connect the battery.
Negative pad, positive pad and pad that connects between the cells.
It also has 2 outputs P-, P+ that connects to my dc-dc buck converter.

I never heard of having to do that and makes the board useless IMO.

Wondering if this is normal and all protection boards have to be
"initialized" before using.

Thanks for your help
 

Tonyr1084

Joined Sep 24, 2015
7,852
First, I'm not the expert on this; but I think the protection board needs to sense a voltage before it will charge. If a battery is too low the P-board might not start charging. I've seen similar situations on YouTube where an older 18650 battery doesn't want to charge when put into a charger. They say the reason for that is because the battery is too low. Once you give it a kick (some voltage) it will start charging the battery.

I've tried that with one that I put into an LED flashlight. By mistake I left it on when I put it away. It was left on for days in the drawer, and when I wanted to use the flashlight again, it was dead. So I put another 18650 in it and put the dead one on the charger. It would not charge. I tried using the tricks and techniques I learned on YouTube but no matter what - the battery wouldn't charge.

On the subject you mention, if a battery is weak but has a voltage, when you connect it to the board, it should see sufficient voltage to start charging. If the voltage is too weak you probably, as you said, have to give it a voltage before it will charge. That makes me suspect there may be an issue with your batteries.
 

Audioguru again

Joined Oct 21, 2019
6,672
Look at the reviews. Some people say it is garbage. Also, Amazon knows nothing about electronics, they sell clothes and shoes.

A Lithium charger circuit is supposed to sense a battery voltage that is too low then attempt to charge at a low current. If the voltage does not rise then the charging is supposed to stop and a warning is outputted.

The reason is that if a Lithium rechargeable battery is charged too low (less than about 2.8V per cell) then the battery might become shorted by metallic Lithium which will explode or catch on fire if charged at a normal high current.

A lithium rechargeable battery cell will have its life shortened if it is discharged below about 3.2V. 3.7V is for storage and 4.2V is for a full charge. A storage voltage is needed because the battery life is also shortened if it is stored at a 4.2V full charge.
 

Thread Starter

noweare

Joined Jun 30, 2017
115
I did not think this was for charging batteries only for protecting the pack from shorts and under voltage. There is zero documentation from the manufacturer on this part. Crap, I was nearly done with this project.

Just wondering if any board I purchase will have to be initialized with a charger to turn on. I hope not.
 

Audioguru again

Joined Oct 21, 2019
6,672
No-Name-Brand zero documentation garbage in, garbage out. Instead buy well-made electronic circuits that are made by a manufacturer with a name and with a detailed datasheet.
 

MrSoftware

Joined Oct 29, 2013
2,188

BobTPH

Joined Jun 5, 2013
8,809
I read a description of another board, and it stated that there Would be no output until you connect a charger. So it looks like a feature.

Note that this needs to be done only once after connecting the battery. So it does not really make it useless.

Bob
 

DanaR

Joined Aug 18, 2020
2
Try sparkfun.com, pololu.com, digikey, mouser.. a google result that lands on Digikey:

https://www.digikey.com/en/maker/blogs/lithium-ion-cell-protection#:~:text=A battery protection circuit will,load current is too high.&text=Battery protection ICs typically use,and share one protection circuit.

For the board that you have now, look up the datasheets for the chips on the board, that might help you figure out how it's supposed to work.
So I did just that... using my phones magnifier was able to get chip numbers. The S-8254A SERIES needs to be either kick-started by connecting a charger or connecting the B+ momentarily to the P+. After reading the specification on how it works it appears as though a lead could be added to the chip VMP pin in series with a 5.1K resistor to the B+ pin. This does not circumvent the protection nor the charging functionality. It simply looks as if a charger is applied and turns on the Power Out FET if the batteries have sufficient charge and the withing maximum current. Before doing this verify this yourself. No guarantees are suggested.

My previous design switched the power from batteries to BP module. The new design has the BP module with the batteries and they always remain connected and are not removed for charging (charging is done onboard). So the Output FET will remain on. The Power Output to load is switched.

Thanks for your help
 
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