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

Thread Starter

noweare

Joined Jun 30, 2017
112
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
4,204
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
943
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
112
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
943
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.
 
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