Hi all, first let me say that I'm an electrical or maker newb, especially compared to all you veterans. But I'm committed to learning the craft because I think it's very fun.

Right now I'm trying to upgrade an old cordless ratchet from the 1980's, it's a Black and Decker 9050.

I have a good Samsung 21700 to replace the old ni-cad batteries in the ratchet. But I need a good protection circuit for it. Preferably a circular one that I can affix to the bottom of the battery. It needs to be able to flow 10 amps continuous, and cut off at 3.0v to protect the battery from the voltage going too low.

I guess it doesn't have to be circular, but it would be nice. Thanks!

 

What sort of circuit do you have in mind for this purpose?

 

Sounds like photonfanatic wants/needs a BMS (Battery Management System) for a single cell 21700 Lithium Ion battery. Something like this:
https://www.amazon.com/ACEIRMC-Charger-Protection-Lithium-Battery/dp/B08MPXHFJB/ref=sr_1_1
It states it's for a 18650 but the number is merely a size reference. The 21700 is slightly longer and larger in diameter. Aside from that the BMS shown is good for 10A.

 

Sounds like photonfanatic wants/needs a BMS (Battery Management System) for a single cell 21700 Lithium Ion battery. Something like this:
https://www.amazon.com/ACEIRMC-Charger-Protection-Lithium-Battery/dp/B08MPXHFJB/ref=sr_1_1
It states it's for a 18650 but the number is merely a size reference. The 21700 is slightly longer and larger in diameter. Aside from that the BMS shown is good for 10A.

Yes that is the type I'm asking about. However, if you look at the specs it says "Protection voltage range: 2.5V-4.2V."

I've read that these lithium batteries don't appreciate being made to go below 3.0v. And if you do that regularly, it shortens their lifespan considerably. My battery is Samsung 45-T 21700.

So I'm looking for one of those you linked, which cuts the power when the battery gets down to 3.0v. I've been searching through amazon but everything seems to cut off at 2.4 or 2.5v.

Unless maybe someone here knows that going down to 2.4v regularly is ok?

 

I've read that these lithium batteries don't appreciate being made to go below 3.0v. And if you do that regularly, it shortens their lifespan considerably. My battery is Samsung 45-T 21700.

Read this. Scroll down to specifications
https://18650battery.com/products/samsung-45t-4500mah-50a-21700-battery
Says "Discharge cutoff voltage 2.5V"