Cant make battery protection trip.

Batteries and Chargers Rechargeable Batteries
1

Im sort of preparing for someone to point out some no brainer mistake here, but tripping the protection shouldnt be harder than just draining the cell.

I have been using my four NCR18650B protected cells from fasttech for a long time. Now I was going to run a regular mAh capacity test to see how they have aged and I decided to just test the function of the pcb protection first. I have had these cells shut down at the proper volgate before. Now I have tried all four, draining them with a simple dc circuit and they all keep delivering power down to 2,7/2.6 volts, one I tried to 2,45 volt to see if thats where the cut off was, but no. I have a fresh battery in the voltage meter.

2

How many amps are the batteries drawing? I seem to recall reading that some protection circuits won’t trip if the amps are too low.

3

This is going to depend on the rate at which you are draining it. Low drain the voltage will go lower before tripping the protection. Too low of drain may not trip it at all.

4

https://www.google.com.au/search?q=NCR18650B&ie=utf-8&oe=utf-8&gws_rd=cr&ei=BxcIV8-XLsXSmwX1uZbQCw

I don’t know if the link will work but it says cut of voltage is 2.5 volts with a constant current discharge at 25 degrees I think that is at one amp?

5

Yep, I can confirm this, and I had the same concern the first time I ran a low mode runtime test with a protected cell.

6

I wonder what you can confirm, I tested a few protection circuits and they tripped exactly at the same voltage with any current drain. I would also be surprised if any manufacturer adds an extra circuit to disable the protection at low currents.

http://lygte-info.dk/info/DischargeProtectionTest%20UK.html

7

Yea i had some cheap ultrafires and i managed to trip them at 2.5 volts i guess because it had fake capacity rating i didn’t pay much attention the light is only about 100 lumen so the current would have been really low…

8

I will keep disharging them to see if I can figure out whats going on. Two of them have slight indentations on the negative pole, the two others seem as fresh as they did out of the box. Actually they are just about a year old. As I recall, last time I played with the protection circuit, I was surprised of how consistently they tripped at at exactly an even voltage, 2,75 or 3 volts, but cant remember which. I am actually thinking of removing the PCB from the two indented cells anyways, so I will get the chanse to have a look for physical defects.

9

Also remember the protection circuits are just that — circuits — and subject to electrostatic damage or just plain failure.
There are good ones and not so good ones. Anyone know what FastTech is selling?
(Remember these would be 3rd party addons after the fact, they don’t come as part of the original manufacturer’s product)