undervoltage cut out

[beetleguise]

I have some protected D cells that cut out at 2.75v, so at what point are the batteries in danger of tripping this protection when I check them at rest? I am guessing around 3.5v, but I really don't know. I used to trip my AW C cells a lot, but it seemed that they were around 3.8v when I checked them resting. I want to try to not trip my batteries if possible because I have destroyed a couple and they are expensive! I don't want to charge my D cells everyday because they are running a 5761 bulb which will instaflash on a fully charged pair of D cells. On the C cells this never happened I am guessing because the voltage dropped much more on the C cells than on the D.
So, at what resting voltage is the undervoltage cutout going to trip when in use?:shrug:

 

[SilverFox]

Hello Beetleguise,

You will have to do some testing to figure this out.

Charge your cells up and do a runtime test until they shut off. Record the time, and immediately charge your cells back up.

Next, once the cells are fully charged, do another runtime test, but this time only let the light run for 80% of your original runtime. Shut the light off, let the cells cool down and rest, then measure the resting open circuit voltage.

Tom

 

[beetleguise]

Thanks, that sounds like a pretty good way to determine when the batteries are getting near the undervoltage cutout, but is that bad for the battery? I had a couple of AW cells internally short or something when they tripped the pcb. The batteries were only about 6 months old, and they dropped down to 1.2 volts and could not be charged. As an experiment, I removed the pcb and tried charging with 5 VDC for a few minutes, but it couldn't save the abused cell.

 

[SilverFox]

Hello Beetleguise,

I forgot to mention that there are always risks associated with testing...

Tom

 

[45/70]

I'm frequently amazed at how many people run their protected cells down until the circuit trips. Hotwire folks, I can understand, it goes with the territory, more or less. :naughty:

I look at the protection circuit like a fire extinguisher in your kitchen. If you have a fire, great, you can pit it out, but the idea is not to have a fire in the first place!

The protection circuit is there as a last resort, not a means to tell you when you need to charge your Li-Ion. Sheesh!

Dave