Is The NiCAD Self Discharging Problem Solved, Or Did I Get A Quirky Bunch Of Cells?

Thread Starter

PGB1

Joined Jan 15, 2013
116
Hello All!
I hope this note finds everyone well & enjoying today!

Almost two years ago, I installed new generic cells in a cordless screw gun's battery packs (9.6 volt NiCAD).
To equalize the cells in each pack, I first charged them as slowly as possible for about 16 hours (100 mA charger for 2800 mA cells). Then I used the tool until the motor noticeably slowed, then I repeated the slow charge. After two trickle charges as explained, I used the tool like normal: Run until noticeably slower, but not dead- then use the factory charger. Each pack was used to depletion about 4 or 5 times on a project before the tool was put away.

Then, all good practice went out the window. I forgot about the tool, so it sat unused for 23 months. (I understand, maybe incorrectly, NiCAD cells get damaged if unused- whether charged or not.) Storage is basement temperature- About 75-F max and 35-F minimum.

After 23 months, I pulled out the tool and the motor sounded as fast as usual. So I immediately pulled the battery pack and tested voltage. For the 9.6 volt packs, I read 9.45 on one and 9.20 on the other. Since that day, I've used the packs on a project for two or 3 discharge cycles each. They perform quite well.

Searching on line about NiCAD self discharge only pulls up articles explaining how they do discharge while unused.
Is the NiCAD self discharge problem solved? Has the chemistry changed, or is the manufacturing procedure that changed? (Or nothing changed & I got a bunch of quirk cells.)

Also, is it OK to leave NiCAD sitting unused on a shelf, or should they be used & re-charged periodically?

Thanks for sharing!
Paul
 

Delta prime

Joined Nov 15, 2019
361
Hi there. :) I am enjoying the day. Thank you very much.
Nickel-Cadmium batteries contain the chemicals Nickel (Ni) and Cadmium (Cd), in various forms and compositions.
An easy way to check if you have a NiCd is to measure its internal resistance and compared with manufacturers datasheet.
Because their internal resistance is so low, they are capable of discharging a lot of power very quickly, as well as accepting a lot of power very quickly. Having such a low internal resistance keeps the internal temperature low as well, allowing for quick charge and discharge times. :)
 

Thread Starter

PGB1

Joined Jan 15, 2013
116
Thanks Jpanhalt & Delta Prime for taking time to reply & explain.

Jphanalt, they're generic, no name. That leads me to believe that they did, indeed, come from somewhere in the Alibaba empire.

Thanks Delta Prime for explaining the composition & resistance factors in NiCd. It's interesting, to be sure!
There's no manufacturer listed, so there's no data sheet specific to these. I did find name brand specifications for this size and capacity cell from a few manufacturers. The specification was 0.15 Ohm per cell for most of the ones that I found. I can use that as a kinda-sorta reference.

Before I test these cells (I have some left overs), I wanted to check to be certain that they should be discharged completely first. Is that correct? Or should there be some residual charge left for testing? (Seems like checking resistance across a cell with a charge might give a goofy reading, plus I'd imagine the meter would not be thrilled.)

Thanks Again!
Paul
 

jpanhalt

Joined Jan 18, 2008
9,647
Thanks Jpanhalt & Delta Prime for taking time to reply & explain.

Jphanalt, they're generic, no name. That leads me to believe that they did, indeed, come from somewhere in the Alibaba empire.
Awhile back, I was rebuilding the battery packs for some older (10+ years) Craftsman cordless tools. Many ebay sellers called them "NiCd" packs. Only the fine print revealed they were "replacements" for NiCd packs and were, in fact, NiMH. I ended up buying NiCds from Tenergy and an assembler who used genuine NiCd's.
 

KeithWalker

Joined Jul 10, 2017
1,019
You do not need to discharge the cells completely. The internal resistance of NiCads increase with the age of the cells.
To measure it you need two 1 ohm 2 watt resistors. Measure their resistance as accurately as you can. If you only have a multimeter available, make up a pair if short test leads using 14 or 16 AWG wire to minimize the effect of lead resistance.
Fully charge the cell.
With a voltmeter connected across the cell, connect one resistor across the cell and quickly record the voltage. Add the second resistor in parallel with the first and record the voltage. Then disconnect everything.
Calculate the current flowing in each of the two measurements.
The internal resistance of the cell is the difference between the two voltage readings divided by the difference between the two current readings.
Regards,
Keith
 

Thread Starter

PGB1

Joined Jan 15, 2013
116
Only the fine print revealed they were "replacements" for NiCd packs and were, in fact, NiMH
I'll bet those self-discharge really quickly on the shelf. Interestingly, at work we had some battery packs rebuilt by a well known battery store chain's local franchise. Those turned out to be NiMH in disguise.
(I have bought Tenergy for important items and they do seem to last through many, many cycles.)


On thing that I do when rebuilding a tool's NiCD battery pack is to buy cells that are at least double the charger's output amperage. (Assuming the charger is current-limiting). It takes longer to charge, but I believe this should help with longevity of the cells.

Thanks Very Much Keith for explaining how to test a cell's resistance. You're a very good teacher.
For fun, I experimented with some cells. The results are after deducting the multimeter's test lead resistance:
A) New AAA Alkaline = 0.15 Ohm
B) Used, but working AAA MiMH 1800 mAh Charged to 0.8 volts = 0.17 Ohm
C) Used, but working AA NiCD 2200 mAh Charged to 1.23 volts = 0.008 Ohm
D) Sub C NiCD 2800 mAh New. Trickle charged to 1.11 volts = 0.015 Ohm
E) Sub C NiCD 2800 mAh Old, Fast self-discharge problem. Trickle charged to 1.22 volts = 1.52 K-Ohm (Huge difference)
F) Sub C NiCD 2800 mAh Not able to charge past 0.52 volts = 1.5 M-Ohm.

This was a fun experiment and I have saved this thread for future reference.

Enjoy This Day!
Paul
 

Thread Starter

PGB1

Joined Jan 15, 2013
116
Thanks for the information about self-discharge and NiMH, Jpanhalt. Now I won't shy away from using NiMH when they are appropriate for the device.
Enjoy Today!
Paul
 
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