Mabuchi540

Ok I've started cycling my ni-cad batteries (sports packs) on a discharger and I've noticed something already that I'm curious about.

Most of the ones I've done so far reach a voltage of approx 6.5 then speed up the descent quite rapidly (but still steady pace) from there down to the 5 volts where I unplug them.

BUT one pack discharged down to 6.5 then dropped almost instantly (less than a second) down to 5.3 volts and spent the last 30 seconds getting down to 5v.

These are all new packs and as I'm new to the whole cycling side of things (I used to just charge and go so to speak) I wonder is this pack the odd one out in a good way or is it stuffed already?

Thanks in advance.

Cole Trickle

This one pack, for how long was it discharged before it dropped? At which discharge rate? Souns like this pack contains a cell with mare capasity then the others, that is, the other 5 dump, and then the last cell keep up the voltage a little longer. That's not good, because this inconsistensy will get worse over time, since the lower capasity cells are overdischarged and the last cell probably is over-charged.

If you can discharge cells indivdually, you can identify this particular cell.

Mabuchi540

....

The discharger is 17.5 amps and the drop happened at the 4m 49 sec mark and reached the 5 volt mark at 5m 19 sec.

I cant test each cell sorry as they are all stick packs for 540 stock class racing.

so far the other packs have taken from 5m 55sec down to 5m 23 sec to reach the 5 volt mark but all of them have started the increased discharge speed around the 6-6.5 volt mark. but none have shown that rapid drop as this suspect pack has.

Mabuchi540

As a side note is it normal for the two cells that the actual battery leads are attached to get hotter than the 4 cells below them in the configuration?

I noticed this on all the packs.

Additional part 2: Just finished the last pack and it had a sudden drop like the one I mentioned in my first post but this one didn't take 30 seconds (5min 19 sec in total) to loose the last .30 of a volt it took 6min 10 sec to reach 5 volts.

Cole Trickle

Are you able to draw actual voltage versus time curves? And post them here, that would be a lot easier to get an overview of.

If you have the equipment, you can test each cell individual in a stick pack. It's just a lot of hazzle...

So with curves, it might be easier to judge, if it's a problem worth concerning. If it's a problem, it might be worth to tear that stick pack apart.... And change the bad cell.

How do this particular pack perform on the track, compared to the others? Any noticable difference?

Are you allowed to run saddle packs? To my experience Sanyo responds really well on an equalizer.

Mabuchi540

Most likely right and it's probably not worth the hassle for $8.99 packs :P But would still like to know which are the best in the batch of 7.

Haven't run them yet as I'm cycling them a few times each to figure out the aforementioned best of the bunch.

I've been writing down some more accurate figures and the "bad" one showed a reading of 6 volts at the 5 min discharge mark and took a total of 5min 35 sec to reach 5 volts.

The "best" one so far has read 6.32 at the 5 min mark and taken 5 min 48 sec to reach 5 volts. The other good packs have all been within .04 of a volt of this pack and 4 seconds of total time.

Thanks for the help.

Cole Trickle

Glad to help

I did a individual test of the cells in my old Sanyo 1700 NiCd pack - if I still have the data somewhere, I'll post it.

What amazed me about this pack, was that all 6 cells was very close to each other - after 3 years use, and some abuse too.