New re-celled 24v NiMh battery (Powacycle) won't start charging

[chazpope]

Hi

It appears that the charger decides not to charge this battery

I just recelled my Powacycle Cambridge battery (this is my third time) with Tenergy D size 10000mah cells - looks like they are the best available at the moment.

After I built the battery the cells were almost empty so I discharged them with a bulb, checked that they are all the same and started charging. The charger showed the red light as usual -and charged for about 4 hours - but after this the charger light went off (rather than turn green as normal). If I connect it again it starts blinking faster and then there is no light and it is not charging.

What this charger usually does is blink red with no battery, then go red to charge and green when ready. I am not sure what a dying-blinking light means but looks like when I connect the battery it decides not to charge it.

The battery itself was charged ok this once and I put it on the bike and it performed greatly until it went flat - capacity was more than I expected. But now I have a flat battery and no way to charge it !

I actually have 2 chargers and batterries - I tried the other charger - it normally shows green with no load - then red and finally green when ready. But it one does not seem to charge the new battery either and shows a blinking green-to-red light. Again I have no idea what this means ?

I opened the battery and could not find anything wrong. The thermo thing measures about 14K - same as the other battery, fuses are all there.

Comparing how the chargers charge the other battery the difference is that there the voltage goes up to say 27V at the start of charging (when the charger seems to be pulsing) whereas on the new one it seems to stay at 24.5 volts - I wonder is it that the new bigger capacity makes it think there is a short so it does not start.

But then again initially I had no problem and charged ok for 4 hours

Any ideas ?

 

[chazpope]

no replies, I guess I should buy another charger ant try that - any recommendations ?

 

[flecc]

I'm wondering if you've wrecked some of the cells. You say that they were empty and you discharged them with a bulb, which is something that really shouldn't be done. NiMh cells shouldn't be discharged below 1 volt per cell and they can fail completely if taken below about 0.7 volts per cell due to the hydride losing it's ability to hold hydrogen.

 

[chazpope]

I doubt it, after I did this the pack got charged to almost full and then delivered that power ok and there was no sign of any damage. I don't see anything wrong with discharging with bulb or whatever now and then as long as there is no reverse voltage situation. On a power drill nothing monitors the discharge state voltage but still they work multiple times before they go bad.

The pack is still capable of delivering 5 amps through that bulb as it was not discharged completely, also I measured individial voltages undert load and they are the same, also the charger should work (charge with a regulated 1.8A) whether or not a cell or two are there or not.

I even tried adding another cell in series and it still did not start charging, so it is a bit of mystery at the moment - and the key is in what it meanswhen the ShenZhen ABT charger blinks green and red ...

 

[flecc]

The cells seem to be ok then, but I stand by what I say about discharging them. The battery industry was always clear on this and NiMh e-bike low voltage cutouts are at 1.1 volt per cell.

The only time I've seen similar alternative blinking conditions was with a charging open circuit, but that doesn't seem to be the case here. Since the NTC thermistor measures ok, there's little else I can suggest, though you could substitute the thermistor with between a 10k and 14k resistor to see if it starts charging then, giving a further clue.