Charging & discharging ni-mhs

[gav79tt]

Just bought some 7.2v ni-mh packs for my nephew to start racing with, ranging from 3700mah - 5000mah.They have all been discharged before i received them, but when i have tried to charge them they dont seem to be getting any charge in them??:confused: i have only ever had lipos so dont know too much about them? im using a core20 charge if it helps? any info on how to get them going again would be much appreciated.:thumbsup:

[SlowOne]

They should have had at least 1.1v in every cell when you got them. If they didn't then it is likely that they can't be recovered. They should be returned to the seller for them to make them work, or to refund you your money.

If you want to check this, plug the cells into your charger, and look at the reading that tells you the pack voltage. It should say 6.6v or above. If it reads less than that, then the chances are that one or more cells are below 1.1v, and likely to be faulty.

Check that your charger is set to NiMh mode, set the charge rate to 1C (max 4.5 amps for the 5000 cells) and start the charge. If nothing is happening, then it is possible that one cell is not working, and it will only take one cell to prevent the pack from working.

When you get some working packs, make sure that you regularly use them, and store them with about 50% charge. Don't let them go flat. We found, in the final days of NiMh cells, that those with capacity from 3300 to 3700 were far more robust than the late ones with 4000 and above. You'll notice that people like Tamiya only sell batteries up to about 2700mAh - there's a reason for that!

I hope that helps, and you manage to sort the problems out. :)

[gav79tt]

thanks for the info.i will try charging them again and see what happens???? hopefully there all ok.
cheers

[damselfly]

NiMh cells will recover fine provided they haven't been discharged to less than about 0.8-0.85V per cell. I discharge my cells to 0.9V and they're still in excellent shape after 300+ uses. I no longer use them though as i'm using LiPo cells.
A good way to recover the cells is to charge them for about 15hrs at 1/10C. I routinely did this after every dozen charges or so and it serves to balance any weaker cells in the pack. This is often recommended for the first charge of any new pack too, as invariably, the pack might of been laying redundant for numerous Months.
Good luck.