nimh batteries and storage voltage

[rondoolaa]

hi,

i got 8 x intellect 3800mah nimh 7.2v batteries off a friend,

they had been discharged and most of the batteries read in total between .684v and 1.3v for a whole 7.2v pack...

i have started to charge them and done them at 2 amp instead of the standard what would be 3.8 amp as they were so low...

they have took over 2 hours charge each to recharge but are peaking ok and seem to have charged ok...

i didnt know you could take nimh batteries so low, is this the norm and do you think they could be damaged in any way for being so low, although they seem fine so far, i guess a run and recharge may answer the could they be damaged question

[SlowOne]

NiMh cells should not be allowed to drop below 0.9v per cell. You seem to have recovered the packs, but as you say, only when you run them and re-charge them will you know if they are any good. The 3800mAh cells are reasonably tough, so you might get away with it. If they were 4000+, I wouldn't give you a prayer!

If they check out OK, then make sure you keep the packs above 6.0v during storage, and cycle them every month to be sure. In all honesty, if you want to run these types of cell, you are better off with NiCad, or with Tamiya packs. Tamiya sell good NiMh cells for the occasional user, as they don't seem to go off as badly as others. HTH

[neiloliver]

Assuming you have the cells in a side-by-side configuration or as saddle packs find yourself a Novak balancer if you can (with so many people using LiPo now I am sure you can get one cheap). Use this to discharge each of the cells down to 900mV after each use and then charger again. With the packs being so old you will have some cells that are weaker than others and balancing the cells individually with ensure that you are not dragging the weak cells down to a very low voltage when you discharge the overall pack.

N

[dexter24]

Originally Posted by neiloliver

Assuming you have the cells in a side-by-side configuration or as saddle packs find yourself a Novak balancer if you can (with so many people using LiPo now I am sure you can get one cheap). Use this to discharge each of the cells down to 900mV after each use and then charger again. With the packs being so old you will have some cells that are weaker than others and balancing the cells individually with ensure that you are not dragging the weak cells down to a very low voltage when you discharge the overall pack.

N

What sort of running temperature would NiMH packs be ok at ??? As i took my B4 buggy out for a bit today and ran my 2 team orion 4000mah stick packs and were quite hot, i used a temp gun on both packs which had been running for about 9mins. One pack was 58.6 degrees C and other at 60.1 degrees C ???

cheers

[rondoolaa]

if you look at the first pack on the left in the pics attached,

starting at the top,

b4 charge it read 1.04 volts for the whole stick pack,

after the charge it read 8.87 volts,

it was charged at 2 amp and took 143 minutes,

the other 3 packs in the pictures (one with flash one without) are marked on what their stats were,

after i left all the stick packs for a couple of hours they all read between 8.35 volts and 8.43 volts,
does this sound ok,

i will run them all tomorrow and then recharge them all again and hiopefully none will go pop during the day, lol,

what approximate running time would you expect to get from a 3800 mah nimh that was charged at 2 amps, as i will be timing them all and measuring temps afterwards too,


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to the poster above, i have ran my 3300 mah nimh batteries and they are too hot to hold onto for more than a couple of seconds after running them for approx 8 - 10 mins, probably around 80 degrees, so yours sound ok to me

[SlowOne]

Those temps sound OK. When charging, try to keep them below 40degC, which your 2A charge should easily achieve. When running, they can get much hotter than that without concern. It sounds silly, but if the heatshrink stays intact, they haven't got too hot! If you can't grasp them in your hand after they've run (for a couple of seconds at least!) then look for other issues - gearing, binding, etc. - before running again.

The numbers look fine, but check them each day until you run. Voltage drop should be minimal, and if it is then the cells are probably good for running in the car. If the voltage drops by 1v or more, then their storage condition (the low volts in your original post) has done for them.

I hope it all works out for you.

[rondoolaa]

the batteries seem fine, they ran for about 15 - 20 minutes each, could even have been longer, and after that time they were just luke warm to touch,

the guy i got them off said they had been stored discharged for about 8 months,

can't believe they were still ok, well happy as my son and myself run both our 1/10th cars off nimh batteries,

so got a few good extras now,

run my 1/18th and 1/16th off lipo though....
dont like the price of lipo for 1/10th, lol

[SlowOne]

Good work! I like a happy ending!