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Apr 21, 2007, 08:18 PM
Blessed by anvils from heaven
Chophop's Avatar
Discussion

My nimh's didn't come back after winter


I have 6 nimh 8 cell batteries that were working fine Feb, they sat due to weather, now in April, I am lucky to get off the ground. Any way to bring them back ?

CH
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Apr 21, 2007, 08:40 PM
Registered User
ebill3's Avatar
Quote:
Originally Posted by Chophop
I have 6 nimh 8 cell batteries that were working fine Feb, they sat due to weather, now in April, I am lucky to get off the ground. Any way to bring them back ?
Try a couple of cycles charging at C/10 for 12 to 14 hours. They ought to come back OK.

Bill
Apr 21, 2007, 08:41 PM
Naturally altered
What brand are they?

Very slow charge followed by regular discharge, do it twice. After chargiing once again, any packs with less than 8 x 1.3 volts has dead cells in them. Put to regular use. If performance is not back after a few high discharge cycles (flying them), they are pretty much toast.
Apr 21, 2007, 09:03 PM
Blessed by anvils from heaven
Chophop's Avatar
Thanx for the replies. Some are Eflite, some Walkera. All act the same. I tried several charge/discharge cycles, but charged at 0.7C . Will try C/10 .

CH
Apr 21, 2007, 10:08 PM
RC Addict
Raydee's Avatar
Funny I ran by this topic because I ran my Nimh cells for the first time today since last fall and they were very weak feeling. I slow charged them on 500mah and I will see if they do any better tomorrow......if not I will be getting lipo's sooner than I planned
Apr 22, 2007, 08:30 AM
Registered User
Hello Chophop,

When you stored you packs were they charged or empty?

Tom
Apr 30, 2007, 03:24 PM
Blessed by anvils from heaven
Chophop's Avatar
I stored them charged. After about 6 cycles they came back to life, and from 2.5 to 7 minutes flight time, about normal. I charged them full and used them straight off the charger, which is what seemed to bring them back. Funny, I just got some lipos that blow the nimh away.

CH
Apr 30, 2007, 09:12 PM
Registered User
I've raced R/C cars for 15+ years. We use the same batteries for the cars, in 6 cell packs,as you're using in your airplanes. However,ours are matched by voltage and run time for optimum performance. They are charged @6 amps and discharged @35 amps when they are matched. We routinely charge @ 6 or 7 amps when we race them. After a race they are discharged @ 35 amps until the pack voltage reaches .9 volts per cell (5.4 in a 6 cell pack). If the pack is to be stored for more than a week we put 10min. of charge back in the pack @ 6amps. If they will be used sooner, we leave them @ 5.4volts. Before charging, we discharge the pack to 5.4 volts and start charging again @ 6 amps. We never trickle charge.
NiMi batteries like to be warm. We use a peak charger that has adjustable peak detect drop back voltage, usually set at .03 volts. The pack will be around 100* when it comes off the charger. In the winter we even use a heating pad to warm the pack up before charging.The difference is quite noticable between a freshly charged pack and one that has sat for a while. Fly with a pack charged at home and then with a pack charged at the field and see if you can feel the difference.
May 01, 2007, 02:11 AM
Registered User
Quote:
Originally Posted by Jim Carr
NiMi batteries like to be warm.
That depends on your priorities. NiMH performs better when warm, but lifetime is reduced. If you prefer your batteries to last long rather than give optimum performance then try to not get them too warm.
May 01, 2007, 09:43 AM
Registered User
When forming (or reforming after a long rest like over winter) charge at 0.1C for 16 hours, any less may not do the job although you can sometimes get by with a 14 hour charge at this rate. Any less time does not bring all cells up to their proper voltage.


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