Battery Help Needed

[boater76]

I ran my SH knock off today. I didn't have the thing full throttle very much. But the thing did fly. It was my first build up. After about 2 minutes it slowed down alot. I was running 2 7 cell GP3300 running on a single 700sc that is jacket and brush cooled with a Jeti 600. I got the packs off ebay a couple of months ago. They were sitting from the time I got them til I charged them myself for the first time today. Before that I don't know how long they have not been used. Any ideas or suggestions to help me out here? Thanks

Ken

[ReddyWatts]

Recharge them and see how many amp hours your charger says it put back into them or charge them at one amp and see how many hours it will take to fully charge them. Should be 3.3 hours for a 3300 amp hour battery.

[Mich. Maniac]

sounds like they were left sitting nearly full charged and have developed the memory that most speak of. I have always had that with these cells. I have now switched to lipo even on my radio shack hummer. they dont seem to do that and are more pricey but have longer life and charge.

[boater76]

Should I discharge them completely then charge them?

Ken

[ReddyWatts]

A NiMH should not be discharged below 1.0 volt. The 3300 hundred rating is from the 1.0 volt reading. Your boat should start slowing down when the batteries get to 1.2 volts, so just recharge them and see how much capacity it takes to recharge them.

[boater76]

I checked the 2 packs this morning and were registering over 10.4 volts and I didn't recharge them or anything since yesterday morning. Whats the deal with that if the boat slowed so fast when I ran it? How do I test the mah with a multimeter? You all don't think there is some sort of electrical problem with the boat do you?

Ken

[boater76]

Heres some more info if it might help. I check each cell and none are dead. The one pack each cell was mid 1.4? range and the other pack the cell were in the upper 1.4? range.
Ken

[Rex R]

it can take 2-3 runs/cycles to get the batteries back in condition after they've been sitting unused for a while.

[ReddyWatts]

You cannot read the actual MAH of a battery with a volt meter, but you can figure it out using your run time, the amps your motor is using and this formula.

Motor load in amps (times) run time (divided by) 0.06 = Battery mah

Example: 35 amps (times) 5.65 minutes (divided by) 0.06 = 3295 MAH used from batteries.

[ED66677]

...They were sitting from the time I got them til I charged them myself for the first time today.

do you mean they were brand new? if so, it is pretty normal that run time was around half (not even) of what it is supposed to be!

Nimh batteries need a breaking in for at least 2 or 3 cycle before they are "ready" for use, you should see (if charger permit) that capacity will go above 3300mAh after the third charge (e.g my GP2200 could be charged at 2560mAh @ 200mA)

If your charger doesn't show capacity then buy a EagleTree from OSE, it'll tell you how many amp they received during charging and how many amp they restituted during run!

for the 3 first charge, stay at 1/10 of capacity so around 300-400mA and remember that most Nimh cell can be constantly charged at .01-.05C to keep them ready at any time, give them a 1C charge just before running in order to warm them up, they'll like it and give you lot of power!