NiMH batteries, specifics

[george kennie]

Mike,
I don't know a heck-of-a-lot  about anything, but this will be my fourth
season using NiMH cells. My experience has been very positive.I leave my
aircraft in the car all the time and it got down to minus seven degrees
here in January and I was worried about the condition of my pack after
such radical exposure. My equipment had been in the car for about 6
weeks under these conditions and when I checked the pak with an ESV it
read 5.2 volts. So much for self-discharge. It has not been a problem
for me. I charge with  a Hi-tec CG-325 reflex charger and most of the
time in the car. It's a detector and only puts back what I took out the
previous flying session. I'm using 1650 ma paks and can fly more flights
than there is enough daylight for. Oh, I also picked up a pak for my
Txmitter at the Wram show and previously was down to  9.7 volts after 4
flights(which made me just a tad uncomfortable), but now I can fly for
10(that's ten) hours at which time the voltage is reading 9.9 volts.
AWESOME!
I know that there are many warnings about overcharging, but with proper
hardware these things seem to do extremely well. If you have the pak on
charge in the car and then start the engine of the car, sometimes the
high current starting drain will trigger a false peak and it will kick
out so you have to be vigilant. I usually reset the charge circuit and
if the pak is full it will revert to trickle within a couple of minutes.
If it doesn't kick out within a couple of minutes I know that it
experienced a false peak some where in the cycle.
I never charge overnight(except a brand new pak which I slow charge
maybe twice with the 50 ma system charger that came with your radio, for
33 hours).I charge my paks on the way to the field and it usually takes
about 15 minutes unless I flew a lot the day before, then it might take
1/2 hour.
I usually do a discharge curve and plot it down to about 4 volts which
allows me to check available time left in the pak at anytime just for
assurance.
Don't hesitate. These things are really good. I would never go back to
Nicads.
Georgie

Mike Hester wrote:

> Ok, I'm sure we're all intimately familiar with nicads, and lately,
> we've become all too familiar with lithium-ions and lithium polymers.
> (If I never hear about another lithium battery, it'll be too
> soon). What I'd like is some detailed specifics regarding the red
> headed stepchild of the battery world, the Nickel Metal
> Hydride. What's the deal with it's performace at low temps? What temps
> are we talking here? What's the scoop on fast charging, rates,
> overheating, etc? I'd like some experienced opinions on
> this. Thanks,-Mike
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