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Old Jan 04, 2002, 01:30 AM
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Adelaide South Australia
Joined Jan 2002
90 Posts
Help me with my NiMh charging problems please?

I have a parkflyer with a 280 motor and a 7.2v 650ma 6x aaa NiMh batteries , I got about a 25 minute flight on my 3rd flight, my 4th and 5th flights were more like 11-15 minutes and Im sure power is down. Im using a "JETI" mini charger on the highest ma setting full charge voltage was 8.2 volts before the 5th flight, it didnt seem to charge the battery for that long and the batt wasnt too hot like it was before my first 3 flights. What should a full charge voltage be and are the jeti chargers any good?? Any ideas whats going on here??
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Old Jan 04, 2002, 01:45 AM
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Leavenworth Ks
Joined Nov 2001
111 Posts
NiMH

AAA NiMH batteries do not like to be fast charged , it is not wise to charge past C1, capacity X 1 or 650mah should not be charged past .650 mah, so each recharge will take about 1 hour. you need to make sure it is completly cooled off before recharging, Peak volatge is not important, what is important is you stop charging when the peak is reached, it is best to have a volt meter going and watch close to see consistant drop in voltage , do not let them get hot when charging, do not trust peak detection , it can and does occasionally screw up and over charge. Do not store the NiMH completly discharged, leave about 1/3 charge in them. NiMH are not nearly as durable as Nicads and can't be abused as much as nicads. If running NiMH I would suggest getting 3 or 4 packs built and recharge the same day as little as possible. As far as I know cycling does't help NiMH , once they are gone they are gone.
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Old Jan 04, 2002, 05:58 AM
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Berkeley, CA USA
Joined Apr 2001
643 Posts
I wish i could find the thread i read...i think it's somewhere else on the 'zone. It said basically that some chargers are better than others, and to have a 'full' battery, you really have to charge it to like 160% capacity, other wise if you charge a 600mAH to 600, it's only at 60% charge. The JETI should work OK, but eventually, you'll want a whattmeter, or a better charger.
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Old Jan 04, 2002, 08:23 AM
an earth bound misfit, I
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St. Pete, Florida
Joined Sep 2001
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Everything Dave said, plus, the reason you did not get full power is probably that the charger shut off on "false peak". With NiMH you have to charge them slower because they can't handle the high charge rate and the charger will shut off early.

If you set it at the lowest mah setting and try again it should work. Also if you think you get a false peak you can start the charge cycle again but keep a close eye on the temp and stop it if they start to get warm.
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Old Jan 04, 2002, 04:19 PM
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Worcester, MA.
Joined Nov 2001
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I'd pretty much agree with everything that's been said so far.

I'd reiterate that charging at current levels that are too high is really bad for NiMH's.

Also, NiMH's are not meant to be re-charged frequently. (I've heard some suppliers say as little as once per day.)

BUT, they should be topped off just before flying. You should fly within a half hour or so of charging to maximize available power. (Or so I've been told. And it's been working for me.)

Good luck,
Dennis-
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Old Jan 04, 2002, 04:33 PM
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Dallas,TX
Joined Jul 2001
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I've also read they don't deliver full charge in cold weather. Could that be an issue with you?

I have several 700mah AAA nimh packs and can say mine charge great at 500ma rate. I've also charged them at 1000ma rate but they get very warm at peak so I charge at 500ma unless I'm at the field and in a hurry to get back in the air.
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Old Jan 04, 2002, 05:46 PM
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Adelaide South Australia
Joined Jan 2002
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I use the 350-800 mah setting on my jeti, should I go lower? seems a good sett for a 650ma batt?? It was 22 deg C here in South Australia.
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Old Jan 04, 2002, 05:58 PM
an earth bound misfit, I
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St. Pete, Florida
Joined Sep 2001
9,429 Posts
That setting should be okay. On the charger page at Hobby Lobby it does not specify for NiMH so it might just not be giving you a full charge. I still think it is false peaking.

Did you slow charge them the first time? A C/10 rate is recommended for the initial charge.

If you set your charger on the lower rate it will take longer but hopefully will not false peak as easily because the voltage increase will be more gradual.

BC
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