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Old Mar 03, 2002, 04:12 PM
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Bad luck or bad charger?

I have 3 packs: 7 x 300mHh NMH, 7 x 370mHh NMH and 8 x 720mHh NMH.

All were trickle charged the first time, and charged on a Dymond Delta Peak Mini Charger, with a regulated 12V supply.

Both the smaller packs are having problems. After poor flight times, I checked voltage under load for each cell.

On the 370mHh pack, one cell starts dropping right away, and after 5 min. is at zero V, while the others are about 1.2V. It is the first cell the + lead gets to.

The charging always seems to go fine. I charge the small packs at .5A and they are slightly warm when it peaks and goes to trickle.

The other small pack has a cell (also #1 in line) that goes negative voltage after a few min. under load.

Both packs behaves in flight almost exactly the same: 5-6 min OK power, then 2-3 min. of a full power slow descent from about 40 feet high.

These packs are running the GWS A motor on a 8.2 oz. slow flyer, which should be getting 10 min. or more flight time.

The 720 mAh pack (charged at 1A) drives a 280 motor for 18 min of hard flying, and cells check out just fine.

Could my charger be damaging the small packs? Or am I just having bad luck with batteries?

Thanks,

James
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Old Mar 03, 2002, 05:34 PM
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oakdale, ny, usa
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I have the same charger. Mine has 3 settings .3, .5 and 1 Amp.

If anything I would say that this charger has a tendency to false peak or stop charging prematurely.

Most of the time I end up pressing the charge button again. The 2nd time the packs get slightly warm and they are of course charged.

If you have the same charger - have you tried charging the 300MA pack at the .3 settings and also the 370MA pack?
Do you leave them on trickle occasionally to equalize the cells?

I'd say the 720MA pack would do well at the .5 setting. 1 amp for a 720Nih pack may be a tad high.

You don't say how old the packs are of if they have been subject to high current loads. Very high current tend to kill Nih cells.

At this point it sounds like your packs are going south. This would be most likely due to use rather than proper charging.

Who did you buy the packs from?
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Old Mar 03, 2002, 06:00 PM
Mountain Models Wannabe
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Ithaca, NY USA
Joined Mar 2001
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Poobs, the packs came from me. The 370 is brand new and is from GP. The .5amp setting is a little high but not excessive. james is using 7 cell packs and I don't think the current draw is excessive. I'd like to know what's going on because if I received a batch of bad batteries, I want to know about it. I'm doing some tests on packs from my stock.

The question I have for the ezoners out there who are using the 300mAH packs is are you having pack failures and, if so, how frequently.

Doug
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Old Mar 03, 2002, 06:35 PM
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oakdale, ny, usa
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Doug:

I think it is great that you have such a drive to protect your customers.

Check the manufacturing dates or batch codes (if any) of your shipment. This is good information to have.

Many times a manufacturer will have a momentary "oops" in the process and the failures will concentrate around a paerticular event in the process.

Another scenario is the user swaping packs around a particular aplicaton. For example - a motor prop combination that will not damage a 720MA pack will toast a 300MA one.

I'm not saying this is the case here however. I'm just saying that all your failures will not be product related.

I'm no expert but If I can be of help feel free to contact me.

Good luck.
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Old Mar 03, 2002, 08:57 PM
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United States, CO, Longmont
Joined Jul 2001
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James. Batteries that are NiCad or NiMAH need more voltage to charge than the 1.2 operating volts might lead you to think. You really can't get them to charge well unless your charger puts out about 1.55 to 1.60 volts/cell or more. Starting with your 12 volt regulated supply, your charger (which has some internal voltage drop, likely can not put out enough volts. This may have lead you to try to get more from the batteries than they had to offer and in turn overdischarged them. This may have damaged them, but even if not, you likely can't get 'em recharged properly. Try a higher supply voltage before giving up.

Regards,
Q
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Old Mar 03, 2002, 09:24 PM
Space Coast USA
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I've had a couple of bad 300mah NiMH cells out of 24. Same scenario as described above. Just replace the bad cell and move on. Slow charge discharged pack at c/10-c/20 before using your regular charger.
hoppy
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Old Mar 03, 2002, 09:47 PM
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To answer a few questions:

The 300 pack has been charged 35 times, with 6 or so overnight trickles. It actually performed a bit better after about 5 charges, but soon after that it went down hill a bit, and remained at that level since.

The 370 pack has 10 charges on it. It's 4th charge was the best, and then it started going.

Both packs have been charged at .5A. And both have only been used on a GWS A motor.

With both packs, after a flight, if I measure voltage with a load, cell #1 (first cell on the red wire) gives zero or negative voltage.

Could charging at .5A have toasted that first cell? I guess I didn't make the mental switch from NiCad to NiMH when I set the .5A.

The packs were never hot, only slightly warm at the end of a charge.

Thanks,

James
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Old Mar 04, 2002, 05:40 AM
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James

Quaker makes a good point.

Now in your case that reverse voltage cell worries me.

Might be a good idea to replace the one cell and start again.


If you have use of a charger such as the Dymond Smart charger, you could do some testing on the defective cell.
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