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Old Apr 9, 2006, 10:33 PM   #1
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I've had my SunPak & DigiPower's for about 2 yrs...don't use them very often so they spend a lot of time just "hanging out" (not plugged in but sometimes in charger as carrier)...but now twice in two months, I've gone to use them but my Nikon Coolpix 2200 says they are empty, if it turns on at all...yet they show as 1.24 avg volts on my meter, so not dead...so...

Thought I'd try running them thru a couple of cycles...charged them up, putting them in camera and letting it sit with repeated 30min timeout on pix review mode until they exhaust...then putting them in my old plain battery tester to futher run them down...figured that would be not that rough on them yet discharge a bit more...

But now the question: How far down to run them? I've read a couple of posts that mention 1.0 volts...so far, I've only gone down to 1.16-1.17 or so...BUT...when I take them out of battery tester and check on voltmeter, they start going back up to 1.21 or so...huh? why?...and thus...given the limited tools I have available to me, what would y'all suggest?

And buying more equipment is out of the question at this point...budget plus limited spaceto transportare the restrictions...

Thanks!


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Old Apr 10, 2006, 6:28 AM   #2
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jhallgren wrote:
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so far, I've only gone down to 1.16-1.17 or so...BUT...when I take them out of battery tester and check on voltmeter, they start going back up to 1.21 or so...huh?
That's because digital multimeter doesn't cause any loads and idle voltage is always higher than voltage under load.
Especially when battery is empty that difference becoems bigger.

1.0V as idle voltage would be extremely empty for NiMH.
Normally voltage should stay quite near 1.2V all the way to near zero capacity.
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Old Apr 10, 2006, 11:04 AM   #3
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Hello Jhallgren,

The voltage rebound is dependent on the load. With low loads you see much less rebound.

To re-condition your batteries, I would suggest that you discharge them to 0.9 volts under a 0.1C load (for a 2000 mAh battery that would be a load of 200 mA). Then let them sit for 30 minutes orso, and do the discharge again.

The purpose of the double dischargeat a low load is to break up any large crystal formation that may have occurred during storage.

After completing the double discharge, charge yourbatteries back up. The bestcharge rate is a 0.1C rate for 16 hours. If you can't do that, charge them normally and leave them on the charger for an additional 8 hours after they have completed the charge.

Two cycles of this conditioning should bring your batteries back to life. If it does not, buy new batteries.

Tom
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Old Apr 10, 2006, 1:24 PM   #4
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SilverFoxCPF wrote:
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(for a 2000 mAh battery that would be a load of 200 mA).
THANKS for the replies! Now then....so bear with me...how would I best create such a load? And determine that it's correct? My skills with my simple pocket meter are limited...

FYI: My charger is CH-4900 by Digital Concepts...a 1 hr at 1400mA style...Yes, I know it's not that good...but it was only one that fit my budget AND was small/light enough for travel....I looked at many different ones...
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Old Apr 10, 2006, 2:32 PM   #5
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Hello Jhallgren,

It sounds like you have a volt meter, but I am afraid you will have to spend a little more on equipment.

Radio Shack sells 50 foot spools of Insulated Wrapping Wire (30 AWG) for around $3.50. You would need to hold one end of the wire against the + terminal of the battery, and the other end of the wire to the - end of the battery. You will also need to read the voltage with your volt meter at the same time.

The wire will provide your load, and when the voltage drops to 0.9 volts, disconnect.

30 AWG wire has a resistance of 0.1032 ohms per foot. 50 feet of wire gives you 5.16 ohms. Using E = IR, we come up with 5.16 ohms providing 214 mA of drain at a battery voltage of 1.2 volts.

So, take your batteries and discharge them in your camera. Hook your wire load and voltmeter up and discharge to 0.9 volts. Let the battery sit for 30 minutes, and hook your wire load and voltmeter up again and once again drain to 0.9 volts.

Now, put your batteries in your charger and charge to full, then leave them on the charger for an additional 8 hours, or so.

Tom
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