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Old Apr 15, 2004, 11:14 AM
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Kan 950 Charged To 2200+ Mah

Use VOLTAGE CLAMP at 10.15 v ( 7x 1.45v) for 7 cell Kan 950 mah NMH overnite charge to 100 ma.

Still charging at 100 ma when disconnected this morning. Monitored with AFI Super Whatt meter

Voltage Clamp is a 400W QUALIDYNE 4 channel output switching power supply with 24v cooling fan acquired from surplus electronic dealer.

Hall
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Old Apr 15, 2004, 12:17 PM
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The battery reached full charge early and the remaining mah went up as excess heat. The c/10 is low enough charge where the overcharge isn't enough to damage the pack. My Hitec 335 will do this every time that I leave a pack overnight. It shifts from a fast charge to a trickle and the mah will still continue to slowly climb.

mw
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Old Apr 15, 2004, 12:52 PM
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Overnite charging is the best way: 100% charge and 100% balance Zero damage

Low cost surplus switchers can be found anywhere
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Old Apr 15, 2004, 01:03 PM
Just fly the darn wing!!!
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Hall woo, what Mark wanted to say is that there are not 2200+mah in your battery. Not sure if you understood this.....there is only 950mah in you battery, everything else just poofed into the air.

Dennis.
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Old Apr 15, 2004, 01:21 PM
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Yes, I think most of the excess MAH was heat in cooking the pack, but I am getting
longer flight times by this slow charge method than fast-charge peakers.

I even had a 8 cell HR 2600 NMH SANYO reach almost 4000 mah.
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Old Apr 15, 2004, 01:22 PM
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I noticed the same thing happened to my FAUP's when charging at 500 mA, roughly C/4. These packs also run on at 1.9A, the Sanyo recommended 1C rate for fast charging. I think my charger cannot sense the -20mV delta for those rates. It works fine with smaller NiMH and is fine with the FAUP's at 4A. But its a cell cooker at lower rates.
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Old Apr 15, 2004, 07:54 PM
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You still only have 2600mah in that pack. The other 1400mah went up in waste heat.

mw
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Old Apr 15, 2004, 07:59 PM
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Leave it on for a week and you can probably get 18,200 mah in it.
h
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Old Apr 15, 2004, 09:11 PM
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And your thinkin, where in the sam hill are these electrons going if the pack only has 950 mah of space? Those electrons wind up in the same place as
data that your delete off your hard drive and where your socks wind up when they get seperated from the their twin.....the 4th dimension!!!!
Ask the wife, she knows where them socks go!!!!!

Dave...
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Old Apr 15, 2004, 09:38 PM
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This sounds like a rather unconventional "slow charge" method if I understand it correctly. Are you connecting your Nimh pack to a power supply that has no adjustable current limit, and just setting the voltage to 1.45 volts per cell? If so, I would expect the initial current to be rather high; way beyond the normal 2C or so limit. I would expect the current to taper off as the cell approaches the peak then the current would start to rise again as the cell heats up and the cell voltage drops.
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Old Apr 16, 2004, 12:46 AM
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This is better than any peak charger trickle charge mode, no appreciable
results.

Yes, the initial charge current will be high, around 5 amp, then self taper to
100 ma @ 1.45v per cell. No current rise at all. Results: longer flight times, around an extra 2 minutes.

You guys should try it, you will like it
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Old Apr 16, 2004, 03:01 AM
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Quote:
Originally Posted by hall woo
This is better than any peak charger trickle charge mode, no appreciable
results.

Yes, the initial charge current will be high, around 5 amp, then self taper to
100 ma @ 1.45v per cell. No current rise at all. Results: longer flight times, around an extra 2 minutes.

You guys should try it, you will like it
You're balancing your pack and that's good. I balance my packs occasionally, but it doesn't take that much of an overcharge to balance them. If you keep this up you'll damage the cells, IMHO. The common experience is that our round cells perform better fresh off of a fast charge rather than off of a slow charge. Your increased flight times can probably be inferred to be from the balancing of the cells only. Every cell in the pack is charged to it's maximum capability. It would be nice if you could give us some better numbers. What were your flight times before and now? What is the measured discharge capacity of your pack before and now? I kind of think that you just weren't getting a full charge before. If you had ONLY been fast charging prior to this you would probably never have seen the pack perform to it's best capability. The real test is to slow charge one cell only and do a discharge measurment. Then fast charge the same one cell and do discharge measurment. I'll wager that you'll not see any significant difference in discharge capacity but the fast charged cell will probably show better voltage under load.
Dave Chewning Sr.
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Old Apr 16, 2004, 07:17 AM
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I have no doubt that it works for you in this instance, but:

There is no way to tell, in advance, what the specific voltage is at which the cells will become fully charged. The termination voltage varies from manufacture to manufacture; from lot to lot and with age. It is also strongly temperature dependent.

If you set the voltage a bit too high, you will overheat the cells; a little too low and they will not fully charge. Which is why the manufacturers have always recommended peak detection for fast charging, or slow charging.

However, if you put a current limiting resistor in series with your supply, the approach you are using works fine. But of course it takes longer. The resistor can be chosen so that the current is somewhat higher at first (say 0.3C or so) and still tapers to around 0.1C.
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Last edited by Bob Baker; Apr 16, 2004 at 10:36 AM.
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Old Apr 16, 2004, 11:16 AM
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1.45V PER CELL IS THE IDEAL CLAMP VOLTAGE.

NO LIMITING RESISTOR NEEDED ON A VOLTAGE CLAMP.

You can fine tune the precision 10 turn trimpot on a QUALIDYNE to adjust the voltage.
Use 1.4V if you like.
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Old Apr 16, 2004, 12:15 PM
Just fly the darn wing!!!
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Westfield, NY
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There's a difference between actually charging your battery and wasting energy by producing nothing but excess heat.
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