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Old 08-27-2005, 10:39 PM   #1
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Thumbs down Smart Tray Accuracy...

I was playing around with the Smart Tray I just aquired, and I was checking my pack voltages after discharging it via the Tray down to .9V/cell. My pack readings were around 7.23ish, taken by my LG DM-311 Multimeter. It is supposed to have an accuracy around 0.05%. I realized it takes the voltage readings while the battery is under load. Once the battery reaches the specified voltage, the load is released, and the voltage of the battery jumps. Here are my voltage readings after discharging to .1V/cell, and letting the pack rest for about five minutes. The readings are taken from the negative side first.

1.095, 1.088, 1.090, 1.151, 1.111, 1.134

Now, it isn't the varying voltages that worries me, it's the fact that the cells clearly aren't down to .9V/cell. Now they average about 1.1, but still. That is on a supposed discharge down to .1V. Is there some way to fix it so that I can get it to discharge to the REAL voltage, not the loaded voltage? I'll see how long I have to leave it on deadshort mode to get it to .9V/cell. Any input/experiences are greatly appreciated.
-Josh
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Old 08-28-2005, 12:49 AM   #2
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did you test while the packs were on the tray? if you take them off batts will charge up somewhat to higher voltage put the tray reading down to .04-.05 try this it should give you better results, many various readings due to battery condition, age of packs ect...
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Old 08-28-2005, 03:15 AM   #3
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The reason why those cells read that kind of voltage after resting for 5 minutes is that it's the natural tendency of rechargable cells, they recover their voltage with no load on them(even though they may have been discharged completely). But if you placed a load on those cells again, the readin would drop FAST back down to very near the point you discharged it to. Frankly, I only get worried if the cell's voltage does NOT recover when the load is removed, that's usually a sign of it shorting out(which means it's about to die). I saw this a lot when I worked on some back-up power supplies for passenger aircraft(they used 20-cell packs of sub-C NiCd cells), the cells that were doing ok quickly regained their voltage after the load was removed, but a bad cell would stay down, or not recover nearly as much as the others in the pack(& in the case of those packs, we couldn't just replace 1 cell, so a bad one meant the whole pack was history, & those things would cost about $650, which included the cells, a casing, a warming blanket(which was used to prevent them from getting cold in the high altitudes those planes cruise at) a thermal sensor & a wiring harness & connector, so I had to be sure when a cell was dead. From the sound of it, Josh, your cells sound like they're doing just fine right now....
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Old 08-28-2005, 08:32 AM   #4
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Well, at least my packs are fine. But then what would be the point of discharging if the voltage just regenerates itself to 1.2?
-Josh
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Old 08-28-2005, 09:12 AM   #5
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It seems that GP's work better if they are discharged before charging. Most people will tell you to discharge to 0v before charging.

If u had equalized to 0v the voltage would stilll go up as soon as you take the batteries of the smart tray. If u want to keep them at 0v then deadshort them.

Expect less runtime and more false peak though.
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Old 08-28-2005, 09:43 AM   #6
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Quote:
Well, at least my packs are fine. But then what would be the point of discharging if the voltage just regenerates itself to 1.2?
Although the regeneration of the voltage, they are still being discharged... I estimate that when youre pack goes to 0.9v there are still about 0.3A left of charge in them.
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Old 08-28-2005, 12:35 PM   #7
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So it's like taking out the mAh, but still having the same voltage?
-Josh
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Old 08-28-2005, 01:03 PM   #8
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Kind of... the voltage that matters when we talk about batteries is the one u get when u are pulling amps from the cell. If the batterie is depleted it will go to -0.9v in a couple of seconds
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