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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Extend a NiMh batteries life?
Is there a way to extend NiMH units battery life?
I have a dozen NiMH 3.6v (3x AAA) 800mAh battery packs that don't seem to charging well just wondering if I can do anything to kick a little more life into them. I have a varible 24V DC power supply but dozen't have a varible current control is there a way of charging them with this? What voltage should I charge them at? |
#2
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Extend a NiMh batteries life?
There are single-cell chargers (such as the MAHA) that are supposedly able
to "rejuvenate" cells using a special cycle. I don't know whether they actually do it, and you'd have to dismantle the pack to get at each cell. Charging nicad and NiMH cells is based on current, not voltage. I would suggest thoroughly "running down" the battery pack until the voltage is 2.7V for several cycles. You have to be careful, because "deep" discharge runs the risk of cell reversal. |
#3
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Extend a NiMh batteries life?
Rik Gossard wrote: Is there a way to extend NiMH units battery life? Don't overcharge them, do let them run down but not below 1.1V per cell, and correct any cells with reverse polarity promptly. I have a dozen NiMH 3.6v (3x AAA) 800mAh battery packs that don't seem to charging well just wondering if I can do anything to kick a little more life into them. I suspect they have reverse polarity or shorted cells. Reverse polarity can be corrected by charging only the affected cell, but charging its entire battery the usual way will never help such cells. A shorted cell can be fixed temporarily by applying brief high-current pulses directly to it to vaporize any conductive whiskers inside it (charge a big capacitor to over 10V, connected it directly to the cell. Repeat until the spark becomes less intense), but the whiskers will grow back in hours or days, so it's better to replace shorted cells. I have a variable 24V DC power supply but doesn't have a varible current control is there a way of charging them with this? What voltage should I charge them at? At more than 3.6V, but far more importantly, limit the current to 1/10H the mA-H rating, or in this case 80mA. With a 24V power supply this can be accomplished by inserting a 250 ohm resistor in series. It should have a power rating of at least 5W to prevent burns. A completely dead battery will need about 14 hours to fully charge this way. |
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