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Old 06-17-2009, 12:01 AM   #1
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Default Nimh Charging/discharging

I just got back into the hobby and bought some 4600 Nimh cells to put together a few packs. I am used to the old NiCd batteries where you had to discharge down to .9v per cell. I had a discharger set up with an auto cut off and (8) 12v bulbs. This set up worked great for my Nicd packs. Now that I have assembled the new 4600 mah Nimh packs, do I need to discharge after use, then recharge or do I just put them back on the charger again? I ran a mew pack in my car for a normal run, then put the new Nimh pack on my discharger, I noticed the lights would flucuate (spelled wrong...) then I heard a few cells hissing and noticed a small amount of fluid coming from a couple of the cells. I Immediatly removed the battery from the discharger and set it aside. I am assuming this pack is wasted, so did my discharger ruin it? Am I supposed to discharge all? Did I discharge at to high of a rate? Any help would be greatly appreciated. Thanx!!

I am using a Chargery 1010B on the Nimh setting and charging @ 5amp, not sure if relevant to the situation or not...
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Old 06-17-2009, 12:16 AM   #2
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NiMh cells do vent... its not all that unusual for new cells or cheap cells to do this often. Unless they pop.. or get extremely overheated, the cells will be fine.

Although you don't have to discharge NiMh, it might be a good habit to do so and to equalize the cells in the pack between each charge This allows you to know how your packs are doing by the amount of time it takes to charge, the peak voltage etc... Just watch excessive heat...

A 20amp 10 bulb (GE1157) discharger should be fine for a 6-cell pack.

Good luck!

Jerome
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Old 06-17-2009, 12:24 AM   #3
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Quote:
Originally Posted by JeromeK99 View Post
NiMh cells do vent... its not all that unusual for new cells or cheap cells to do this often. Unless they pop.. or get extremely overheated, the cells will be fine.

Although you don't have to discharge NiMh, it might be a good habit to do so and to equalize the cells in the pack between each charge This allows you to know how your packs are doing by the amount of time it takes to charge, the peak voltage etc... Just watch excessive heat...

A 20amp 10 bulb (GE1157) discharger should be fine for a 6-cell pack.

Good luck!

Jerome
So it is normal for me to hear the cells hissing???? Again, alot has changed since I was last in the hobby. IThe cells have not made any noise during charging. The cells I purchased are Ener-G 4600 mah. I got 25 cells for less than $50.00...
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Old 06-17-2009, 12:44 AM   #4
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After you have cycled them a few times, they should not be venting all the time... If they can't handle a 5amp charge or a 20amp draw.. then they are not going to last long with r/c.

I know these cells have been around for about a year or so.. but the serious racers in my area don't use them.. and LiPo has taken over now. Maybe somebody else on the forums have used them.

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Old 06-17-2009, 03:00 AM   #5
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I'd say the hissing cells are stuffed. I always discharge my packs to 5.4 volts, and every 3 or 4 charges put them on the balancer.
The lights should not flicker on the discharger, i'd say that was a bad sign too.
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Old 06-17-2009, 08:27 AM   #6
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Putting packs together without matching them is only going to make your problem worse especially if you don't use a discharge tray to equalize them. Having nimh cells vent doesn't always mean they are or will go bad. With cells that aren't matched they could be far enough off from each other to cause real headaches. When I've had unmatched packs vent cells they're usually dead. My matched packs were fine and vented much less and less often.
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