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NiMh battery problems

Old 05-08-2015, 09:12 AM
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multimike
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Default NiMh battery problems

I bought a bunch of inexpensive ( see cheap) AA NiMH batteries from China , so far none will hold a charge, 20 hours at 50 MaH and all I get is 35 MaH out of a 3000 MaH, the voltage goes up but as soon as I put the under load they drop like a rock , I have tried different chargers with the same results !!
Old 05-08-2015, 11:15 AM
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Rodney
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Take one apart (dissect it) and you will see why. Let us know what you see.
Old 05-08-2015, 01:20 PM
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multimike
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Ok so I cut one apart and not sure what I should be looking for, there was the metal case and then a layer of black STUFF and then a layer of mesh and then some fabric separating it Mike
Old 05-08-2015, 06:32 PM
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Look at the connections for the cells
Old 05-08-2015, 08:10 PM
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A. J. Clark
 
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To give it a chance you need to at least charge it at 300 ma for 15 to 20hr
and cycle it 2 to 3 times.
Old 05-08-2015, 08:37 PM
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JohnBuckner
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Pretty hard maybe to even find a modern charger that will go that low , 35mah. If your cells do have a 3000 mah capacity as you seemed to indicate then a standard overnight charge rate would be 300 mah as AJ mentioned above. Charging 3000 mah capacity cells at 35mah would never work.

Most modern four button chargers will not go lower than 100 mah and are adjustable upward in 100 mah increments.

John
Old 05-09-2015, 06:14 AM
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multimike
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Thanks guys, OK I put them on charge at 150 MaH for 20 hours and this is the second try at that charge rate and it made no difference, even though it shows the voltage rising as soon as I put them under load they drop, I have smart chargers that I can set for any charge rate Mike
Old 05-09-2015, 06:17 AM
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multimike
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Thanks guys, OK I put them on charge at 150 MaH for 20 hours and this is the second try at that charge rate and it made no difference, even though it shows the voltage rising as soon as I put them under load they drop, I have smart chargers that I can set for any charge rate I will try them at 300 MaH charge rate Mike
Old 05-09-2015, 06:49 AM
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All Day Dan
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You should charge them at one tenth their rated value, 300ma, and cycle them three times before you do anything. Dan.
Old 05-09-2015, 09:55 AM
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Rodney
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What load are you putting on them. The standard test is to discharge at 0.33C down to 0.9 volts/cell if comparing to factory specs. If you discharge at a higher rate, you will get a lower mah reading. What does the voltage drop to while under load at the beginning of the test; if above 1.2 volts per cell, pretty typical.
Old 05-09-2015, 10:08 AM
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thats what happens not buying american items
Old 05-09-2015, 11:54 AM
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SeaJay
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OK, fair enough!!!

What rechargeable Batteries are made in the Good Ol US of A?? Sony? Nope! Sanyo?? don't think so! Panasonic, Eneloop, Nah! I personally don't mind, and actually prefer buying US made products, but sometimes it's just not Possible, or prohibitively expensive!

Craig!
Old 05-09-2015, 12:37 PM
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049flyer
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Are you sure that these AA Nimh cells are 3000 ma? I've not seen cells this small with that capacity. Additionally, are you certain you are charging at a constant rate for 20 hours? Many chargers can only do fast charges which are not necessarily constant rate and many will time out or peak out long before you get to 20 hours. It is important that the batteries are charged at a constant rate for the entire period, not a peak charge or anything else that alters the charge rate.

Difficult these days to find simple constant current chargers with adjustable rates.

Last edited by 049flyer; 05-09-2015 at 02:09 PM.
Old 05-09-2015, 07:07 PM
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A. J. Clark
 
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What voltage are the batteries rated at and what voltage are they dropping to?

The battery voltage will charge up past there normal rated voltage.
If the battery is just dropping under load to it's rated voltage that's normal.
Old 05-10-2015, 02:02 PM
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multimike
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OK guys I found the problem. just weigh them, they are 1/3 the weight of a GOOD cell, the company has refunded our money and I used it to buy some brand name ones that worked right out of the package thanks again for all the info Mike
Old 05-10-2015, 03:44 PM
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All Day Dan
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You can get good batteries from

http://www.hangtimes.com/nobsbatteries.html

Dan.
Old 05-10-2015, 04:49 PM
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invertmast
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Just get A123's
Old 05-10-2015, 11:47 PM
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OK guys I found the problem. just weigh them, they are 1/3 the weight of a GOOD cell
Funny you should mention that.

I do emergency light repairs & a lot of the battery packs (4000 mAh D size) that crap out early have cells that
are lighter than I would expect.

New technology that doesn't work? The Chinese short changing us on materials? Hmmmm ....
Old 05-11-2015, 05:45 AM
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multimike
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If you look inside that LIGHT D dry cell you will find a C cell in there Mike
Old 05-11-2015, 09:21 AM
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Originally Posted by invertmast View Post
Just get A123's
+1
Old 05-12-2015, 12:47 PM
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ronwc
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Originally Posted by multimike View Post
I bought a bunch of inexpensive ( see cheap) AA NiMH batteries from China , so far none will hold a charge, 20 hours at 50 MaH and all I get is 35 MaH out of a 3000 MaH, the voltage goes up but as soon as I put the under load they drop like a rock , I have tried different chargers with the same results !!
I made the same mistake a few years ago. My first clue something was wrong with them was that they were very light. I charged and cycled them twice on an Elite cycler and they came out about 400mah if I remember right. Got my money back, and went to these, which actually cycle higher than advertised - http://www.ebay.com/itm/Tenergy-1110...item5b0591c066

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