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Old 01-21-2003, 06:31 PM   #1
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Default Fried Batteries Anyone????

I was just wanting some help please on charging NiMH Batteries with a non peak detecting charger. I have a programmable charger with 5 different charge/discharge functions for charging NiMH batteries and Nicads. When I charge my batteries I usually use the discharge/ charge function which discharges the pack and then charges it. The problem is that it will keep charging my packs well past their rated Mah.
For example my 2400mah NiMH Packs if left to go unattended will charge up to 2700mah before the charger beeps to say it has reached it maximum charge.
When should I stop charging?? Should I stop at the Mah rating of the battery or a little higher or lower??
I just fried my set of 2400Mah NiMH batteries by leaving them on and forgetting to watch them. They were sizzling for a few minutes after I took them off charge and leaking from the end
Any help is always appreciated..

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Old 01-21-2003, 06:44 PM   #2
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Hook a digital voltmeter up to it to so you can monitor the voltage drop of the pack, when the volts drop .02-.03 volts per the pack take them off. You let them drop any more and you'll be overcharging them. Make sure you have a volt meter that reads down to the hundreths. A meter type voltmeter won't be sufficient. You want the screen to say .01 when the volt meter isn't measuring any voltage. You can also monitor them by temperture but the volt meter is gonna be more accurate in your case.

NiMH's: .02-.03V
NiCads: .07-.09V

Both Reedy and Novak make accurate NiMH chargers that are affordable.
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Old 01-21-2003, 07:02 PM   #3
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So you are saying that the volt meter should Increase then peak and then drop down .02-.03 of a volt then I should stop charging.
My Charger has a switchable readout that shows Output Volt, Output amp and mAh. If I switch it to Output Volt will this show the same thing as using the voltage meter?

Thanks for the help

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Old 01-21-2003, 07:05 PM   #4
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Just hook up the volt meter and when the volts start to drop cut the charger off before they drop .03V's. This is gonna be hell especially at a track during races so if you're seriously into the hobby and there's a track where you want to race, I strongly suggest you look into a Reedy or Novak charger for NiMH's.
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Old 01-21-2003, 07:07 PM   #5
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If you do use the volt meter you're gonna have to watch the screen on the volt meter untill the volts start to drop.
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Old 01-21-2003, 07:07 PM   #6
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Default Fried Batts

Steevo,

Batteries, when in good condition, usually accept 5-12% more charge than their rated capacity. And when discharged at a high rate (20-30 amps), it gives 5-10% less than rated capacity unless you are using top of the line matched cells. What probably caused your batteries to fry was too high a setting for voltage drop detection also called millivolts cutoff. NiMH batts are very sensitive to this while NiCds are less so as stated in the previous post. Hope this helps.


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Old 01-21-2003, 07:13 PM   #7
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Steevo, I forgot to tell you, if you cut the charger off after the volt's drop .02-.03V and the pack is still cold by temperture or even slightly warm, you had what is called a "false-peak". Put them back on charge and monitor their volts again, the next time the should be fairly warm but not to hot to where you can't hold them.
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Old 01-21-2003, 07:20 PM   #8
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Quote:
Originally posted by Steevo
So you are saying that the volt meter should Increase then peak and then drop down .02-.03 of a volt then I should stop charging.

Thanks for the help

Steevo
The volt meter isn't gonna do anything to the pack but measure its voltage. The volt meter and your eyes are gonna become the delta-peak detection of your charger so you don't overcharge anymore batteries. Remember, when you do this, you will need to watch the screen on the Vmeter untill the volts drop, when they drop .02-.03 volts cutoff the charger.
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Old 01-21-2003, 07:24 PM   #9
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Thanks for the advise guys.
Do you think the batteries that I fried will be any good for anything other than the bin?? I put them in the car and they seem to work OK.
Unfortunately I will have to stick with this charger cause i don't have the money to buy another. I only just bought it not long ago.

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Old 01-21-2003, 07:54 PM   #10
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If those batteries leaked then I wouldn't use them even though they seem to work. Reason I say this is because they might seem fine now but down the road something terrible might happen to them due to their incorrect cell struture when charging or discharging them.
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Old 01-21-2003, 08:21 PM   #11
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Unhappy fried batteries.....umm good

Steevo;

Your charger sounds similar to the INTEGY 16-2.X like I have.

Output volts should be the same as pack voltage. You should be able to read down to 2 decimal places (.00) If not then a DVM is better.
What makes you think that the charger is NOT a peak detection type?

If you discharge, then immediately recharge without allowing for a cool down period, your packs WILL overheat. Your packs should be allowed to cool to the surrounding ambient air temperature before charging.

Has anyone else heard of 2400 Nickle Metal Hydride Batteries? I always thought that 3000 was the start of NiMh.
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Old 01-21-2003, 08:46 PM   #12
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Hello Pops,
The charger will read to .00 of a volt so it should be OK.
I assume that it is not a peak detection charger because it seems to charge some of my packs well over their rated mAh before beeping to tell me to switch it off.
OK I have just read the Instructions and it does say "Peak detector Autocut circuit with MOSFET" If this is the case then why does it continue to charge the cells well above their rated mAh..
My batteries are high voltage NiMH Sub C size rated at 2400mAh.
It is written on the side of the battery. But the charger will charge them to at least 2600mAh if left unattended.
I do notice that my 3000mAh Packs only charge to about 3050mAh before the unit beeps to tell me to stop charging.
I am a little confused as to what is going on???

Steevo

Last edited by Steevo; 01-21-2003 at 08:49 PM.
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Old 01-21-2003, 08:48 PM   #13
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I just thought maybe I am charging at too high an Amperage?? I charge all the packs at about 5 Amps. It is variable from .5 Amps to 5.5 Amps

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Old 01-21-2003, 09:25 PM   #14
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Default charging at too high an Amperage??

Steevo;

I charge my 2400 NiCd packs at 6.5 amps with no Ill effects.
I may have the problem figured out. Most 2400 packs are usually NiCd and NOT NiMh. Is it possible the charger may be automaticly setting the threshold to NiCd settings and over charging your packs?

Do you have a link that I can go look at the packs and charger that you have. Maybe I can figure something out with a little more information.
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Old 01-21-2003, 09:30 PM   #15
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Hi Steevo,
Don't know if this will help but.....Try charging by temperature. Yes,I said temperature. I use Pro-Match batteries and if you check out there website www.promatchracing.com Jeff Roe suggests charging both Sanyo and Panasonic 3000 by temp. Now, I know you said you have 2400mah NMH. For me thats a bit odd.....maybe down under you have them but in the U.S. the standard NMH is 3000mah. Anything lower falls in the NiCad range.
Pro-Match sells the digital thermometer for around 20u.s. Maybe it will work for you
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