NiMH Cycle Weirdness - What's going on here?  
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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> NiMH Cycle Weirdness - What's going on here?
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NiMH Cycle Weirdness - What's going on here? - 7/26/2003 9:41:07 PM   
RickVB



Posts: 610
Joined: 8/21/2002
From: Novi, MI, USA
Status: offline 		I have three brand new 1800mah NiMH packs that I got from OnlyBatteries.com. I am using my Dymond Super Turbo to charge them exclusively, always in a NiMH mode. I charged each one at a 200ma rate first; they each took from 1825 to 1875mah of charge.

Next, I cycled them at 500mah discharge, 900mah discharge. Every time I cycle them (so far), the discharge and charge decreases! The second time I get about 1650mah both on charge and discharge, the third time about 1450mah, the fourth time I get about 1300mah.

I haven't cycled any of them more than four times yet, but they've all behaved exactly the same. I haven't dinked with any of the default overall settings like voltage thresholds on the Super Turbo. What the heck is going on here???

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Rick Vera-Burgos
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NIMH - 7/26/2003 10:07:01 PM   
Flying Geezer



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Status: offline 		Try letting them cool for an hour, before discharging them.

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Re: NiMH Cycle Weirdness - What's going on here? - 7/26/2003 11:15:36 PM   
Red Scholefield



Posts: 4907
Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline 		[QUOTE]Originally posted by RickVB
I have three brand new 1800mah NiMH packs that I got from OnlyBatteries.com. I am using my Dymond Super Turbo to charge them exclusively, always in a NiMH mode. I charged each one at a 200ma rate first; they each took from 1825 to 1875mah of charge.

Next, I cycled them at 500mah discharge, 900mah discharge. Every time I cycle them (so far), the discharge and charge decreases! The second time I get about 1650mah both on charge and discharge, the third time about 1450mah, the fourth time I get about 1300mah.

I haven't cycled any of them more than four times yet, but they've all behaved exactly the same. I haven't dinked with any of the default overall settings like voltage thresholds on the Super Turbo. What the heck is going on here??? [/QUOTE]

Any idea of where OnlyBatteries.com gets their cells from? From their web site it appears you may have gotten some manufactured in China where some production lots are fine and others they are not. Good process control isn't something you can easily copy. Rapid capacity fade with cycling is one indication that the manufacturing process has slipped out of range somewhere.

But you got them at a price almost as good as Radical R/C Sanyo packs.

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Re: Re: NiMH Cycle Weirdness - What's going on here? - 7/27/2003 7:05:42 AM   
RickVB



Posts: 610
Joined: 8/21/2002
From: Novi, MI, USA
Status: offline 		[QUOTE]Originally posted by Red Scholefield
But you got them at a price almost as good as Radical R/C Sanyo packs. [/QUOTE]

Um, no, I paid $9.33 a piece for them; I don't think Radical R/C is anywhere near that. Small consolation if they're worthless. Do I understand that that is your diagnosis?

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NiMH Cycle Weirdness - What's going on here? - 7/27/2003 7:17:25 AM   
Geistware



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From: Locust Grove, GA, USA
Status: offline 		Red, at higher loads, would the voltage drop lower even though the available capacity is the same. I would think that a 1650maH pack with a 200ma load will have a higher voltage at 10% of rated capacity remaining compared to the same pack, same remaining capacity with a 1000ma load.

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Re: Re: Re: NiMH Cycle Weirdness - What's going on here? - 7/27/2003 4:48:18 PM   
Red Scholefield



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Joined: 12/8/2001
From: Newberry, FL, USA
Status: offline 		[QUOTE]Originally posted by RickVB
Um, no, I paid $9.33 a piece for them; I don't think Radical R/C is anywhere near that. Small consolation if they're worthless. Do I understand that that is your diagnosis? [/QUOTE]

That is the best shot I can give without having the samples in hand.

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Update - 7/29/2003 11:45:37 PM   
RickVB



Posts: 610
Joined: 8/21/2002
From: Novi, MI, USA
Status: offline 		Red, the last three cycles (I'm up to seven) on one pack has leveled off to about 1650mAH charge, 1500mAH discharge after 24 hours. This seems to fall within the +/- 10% expected capacity and 10% charge loss per 24 hours rules-of-thumb. Are these still throw-aways in your opinion?

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Novi, Michigan

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Re: Update - 7/30/2003 12:18:33 AM   
Red Scholefield



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From: Newberry, FL, USA
Status: offline 		[QUOTE]Originally posted by RickVB
Red, the last three cycles (I'm up to seven) on one pack has leveled off to about 1650mAH charge, 1500mAH discharge after 24 hours. This seems to fall within the +/- 10% expected capacity and 10% charge loss per 24 hours rules-of-thumb. Are these still throw-aways in your opinion? [/QUOTE]

I wouldn't use them in my best plane, but if you keep your eye on them, preflight loaded voltage check, etc. You might get some decent use out of them. Particularly if they seem to finally settle out and the capacity stays fairly constant for a while.

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NiMH Cycle Weirdness - What's going on here? - 7/30/2003 12:09:41 PM   
IronZ



Posts: 219
Joined: 12/27/2001
From: Tipp City, OH, USA
Status: offline 		Did you do some slow charging, without peak detection, to "form" the batteries? Might be worth a shot.

IronZ

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NiMH Cycle Weirdness - What's going on here? - 7/30/2003 7:34:11 PM   
RickVB



Posts: 610
Joined: 8/21/2002
From: Novi, MI, USA
Status: offline 		[QUOTE]Originally posted by IronZ
Did you do some slow charging, without peak detection, to "form" the batteries? Might be worth a shot.

IronZ [/QUOTE]

My understanding that ~C/10 is the rule for forming charge rate. As I wrote in the first posting, I charged them first at a 200ma rate. That resulted in a ~1850mAH charge.

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Rick Vera-Burgos
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NiMH Cycle Weirdness - What's going on here? - 7/30/2003 9:16:00 PM   
IronZ



Posts: 219
Joined: 12/27/2001
From: Tipp City, OH, USA
Status: offline 		Was that on the Super Turbo? They may be false peaking on the ST. I had to slow form my NiMH's 3-4 times on a slow multi charger without peak to get them to start peaking correctly on my Supernova. It is my understanding (and experience) that you need to form them without peak detection. You might want to give it a shot.

IronZ

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NiMH Cycle Weirdness - What's going on here? - 8/1/2003 1:31:32 PM   
RickVB



Posts: 610
Joined: 8/21/2002
From: Novi, MI, USA
Status: offline 		Yes, all the charging has been done on the ST. Each one has charged over 1850mAH the first time (at 200mA), and the dropped drastically. I tried different rates for the second and subsequent charges for each of them, including 200mA for the last one, and it didn't make any difference, I never saw anywhere near 1800mAH again.

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Novi, Michigan

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NiMH Cycle Weirdness - What's going on here? - 8/1/2003 7:17:25 PM   
elevator_up



Posts: 298
Joined: 6/3/2002
From: Wilmington, Delaware, USA
Status: offline 		I had a similar problem once with firebird batteries (ie high discharge). I cycled 4 times at c/10, 2 hour min between cycles. It took a long time but it brought them back to normal.

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NiMH Cycle Weirdness - What's going on here? - 8/1/2003 11:13:07 PM   
Shortman



Posts: 5971
Joined: 2/25/2002
From: Clovis, CA, USA
Status: offline 		break them in with a wall wart charger, not the Dymond Super Turbo...


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NiMH Cycle Weirdness - What's going on here? - 8/1/2003 11:40:20 PM   
RickVB