Poll

How long have you kept any NiMH cell in active service?

up to 2 years
3 (15%)
up to 3 years
1 (5%)
up to 4 years
0 (0%)
up to 5 years
3 (15%)
> 5 years
13 (65%)

Total Members Voted: 19

Author Topic: Longevity of NiMH cells  (Read 15489 times)

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Offline saturation

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Re: Longevity of NiMH cells
« Reply #25 on: June 13, 2011, 04:14:52 pm »
Some additional studies suggest at worse, it doesn't do anything more than regular pulse charging, so it doesn't have a determental effect; the bigger killer of NiMH is heat.

http://en.wikipedia.org/wiki/Battery_charger#Pulse 

Those are interesting waveforms for a charger, shows the Maha engineers have really kept up with the charging literature.  Its like a burp charger...
yea the nasa pdf is 1997. but now its gone in maha c9000. maybe they found out its not a good thing? maybe i should open up my charger if i can get rid of the "burp".
very very nice machine you have there russel! i wish there is such a small size sold locally here.

Best Wishes,

 Saturation
 

Offline Russel

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Re: Longevity of NiMH cells
« Reply #26 on: June 13, 2011, 07:14:30 pm »
Very nice.  I didn't realize they made them so compact,  ... can be on most home lab's bench, if you have the room!  New ideas for my tools.  You can make very nice custom cases, knobs, even rare spare parts with a lathe, but I always found them fairly large and noisy, but its the right answer to make accessories, such as for the Maha C9000 charger.

They are quite handy once you get the hang of using them. I've also got a little Sherline mill. Using a mill, lathe and rotary table, you can machine just about anything within the size limits of the machines. The photos are of a knob that I made (sorry didn't get a photo of it completed) a little steam engine and the crankcase to a small three cylinder radial engine that I'm building. Basically, your limits are size and your imagination.

Some additional studies suggest at worse, it doesn't do anything more than regular pulse charging, so it doesn't have a determental effect; the bigger killer of NiMH is heat.

One of the nice things about the MH-C9000 is that it terminates the charge early, and dropping the charge rate (when the display indicates done) down to 100mA for two hours to completely top the cells off. That helps reduce the heat generated in the cells as they charge, especially when they are almost fully charged. I don't bother with the two hour top off charge, I remove the cells when the charger indicates "done." Hopefully, that will help extend the life of the cells. Besides, another 200mAh isn't going to make a great deal of difference in a 2000mAh cell, at least in any of the applications that I use AA cells in.
 

Offline saturation

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Re: Longevity of NiMH cells
« Reply #27 on: May 27, 2014, 04:31:27 pm »
This month, my oldest working set of NiMH AA cells, standard discharge rates, no-name brand, have finally died.

Put in service in 1-2006, they were occasionally speed charged at 1C, until I abandoned all chargers but the Maha C9000 in 2010.

In 2010,  the labeled capacity was 2000mAH, the Maha C9000 rated them at 1600 mAH x2, and 1000mAH x2. 

Between 2010, and May, 2014, all cells continued to work per the Maha rating, until early this year the updated rating is now 1400mAH and 800mAH.  However, early this year the self discharge rate rapidly crept up to this week at 100mA/hr so batteries discharge in one day.  Last week, 2 cells now report "HIGH" and now can only be charged at 0.1C or less.

The decline in capacity was relatively 'sudden' given the service interval of 9 years. 

Although only a sample of one set of cells, it shows that proper charging can indeed extend the life of even consumer cells to near 10 years, as mentioned at the start of the thread.

In a prior test, I revitalized a set of RadioShack 1000mAH cells from 1998 that had been left unused for 5 years, and while capable of holding 700-900mAH, its self discharge rate was also about 100mA/hr in 2010 after restoration, but it did suggest old cells could be 'restored' by a charge algorithm.

Today, marked the end of the experiment with an old set of cells in continuous use from 2006.



Best Wishes,

 Saturation
 

Offline G7PSK

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Re: Longevity of NiMH cells
« Reply #28 on: May 27, 2014, 05:00:43 pm »
I have some Nicd's that came with a Kenwood radio in 1994 that stil work well, and some NiMh that are well over ten years old.
 

Offline saturation

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Re: Longevity of NiMH cells
« Reply #29 on: May 27, 2014, 05:40:52 pm »
I've not had similar luck with NiCd, but to good to know there are other history's of long life. 

I currently have 10 eneloop AA that are now in their 5th year, and have no change in mAH or discharge rates [ as tested with a Maha C9000] but these have never been subject to fast rates or overheating as my older cells and the cells mentioned here.



I have some Nicd's that came with a Kenwood radio in 1994 that stil work well, and some NiMh that are well over ten years old.
Best Wishes,

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Offline denelec

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Re: Longevity of NiMH cells
« Reply #30 on: May 28, 2014, 12:39:33 am »
I'm still using an Oral-B rechargeable tooth brush I bought in february 2003.
It got an internal single NiMh cell.
 

Offline madires

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Re: Longevity of NiMH cells
« Reply #31 on: May 28, 2014, 11:44:41 am »
I'm still using an Oral-B rechargeable tooth brush I bought in february 2003.
It got an internal single NiMh cell.

The NiMH cells of the later models don't last that long. The professional care series seems to be the worst yet, just after a year the runtime was down to 50%. I can't understand why Oral B uses cheap cells because that could ruin the brand. Unfortunately they don't got that nice mechanism to open the brush anymore, but with a little bit of force it will open too. The Japanese manual shows how to open it for recycling, the manuals for other languages don't.  >:(  I've replaced the cells of three brushes so far and guess what, the new cells are still fine after a year.
 

Offline justanothercanuck

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Re: Longevity of NiMH cells
« Reply #32 on: May 28, 2014, 08:41:25 pm »
I don't really think anyone should trust that Cobasys document.  It was written in 2005 while Cobasys was still owned by Chevron-Texaco and while they were still blocking use of NiMH in any form of EV.

http://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries
Maintain your old electronics!  If you don't preserve it, it could be lost forever!
 

Offline saturation

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Re: Longevity of NiMH cells
« Reply #33 on: May 29, 2014, 07:36:28 pm »
The cobasys paper mentions some reason for longevity but in the end, it will depend on actual production quality and chemistry of the maker of the individual cell. 

There is very little published data about the true calendar life of cared for NiMH cells.  However, to refresh the concepts raised on this thread years ago, the most most important practical study was the Toyota Prius; it used NiMH packs that were later tested at 10 years of use for its performance, and have been used thereafter in 2 generations of Prius vehicles.  Its one of the largest test of NiMH technology in single vendors [ Panasonic and Toyota] that demonstrate its resilience to repeated charging and its calendar life [ often quoted as 2-5 years even in Panasonic's literature].

http://en.wikipedia.org/wiki/Toyota_Prius#Batteries

http://www.panasonic.com/industrial/includes/pdf/Panasonic_NiMH_Overview.pdf


I don't really think anyone should trust that Cobasys document.  It was written in 2005 while Cobasys was still owned by Chevron-Texaco and while they were still blocking use of NiMH in any form of EV.

http://en.wikipedia.org/wiki/Patent_encumbrance_of_large_automotive_NiMH_batteries
Best Wishes,

 Saturation
 


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