NiMH

Discussion in 'General Electronics Chat' started by R!f@@, Dec 14, 2010.

  1. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    [​IMG]

    What the heck is wrong with these things. :confused:
    They show 1.1V but my charger refuses to charge them.
    If I load it I get 35mA max....

    Is there any way to revive them
     
  2. debe

    Well-Known Member

    Sep 21, 2010
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    Hi R!f@@, Have had some sucess by flashing 12V dc across single cells, seems to shock them into life again.
     
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  3. nerdegutta

    Moderator

    Dec 15, 2009
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    Like defibrillation?

    "Clear!"
    Zapf!
    "Wait... wait...waaaaait. We got a live one here! YES!!! Give him room. Okay, next. Clear!"
    Zapf!

    Zapf!

    "I think this one got away. Clear"

    ZapfZapfZapfZapfZapfZapfZapf!

    "Umh, Now he's gone"

    Sorry about that. :)
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I made a reflex battery charger once.
    That can "breath" the health back into the batteries.

    Here is an other thread wich talkes about this type of batter charger:
    http://www.edaboard.com/thread106948-4.html

    Bertus
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    But they can die from old age.
     
  6. tyblu

    Member

    Nov 29, 2010
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    NiMH are 1.1-1.2V fully charged
    edit: i think hydrogen is used as an active ingredient so be careful zapping it
     
    Last edited: Dec 14, 2010
  7. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    If u here any news about a hydrogen bomb going off in Maldives.

    You should know it's me, fiddling with the unknown
     
  8. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    They aren't old Bill..

    Daryl.....are u talking about clearing the memory effect of these cells..
    how long should I apply 12V.

    Is it 12V /cell?
     
  9. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Batteries of that type will behave that way if allowed to overheat while charging. They never again can deliver current. (I think it boils away too much of the liquid portion of the electrolyte)
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    On the Amtel Products - AVR Solutions page, in the block Battery Management, you can find application note AVR450.

    Bertus
     
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  11. BillB3857

    Senior Member

    Feb 28, 2009
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    Too many beans last night and the gas went the wrong way. You have Ni-MH, Not Nickel-Cadmium. Duh...at this end.
     
  12. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Bertus....
    The note is for a charger right ?

    My actual problem is that the cells are not charging. My charger is OK.
    I can charge new ones but these old ones are not that old, may be a year or so but at first they charged pretty well, now the darn thing just won't hold or charge.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    In the first post in this thread I gave a thread from an other forum that shows the reflex method.
    It uses discharge cyles during charging.
    The discharge is to remove the gass bubbles on the electrodes.
    With the reflexcharger I have revived several old Nicd and Nimh cells.

    Bertus
     
  14. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    I can't seem to access any links there bertus
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    Please look at the datasheet of a Ni-MH battery cell before making incorrect remarks.
     
  16. tyblu

    Member

    Nov 29, 2010
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  17. R!f@@

    Thread Starter AAC Fanatic!

    Apr 2, 2009
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    Does NiMH goes above 1.2V..?
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    The graph I posted shows 1.5V when fully charged at a high current.
    It is 1.4V when fully charged at a low current.

    I just measured the voltage of some Ni-MH cells I fully charged a couple of weeks ago and they measure 1.34V without a load.

    Here is a discharge graph:
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    Rifaa,
    During charging, yes - it can go above 1.2v. See the plot that Audioguru posted.

    "Zapping" can work for NiCD batteries (I've fixed some that way) - but it is hardly ever effective for NiMH cells. "Zapping" is inherently hazardous, which is why I haven't discussed it before now. It is all too easy to "zap" too much, and have the battery rupture forcefully, sending shrapnel and chemicals in various directions. Temperatures and pressures inside the battery shell can and do skyrocket unpredictably. I advise against attempting to "zap" your NiMH batteries; your safety is worth much more than a pair of batteries.

    If you decide to attempt it despite my advice, wear suitable protective gear:
    1) Eye protection - complete coverage.
    2) Face protection - At least several layers of heavy cardboard stock.
    3) Hand protection - leather gloves.
    4) Body protection - wear a leather or thick denim jacket, and a leather shop apron.
    5) Do not hold the battery in your hand(s).

    It sometimes works on NiCD's that have not experienced cell reversal.
    NiMH cells have a shorter service life than NiCDs, and are more easily damaged by improper charging. High temps will kill them quickly.
     
  20. retched

    AAC Fanatic!

    Dec 5, 2009
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    I agree with the sarge. While zapping batteries in my past, I used a camping cooler for a "blast chamber".

    I use the same cooler for capacitors when working on high charge/discharges projects.

    Dont play around. You have enough experience to know how to be safe, but the amount of money you would have to spend to be safe is MANY times the price of a set of batteries.. Not to mention the amount of money you would loose while mending your injuries.
     
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