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the lie of rapid NiMH self-discharge

Discussion in 'Electronic Repair' started by William Sommerwerck, Dec 12, 2011.

  1. I've never had problems with the supposed rapid self-discharge of NiMH
    cells. And now I have proof.

    Almost two years ago, I visited a friend in Gold Bar WA for Christmas. I
    took some camera equipment, including freshly charged NiMH cells for the
    flash. I didn't take any flash pictures, so the cells remained unused in the
    camera case -- which I just got around to unpacking yesterday. (Really.)

    Four of the cells were 2700mAh Sanyo AAs. They all measured about 1.23V,
    rather lower than the 1.4V NiMH cells commonly charge up to, but close to
    the "nominal" 1.25V of NiMH and nicad cells. Contrary to Urban Legend, they
    were not completely discharged.

    I put them in a Canon 580EX II, and the flash fully charged up in less than
    two seconds. I fired off some shots. The first few recycled "instantly". The
    last two took about a half a second. I didn't run down the cells, but it was
    obvious that two years of sitting on the shelf had no rendered them
    unusable.

    The belief that NiMH cells rapidly self-discharge is utter malarkey. Where
    it came from, I don't know.
     
  2. Then why can four NiMH cells sit for two years and still be able to properly
    power a high-drain device?
     
  3. so you got dead battery performance and maybe 3 flashes and therefor
    batteries don't self discharge?
     
  4. Where did I say ANY SUCH THING?

    I'm going to jump down your throat on this one, because I find most people
    don't understand plain English. If I say "Some people have trouble getting
    along with their bosses", most readers interpret that as "All people have
    trouble getting along with their bosses." Really.

    The cells WERE NOT DEAD. After two years they were at the nominal voltage
    for a nicad or NiMH cell. Furthermore, they operated the flash without any
    difficulty.
     
  5.  
  6. mike

    mike Guest

    Your test was unscientific, undocumented, anecdotal, incomplete.
    You are certainly entitled to draw any conclusions you wish
    and base your personal decisions on those conclusions.

    Your blanket statement about NiMH based on your sample-of-one
    anecdote requires extrapolation beyond reason. "Proof" is not
    a word I'd have used to describe your result.

    I can say that my personal experience differs from yours.
    And I get along just fine with my boss. Really!!
     
  7. sorry you got 100 full power flashes before the batteries died.
    people that talk about jumping down throats really need to shut the ****
    up and not be talking about how to get along with a boss. Really.
    There's nothing quite like the no load battery test.
    yeah, for 3 flashes until the flash was unable to even recycle anymore.
     
  8. I didn't run down the flash. I will do so tonight or tomorrow.

    1.25V is considered the nominal operating voltage of nicad or NiMH cells.
    (The point another poster made about the relatively flat discharge was
    well-taken.) The "discharged" point is, as it is for cells of most
    chemistries, 1.0V.
     
  9. You're determined to deliberately misread what I wrote, aren't you?
     
  10. Go slam some doors or something, you might be better at that than testing batteries.
     
  11. mike

    mike Guest

    What was the load current for your voltage measurement?
     
  12. Thanks. That would be interesting.
     
  13. Then what is the problem? A 50% loss of capacity is hardly disastrous.

    But they weren't "almost dead".

    This morning, I did what I should have done before I posted. Over a period
    of a half-hour, I fired the Canon 580EX II over 100 times AT FULL POWER. The
    recycling time was 3 to 3.5 seconds (not unreasonable for full-power
    recycling), and the final cell voltage was about 1.21V (before the cells had
    time to recover).

    100 full-power flashes is not "almost dead". Had I fired on automatic, at a
    moderate aperture, not using full power, I could easily have gotten 200 or
    300 flashes. And had I been willing to tolerate a 5-second recycle, I
    probably could have gotten another 100 full-power flashes.

    That isn't what I observed this morning. The cells, which had sat for almost
    two years since being fully charged, were perfectly usable for 100
    full-power flashes. I probably have gotten another 100 flashes, but I didn't
    want to take the chance of abusing the flash.

    The cells are Sanyo Superlattice Alloy EVO, model HR-3U. They were not
    shipped pre-charged, and as far as I can tell, they are not
    slow-self-discharge ("eneloop") cells. The Sanyo USA site has no information
    about them. However, they are available from Batteries America. (Thomas
    Distributing doesn't list them.)
     
  14. Phil Allison

    Phil Allison Guest

    "Jeff Liebermann"

    ** I have several sets of AA NiMH cells - all Sanyo brand and rated at 1700
    to 2500 mAH.

    Self discharge is a REAL problem, but no worse than with NiCds.

    In general, charged cells lose 90% of capacity in about 6 to 8 weeks -
    taking a full 6 hour charge at 400mA to recover.

    In my Canon A430, the uncharged cells will run the back display for a few
    minutes, let me take a few shots and maybe one flash before the camera shuts
    down.


    .... Phil
     
  15. But it isn't, of course. The voltage was at the nominal 1.25V when I
    started, but this is well below the end-of-charge voltage for NiMH cells.

    It was "scientific" in the sense of mimicking photographic use. 100+
    full-power shots in a half hour, three at a time, is fairly extreme use.

    Of course. That's one of the problems with nicad and NiMH cells.

    However, the fact that the cells read about 1.25V showed they WERE NOT fully
    charged. But despite having sat for two years, they were able to give 100+
    full-power shots. The point is that their were perfectly usable without
    having to be recharged. This contradicts belief that NiMH cells rapidly
    self-discharge. (Rates of 1% or more per day are stated.)

    I might disable the flash's auto-shutoff and let the cells run down to 1.0V,
    then see whether it can still fire more than once. (I have no desire to keep
    popping the flash.)

    PS: Sanyo says their current eneloop cells (rated at 1500 charge cycles)
    will hold as much of 75% of their charge for 3 years.
     
  16. I wonder if the "spectacular" behavior of my 2700mAh Sanyos has anything to
    do with their "superlattice alloy" construction. These appear to be the only
    Sanyos using this design. (That's life, I guess.)

    http://en.wikipedia.org/wiki/Superlattice

    Anyone care to explain this article to me?
     
  17. This is the typical "doubling of chemical reactions with each increase of
    10°C" rule.

    Right before Christmas 2009, I packed up my camera bag for a visit to Gold
    Bar, WA. Two packs of NiMH cells were in the bag. When I came home, I put
    the bag on the living room floor, where it has remained for almost two
    years. The Pacific Northwest is cooler than the rest of the country. The
    cells were exposed to "high" temperatures only intermittently, during the
    warmer days of Summer.

    Hmmm... Is there a purple owl on these cells?
    Agreed, but we don't know whether the "superlattice alloy" has magical
    powers.

    Well, it was around Christmas... Elves, perhaps? Brownies?

    Speaking of which... One of Stan Freberg's less-well-known recordings is
    "Yulenet", with Joe Friday trying to convince a doubter named Grudge that
    there really is a Santa Claus. When they visit the North Pole, they're
    greeted by a brownie from the South Pole (Daws Butler doing a silly
    mock-Southern voice) who's helping out while Santa is away. I can imagine
    the flap such a joke would cause today...
     
  18. Extremely interesting.

    I'll contact Sanyo and ask them about the self-discharge of my specific
    cells.
     
  19. josephkk

    josephkk Guest

    In for a penny's worth; i add that this might be some freaky low self
    discharge cells for the given process, perhaps at some process corner for
    the set.

    ?-)
     
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