After about 8 years using dozens of NiMh cells I have now had a single failure of one of the early AA cells where normal charging wouldnt pull it back. I did the old capacitor discharge trick we used to use on NiCd cells and that worked immediately. (32,000uF I tried set @12v) Anyone had experience with prognosis for such a cell? Self discharge rate higher than normal? Subsequent failures? Charlie+
Tell us more about your "trick" .... when and how does it apply.
It applied to older NiCd batteries, where a common failure mode is 'whisker' growth in the cell. You put a short pulse of very high current through the cell, to destroy the whiskers, and make the cell work again. Once a cell has displayed this behaviour, it tends to become more frequent, but the fix is a well known trick to get such cells to work, and often seems remarkably effective.
Best Wishes
On Thu, 25 Aug 2005 20:22:30 GMT, "Roger Hamlett" wrote as underneath my scribble
Well it looks as though noone around has any history in this, so Ill do a discharge capacity check on the failed cell and report the result in comparison with some cells out of the same (old) batch which have not failed. Thaught someone else might have done this already!! Only time passing will tell if there is a re-occurance problem that follows failure. Im amazed at the reliability of these old (1300mAh) NiMh cells. Charlie+
My feeling with those cells is that if they've been thru many cycles, they are on their last legs and should be replaced. The capacity has probably diminished, and you risk having one or more die prematurely when being discharged. Ya know, we're not all NASA making Shuttle launches, but it's inconvenient to have to replace a set of AA cells while doing a photo shoot. It's easy to justify spending a bit on new cells every few years just to keep them fresh and in good condition. Let the old ones be used in toys or some other non-critical device so that you won't be dissapointed when they quit. Like your electric toothbrush, which seems to be the latest fad judging by the ads on TV.
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