Failed NiMh cell pull back

[Charlie+]

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+

 

[Ron]

On Tue, 23 Aug 2005 09:13:48 +0100, Charlie+ <charlie@xxx.net> wrote:

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.

 

[Roger Hamlett]

"Ron" <racer007@tm.net.my> wrote in message
news:2v4sg1p3qmt1mkl9a82pvpsc6b239fd64f@4ax.com...

On Tue, 23 Aug 2005 09:13:48 +0100, Charlie+ <charlie@xxx.net> wrote:

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

 

[Charlie+]

On Thu, 25 Aug 2005 20:22:30 GMT, "Roger Hamlett"
<rogerspamignored@ttelmah.demon.co.uk> 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+

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.

 

[Watson A.Name - \"Watt Su]

"Charlie+" <charlie@xxx.net> wrote in message
news:m4llg1l3l4o2rinabevuoqdjmroihit9r5@4ax.com...

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+

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.