MrAl
Flashlight Enthusiast
Hello there,
This discussion is related to constant slow charging of NiMH cells
24 hours a day, 7 days a week. The cells are rated 2200mAh and
they were on charge at 90ma 24/7 for the past 8 months, and
they worked fine in a shaver up until now, when a few days ago
they failed.
A while back i had a problem with a shaver of mine that took two
tiny NiCd cells (not NiMH cells). Not only did i not feel like buying
any of them nor did i feel like replacing the cells in the shaver with
tiny little things that hold little charge, i also happened to have some
AA NiMH cells, made by "Digital", that i wasnt using. I had four of them,
and i used two of them in the shaver (it takes two cells, although not
really that size). Of course the shaver had to be physically modified,
but i did *not* modify the charger, even knowing that i was going to
now use NiMH instead of NiCd. Normally i would never do this, but
i felt i could get away with it if i called the whole thing a 'test', and
i would then actually get some results about what happens when
a NiMH is charged continuously for 24/7.
Ok, that was 8 months ago, and now after that 8 months i had to
replace the cells again because they would no longer hold enough
charge to shave even for a minute with.
As mentioned, the charge rate was 90ma and that's very low for
cells of this capacity, but it worked for 8 months and then the
cells gave out.
So i guess if anyone plans on doing this they have some idea what
to expect now, i know i do.
BTW, the cells were fairly new when they were first installed,
cycled maybe 15 times max. Also, they do not get warm at all.
Because my main test was to see how long they would last, and i
did that and found out, i made no attempt to charge them up
using a standard quick charge (1 or 2 amps) nor a fast 4 amp charge.
I might do that next, just to see if they work if they were charged
with a heavy current after being charged with such a light current
for so long. The standard charge for these cells is 150ma slow or
higher at 1.4 amps for fast.
Also interesting is that they lasted this long, realizing that they
were constantly being overcharged, day after day. This must
say something about slow charging, at say 150ma for 20 hours
or maybe the 90ma for longer. I guess it works to some degree,
even without end of charge detection, because these cells were
running 24 hours a day. If i only charged them when they needed it,
like say once a week, at 90ma for say 40 hours (just to be sure)
i wonder how long they would have lasted. Since 40 is close to
48 hours, which is two days, i guess we could say they might have
lasted around 7/2 or 3.5 times longer, which is 28 months.
28 months wouldnt be too bad i guess, considering they could
be charged with a small diode and a small wall wart and one
small resistor!
This discussion is related to constant slow charging of NiMH cells
24 hours a day, 7 days a week. The cells are rated 2200mAh and
they were on charge at 90ma 24/7 for the past 8 months, and
they worked fine in a shaver up until now, when a few days ago
they failed.
A while back i had a problem with a shaver of mine that took two
tiny NiCd cells (not NiMH cells). Not only did i not feel like buying
any of them nor did i feel like replacing the cells in the shaver with
tiny little things that hold little charge, i also happened to have some
AA NiMH cells, made by "Digital", that i wasnt using. I had four of them,
and i used two of them in the shaver (it takes two cells, although not
really that size). Of course the shaver had to be physically modified,
but i did *not* modify the charger, even knowing that i was going to
now use NiMH instead of NiCd. Normally i would never do this, but
i felt i could get away with it if i called the whole thing a 'test', and
i would then actually get some results about what happens when
a NiMH is charged continuously for 24/7.
Ok, that was 8 months ago, and now after that 8 months i had to
replace the cells again because they would no longer hold enough
charge to shave even for a minute with.
As mentioned, the charge rate was 90ma and that's very low for
cells of this capacity, but it worked for 8 months and then the
cells gave out.
So i guess if anyone plans on doing this they have some idea what
to expect now, i know i do.
BTW, the cells were fairly new when they were first installed,
cycled maybe 15 times max. Also, they do not get warm at all.
Because my main test was to see how long they would last, and i
did that and found out, i made no attempt to charge them up
using a standard quick charge (1 or 2 amps) nor a fast 4 amp charge.
I might do that next, just to see if they work if they were charged
with a heavy current after being charged with such a light current
for so long. The standard charge for these cells is 150ma slow or
higher at 1.4 amps for fast.
Also interesting is that they lasted this long, realizing that they
were constantly being overcharged, day after day. This must
say something about slow charging, at say 150ma for 20 hours
or maybe the 90ma for longer. I guess it works to some degree,
even without end of charge detection, because these cells were
running 24 hours a day. If i only charged them when they needed it,
like say once a week, at 90ma for say 40 hours (just to be sure)
i wonder how long they would have lasted. Since 40 is close to
48 hours, which is two days, i guess we could say they might have
lasted around 7/2 or 3.5 times longer, which is 28 months.
28 months wouldnt be too bad i guess, considering they could
be charged with a small diode and a small wall wart and one
small resistor!
Last edited:
Jokes!
