Thanks Cory,
Just what I wanted to hear (except the part about the first one dying, I
understand the case is plastic welded or glued?).
The one I had just had screws (so of course I took it apart to see
if I could see what was wrong). It didn't die right away, but one of the
slots didn't seem to work quite right. Numbers didn't add up, and one
time it didn't stop charging a battery and it got quite hot. After that
one time, that slot smoked. When I investigated, I saw a charred
surface-mount component that looked like the current sense part. Makes
sense, given the way it failed. I just chock it up to a bad apple... the
new one is so far going fine.
My current chargers are
either 2 or 4 cell units and whilst all my cells are Sanyos and all have been
kept in their original sets I know I've got some bad cells in there. I got as
far as buying some single AA battery holders and borrowed my mates top end
battery charger/conditioner (Duratrax IntelliPeak Ice
http://www.duratrax.com/caraccys/dtxp4170.html) but I'm just too lazy to run
the full condition cycle for each cell (24 in all).
I finally realized that it would take awhile for me, too. What I
ended up doing was not running a "refresh" cycle on them, but rather a
"test" cycle. Refresh does a C/D cycle repeatedly until it doesn't see
any improvement in capacity. It only shows the final mAh rating, though.
I wanted to see how bad of shape my cells were in, so I did a Test. In
that mode, it charges to full, discharges, and then chargest back up...
showing the mAh capacity during the discharge. I did a few (2-3) on each
cell... enough to convince myself that I'd gotten most of the improvement
from recycling. It does take a few to get them back in shape.
It does take awhile, though, still. I maxed it out at 1000mA each
(discharge is half of charge). I kept a little CPU fan on them to keep
them cool. I was able to go through 2-3 test cycles on 20 cells or so
in about a week. I could do about two complete cycles per day at that
rate. Refresh would have been easier, but I wanted the info... :)
So this little unit looks
like it will do me well, the only disappointment is that it requires a 3VDC
supply (which is understandable I guess as it keeps dissipation down).
Do you know of any suitable 12VDC to 3VDC switch-mode convertors to buy or
build? I have a heap of old switchmode VRMs from ancient motherboards, it would
be nice to be able to use one of them.
If it were *me* I'd build one, but then again I like dabbling in
power electronics. A VRM from a computer is a good idea, (WAY more power
than you need), but I'm sure there's a lot more info in the pins than a
simple wiring would allow. Likely clocks, rates, voltage setting, etc.
It's not too hard to build a buck or buck/boost converter to go from 14v
down to 3v at a few amps. Lots of chips out there (like the old TL494).
Maxim makes lots of integrated IC's that make SMPS easy. There's even
some that come in the TO-220 package like the linear regulator series
(LM7805, etc), but are switching. Add an inductor, and you're good to go.
-Cory
--
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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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