tourtelot asked:
Anyone know a good technique for "conditioning" nicad cells in an M.15?
<<
>From the way you asked your question it sounds like you mean discharging the
>cells. Often people
refer to zapping to clear shorted cells. To fix the shorted cells you need to
open the pack to zap
the bad cells individually , and the success rate is often only about 50%.
CH suggested shorting the mirror switch connector on the base plate of an MD1
to run the motor
continuously to discharge the cells. Apart from not wearing out your camera
this is much more
gentle on the cells (good), but is very tedious and you don't know when to
stop. The MD1 I
measured a while back draws about 70mA with no camera mounted, so if we assume
the cells are rated
at about 200mAh it would take up to 3 hours of running, to discharge a freshly
charged set of
cells.
Although people always focus on battery "memory effects" the string of cells is
so long in the
M15V, that you are most likely to damage the battery through cell shorts or
venting in the cells
if you try to do a conditioning discharge (result of reverse charge effects on
weakest cells).
This happens due to inevitable cell capacity mismatches. If you really insist
on doing this, I
would only recommend you discharge slowly (hours) while monitoring battery
voltage and **stop
discharging at about 12V**. The simplest way to do this is to make a crude
adapter to fit the
M15V connector. (described below) First switch on the M15V pack (sequence or
single mode), then
hook up a resistor (220 Ohm 1W) in parrallel with a voltmeter and connected
across pins J103 and
J106 (the pins for the M15V are the same as those shown for the 18V control
grip diagram I posted
to Mark Dapoz's website, which shows layout of all connector pins). Disconnect
when voltage hits
12V (2-3hrs for fully charged pack). If you want to make it a more reliable
setup you don't have
to watch, hook up a 12V 500mW zenner diode in series with a 100 Ohm 1/2W
resistor across those
pins and this will take somewhat longer to discahrge, but it will automatically
stop diascharging
at 12V. The positive end of the zenner (marked with line) ** must ** go to pin
# J103.
If you have no electrical skills here is another alternative: set up the pack
on it's side and
and apply a weight (or rubber band?) and small piece of plastic to push in the
voltage test
switch. This applies a load of about 70mA to the cells and automatically
reduces this to about
50mA as the voltage drops and the LED goes out (I don't know the exact voltage
level at LED cut
out). You can monitor the voltage on pins J103/J106 as before, provided you
switch the pack on.
How to make a crude adapter for the connector: take a sturdy piece of cardboard
or thin plastic
and cut a rectangle to fit exactly in the battery connector. Mark out the
posion of the two pins
to connect to, and make small holes for two small round head screws. Insert
screws with heads
facing toward battery. You can now attach leads to the two screws and apply
rubber bands to hold
the plastic down against the battery pack connector.
Regards,
Tim Hughes
TimHughes@xxxxxxxx
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