Hans writes:
<< I've just replaced the dead Ni-Cd cells in my M.15V Ni-Cd Contol Pack 2
with
Ni-MH cells (Varta V150H) which I took out of two 9V batteries. I used 12
cells
(leaving two unused) following the instructions from 'The Camera Repair
Resource
Guide' from Lee's site and it works. However, Motor Drive performance has
dropped from 5fps (with the M.18V Control Grip) to 4fps.
Questions: (1) has the original pack with the Ni-Cd cells the same problem (I
bought it when it was already dead) and (2) will adding the two extra Ni-MH
cells (which is possible according to Rand E. Tomcala) boost performance
back to
5fps or will it only add to the number of films that can be driven by one
charge? >>
Various list members responded with comments and shared their experiences
in doing the same modifications. There seemed to be no consensus on whether
the voltage or differences in cell chartacteristics (such as internal
resistance )
made a difference to the MD speed.
Hans,
I have not timed my MD's with different voltages so cannot comment
directly
although somebody with a high current variable voltage supply could easily
check
this. However there is some information from Olympus on this in the service
manual for the MD1:
"Maximum Sequential Frame Speed : 5frames a second (18V) "
By specifying 18V the implication is that it may not achieve 5FPS at
lower
voltages. However further on in the spec the operating Voltage range is
specified
as 10-18V for "high power Alkaline UM3 batteries" (AA cells) but only 9-16V
when using a "constant" (voltage) "power supply ( higher than 2A )" the
implication
of this spec is that you should not use the MD above 16V if the
battery/power supply
internal resistance is very low. (e.g. say D cell Nicd's) Thus: don't use a
high current
external power source above 16V. We can now interpret the earlier 5FPS 18v
spec
as applying when Alkaline AA's are used, with actual terminal voltage then
dropping
to something more like 16V when driving the motor.
The MAC control unit (see unofficial SIF site ) limits the maximum
settable speed
to 4FPS. The MAC unit uses a 1.5A 15V supply (specified I think at 1A?).
This slower
timing is, no doubt, to make sure the motor runs reliably when triggered by a
timer rather
than the uncontolled flat out speed used in some of the battery units.
Comment : I recently have been playing with one of these MAC units and it
really works nicely despite the simple analog timer design.
I don't know what the specifications for the internal resistance of
the small NiMh
cells versus the NiCd cells is but it might well be that this is why the NiMh
cells do
not do as well as expected. (with a higher resistance the terminal voltage
would
drop to a lower value when loaded) There are relatively few suppliers of the
flat NiCd cells
and often Varta cells are oem'ed by other well known brand names. You could
try
checking the specs for Varta's cells by inquiring on their website.
DC motors as used in the MD's have a voltage dependent speed so we
expect
the max drive speed to be at least partly dependent on voltage except where
timed
triggering is used like in the MAC unit. Another variable is MD lubrication
which
seems to make a big difference to the winders I recently refurbished.
Tim Hughes
Hi100@xxxxxxx
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