Hi Zuiks,
I have been modifying an M15V Battery pack and have been doing some
measurements on
current draw using an MD2 on the M15V (the 12 cell NiCd pack). Here are some
technical details.
The MD2 spec from Olympus is that inspection standard for operating current is
350mA (winding).
and for rewinding is 350mA. They also quote 600mA as operating current!
To get some idea of the actual current I hooked up a 10milliohm current shunt
(hooked to a digital
scope) in series with the cells from a M15V. I used an OM2 (with no film) set
to manual 1/1000sec
on an MD2.
First I measured average current using a DVM. When running in sequence mode it
was 600-700mA.
Similar to Oly higher spec. (Variation is because DVM does not truly average
over start/stop/wind
time ) Then I looked at captured current waveforms on scope. Peak current at
start of wind was ~3A
which caused cells to drop to ~12V briefly at peak current. My guess is new
cell voltage would
droop less particularly at end of a 36 frame continuous wind. Current drops off
linearly from peak
start current of ~3A to about 630mA after about 60mS or so and then stays
approximately constant.
Total wind current time was about 170mS. It is interesting to see the brief
motor current spike
(~1.5A,10mS) at end of wind when the motor current is reversed briefly to brake
motors. (The MD1
does not reverse the current, it only shorts the motor.)
Measured over 36 frames in sequence mode, the average FPS was only ~4FPS
(9sec), lower than the
spec of 5FPS (~7.2sec). Probably slower due to older cells with higher
resistance. But this also
implies a higher peak current with new cells.
The Oly spec for the M15V with MD2 is 30 rolls of 36 exp.
If we assume 0.6A average current at 5FPS (7.2sec/roll), total time 30 rolls =
216 seconds. This
is then 0.6A * 216sec/3600 = 36mAh. Rewind time is spec'd at 10sec so
30*0.35A*10/3600 = 30mAh.
Total rew + wind = 66mAh. We don't know the cell spec, but given the vintage
they were probably
in the range of 120mAh to 200mAh at most. (Modern NiCd's of this size with
foamed plates could be
as high as ~300mAh. ) The low extraction efficiency (66/120 = ~50%) probably
reflects the very
high peak current and high mean current (~15C+ peak and ~3C mean rate!). At end
of discharge the
internal resistance is the problem for these high peak discharge rates. It also
explains why the
packs are so easily damaged by over discharge.
Out of interest I reran the current tests with a DC regulated suppply (~2A)
connected in parrallel
with the 15V cells to increase peak current and improve regulation. Average
frame rate over 36
frames was still below 5FPS (~4.4) but peak current almost doubled (5A+) and
voltage was almost
constant at peak current. Running the same setup but off the MAC control
intervalometer the camera
ran ok at the intervalometer max speed (4FPS). The MAC runs about 17V unloaded
using an
unregulaterd internal supply with an internal 12.4VAC 2A transformer.
I have not measured the MD1 current, but I assume the current will be less as
it only uses a
single motor.
Regards,
Tim Hughes
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|