Warren wrote:
>>I was
thinking of putting in a smaller set of silver oxide
batteries and a small magnetic reed switch inside the
battery compartment so I can turn the battery on and
off. Does anyone have an opinion as to whether or not
a smaller SO battery will have sufficient current
capacity and if so which one might be suitable.
<<
There are a lot of silver oxide battery sizes but most are not suitable for
OM applications. The reason is, that they are aimed at the watch market and
are not "high rate cells". Watch cells are often NaOh rather than KOH cells.
That is, they cannot produce the high pulse currents without significant
voltage drop. Even the ones that are pulse rated generally have larger
voltage drop particularly at the end of life. The capacity generally scales
directly with volume. One of the few smaller batteries that stands some
chance of working is the 393 (IEC No : SR 48 ). This is a 7.9 x 5.4 mm. (vs
11.6*5.5mm of the 357/IEC SR44) The capacity is 40 to 500f the 357
depending on vendor. You might optimistically expect 30-400f the 357 cell
life but read on..
I have dealt with a number of battery vendors professionally who have shared
unpublished information with me so I have to be a bit careful what I say. The
393 cells **from at least one vendor** have only a slightly higher impedance
at start of discharge than a 357, but after 10 0ischarge it increases by a
factor of 3 to 6 times vs an increase of 2 to 3 times in the case of the 357.
After that it declines back to a value nearer initial and then increase to
end of life. But on average the 357 impedance curve is much flatter, and the
impedance of the 393 is significantly higher over most of the curve. The
early peak in the impedance-discharge curve may cause the camera to lock up
after only a small amount of use. Bottom line expect a lot shorter and more
erratic battery life.
Also, even new cells from old stock (1-2years) AgO cells often have
significantly increased impedance and thus reduced capacity depending on the
vendor. This probably accounts for some percentage of "new battery" failures
in OM use. Energizer brand cells probably age better than many other brands
because of improved technology.
Remember even Silver oxide cells have a small amount of mercury in them (<1%)
so take advantage of any battery recycling if your local store or refuse dump
will take them back..
Hamlin makes some small reed switches but beware if you cut the leads short
the sensitivity drops a lot.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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