I did some web research on batteries a bit ago and learned a few things.
Many silver oxide batteries come in 2 versions, high drain and low
drain. Looking at the specs, it doesn't make any sense, capacity,
voltage curve, everything the same except the low drain ones couldn't
maintain voltage under short, heavy loads. So why not just make the
better one? The answer turns out to be somewhere outside the published
specs. It turns out that there is an internal difference (mechanical?
chemical? both?) which made a big difference in how well they could be
sealed against leakage. Notice I said 'made' and 'could', past tense.
Apparently that problem has been largely solved. However, long before
seals were improved, watch manufacturers and repairers insisted on the
low drain designs. Makes perfect sense, they have no need for transient
high drain capability and their work can be ruined by corrosion from
leaky batteries.
So what does all this mean to us? Well, auto exposure OMs, and all other
similar cameras, really, use low current while metering, then high
current during the actual exposure as electro magnets are used to
control the shutter. So we need high drain design batteries to get
reasonable life and reliable performance. However, battery equivalence
charts completely ignore the difference, going only by size and voltage.
With the particular size used by OMs, things are even more complicated.
Leaving aside the lithium and alkaline versions, which are not suitable
for OMs except in an emergency, there are 3 different silver oxide
designs (at least). The low drain version is the 303 and the high drain
version is the 357... and the 76! The only data sheets I've looked at
are for Energizers. All 3 batteries are the same size and have the same
nominal voltage. The 303 and 357 both have 175 mAH capacity, while the
EPX76 has 200 mAH capacity and is "Designed specifically for Photo use".
Simple, huh? Well, not really. I don't know what photo use the EPX76 is
designed for, but it is not for OM bodies. The 303 and 357 have
essentially identical discharge curves, starting at 1.6v, slowly
declining to 1.55v over the first 100 hrs and staying there, dead flat,
to 700 hrs, where they just fall off a cliff. thus they will run in an
appropriate application accurately and reliably, then die suddenly.
(ALWAYS carry spares, they are SUPPOSED to ide without warning!) Thus
the 357 never has an intermediate voltage to lead to annoying, seemingly
random, seemingly non-battery related lockups. OMs intentionally lock up
when battery voltage under the load of shutter is relase is insufficient
to assure proper exposure.
So what about the EPX76? It's the right size and the right chemistry,
even the same drain response when new as the 357, but...... A look at
its discharge curve shows the price paid for the extra capacity. It
starts out like the others, but at about 400 hrs, starts a long
downslope to 1.2v at 750 hrs., then descends more rapidly after that,
but not as precipitously as the 357. What all that means is that it will
give less overall life than a 357 because it drops below the voltage
needed to operate the shutter sooner. So the extra capacity is at
voltages that won't operate the camera! Worse than that, it means
unreliable response as it nears the OM minimum voltage. It may work for
widely spaced shots, but drop enough voltage after a couple of quick,
longer exposures to lock up on the next one. But then, but the time you
reset the camera, try the battery check, puzzle over it and try another
shot, it works, only to fail again apparently at random. Then you start
asking "What the hell is wrong with this camera?" and don't change the
batteries that seem ok until someone on the list insists that is the
first thing to do before panicking.
I believe, but don't know where I got it, that the SR44 and SR44W are
the low and high drain designs. Anybody know? Or is the SR44 a 357 and
the SR44W an xx76x? I also don't know if the
Varta V76PXs you have been using are EPX76 equivalents, but I'll bet
they are, so you should expect better performance from the 357s.
Moose
distinctivedeal@xxxxxxxxxxxxxxx wrote:
>Thank you everyone ... I got a bunch of 357s from xBay ... I will use them
>in my OM-2 and OM-4, even though my -4 does have the t(i) circuit.
>I figure they are just better SR44 silver oxide cells
>Alex
>
The olympus mailinglist olympus@xxxxxxxxxx
To unsubscribe: mailto:olympus-request@xxxxxxxxxx?subject=unsubscribe
To contact the list admins: mailto:olympusadmin@xxxxxxxxxx?subject="Olympus
List Problem"
|