Olympus OM1 - Batteries?

[scottwramsay]

I just got hold of a very well preserved Olympus OM1 which needs a new battery. The manual recommends a "1.35 volt mercury battery (Eveready or UCAR EPX625, Mallory PX625, or equivalent)" but the closest thing I found today was a Kodak 625A 1.5V alkaline battery. The shopkeeper said that over time the letters can change but the number is what tells you what basic type of battery you have, and that he doesn't know of any these days that go below 1.5V.

Do they exist, or will I be able to get by with this one? I don't want to put it in my camera without (a) second opinion(s)...

[John]

Bit of a can of worms Scott. The 1.5 volts will give you incorrect meter reading.

The short answer is that these guys claim to be able to supply a suitable replacement.

http://www.smallbattery.company.org.uk/sbc_mrb625.htm

[AlanM]

You can also get the OM-1 converted to use the modern cells, which would involve opening up the camera and adding a couple of components to deliver the correct voltage / current to the metering circuit

[yoker brian]

Hi Scott - I don't know if this is what your after. I found it after searching the RS Components website looking for PX625 ; it lists an alternative as LR9

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=searchProducts&searchTerm=PX625&x=0&y=0

Let me know how you get on

[br-cmr]

The LR9 is 1.5v. For most purposes that's "good enough", but apparently the OM1 metering requires 1.35.

I must admit I find this a little surprising - I would have thought that the circuitry would incorporate some sort of regulation, to accomodate the fact that any battery's voltage will decrease as it discharges.... but hey...

[Doorstop]

Batteries actually lose very little voltage over a discharge cycle right up until the point of complete failure.



As the charge is dissapated the internal resistance of the cell increases and consequently prevents the cell from giving full calculated (at full charge) circuit current. In laymans terms the current runs out long before the voltage does.

The X axis shows the cell characteristics normalised as a percentage of cell capacity so that the shape of the graph can be shown independent of the actual cell capacity. If the X axis was based on discharge time, the length of each discharge curve would be proportional to the nominal capacity of the cell with the lithium ion curve in particular disappearing off the end of your monitor.

[Reenie Bujman]

Wow! A-level physics come back to haunt me. Thanks Doorstop.

I've got a battery charger that does "normal" batteries and provided you don't allow the batteries to run right down, it seems to recharge them indefinitely. I guess the graph explains this.

[Doorstop]

I didn't mean it to sound like a physics lesson, I was just imparting some infromation is all.

Apologies to anyone who had flashbacks of ticker-tape machines and equations of motion.

Incidentally, the best batteries to look for as replacements at the moment are lithium polymer ... long plateau discharge characteristics giving stable voltage and A(h) over the extended output period with none of the cell memory charging problems of the old NiCD (and to a lesser extent NiMh) cells.

[br-cmr]

true - but all of those graphs look like there's at least a 10% different between "brand new" and "just about dead" - the same difference as there is between 1.35V and 1.5V...

[Doorstop]

The graphs have been normalised to show the average characteristics of the batteries in question .. most cells output at nominal stated voltage over their discharge cycle with the said cycle varying in length with the drain placed on the cell by the apparatus it feeds.

Thats what the Ah (Ampere Hours) value on a cell means ... if a cell has a value of 100mAh it means the cell will supply 100mA for an hour or 1mA for 100 hours depending on the current drain of the load attatched. It is also guaranteed to provide a pd equal the stated cell voltage for that time.

The voltage only actually drops off noticably towards the end of any discharge cycle, and although this sounds daft .. most batteries should be changed before they actually run out for peak performance.

Most modern electronics are manufactured to compensate for a moderate fluctuation in cell output, whether up or down, with capacitance to raise a dip in voltage or reactance via resistors and inductors to absorb spikes, older electronics are much more susceptible to variance in supply voltage.

[br-cmr]

I suspect we're violently agreeing with each other here....

[scottwramsay]

I ordered one from the Small Battery Company - thanks JohnR. It's a shame I don't have it for tonight - it's getting its first outing in town taking photos of some dressed-up-drunks. And I'm with the photo society from uni - don't worry, we'll be careful...

[John]

Cheers Scott - Come along to the next HG drinks night if you want to photograph some dressed down drunks.

[hungryjoe]

Buy a kodak grey card and shoot a number of shots increasing and decreasing (bracketing) your exposures using the film speed dial rather than the bracketing dial. Compare the results with the grey card, and if the results for the film you used are different, then use the film speed which matches your grey card. Use the difference in stops ( a third increments if memory serves) for faster or slower film speeds.
Nae fiziks.

[scottwramsay]

Was that posted in the right thread?