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Mercury battery...comprehensive solutions! Sorta...

J Lochner , Sep 17, 2004; 04:51 p.m.


Mostly has to do with the mercury PX625 cells...

Do you have an old/classic camera whose meter was made for a mercury cell? Do your exposures never come out right because you're using alkalines or whatever?

Well...I have found the most comprehensive resource about how to overcome the mercury cell problem! Check it out! I'll summarize and list the options here for those that don't want to read that pdf file:

1) Find some old mercury PX625! RARE...but can be found every once in a blue moon. Check eBay...apparently there some for auction a few months ago. Otherwise, keep an eye on the following sites:

http://www .smallbattery.company.org.uk/sbc_px625.htm

http://www.px625.com/px625/ main.cgi

The chances they'll find some more stock is slim...but possible.

2) Find some old mercury PX675 cells! Apparently, they fit MOST PX625 compartments. Otherwise, people use little rubber plumbing grommets to make sure they fit snug! 675's ARE in stock here: http://www.px625.com/px625/ main.cgi

A rubber grommet may not work in all cases. If you're not creative/resourceful enough to figure out how to make them fit, this guy will sell you a metal adapter: http://paulbg.com /Nikon_F_meter_batteries.htm

3) Zinc-air cells. These are not a terrible option. Voltage is the same as mercury...and the flat constant output characteristic is the same. The only real downside is they're not very cheap...and once you pull the battery tab, they typically don't last very long. And since they need oxygen to function, it won't work in a air-tight battery compartment. Once the tab is pulled and the battery takes in oxygen, the cell usually lasts 6 months or less...but it depends on humidity and temperature and stuff...so sometimes it can last upto 18 months. It is recommended that you take the batter out and put the seal back on the battery when not in use. There's a zinc-air cell called a "Wein Cell"...it's supposed to last longer than normal zinc-air cells because it has fewer holes for air...but people haven't noticed a big difference.

4) Alkaline. Usually not a good option. Voltage starts too high...and the sloping discharge curve shows it ends up to low. There's a very very very narrow window when your exposure meter will expose correctly. Deviatations due to an alkalines non-constant voltage can be upto 4 light values in either direction. BUT...it can work some SOME older cameras.

5) Silver-oxide 625 replacement. This can potentially work. They have a constant discharge voltage, just like mercuries. But they're voltage is way too high. So your exposures will be off. Fortunately, since it has constant voltage, the exposure will be off by the same amount all the time. So you can adjust for that yourself on the camera. Just set the film speed off by 1-4 stops, whatever makes it right. The battery life is not as good as a mercury cell...but not as bad as a zinc-air cell. They're not as expensive as either one.

6) Use a silver-oxide 675 hearing aid battery! These can sometimes fit without any type of adapter. Might need a rubber grommet, just like the mercury 675's. Silver oxide 675's have the same voltage as the mercury 625/675...and they discharge flat with constant voltage. So these work really well. Plus, they're real cheap. And if you need...you can use that metal adapter made by Paul: http://paulbg.com /Nikon_F_meter_batteries.htm

7) You can get your camera permanently fixed by a camera repair guy. This is probably the best long term solution. But you gotta find the right guy for your particular type of camera. And the initial cost can be high...could be around $100.

8) Use the silver-oxide 625 replacement with an adapter that corrects for voltage. Silver-oxide has the same flat discharge curve as mercury...but the 625 replacement voltage is too high. So...the MR-9 seems to be the most popular adapter to reduce voltage. They work OK. Except most of these adapters are a teeny bit large so you may not be able to close you batter compartment door all the way. Also, the MR-9 only allows for a maximum drawn current of 200 microamperes...which is fine for super low draw camera's like the Rollei 35's. But most cameras draw more than that.

To get an adapter that allows for more current draw than a MR9...you can either build one yourself as outlined in the PDF file I linked above. OR...you can buy a ready-made one from the guy that wrote the document (Frans de Gruijter). He also sells a small kit so you can make it yourself. An adapter from Frans de Gruijter, with a BAT83 Schottky diode, is the best option for most applications.

You can find the MR9 here: http://www.criscam.com/mba.htm


J Lochner , Sep 17, 2004; 04:52 p.m.

If anyone knows anything more...or if I've posted something wrong, let everyone know!!!

Miles S. , Sep 17, 2004; 05:02 p.m.

9) Build a battery adapter with appropriate diode it it. Or solder a diode inline with the wire from the battery compartment. See, http://www.rolleiclub.nl/batt-adapt-US.pdf

10) Recharge your existing Hg cells. There are purpose built chargers for Hg button cells. Besides you haven't been throwing out these highly toxic batteries, or have you?

J Lochner , Sep 17, 2004; 05:13 p.m.

I think I mentioned #9...at least the build your own part. And the very first link in my post is Frans de Gruijter's PDF document.

But...I did NOT know you could recharge mercury cells! That's news! I have not been throwing them out...cuz I've never used a mercury cell...yet!

Charles Stobbs , Sep 17, 2004; 10:01 p.m.

I have been using #675 zinc/air cells (hearing aid batteries) in Canonets, Oly 35RCs EDs and ECs. They are less than $1 each which I think is pretty cheap compared to the cost of film and processing.I don't know what their life span is expressed in rolls of film or months but at least 2 or 3 rolls of film in a 2 month period. I don't have any experience much below freezing. They are stocked in most drug stores and are no danger to you or the environment. In the above applications o-rings, plastic sleeves, and a little aluminum foil will fit them properly.

jason hopper , Sep 18, 2004; 12:12 a.m.

To my chagrin, just found another thing about zinc-airs: unmasked, as they charge up they may expel oxidation by-products through those breather holes. If you use zinc-airs, let them charge up out of camera.

Gary Watson , Sep 18, 2004; 09:57 a.m.

11) Disregard all the above and buy a decent lightmeter.

J Lochner , Sep 18, 2004; 12:49 p.m.


Yeah, that works too...sometimes. But sometimes it's not convenient to always carry a light meter in addition to the camera. And sometimes I need to shoot fast...just focus, shoot...focus, shoot...focus shoot. I don't want to have the point the light meter, get the values, adjust the aperature, adjust the shutter speed, focus, and shoot. For some situations, that takes way too long...my shot is gone.

David M , Sep 19, 2004; 12:52 a.m.

Mercury batteries are no more toxic than lots of other forms of mercury, chemical companies pour mercury into our rivers and oceans every day, thats why you are advised to ration your input of fish. There is mercury in your tooth fillings and people are buried with them every day. Mercury is used in thermometers and many many other products. I would not be worried about disposing of your mercury batteries.

Dan Fromm , Sep 19, 2004; 12:29 p.m.

Um, Gary, I have three decent lightmeters, two of them fairly freshly overhauled (both last spring/summer) and working. Weston Master V, Gossen LunaPro. The Master has a selenium cell, doesn't need external power.

Relevance to this thread? The LunaPro (also known as LunaSix III) uses mercury batteries. Bogen, Gossen's US distributor, sells a little cylinder, presumably with diode, that holds 2 SR44 cells and fits the LunaPro (and all LunaSix) battery compartment. Works like a charm. Also fits my Canon 814LS' (814AZ adapted to diabolical B&H double system sound) battery compartment and works well there too. Around $20 at retail. Can't imagine why the C.R.I.S. single cell adapter costs $30.

I use the Master mostly as a sanity check on the LunaPro, and I use the LunaPro quite a bit with the narrow angle attachment. Not sure why, they're both good meters and neither has bad ergonomics.

My dud is a LunaSix II. Functions, smells of cooked electronics, is very inaccurate, clearly needs service. Haven't been able to justify the expense because the III works well AND accepts attachments.



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