Zinc-Air cells.

E. von Hoegh · May 13, 2014

I just put new Z-A cells in my LunaSix and checked it against the two other meters I use regularly, a Weston Master III and a Nikkormat FTN.

Pointed at the skylight, solid bright white featureless overcast -
Gossen f:16 @ 1/200
Weston f:16 @ 1/200
N-mat f:16 @ 1/60 (*)

Pointed at a white wall, same room -
Gossen f:4 @ 1/30
Weston f:4 @ 1/40
N-mat f:3.5 @ 1/30 (*)

* the Z-A cell in the Nikkormat has been there for 37 months. I'll get my Fluke out and measure the OC voltage later on today; I think the internal resistance has risen to the point where it is no longer useful, it used to agree with the Gossen +- 1/3 stop across the range. This is the longest one has ever lasted.

The cells in the Gossen are fitted into "Cs" made of bare #12 AWG wire. 3 of the four airholes are blocked off by using gold nailpolish (just in case it's conductive) to glue three 1/16"~ squares of Al foil over the airholes of each cell. The needle goes to the far end of the red block on test, I replace the cells when it falls to the near end of the red block. They last 2+ years.

Tom1956 · May 13, 2014

Man that Nikkormat is way off. I hope it's just the batteries and not a bad meter cell. I think if the cells in either of my Nikkormats went bad, it would be like a death in the family.

AgX · May 13, 2014

But the open circuit metering won't tell you the effect of risen resistance/voltage drop under load.

E. von Hoegh · May 13, 2014

Tom1956 said:
Man that Nikkormat is way off. I hope it's just the batteries and not a bad meter cell. I think if the cells in either of my Nikkormats went bad, it would be like a death in the family.

It's behaving precisely as I would expect it to, with a moribund cell in it - the more current demanded from the cell, the greater the error.

E. von Hoegh · May 13, 2014

AgX said:
But the open circuit metering won't tell you the effect of risen resistance/voltage drop under load.

Correct. But it might give others some useful information, maybe. Not everyone has an assortment of resistors around, but multimeters aren't that uncommon.
I'll see if I can find some resistors to put it under a known load.

CJBo001 · May 13, 2014

Why would you even think of using a zinc-air cell after 37 months?

E. von Hoegh · May 13, 2014

CJBo001 said:
Why would you even think of using a zinc-air cell after 37 months?

Because I put it in the camera that long ago. Until a few weeks ago it was working accurately, then I began to notice that it was disagreeing with the meter in my head.
Cells and batteries are typically used until they cease performing properly.

E. von Hoegh · May 13, 2014

I turned the meter in the Nikkormat on and left it pointed at the skylight for about 5 minutes. Then I removed the cell and put the meter on it, it was climbing past 1.2v and after about half an hour was at 1.370v. The new cells are 1.431v.

E. von Hoegh · May 13, 2014

Tom1956 said:
Man that Nikkormat is way off. I hope it's just the batteries and not a bad meter cell. I think if the cells in either of my Nikkormats went bad, it would be like a death in the family.

It's back to normal, with a new 675 in it.

ic-racer · May 13, 2014

E. von Hoegh said:
3 of the four airholes are blocked off .

I use a lot of zinc cells but have never done this. Does that make them last longer?

E. von Hoegh · May 13, 2014

ic-racer said:
I use a lot of zinc cells but have never done this. Does that make them last longer?

"....3 of the four airholes are blocked off by using gold nailpolish (just in case it's conductive) to glue three 1/16"~ squares of Al foil over the airholes of each cell. The needle goes to the far end of the red block on test, I replace the cells when it falls to the near end of the red block. They last 2+ years."

AgX · May 13, 2014

Altered hole area was one of the Wein cells alterations to standard Zn-Air cells.

E. von Hoegh · May 13, 2014

AgX said:
Altered hole area was one of the Wein cells alterations to standard Zn-Air cells.

Yes, but: The Wein cells are far more expensive than 675 hearing aid cells - two Wein cells cost more than 8 675s at the local stores. Wein cells have two holes, and last at best a few months. There's no reason why you can't block off one hole, though.

E. von Hoegh · May 13, 2014

Something I forgot to mention is that the 675s are slightly thinner than the original cells. I use a roughly .030" x 5/8" disc of copper between the cells in the Gossen meter to make up for this.

Chris Douglas · May 13, 2014

E.

I have never tried blocking the holes, but it sounds like it is working for you. I use the same hearing aid battery in my OM-1's and it works fine for a few months. I change them often since they are very cheap. I use a V shaped piece of paperclip to take up space, and an o-ring to center the cell. The paperclip fits snugly in the battery cover so it stays in there while changing the battery. Thanks for sharing.

Chris

Newt_on_Swings · May 13, 2014

Wouldn't blocking off the holes on a camera that you use the meter frequently on drain it so that it would be inaccurate until you let it rest and have it recharge through a slow reaction with air? I remember I had tried to use these zinc cells, with all holes uncovered in a camera that was very dependent on batteries, an om-40 and it frequently ran out of juice and had the shutter lock up when it drained only to come back after sitting for a bit. I only used the zinc ones that one time as I got them on sale at Walgreens. I went back to silver oxide batteries after that.

bsdunek · May 13, 2014

Interesting. Just the other day I put two new zinc-air cells in my Nikon FTN meter and it still wouldn't work. I checked the voltage and one was at about 0.3 volts. The other was OK. Guess some of them don't always work right even when new. I had never had this happen before.
We are off to Japan in less than a week, and I have decided to take a small multi-meter just so I know if the cells are performing properly. Kind of a pain, but better than not knowing if the problem is the cells or the meter.

Xmas · May 14, 2014

Newt_on_Swings said:
Wouldn't blocking off the holes on a camera that you use the meter frequently on drain it so that it would be inaccurate until you let it rest and have it recharge through a slow reaction with air? I remember I had tried to use these zinc cells, with all holes uncovered in a camera that was very dependent on batteries, an om-40 and it frequently ran out of juice and had the shutter lock up when it drained only to come back after sitting for a bit. I only used the zinc ones that one time as I got them on sale at Walgreens. I went back to silver oxide batteries after that.

A OM-40 can use SR44 or LR44, but uses lots of current on long exposures, I use the LR44 and carry a spare set.

The air cells won't do 100% performance immediately after activation even if all the air holes are open. The modern hearing aids normally have a low duty cycle cept in a DISCO.

They are not wonderful on battery dependent cameras a silver cell and Shockety diode better.

The mercury cells were not very high current anyway.

AgX · May 14, 2014

Cruzingoose said:
The cell requires OXYGEN to operate, think fuel cell, and in the closed and sometimes sealed space in cameras, there is no available oxygen...

I do not consider the cameras from the era we are talking about as air sealed. Furthermore many caps of battery enclosures intended for Hg-cells have got a venting hole.

Jaf-Photo · May 14, 2014

Zink-Air batteries deteriotate quite qyickly after you remove the protector foil.

I only use the same cell for a few weeks. Luckily they are cheap so I keep a 6-pack in my bag and replace them frequently.

Especially for inportant shots.

bsdunek · May 19, 2014

E. von Hoegh said:
Something I forgot to mention is that the 675s are slightly thinner than the original cells. I use a roughly .030" x 5/8" disc of copper between the cells in the Gossen meter to make up for this.

Maybe that's why I have had some trouble with the 675's. I thought it might be some corrosion of the brass rings I use, but even with them polished I've had trouble. I'll try your idea. Thanks,

Newt_on_Swings · May 20, 2014

I just use a tiny square of folded over aluminum foil. Works like a charm.

E. von Hoegh · May 20, 2014

Cruzingoose: (snip)
"The cell requires OXYGEN to operate, think fuel cell, and in the closed and sometimes sealed space in cameras, there is no available oxygen so the cell can not deliver the current (milliamps) required to operate the meter in bright light conditions, the voltage drops under the load and the meter is unable to get the current needed for proper reading, but the cell may supply enough current under lower light. Sealing the holes starves the cell of oxygen reducing the power available" (snip)

JAF Photo:
"Zink-Air batteries deteriotate quite qyickly after you remove the protector foil.

I only use the same cell for a few weeks. Luckily they are cheap so I keep a 6-pack in my bag and replace them frequently.

Especially for inportant shots. "

You guys crack me up. Here I've been using the darn things for the past 9 or so years, I never realized they didn't work.

Tom1956 · May 23, 2014

I'm 51-49 in favor of the 357 camp. Although I've studied the curves as they are available online. The evidence for EvH's method is respectable. I believe he has found a happy medium between capacity and discharge curve. The 625 was king, but dethroned by non-sequitur law, in retrospect. His method is a viable replacement, and has satisfied my standards for that need. Presently I'm using Duracel 357's as available at a good 3-pack price at the local Family Dollar. Their capacity is excellent, and their discharge curve is fair. Any way you look at it, you have to keep on top of all your equipment. Any sloppiness translates to more test strips and prints in the darkroom before a "good print" finally comes up in the chemical.

Jaf-Photo · May 23, 2014

E. von Hoegh said:
You guys crack me up. Here I've been using the darn things for the past 9 or so years, I never realized they didn't work.

You probably got the less known and more expensive Uranium-Air battries

Zinc-Air cells.

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