YashicaMat 124G Battery (Again)

[bvy]

Last summer I bought a YashicaMat 124G. Used it, loved it, but I hadn't taken it out since October. This week, I pulled it out and blew the dust off, but failed to check the battery/meter and was left high and dry when I went to use it.

Two problems:

1. Why would the battery completely discharge over five months' time? The top has to be open, it seems, to turn the meter on, so I wouldn't have expected it to drain the battery while being closed up and stored.
2. I bought the battery in August, and have no idea now where or how I got it. The battery has nothing inscribed on it to identify it. On the positive side is a plus sign with four dots at each end of the cross; on the negative side is what looks like a piece of round foil starting to unpeel over a rectangular nub. I seem to recall going through some pains to find the right voltage, but can't find anything in my e-mail or other records. This makes me think I got it locally. It's the same shape and size of a 625.

Appreciate any help. Thanks.

 

[ic-racer]

The zinc-air cells will have a limited life span as soon as you peel the sticker off the back; this is irrespective of use. If you can remove the metal ring, you can re-use it on common 675 cells. You can stock up on 675 cells at your local drugstore.

 

[E. von Hoegh]

Block off three of the four airholes and a zinc-air cell will go on for years. The one in my Nikkormat has been there three years this month - it's still active.

 

[Pioneer]

I worked with the zinc air batteries for awhile but finally broke down and bought the MR-9 battery adaptor from CRIS. A tad pricey at $36, but in the past few years I have not had to worry about used up battery problems that occur at very inopportune times.

 

[BobD]

I also use the MR-9 adapters (though I paid a lot less than $36 for them) and they work fine. It seems like the best solution to me. There's a few on eBay USA right now for about 9 bucks.

 

[bvy]

This is from the item description for the MR-9 adapter I'm looking at on eBay:

Use of 386 / SR43W Silver Oxide battery (1.55 V) to convert voltage to be equal to obsolete MR-9 PX625 PX13 Mercury battery (1.35V).

So this thing actually "converts" the votage from 1.55 down to 1.35? How does it do that? Anyway, the one I'm looking at is $25 with shipping and comes from Thailand -- many sold and good feedback.

 

[ic-racer]

So this thing actually "converts" the votage from 1.55 down to 1.35? How does it do that? k.

Walter H. Schottky

 

[Pioneer]

Not too sure but it seems that ic-racer is suggesting that the MR-9 works on the Schottky Barrier principle.

However it actually does work and I have found them invaluable in any camera that originally required the mercury batteries. There is also a similar version that is used for the Pentax Spotmatic.

 

[tkamiya]

When you place a diode in series with a circuit and in forward direction, voltage drops across the diode at a predictable amount. For Silicone diode, this is about 0.7 volts. For germanium diode, this is about 0.3 volts. This is unlike resisters where voltage drop depends on current flow. I don't know what the forward voltage drop is for Shotottky barrier diodes are.

I *think* most of these adapters use germanium diode to drop 1.5 volt to 1.2 volt

 

[DWThomas]

More than one wanted to know here. Although that quotes the forward drop as "0.15–0.45 volts." Don't know if maybe that broad range is dependent on specific materials, or perhaps there is a narrower spec over limited current range. Their big deal was in fast switching, and higher efficiency due to lower drop across the diode in power conversion. The mercury cell adapter is just an accidental benefit.

I own one of those MR-9 thingies, but haven't really put it to use yet as I have several separate meters to choose from.

 

[ic-racer]

http://www.butkus.org/chinon/batt-adapt-us.pdf

 

[E. von Hoegh]

More than one wanted to know here. Although that quotes the forward drop as "0.15–0.45 volts." Don't know if maybe that broad range is dependent on specific materials, or perhaps there is a narrower spec over limited current range. Their big deal was in fast switching, and higher efficiency due to lower drop across the diode in power conversion. The mercury cell adapter is just an accidental benefit.

I own one of those MR-9 thingies, but haven't really put it to use yet as I have several separate meters to choose from.

The forward drop will remain constant over a certain current range, which is dependent on the characteristics of that particular diode.