PX 625

[truls]

One may wonder why manufacturers never made a same size px625 battery replacemment in 1,35V, to fit in older cameras. There are a lot of old cameras using this button cell.

[Stephen]

One answer, mercury, now banned, it leaves the replacement designs unable to match performance, voltage, etc. Mercury worked well, a great pity , but it cannot be directly matched.
Stephen.

[Deleted]

Is that the same mercury that we used to push around with our fingers because we were fascinated by the way it moved? A few years back they shut down a local school for several days because a large broken mercury thermometer was found on the grounds. Nowadays for every action there seems to be an equal and opposite overreaction. (and yes, I know that's where the term "mad as a hatter" comes from).

W

[Stephen]

Yes, the very same deadly stuff we played with....it's actually the oxide than is deadly, and fumes from heated mercury, but it got the lot banned, as it was entering the water table via rubbish burials.
There are air zinc replacements, some cameras will take other cells and still work, and there are ways of using a built up battery, details on net.

Stephen

[truls]

Jul 18, 2014 11:35:42 GMT -5 Stephen said:

Yes, the very same deadly stuff we played with....it's actually the oxide than is deadly, and fumes from heated mercury, but it got the lot banned, as it was entering the water table via rubbish burials.
There are air zinc replacements, some cameras will take other cells and still work, and there are ways of using a built up battery, details on net.

Stephen

Could it not been made a silver oxyde "mercury replacement" with same voltage and size? I am no electrician, but cannot understand what should be problem creating - we live in the twenty-first century. Is mercury really dangerous, or are the organizations making this up? Mercury are in use in a lot of applications: Mercury in other uses, why not battery?

[Stephen]

The science seems proven, and the law set in various countries across the EU and the States to ban the uses of mercury, or restrict to scientific experiments, and the problem is that silver oxide does not produce the same voltage or capacity as a Mercury battery.

Zinc air is near, but very low capacity. If we knew how to make other batteries so easily then electric cars would actually work properly!

Each chemistry used has a particular voltage standard, very difficult to alter. Edison wasted years testing batteries, convinced that even if it was only chance, he would come upon new combinations, but he did not. His Salt Chloride for cars worked, but was not as good as a acid battery, but recent developments are returning to modified salt chloride, as they are so dead cheap to make!

Even Lithium proved a nuisance at first, it has double the voltage of normal types, meaning new designs to use them.

As silver oxide battery produces a voltage of 1.6 volts, and falls away to a lower voltage as it discharges, but the Mercury is 1.35, and falls very slowly to discharge.

The silver cell can be modified by electronics to give 1.35, but it falls faster and gives a shorter life than mercury, there are designs using Zener diodes to produce the 1.5 volts from 1.6 volts on the net, to make yourself from an old battery casing. You can also purchase these commercially.

Stephen.

[Deleted]

The zinc oxide batteries are expensive and don't last very long after they are activated. Too bad all cameras didn't use a "bridge circuit) like in the Pentax Spotmatic. The camera originally used mercury batteries but works with newer batteries, too. For my Nikon FTn I had an adapter that allow using modern hearing aid batteries. I think that's the same one Stephen mentioned.

W.

[truls]

Stephen and Wayne: Thanks, I now understand and accept the problem creating a mercury replacement. We have to live with zinc air and other setups. May be a valuable camera should be modified to accept 1,5V battery, e.g. Leica M. Spotmatic and (some or all) Praktica can use 1.5V battery.

[hansz]

I thought, only the Praktica 5B accepts 1,5V natively...
Hans

[Deleted]

Jul 19, 2014 2:37:50 GMT -5 hansz said:

I thought, only the Praktica 5B accepts 1,5V natively...
Hans

Nope. Pentax (at least the Spotmatic) can use silver batteries with no problem.

[Stephen]

The bridge circuit solves the voltage, Pentax used it despite being more expensive as it needs a more sensitive meter,
but it cannot quite address the steeper discharge curve of a silver oxide battery. Mercury gave a slow fall off till right at the end of the graph, and gave stability.
With a Pentax and a Silver battery, in theory the quicker fade will be covered by the bridge circuit, as the voltage appears not to matter, but there are limits due to the coils characteristics, and the bridge resistances, and the silver cell will reach a point where the meter stops far sooner than a mercury battery. To add insult to injury the silver cell will not be quite flat at the point the meter stops working.

All calls for the use of a Weston Meter!!!

Stephen.

[dps3006]

I am a zinc air cell guy. I buy them very cheaply on the internet and have a good selection of O-rings to make them fit in various battery compartments. I would say the hand held light meters I use them in (Miranda Cadius & Gossen Luna Pro) are off about 1/2 stop. I get 4-5 months per battery. I do mainly B & W work. I am with Stephen on the Weston meter. I also have a little Gossen Pilot which is quite accurate and very handy. I use it the most.

Doug

[philbirch]

I prefer the Alkaline type. At least it doesnt go 'off' when the cameras's not being used. I pull the battery when not using the camera