Preparing to convert SRT to Silver oxide

John Koehrer · Dec 15, 2008

Advantage to the adapter though is you can move it from one camera to another if you wish.
Although you have the skill to install the diode, many do not. Their alternatives are pay a technician to do it or go with the cris adapter or have you do it.

Terry Again · Dec 20, 2008

Hi All,
I Wonder If anyone can point me to or tell me why a diode is used instead of a resister to reduce the voltage of the battery? I remember little about things electrical!! And anyone that's done the conversion themselves pm me or mail me details not covered by that page on Rokker files? It'd be easier IF you mailed me at home but I can try to figure out the PMing way here as I've done it on other sites!:confused: Or has this thread died? RIP Happy Holidays People!!

chriscrawfordphoto · Dec 20, 2008

Terry,

I think a resister won't work because it doesn't drop the voltage the same in different current loads. On a CdS meter, like the SRT has, the battery puts out 1.35v but the amount moving through the circiut is altered by the resistance of the CdS cells, which changes based on how much light hits the cells, so a resister placed in the circuit won't always gve the required .2v drop, which must always be the same drop no matter how much current comes through it from the CdS cells. A diode does produce the required voltage drop no matter how much current the CdS cells pass through.

Steve Smith · Dec 20, 2008

You could use a resistor. In fact, the meter most probably already has a series resistor anyway. The problem is that you would need to work out or find by trial and error the correct resistance for each type of camera you modify.

With a diode you know that the voltage with a new type of cell will be very close to that of the old mercury cell so the meter should still be good (assuming it was correct with a mercury cell).

Steve.

Terry Again · Jan 4, 2009

Hi,
Has anyone used Garry's Camera shop for service? How was their work and turn around time and were there any surprises? I've had a member made me an offer to convert the SRT to silver Oxide's that's very good!! I just wonder about the rest of the camera's condition since it's age has been mentioned.
Thanks,

mgb74 · Jan 4, 2009

Terry Again said:
Hi, Anyone ever use Garry's Camera shop for repairs? It seems aspart of their general maint. of SRT cameras conversion to silver oxide battery is part of the checking of function of shutter etc...... which at the 53 bucks I can maybe save for IF The tests I just had show I have cancer? then I guess all my money goes to damn Docs!!Damn Genetics!! Happy holidays

I had Garry CLA 2 bodies about 3 months ago. So far, so good. I'd use him again.

Chazzy · Jan 4, 2009

Terry Again said:
Hi,
Has anyone used Garry's Camera shop for service? How was their work and turn around time and were there any surprises? I've had a member made me an offer to convert the SRT to silver Oxide's that's very good!! I just wonder about the rest of the camera's condition since it's age has been mentioned.
Thanks,

Garry's fixed my Minolta X-700 and gave it a CLA for $50, after another shop had said that the camera couldn't be economically repaired. So I'm a satisfied customer.

domaz · Jan 4, 2009

How about using an adjustable step-down regulator with with some kind of higher voltage battery like a CR123. That way the voltage is always 1.55 or whatever you want it to be.

chriscrawfordphoto · Jan 4, 2009

domaz said:
How about using an adjustable step-down regulator with with some kind of higher voltage battery like a CR123. That way the voltage is always 1.55 or whatever you want it to be.

The 123 won't fit in the camera, it was made to use a single button-cell battery. You could probably do it if you were willing to accept having a battery box hang under the camera, or have it in your pocket with a cord to the camera. Someone online designed one like that for Olympus OM cameras. It doesn't have a regulator because the OM 2s and OM 4 have built in voltage regulation and were designed to work with two 1.5 volt batteries. So, his design used two AA batteries..the purpose was to improve cold-weather performance because cold reduces the voltage a bit with the little silver-oxide buttons the OM cameras used, and AA batteries are more resistant to cold.

ath · Jan 5, 2009

domaz said:
How about using an adjustable step-down regulator with with some kind of higher voltage battery like a CR123. That way the voltage is always 1.55 or whatever you want it to be.

Works like a charm. LP2951 adjusted for 1.35V running from a Lithium 1225 button cell (fits in a 625 battery compartment). Needs a proper on/off switch because of the quiescent current.

Steve Smith · Jan 5, 2009

Having given advice earlier in this thread I now have to do this modification myself as I have just acquired a couple of SRT100 bodies. I will post some instructions and pictures later (assuming it all goes to plan!).

Steve.

Steve Smith · Jan 5, 2009

ath said:
Works like a charm. LP2951 adjusted for 1.35V running from a Lithium 1225 button cell (fits in a 625 battery compartment). Needs a proper on/off switch because of the quiescent current.

You could probably use the existing power switch on the SRT cameras. Unfortunately that switch also incorporates a battery check position which may not be re-wireable to operate with a regulator.

Steve.

ath · Jan 5, 2009

Steve Smith said:
You could probably use the existing power switch on the SRT cameras. Unfortunately that switch also incorporates a battery check position which may not be re-wireable to operate with a regulator.

Steve.

I did this modification (LP2951) for a lightmeter with CDS cell (Weimarlux CDS from GDR) which has a pushbutton to activate the metering.
For my SR-Ts I found it more easy to recalibrate one to a silver cell (recalibration had to be done anyway); the other one is still on mercury and will be adapted to 1.55V when the battery goes down.

Alternatively I will simply place the diode in line between the battery compartment and the switch. Easy to reach after unscrewing the bottom plate.

Steve Smith · Jan 5, 2009

ath said:
Alternatively I will simply place the diode in line between the battery compartment and the switch. Easy to reach after unscrewing the bottom plate.

That's what I'm going to do. I have ordered some PX625A cells which are 1.5v cells in the same package as the old mercury cell.

Steve.

ath · Jan 6, 2009

Steve Smith said:
That's what I'm going to do. I have ordered some PX625A cells which are 1.5v cells in the same package as the old mercury cell.

Steve.

Make sure, that the Battery is not only 1.5V but also silver. Alkaline is not stable enough for this. AFAIK the PX625A is alkaline.

Steve Smith · Jan 6, 2009

ath said:
Make sure, that the Battery is not only 1.5V but also silver. Alkaline is not stable enough for this. AFAIK the PX625A is alkaline.

That's a good point. Your lithium cell idea looks more promising now. Not necessarily with a regulator though. I may do some experiments with an LED in series instead of the schottky diode. A 1.7v drop with a 3v cell = 1.3v so it could work.

I know the regulator is the most accurate approach but I also like to think in terms of simplicity.

Steve.

ath · Jan 6, 2009

Lithiums are quite unstable as well.
If you look for a stable primary cell afaik there is only siver oxide and mercury.
(edit: and zinc air of course)

Terry Again · Jan 12, 2009

Hi Again all,
I have been informed that zinc air batteries that can be purchased at stores in towns have them cheap like .70$us? I guess that would be in the 675 size? What problems does that have with it and can it be solved with an O ring of rubber? I see there's a guy on the bay that sell the adaptors I wonder if there is plans for it on the web so one can do it oneself? Any other drawbacks to this method of battery I hope someone can answer these questions,please!!

Arvee · Jan 12, 2009

If one purchases one Wein cell, it is actually a 675 with a snug metal ring around it. When the battery expires, simply go to your local Walgreen's etc. and buy a package of 675 hearing aid batteries. Push the old battery out of the ring and install a new one. You're in business. I have been doing this for years.

Some cameras will not work with the rubber washer/grommet around the battery as contact is needed to the outside wall of the battery compartment.

If you want to prolong the life of the battery during times of non-use, simply put Scotch tape, or any tape for that matter, over the little holes that allow air inside the battery. This keeps the electrolyte from drying out prematurely. Zinc-air batteries have a shelf life of several years (4-5) as long as you keep those holes closed.

-Fred

mgb74 · Jan 12, 2009

A #9 O-ring around a 675 zinc air battery works for me. Does, of course, require that electrical contact be at the top and bottom of the battery.

Terry Again · Aug 29, 2009

I saw another post asking this same battery question and I wonder about making this and other mercury battery substitutes questions and answers in a sticky where it could be found easy?

Terry Again · Jun 11, 2010

Hi all, I wonder IF anyone knows of a source for Energizer 357/303H batteries not the 357/303 everyone has listed for sale? The 357/303H has a flatter discharge curve like the mercury battery has sort of has from what I can find out so far!! I hope someone knows?
Thanks,

Preparing to convert SRT to Silver oxide

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