Permanent upgrade/replacement for 1.35V mercury batteries - voltage regulator

fpd2 · Jul 23, 2022

Hi,

Out of boredom and pursuit of perfection, I have manufactured a small batch of 1.35V and 2.7V voltage regulators. The reason is simple: I wanted to solder them into my cameras and meters, so that I can use any batteries I can buy (up to 5V). Minimum order quantity made me order 10x more than needed. I also thought that the CRIS adapter is way overpriced for what it is. Here, the output is always stable 1.35V or 2.7V, regardless of current draw, temperature, etc. Which is not the case with Schottke diodes. Size is miniature, 6x6mm. I called it "stable625" and posted on well-known auction website.

I have received mixed reactions in facebook groups - some were very positive, some were quite the contrary.

Here I present a sample installation in my Yashica 124G TLR. There are 2 ways to do it, one is in the side compartment, the easier one is by the light meter. This camera uses switching by ground. I also added it to Gossen Lunapro and Sekonic L-136.
The flaw of this solution is obvious: there is a quiescent current, very small circa 20uA, but I haven't tested the battery drain. My rough calculations would put a SR44 coin cell in range of 2 months. That's why so far I've used devices with some kind of switch between the battery and the electronic circuit. Regarding Gossen Lunapro, I have to keep the batteries out when not used. Not a big deal.

Let me know what you think!
Best regards

4season · Jul 23, 2022

fpd2 said:
Let me know what you think!

With that custom PCB, it looks like a tidy piece of work! Can't recall exactly what IC I tried it with, maybe Texas Instruments TPS709135DBVT (1.35V), but my result was too bulky to fit into 35 mm SLRs like Olympus OM1. But quiescent current rating for that chip is much lower - 1 microamp.

Ideally I'd like to use some cheap and common 3.6V lithium coin cell in place of the mercury battery; hopefully less likely to leak, and could potentially run the battery really far down before needing replacement.

fpd2 · Jul 23, 2022

4season said:
With that custom PCB, it looks like a tidy piece of work! Can't recall exactly what IC I tried it with, maybe Texas Instruments TPS709135DBVT (1.35V), but my result was too bulky to fit into 35 mm SLRs like Olympus OM1. But quiescent current rating for that chip is much lower - 1 microamp.

Well, I haven't measured the quiescent current, just cited from the datasheet. In real life it can be much lower. Supposedly it's good practice to remove batteries from devices not used for prolonged time

cmacd123 · Jul 23, 2022

the background draw is always the trick with that sort of regulator. If someone could magically solve that (and it would likely take real magic) they would have unlimited sales.

still I can see where it might be worthwhile for cameras and meters that Absoutly MUST have 1.35 volts. after all a sr44 is often not much more than a dollar, (and with a regulator an LR44 might work in some cameras) and LR44 batteries are multiples on a card at the dollar store.

the AIR cell is only good for a month or two and it costs at least 10 times the price of an LR44.

fpd2 · Jul 23, 2022

cmacd123 said:
the AIR cell is only good for a month or two and it costs at least 10 times the price of an LR44.

Exactly. And you can buy it anywhere. It works both with LR44 and SR44, SR44 of course has a higher margin of "life", since it's 1.6V and the regulator should be doing its job until about 1.38V. Any input up to 5V would work.
Did the 2.7V version (simulating 2x PX625) as well specifically for vintage spot meters. The ones with more modern batteries are somewhat expensive. Any input up to 6V is fine.

4season · Jul 23, 2022

fpd2 said:
Did the 2.7V version (simulating 2x PX625) as well specifically for vintage spot meters. The ones with more modern batteries are somewhat expensive. Any input up to 6V is fine.

2.7V would be perfect for some Nizo Super-8 cameras which have a 6V main battery, and separate 2.7V meter battery - plenty of room inside those cameras.

fpd2 · Jul 23, 2022

4season said:
2.7V would be perfect for some Nizo Super-8 cameras which have a 6V main battery, and separate 2.7V meter battery - plenty of room inside those cameras.

Oh yes, you could tap it to the main 6V battery. Good to know! Thank you

Bill Burk · Jul 24, 2022

Just installed your 1.35v circuit in a shoe meter, a Yashica YEM35 Super.

Works great!

AgX · Jul 24, 2022

cmacd123 said:
LR44 batteries are multiples on a card at the dollar store.

the AIR cell is only good for a month or two and it costs at least 10 times the price of an LR44.

But the no-name button cells sold for cheap (aside of Lithium cells) to me seem all to leak within the package in short time. Even a batch of Silveroxde batteries I bought at the Aldi were leaking after 3 years of storage still in their blisters.

Anon Ymous · Jul 24, 2022

AgX said:
But the no-name button cells sold for cheap (aside of Lithium cells) to me seem all to leak within the package in short time. Even a batch of Silveroxde batteries I bought at the Aldi were leaking after 3 years of storage still in their blisters.

The LR44 batteries I've bought from Lidl have never leaked. In fact, I don't recall seeing any LR44 cells leaking. Am I lucky?

@fpd2 Nice!

Nitroplait · Jul 24, 2022

cmacd123 said:
the AIR cell is only good for a month or two and it costs at least 10 times the price of an LR44.

That is if you buy overpriced Wein cells.
Zinc-air hearing aid cells are less than $2 for 6 and can be found everywhere.
Cheap dumb brass adapters can be easily sourced if one thinks it is too troublesome to make your own.
I use these in my Nikon F FTn, Leicameter MR, Pentax Spotmeter, Ricoh 500G and others.
I rotate the cells between the cameras I use and I rarely get less that 4 month out of a cell, normally it is closer to 6 month.
So haven't found a reason to do a deep dive to add a voltage regulator.

Nicholas Lindan · Jul 24, 2022

In many cameras that turn the meter on and off (Nikon cameras that turn the meter on when you flick the wind lever come to mind) the circuit can be installed after the meter on off switch.

Of course, Nikon cameras don't need the regulator circuit, (un)fortunately.

It should be possible to use a pico-power microprocessor as a software-defined voltage regulator. The processor can wake up a few times a second and test if the metering circuit is active and then provide a regulated 1.3 volts. Unfortunately the Atmel AVR class processors need 1.8V to work - that should allow their use in cameras and meters that work on two '625 mercury cells.

fpd2 · Jul 24, 2022

Bill Burk said:
Just installed your 1.35v circuit in a shoe meter, a Yashica YEM35 Super.

Works great!

Thank you Bill!

AgX said:
But the no-name button cells sold for cheap (aside of Lithium cells) to me seem all to leak within the package in short time. Even a batch of Silveroxde batteries I bought at the Aldi were leaking after 3 years of storage still in their blisters.

Just checked the pack of SR44 I bought at local grocery store (kroger) - expiration date is 4 years from now, so yes, seems like 3-4 years storage is maximum for any of them. Although I have seen them leak only after about 8+ years myself.

Bill Burk · Jul 24, 2022

1.35v conversion installed in YEM35 Super

fpd2 · Jul 24, 2022

Bill, what did you use to secure it to the wall? Hot glue?

Bill Burk · Jul 24, 2022

fpd2 said:
Bill, what did you use to secure it to the wall? Hot glue?

The one lead going down from “Out” is solid 23 gauge piece of wire soldered to the tab on the meter deck. I should have made the red insulation a sixteenth inch shorter because this placement interferes with the “lock” when you turn off the meter. Luckily it bent down gracefully out of the way without interfering with the lock or the power switch. Looks roomy but really it’s got pieces packed in like sardines.

Philippe-Georges · Jul 25, 2022

What about this, sorry it's in Dutch, but you get the picture...
At least you don't have to 'transform' your camera.

albada · Jul 25, 2022

What chip is in this device? I'm looking at the datasheet for the TPS709135DBVT mentioned above, and its max is 350 uA. That's less than a milliamp. I'd be concerned that a galvo-based meter might draw more than that.

AgX · Jul 25, 2022

Philippe-Georges said:
What about this, sorry it's in Dutch, but you get the picture...
At least you don't have to 'transform' your camera.

This is the THE standard text on the issue. Often referred to here. There are various English versions by the author online too.

This seems the latest:

The mercury cell problem and its solutions - [PDF Document]

1 The mercury cell problem and its solutions. Index. Page 1: Index and general information on mercury battery problems and solutions. 2: Detailed information on mercury,…

vdocuments.mx

fpd2 · Jul 25, 2022

Philippe-Georges said:
What about this, sorry it's in Dutch, but you get the picture...
At least you don't have to 'transform' your camera.

I have already answered that in my first post. The voltage regulator is superior to all of that given the shortcomings of Schottky diodes and non-linearity of battery voltage over time, except for the fact it's made for repair technicians and not end users, it's not user friendly at all. The modified camera is much more user friendly though, in my opinion.
The whole point of this is to transform the camera so that it is permanently upgraded and accepts any battery. The goal was not to create another adapter iteration for plug and play use. Sorry if I was unclear on that.

Now, if you somehow incorporate this voltage regulator into a battery LR44/PX625 adapter, that would be cool. It's too thick as far as I've measured, you can't go much thinner unless you completely redesign the PCB and then have a custom adapter shell made out of metal and insulating material, to keep the + sides separate and retain common GND. Still, according to my estimates, LR44 or SR44 would be too thick and you are stuck with thinner coin cells, which have much smaller capacity, and you are stuck with the battery drain regardless.

grain elevator · Jul 25, 2022

Nitroplait said:
That is if you buy overpriced Wein cells.
Zinc-air hearing aid cells are less than $2 for 6 and can be found everywhere.
Cheap dumb brass adapters can be easily sourced if one thinks it is too troublesome to make your own.
I use these in my Nikon F FTn, Leicameter MR, Pentax Spotmeter, Ricoh 500G and others.
I rotate the cells between the cameras I use and I rarely get less that 4 month out of a cell, normally it is closer to 6 month.
So haven't found a reason to do a deep dive to add a voltage regulator.

This. Actually I can buy 6 zinc-air batteries for 1,10 € at the 1,10 € store (they adjusted for inflation, I kid you not!) or online.
But I applaud the OPs perseverance and skill! If perhaps a switch could be added, the battery drain issue could be circumvented? With a new battery cover that allows access?

fpd2 · Jul 25, 2022

grain elevator said:
This. Actually I can buy 6 zinc-air batteries for 1,10 € at the 1,10 € store (they adjusted for inflation, I kid you not!) or online.
But I applaud the OPs perseverance and skill! If perhaps a switch could be added, the battery drain issue could be circumvented? With a new battery cover that allows access?

This voltage regulator is installed deeper in the camera, so you can install the switch anywhere if you drill a hole. It seems a bit drastic, so I use it on cameras with a built-in switch.

runswithsizzers · Jul 25, 2022

@fpd2 - thanks for sharing your project. My Konica Autoreflex T4 is presently with Greg Weber in Fremont, Nebraska getting a CLA and battery conversion. As you may know, he specializes in repairing Konicas, many of which need the meters converted to modern batteries. It sounds like your voltage regulator might work nicely in Konicas, but he may have his own preferred method.

AgX · Jul 26, 2022

fpd2 said:
I have already answered that in my first post. The voltage regulator is superior to all of that given the shortcomings of Schottky diodes and non-linearity of battery voltage over time, except for the fact it's made for repair technicians and not end users, it's not user friendly at all. The modified camera is much more user friendly though, in my opinion.
The whole point of this is to transform the camera so that it is permanently upgraded and accepts any battery. The goal was not to create another adapter iteration for plug and play use. Sorry if I was unclear on that.

-) the appliances in original state had to cope with the fall-off of cell voltage. This was tried to cope with by choice of cell system: Mercury. The advised alternative of the Silveroxide cell has same fall-off/linearity as the Mercury cell
Thus by choice of cell the original state can be achieved.

-) one may argue that a Shottky diode introduces additional non-linearity

-) that document referred to explicetaly has it about a modifaction of the camera, even dedicated to its metering drain. Thus it is not only about an adapter solution.

AgX · Jul 26, 2022

So the user has choices...

-) use a Zn-Air cell, that deteriorates in short time after being activated (some advise to reseal it between uses)

-) use a Schottky diode adaptor/camera-modfication, with its shortcomings

-) use a complex regulator for ideal voltage stability, only as camera-modification, which needs a switch or to take out the cell between uses

Permanent upgrade/replacement for 1.35V mercury batteries - voltage regulator

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The mercury cell problem and its solutions - [PDF Document]

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Permanent upgrade/replacement for 1.35V mercury batteries - voltage regulator

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