Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Mercury battery = NO voltage regulator?
Post new topic   Reply to topic
Home   Film SLR / TLR Cameras
View previous topic :: View next topic  


PostPosted: Tue May 06, 2025 9:40 am    Post subject: Mercury battery = NO voltage regulator? Reply with quote
Apologies if I am the one posting most of the questions under Film SLR / TLR Cameras.

Here is my question for today. If a camera (or a light meter) has a mercury battery (PX625, PX13), does that always mean that the camera does not have a voltage regulator? Or are there mercury battery cameras that do include a voltage regulator?

Since the mercury batteries had a very stable voltage output, omitting a voltage regulator might be an obvious place to save money.

Regards, C


PostPosted: Tue May 06, 2025 11:57 am    Post subject: Reply with quote
As you say, the mercury battery voltage is very stable. There is always a possibility that a camera from the mercury battery era used a voltage regulator, but I would consider it unlikely. Especially if it only uses one mercury battery since the regulator itself would eat up quite a bit of the available 1.35 Volt.


PostPosted: Tue May 06, 2025 12:12 pm    Post subject: Reply with quote
RokkorDoctor wrote:
Especially if it only uses one mercury battery since the regulator itself would eat up quite a bit of the available 1.35 Volt.


Good point, I hadn't considered that. The question arose because I saw someone advertise a camera that takes a mercury battery (an OM-1, to be specific) who includes a Varta V625U (didn't know it existed) which appears to have the same shape as the PX625 but is 1.5 volts alkaline (so, decreasing voltage). Without a voltage regulator in the camera it seems to me it would be pointless to include such a battery except for purposes of selling the camera.

Thank you.

Regards, C.


PostPosted: Tue May 06, 2025 1:05 pm    Post subject: Reply with quote
You can't make assumptions on the design of the meter circuit just on what type of battery is used. Many cameras were voltage tolerant and would work perfectly well with a range of supply voltages often by using a bridge design for the meter circuit. I don't know about the OM-1. You should check that out before condemning the seller for fitting a modern equivalent battery. Maybe it works fine or maybe the difference in meter reading is insignificant. I've repaired a lot of cameras where the meter is a stop or more out of whack and the owners were completely unaware of it.


PostPosted: Tue May 06, 2025 1:09 pm    Post subject: Reply with quote
I didn't intend to condemn the seller. As a matter of fact, I recently purchased an reconditioned OM-2 from them (with the design flaw corrected, possibly at the expense of an OM-40 which apparently has a compatible prism) and am more than happy with it. With this OM-1 it was more of a case of "hmm, that is interesting". I put this seller om my "to be checked from time to time for interesting things" list Smile

I agree that my previous answer may have come across as a bit cynical. That was unintentional.

Regards, C.


PostPosted: Tue May 06, 2025 4:51 pm    Post subject: Reply with quote
The Canon EF from the 1970's had a voltage regulator and used 2 x mercury cells.


PostPosted: Tue May 06, 2025 5:17 pm    Post subject: Reply with quote
monopix wrote:
You can't make assumptions on the design of the meter circuit just on what type of battery is used. Many cameras were voltage tolerant and would work perfectly well with a range of supply voltages often by using a bridge design for the meter circuit. I don't know about the OM-1. You should check that out before condemning the seller for fitting a modern equivalent battery. Maybe it works fine or maybe the difference in meter reading is insignificant. I've repaired a lot of cameras where the meter is a stop or more out of whack and the owners were completely unaware of it.


+1 voltage doesn't matter to a balanced bridge circuit https://www.allaboutcircuits.com/textbook/direct-current/chpt-8/bridge-circuits/


PostPosted: Tue May 06, 2025 7:47 pm    Post subject: Reply with quote
DigiChromeEd wrote:
The Canon EF from the 1970's had a voltage regulator and used 2 x mercury cells.


Interesting - that means I could/should reactivate my beautiful EF Wink



S


PostPosted: Wed May 07, 2025 6:36 pm    Post subject: Reply with quote
You can also use one of these with a silver oxide 386 battery to replace a mercury 625 battery.
https://www.smallbattery.company.org.uk/sbc_mr9_adapter.htm


PostPosted: Fri May 09, 2025 1:47 pm    Post subject: Reply with quote
Vintage_Photographer wrote:
You can also use one of these with a silver oxide 386 battery to replace a mercury 625 battery.
https://www.smallbattery.company.org.uk/sbc_mr9_adapter.htm


I've always wondered how these work; I am not familiar with zener diodes as low as 0.2V, and Schottky diodes with a stable forward voltage drop as low as 0.2V I believe need more current than your average vintage camera light meter draws.

A resistor is pointless unless the current draw is known and stable.

Anyone know how these work?


PostPosted: Sat May 10, 2025 5:39 am    Post subject: Reply with quote
RokkorDoctor wrote:
Vintage_Photographer wrote:
You can also use one of these with a silver oxide 386 battery to replace a mercury 625 battery.
https://www.smallbattery.company.org.uk/sbc_mr9_adapter.htm


I've always wondered how these work; I am not familiar with zener diodes as low as 0.2V, and Schottky diodes with a stable forward voltage drop as low as 0.2V I believe need more current than your average vintage camera light meter draws.

A resistor is pointless unless the current draw is known and stable.

Anyone know how these work?


PWM on a chip is my guess


PostPosted: Fri May 16, 2025 10:43 am    Post subject: wheatstones bridge Reply with quote
the Alpa and at least some Practicas used bridge-coupled meters so voltage variation was irrelevant, ansd a japanese company sells tiny batterycompartment units that can use different cells in a 625 compartment.
p.
Post new topic   Reply to topic
Home   Film SLR / TLR Cameras
Page 1 of 1