# Imhof quartz: Battery ideas for 1.35 volt replacement

#### moc

##### Newbie
I have recently acquired a late 70s/early 80s Imhof Swiss quartz clock (I like Imhof mechanical clocks, this is my first quartz).

A problem though: it takes an odd 1.35 volt battery which is approximately the same width as a AA battery (slightly larger), about 1/3rd the length of a AA (no idea of the model # of the battery).

Judging from the voltage, size, era, etc., I am just about certain that the original was a mercury, now long gone.

Any ideas as to coming up with a suitable replacement. (I'm hoping that I don't have to use some sort of Zinc/Air type as using those with old cameras has been less than good...)

Many thanks to all with any ideas.

#### Phil G4SPZ

NAWCC Member
You're probably right, mercury batteries had a high energy density but they are banned nowadays due to the toxic content.

I have had some success in replacing mercury batteries with NiMH (nickel metal hydride) rechargeable cells, which have a terminal voltage when fully charged of around 1.3 volts per cell. You can get these in 1/3 AA size, this is one example: Vinnic 1/3AA NiCD 1.2V 130mAh

The problem is that these batteries will need frequent recharging from a constant current source. It might be an easier option to fit and connect a cell holder for a standard AA or AAA NiMH cell, then with a standard charger you can keep a few ready and pop in a fully charged battery whenever it's needed.

Phil

#### Styrofoam_Guy

##### Registered User
If the rechargeable battery doesbn't work I suggest you put in an AA battery holder and use a standard AA battery. To get the 1.5V down to 1.35V you will have to add a resistor into the circuit.

To calculate the resistor needed you will need to know the current the quartz movement draws. You can use a web site like below to calculate the resistor value you need.
Supply voltage: 1.5V
Forward voltage: 1.35V
Forward Current: ??
LED Series Resistor Calculator | DigiKey Electronics

#### Phil G4SPZ

NAWCC Member
The series resistor idea might not work. The current drawn by a quartz movement is not constant like an LED. It consists of a low level continuous current due to the crystal oscillator and divider circuits, on top of which are superimposed much larger short ‘spikes’ or pulses of current as the motor indexes round once per second.

The voltage dropped by the resistor will therefore not be constant. A sufficiently high value of resistance to drop the 1.5V to 1.3V during the idling state will drop far too much voltage during the one second pulses, and the motor probably won’t run. Similarly, a resistor which will drop the correct voltage during peak pulses will leave the circuit over-run between pulses.

There is no reason why the rechargeable battery won’t work. The only problem is the inconvenience of recharging.

#### David S

NAWCC Member
Perhaps a small signal Schottky diode could be used in series with a primary alkaline cell, with a capacitor on the output of the diode to supply the peak currents.

David

#### praezis

##### Registered User
A humble question: is there any issue with 1.5V? I would doubt there is. It will not damage the circuit, at most a slight adjustment will be needed.

Frank

#### moc

##### Newbie
Phil,

Thanks for your suggestion... This might be the best way to go (even with the limitations).

I'm kind of surprised that there isn't an 'off the shelf' solution as many of these early Swiss quartz clocks seem to be high quality timepieces.

Martin

You're probably right, mercury batteries had a high energy density but they are banned nowadays due to the toxic content.

I have had some success in replacing mercury batteries with NiMH (nickel metal hydride) rechargeable cells, which have a terminal voltage when fully charged of around 1.3 volts per cell. You can get these in 1/3 AA size, this is one example: Vinnic 1/3AA NiCD 1.2V 130mAh

The problem is that these batteries will need frequent recharging from a constant current source. It might be an easier option to fit and connect a cell holder for a standard AA or AAA NiMH cell, then with a standard charger you can keep a few ready and pop in a fully charged battery whenever it's needed.

Phil

#### moc

##### Newbie
An idea, but I'm not sure that there is room in the clock for a battery this size.

Thanks, Martin

If the rechargeable battery doesbn't work I suggest you put in an AA battery holder and use a standard AA battery. To get the 1.5V down to 1.35V you will have to add a resistor into the circuit.

To calculate the resistor needed you will need to know the current the quartz movement draws. You can use a web site like below to calculate the resistor value you need.
Supply voltage: 1.5V
Forward voltage: 1.35V
Forward Current: ??
LED Series Resistor Calculator | DigiKey Electronics

#### moc

##### Newbie
David,

Perhaps a good idea, but, quite honestly, I would not even know how to begin with this approach (I'm not advanced enough in electronics to figure it out!).

Martin

Perhaps a small signal Schottky diode could be used in series with a primary alkaline cell, with a capacitor on the output of the diode to supply the peak currents.

David

#### moc

##### Newbie
Frank, a very good question. Somewhere I read that 1.5 would not work. Maybe it is worth a try...

I have heard that with obsolete camera mercury batteries (at 1.35 volts), on many cameras they often won't work correctly, though some with regulator circuits will do ok.

Thanks for your idea!

Martin

A humble question: is there any issue with 1.5V? I would doubt there is. It will not damage the circuit, at most a slight adjustment will be needed.

Frank

#### Kevin W.

NAWCC Member
These clocks take a LR 50 and are available on Amazon and Ebay.
I re read what is posted, and i believe the same,it needs to be 1.35 volts.

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#### Kevin W.

NAWCC Member
Problem was solved and my CPR clock is working well.

#### Phil G4SPZ

NAWCC Member
Problem was solved and my CPR clock is working well.
How did you actually solve the problem, Kevin?

NAWCC Member

#### Phil G4SPZ

NAWCC Member
Very interesting, thanks Kevin. I have used that company before and their stuff is very good quality, although a tad pricey. Worth it though for a rare clock.

#### Kevin W.

NAWCC Member
Thanks Phil, i felt it was a good buy for me, and i did not know of any other sources. I was very grateful for the help i received.

#### moc

##### Newbie
Well, after posting this original message over two years ago, I finally got moving and found the correct battery adapter for my 1.35 volt Imhof quartz clock. As other's mentioned, it was a MR-50 adapter that uses a common SR44 (or 357) silver oxide battery. The clock now works great (and accurately)!

As an fyi, the alkaline version (LR44?) is not recommended as performance is unsuitable and/or short.

Yes, the adapter was pricey, but I'm happy. In corresponding with the seller in Japan, I discovered that this adapter is now 'out of production'. I mention this so that anyone thinking that they might want one to act soon.

I got mine via Ebay, from seller: takehitogu-0

He had a better price than the other seller, and was a breeze to transact with (a great guy). I get no commission (smile), but just wanted to let people know in case they are considering one of these.

Hope that this info is of help to someone out there...

Martin

Kevin W.

#### novicetimekeeper

##### Registered User
can't you just use a voltage regulator? They cost around £0.40

#### praezis

##### Registered User
I finally got moving and found the correct battery adapter for my 1.35 volt Imhof quartz clock. As other's mentioned, it was a MR-50 adapter that uses a common SR44 (or 357) silver oxide battery. The clock now works great (and accurately)!
Congratulation .
However with this adapter and the tiny 357 you lost a lot of capacity / running time. I suspect, this pricey adapter contains nothing more than the schottky diode (<\$0.05) that David mentioned above.

Frank

#### Cheezhead

##### Registered User
For future reference here is a very inexpensive solution that might work although I have not tried it. Use an AA battery holder mounted externally to the clock if needed and wire a diode in series with the battery with polarity to result in a lower voltage output. A diode wired correctly has a normal voltage drop and the wrong polarity will result in near zero volts. Due to a battery clock's very low current draw a 1 amp diode will handle the load with ease. The digital voltmenter was previously checked for accuracy. Three different diodes with each in series with the battery had open circuit (no load) voltage outputs as follows:
1.63 volts from a new alkaline battery
1.34 v 1N5624 3 amp diode
1.29 v 1N5660A 8 amp diode
1.35 v 1N3673A 12 amp diode

#### Cheezhead

##### Registered User
I was in a hurry to post but took a few minutes to check my suggestion on a clock that still runs at 1.219 volts. With a diode in series with that battery the clock would not run at 0.946 volts. It did run while using the diode in series with a slightly used 1.589 volt battey brought down to 1.306 volts. This makes it appear that the very expensive Kanto MR-50 holder uses a simple diode in series with a battery. It's possible that the tooling and part cost for the Kanto holder are relatively expensive for a very low volume item. A work friend would say: It's High but it's Here!

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#### moc

##### Newbie
Congratulation .
However with this adapter and the tiny 357 you lost a lot of capacity / running time. I suspect, this pricey adapter contains nothing more than the schottky diode (<\$0.05) that David mentioned above.

Frank
Frank (& David):

I have no doubt that you are correct in that a cheaper solution (using a diode) is available. However the form factor of the original MR-50 battery size seems to make engineering this alternative a little complicated (and labor intensive)...

Also, I'm sure that you are correct in suspecting that the life of a 357 battery will be a lot shorter compared with the original MR-50 (mercury) battery. (I think that was why these clock makers originally favored the MR-50, however I also understand why mercury based batteries were phased out.)

#### Cheezhead

##### Registered User
This thread got me going so I found on Wiki that the voltage drop of a Schottky diode is stated to be 0.15 to 0.46 volts while a silicon diode has 0.6 to 0.7 volts drop. My measurements on what I believe are ordinary diodes in series with the alkaline battery show smaller drops ranging from 0.28 to 0.34 volts. I can't explain that as electronics are not my main area of knowledge. Perhaps someone here might be able to explain the discrepancy or find someone who can.

If the battery life with the MR-50 holder is not satisfactory and it is annoying to make frequent battery changes then it could be a simple matter to use double-side sticky tape or quick-set adhesive or the like to fasten an AA battery holder with added diode to the back side of the clock where it will not be seen if there is no place to hide the holder inside the clock. I have used a short length of wooden dowel with a shingle nail in each end with entrapped wires connected under the nail heads to fit in the clock's battery holder to power a nice Swiza quartz clock that did have room inside for the AA battery holder. Alternately it may be possible to solder wires directly to the clock battery holder's contacts. Yet another solution would be to embed the AA battery holder in a nicely finished oak or walnut board kept under the clock.

#### moc

##### Newbie
Cheezhead,

So far, so good with the MR-50 adapter.

That said, I liked your ideas, particularly the one about embedding the battery holder in the oak or walnut board.

Thanks!

Cheezhead

#### praezis

##### Registered User
This thread got me going so I found on Wiki that the voltage drop of a Schottky diode is stated to be 0.15 to 0.46 volts while a silicon diode has 0.6 to 0.7 volts drop. My measurements on what I believe are ordinary diodes in series with the alkaline battery show smaller drops ranging from 0.28 to 0.34 volts. I can't explain that as electronics are not my main area of knowledge.
Voltage drop of a diode is dependent on the current flowing (according an e-function). If you have the nearly zero current of your tester only, you will get too low figures.
You should test voltage drop with a current similar to that of the driven quartz motor.

Frank

Cheezhead
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