Imhof quartz: Battery ideas for 1.35 volt replacement

Discussion in 'Electric Horology' started by moc, Feb 6, 2019.

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  1. moc

    moc Newbie

    Apr 22, 2014
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    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.
     
  2. Phil G4SPZ

    Phil G4SPZ Phil
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    Oct 18, 2018
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    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
     
  3. Styrofoam_Guy

    Styrofoam_Guy Registered User
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    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
     
  4. Phil G4SPZ

    Phil G4SPZ Phil
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    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.
     
  5. David S

    David S Registered User
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    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
     
  6. praezis

    praezis Registered User

    Feb 11, 2008
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    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
     
  7. moc

    moc Newbie

    Apr 22, 2014
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    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


     
  8. moc

    moc Newbie

    Apr 22, 2014
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    An idea, but I'm not sure that there is room in the clock for a battery this size.

    Thanks, Martin

     
  9. moc

    moc Newbie

    Apr 22, 2014
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    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

     
  10. moc

    moc Newbie

    Apr 22, 2014
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    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


     
  11. Kevin W.

    Kevin W. Registered User
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    #11 Kevin W., Oct 30, 2019
    Last edited: Oct 30, 2019
    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.
     
  12. Kevin W.

    Kevin W. Registered User
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    Problem was solved and my CPR clock is working well.
     
  13. Phil G4SPZ

    Phil G4SPZ Phil
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    How did you actually solve the problem, Kevin?
     
  14. Kevin W.

    Kevin W. Registered User
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  15. Phil G4SPZ

    Phil G4SPZ Phil
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    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.
     
  16. Kevin W.

    Kevin W. Registered User
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    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.
     

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