How hot is too hot? - repaired 1948 kitchen clock

Discussion in 'Electric Horology' started by Minneapolis51, Feb 26, 2020.

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  1. Minneapolis51

    Minneapolis51 Registered User
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    Feb 12, 2020
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    I repaired my old kitchen clock, manufactured in October 1948. I got a new old stock coil and put it in. Oiled judiciously. Now it runs very quietly and smoothly.

    But I wonder if it's running too hot on its 12 hour first run after the repair.

    When I touch my knuckle to the metal over the new coil, I can hold it there about seven seconds before it's too hot for my skin.

    It was the identical part number from the original.

    You can see in this picture right by the two screws over the coil and the left part of the motor, where I placed my knuckle, and this is the place it is the most hot.

    20200225_231319.jpg
     
  2. roughbarked

    roughbarked Registered User

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    #2 roughbarked, Feb 26, 2020
    Last edited: Feb 26, 2020
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  3. Kevin W.

    Kevin W. Registered User
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    I work at the Veritas Tools machine shop.
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    One of the reasons why i wont run any clock thats electric in my home thats doubtful and runs too warm for my liking.
     
  4. Minneapolis51

    Minneapolis51 Registered User
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    Thanks. I am going to read the article you posted right now.
     
  5. Minneapolis51

    Minneapolis51 Registered User
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    I have decided to retire the clock. Although the insulation on the "new" coil wires looked very good, and I did further cover it with heat shrink insulation, the coil heat makes me too nervous.

    I don't know if there is an internal short or something in the NOS coil that is causing the heat. I don't know what kind of heat was normal for this clock (but I did see a blackish oxidation all on the inside of the clock that had a "smoky" look to it, likely from deteriorating coil insulation over the 52 years it ran).

    I can consider a quartz movement conversion. But I probably will just use the clock as a non-working nostalgia piece that reminds me of my childhood.
     
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  6. roughbarked

    roughbarked Registered User

    Dec 2, 2016
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    Blackish oxidation. hmm. It is Carbon. Was this there before or after the coil change?
     
  7. Minneapolis51

    Minneapolis51 Registered User
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    It was there before, from the 52 years of use.

    The inside of the case looked like smoke had deposited on the inside of the plastic case and the aluminum back, but there no evidence of fire on any part of the clock mechanism or transformer coil.
     
  8. James McDermaid

    James McDermaid Registered User
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    Apr 29, 2011
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    I work with old coils in old radios and things all the time not to say that there may be something wrong with your new old stock coil.

    Maybe the new coils is made for 50 cycle power. Maybe the iron core is not as tight or secure, in the case of solenoids I have found if the magnetic core is missing or modified they go up in smoke.

    I have seen many of these synchronous clocks with what looks like soot from the heat of the coil in the motor.

    And don't get me wrong always error on the side of safety, I unplug old stuff I don't fully trust.

    Jim
     
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  9. RODALCO

    RODALCO Registered User

    Mar 27, 2006
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    Interesting reading here. a 50 Hertz coil on 60 Hertz would be less warm as the higher frequency increases the Inductance of the coil (more cycles) , less current flows and the coil runs cooler. The other way around you would have to reduce the voltage by 5/6.

    I have a German T&N clock with 24 Volts impulse minutes from a master clock, and a separated seconds drive via a synchronous motor.
    That motor was designed for 220 Volts , and our nominal Voltage is around 235 to 242 Volts in New Zealand.
    That motor was also running too hot for my liking.
    I added 2 x 2 Watt 1 kilo Ohm power resistors in series with the motor (on stand offs).
    Now the motor runs cool and has been going safely like this for over 10 years now.
    The clock has a metal casing and is Earthed.
    It is better to get rid of heat in a power resistor then in motor winding, as long the resistor can dissipate its heat safely.
     
  10. RODALCO

    RODALCO Registered User

    Mar 27, 2006
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    Just had a look at the easiest accesseable T&N clock as I have two of them connected up.
    The modification was done in 2006 which makes it 14 years of continuous service.
    I used 1 x 1 kilo Ohm resistor in series with one of the motor terminals.
    20200422_213525.jpg
    220 Volts AEG Motor on left, resistor above mechanism. 24 V clock coil on right.
    20200422_213542.jpg
    1 k Ohm 2 Watt series resistor.
     

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