Electric clock -how to assist contacts please?

Discussion in 'General Electronics Chat' started by malc77, Jun 1, 2013.

  1. malc77

    malc77 Thread Starter New Member

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    Hi- I have a Synchronome electrical 'master' clock - it is about 60 years old and has no electronics -just an electrical supply of about 6 volts. It has a pair of simple contacts which actuate every half minute which sets a gravity arm to drive the master clock pendulum together with several slave dials - the total current is about 0.3 amp for about one fifth of a second every half minute.
    The contacts on my clock are worn and I have refaced them, but I can see they will soon be useless - there is some slight sparking across them as the load is inductive due to the coils in the circuit - the steady DC voltage is about 6 volts.
    Can anyone help me with a circuit which would assist the contacts (I still wish to keep them) but perhaps allow them to just trigger a Darlington transistor BU941 or something similar. .....I know little about electronics so a circuit with values would be ideal....Parts for the clock are obsolete.
    I have tried searching the Forum but cannot see anything suitable. Anyway, many thanks if you can help me.
  2. Dodgydave

    Dodgydave Well-Known Member

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    You can reduce the sparking by placing a capacitor across the contacts, and put a back emf diode across the coil, same principal as the old "points " system on a car.

    Best way is to use a transistor slave driver for the contacts, in the drawing the load is your coil, do the contacts switch the positive or negative supply?
    Last edited: Jun 1, 2013
  3. THE_RB

    THE_RB AAC Fanatic!

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    Can you give more info on the working of the clock? Photos etc?

    I'd like to know what drives the contacts, every half a minute. Is that driven from a small AC mains synchronous motor? Or is that driven from the clock mechanical movement, just to raise the gravity drive weight?

    There might be a number of ways to solve the problem.
  4. GopherT

    GopherT Well-Known Member

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    It is also possible to replace the graphite contacts. Brushes from an electric motor can be used to replace the current brushes. Many sizes and shapes are available. I personally like to keep older items in their vintage design. I think new components ruins the vintage feel.

    I look forward to the photos.
    malc77 likes this.
  5. vk6zgo

    vk6zgo Active Member

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    It sounds very similar to the Pulsynetic clock they had at one of my old workplaces.
    It was a "Grandfather" clock,with two sets of contacts:

    One set was to send electrical pulses to the slave clocks every minute.

    The other set operated when the pendulum swing dropped below a set arc,when it operated an electromagnet,attracting the pendulum so that its arc was again at its maximum.
    The contact then released.

    There are a few websites referring to Pulsynetics.
    If your Synchronome is similar,the information on them may be useful.
  6. malc77

    malc77 Thread Starter New Member

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    Thanks- the contacts switch the positve supply.
  7. malc77

    malc77 Thread Starter New Member

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    Incidentally, I already have a capacitor and diode in place - but very slight arcing still takes place. The contacts operate about one million times per year....I am trying to keep the clock fairly original too.
    Regards
  8. malc77

    malc77 Thread Starter New Member

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    The contacts are fitted to a gravity arm which is released and pushes the pendulum every half minute - this short pulse actuates the clock dials (which have inductive coils windings) and resets the gravity arm until the next actuation 30 secs later.
    I am really trying to keep the clock as original as possible and avoid too much obvious electronics!
    Regards.

  9. malc77

    malc77 Thread Starter New Member

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    Thanks- Yes my Synchronome is very similar to the Gents Pulsynetic, although they didn't normally have two sets of contacts.
    What you describe sounds more like a Hipp toggle clock where the arc is maintained only when it falls (whereas the Pulsynetic and Synchronome are impulsed every 30 seconds irrespective of pendulum arc)
    Regards


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