Electric clock -how to assist contacts please?

Thread Starter

malc77

Joined Jun 1, 2013
5
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.
 

Dodgydave

Joined Jun 22, 2012
11,277
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?
 
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THE_RB

Joined Feb 11, 2008
5,438
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.
 

GopherT

Joined Nov 23, 2012
8,009
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.
 

vk6zgo

Joined Jul 21, 2012
677
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.
 

Thread Starter

malc77

Joined Jun 1, 2013
5
Thanks- the contacts switch the positve supply.
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?
 

Thread Starter

malc77

Joined Jun 1, 2013
5
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
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?
 

Thread Starter

malc77

Joined Jun 1, 2013
5
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.

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.
 

Thread Starter

malc77

Joined Jun 1, 2013
5
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


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.
 
I, as a new member, have found the thread on replacing the arc suppression and similar for an Electric Clock to be the most down to earth on the Webb. However my problem is that I do understand the need to cut out the sparking on a Gents Pulsynetic Clock but mine has an ancient pair of condensers in square cans and what, I think, is a wire wound choke.I can only run the clock by cutting this out and I wonder if anyone can tell me what diode to wire across the contacts-respecting polarity-to take the place of the old system. What I really need is a part name/number for a 12 volt supply at about 0.20 amp.
 

crutschow

Joined Mar 14, 2008
34,201
.............................. However my problem is that I do understand the need to cut out the sparking on a Gents Pulsynetic Clock but mine has an ancient pair of condensers in square cans and what, I think, is a wire wound choke.I can only run the clock by cutting this out and I wonder if anyone can tell me what diode to wire across the contacts-respecting polarity-to take the place of the old system. ................................
Just about any diode will work, such as the common 1N4148. The way to connect the diode is determined by where the contact is connected with respect to the coil and battery. The idea is to route the inductive current from the contact back to the other side of the inductor (allowing the inductor current to momentarily continue to flow when the contacts open). A common way is to connect the diode directly across the coil with the cathode to the plus side of the coil.
 
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Just about any diode will work, such as the common 1N4148. The way to connect the diode is determined by the where the contact is connected with respect to the coil and battery. The idea is to route the inductive current from the contact back to the other side of the inductor (allowing the inductor current to momentarily continue to flow when the contacts open). A common way is to connect the diode directly across the coil with the cathode to the plus side of the coil.
Thank you for the advice,This is a simple series circuit and should prove no problem to do what you say. The reference number is what I wanted,Again thanks,Paul
 
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