All About Circuits Forum  

Go Back   All About Circuits Forum > Electronics Forums > General Electronics Chat

Notices

General Electronics Chat Discussion forum for general chat about anything electronics related, including asking questions about material in the All About Circuits E-book, Worksheets, and Videos.

Reply   Post New Thread
 
Thread Tools Display Modes
  #1  
Old 06-01-2013, 01:45 PM
malc77 malc77 is offline
New Member
 
Join Date: Jun 2013
Posts: 5
Default Electric clock -how to assist contacts please?

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.
Reply With Quote
  #2  
Old 06-01-2013, 02:43 PM
Dodgydave's Avatar
Dodgydave Dodgydave is offline
Senior Member
 
Join Date: Jun 2012
Location: Liverpool,UK. GMT
Posts: 1,751
Default

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?
__________________
NECESSITY IS THE MOTHER OF INVENTION !

Last edited by Dodgydave; 06-01-2013 at 02:50 PM.
Reply With Quote
  #3  
Old 06-02-2013, 02:06 AM
THE_RB's Avatar
THE_RB THE_RB is offline
Senior Member
 
Join Date: Feb 2008
Posts: 5,193
Default

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.
__________________
Roman Black - PICs and electronics. Author of BTc PIC-sound encoder, Shift1-LCD project, the TalkBotBrain talking PIC controller, LiniStepper open-source microstepping motor driver, the Black Regulator 2-transistor SMPS, and probably some other stuff; www.RomanBlack.com
Reply With Quote
  #4  
Old 06-02-2013, 04:08 PM
GopherT's Avatar
GopherT GopherT is offline
Senior Member
 
Join Date: Nov 2012
Location: Western PA (USA) (GMT -5)
Posts: 1,763
Default

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.
Reply With Quote
The Following User Says Thank You to GopherT For This Useful Post:
malc77 (06-05-2013)
  #5  
Old 06-03-2013, 06:17 AM
vk6zgo vk6zgo is offline
Senior Member
 
Join Date: Jul 2012
Posts: 604
Default

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.
Reply With Quote
  #6  
Old 06-05-2013, 08:39 AM
malc77 malc77 is offline
New Member
 
Join Date: Jun 2013
Posts: 5
Default

Thanks- the contacts switch the positve supply.
Quote:
Originally Posted by Dodgydave View Post
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?
Reply With Quote
  #7  
Old 06-05-2013, 08:41 AM
malc77 malc77 is offline
New Member
 
Join Date: Jun 2013
Posts: 5
Default

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
Quote:
Originally Posted by Dodgydave View Post
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?
Reply With Quote
  #8  
Old 06-05-2013, 08:45 AM
malc77 malc77 is offline
New Member
 
Join Date: Jun 2013
Posts: 5
Default

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.

Quote:
Originally Posted by THE_RB View Post
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.
Reply With Quote
  #9  
Old 06-05-2013, 08:49 AM
malc77 malc77 is offline
New Member
 
Join Date: Jun 2013
Posts: 5
Default

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


Quote:
Originally Posted by vk6zgo View Post
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.
Reply With Quote
Reply   Post New Thread

Tags
, , ,


Related Site Pages
Section Title
Textbook Switch contact design : Switches
Worksheet AC motor control circuits
Worksheet DC motor theory
Worksheet Time constant circuits
Textbook Relay construction : Electromechanical Relays


Similar Threads
Thread Thread Starter Forum Replies Last Post
Standard Electric Time clock obmcclintock The Projects Forum 6 01-22-2013 08:45 PM
PIC16f690 interfacing with LCD 16x2 andyv Embedded Systems and Microcontrollers 19 04-17-2012 07:36 AM
What kind of motor and circuit to use for electric analog clock? morganj2003 General Electronics Chat 4 06-14-2011 12:17 AM
Real Time Clock RG23 General Electronics Chat 64 01-14-2011 08:59 PM

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT. The time now is 03:06 AM.


User-posted content, unless source quoted, is licensed under a Creative Commons Public Domain License.
Powered by vBulletin
Copyright ©2000 - 2014, vBulletin Solutions, Inc.