Old School Clock - How to get it to work without a Master?

Discussion in 'General Electronics Chat' started by Dalaran, Mar 11, 2011.

  1. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I recently purchased an old school clock from a show but didn't realize it is suppose to be hooked up with a master clock to run properly. When plugged in the clock works but there is no way to adjust the time on it. There is a single extra wire which I am under the impression is to go to the Master clock to adjust the time. To my understanding the Master either tells this clock to stop (if it is fast) or to speed up (if it is slow) through this wire. However, I can't seem to find any information and how this is transmitted through the single wire.

    Is anyone aware of what voltage needs to be applied to this wire in order to get it to speed up and stop?

    Your help is appreciated.

    -Steve
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
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    With the clock unplugged, it will be accurate twice a day. Wait for one of those moments and plug it in again. Piece of cake.
     
  3. rogs

    Active Member

    Aug 28, 2009
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    This type of clock often works by receiving a low current impulse at a fixed interval - typically once every 30 seconds. This site: http://www.hvtesla.com/masters/index.html illustrates typical examples of master/slave clock arrangements.
    By wiring the slave clocks in series, it is possible to drive any number of slaves from one master clock impulse generator.

    Although they were usually electronmechanical in operation, you can recreate a 'master clock' using an electronic crystal oscillator and divider, driving an external relay or solid state current sink devices, which is designed to provide a (typical) 200mA pulse every 30 seconds.

    I fitted one to an old bowling club clock 'slave', a while back. (Video of the installation here: http://www.vimeo.com/1084861 if you're interested)

    If that's the kind of thing you're looking at, I'll try and find the circuit if it's likely to be of any use?
     
  4. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    rogs - thanks very much for the reply. If its not hiding too far I'd love to take a look at the circuit used.

    This is a classic analogue North American school clock which would be one of many slaves all connected to the single master. I believe these were only time corrected once an hour or maybe even once a day (I remember being in class and seeing the needle stop... those were the worst minutes!). It doesn't need anything applied to it in order to tick along. Does the one your referring to require a impulse every 30 seconds to keep it going?

    I'm still a little confused on exactly what signal needs to be applied in order to get the clock to stop/speed up.

    Again, thanks for your help.

    Jaguarjoe - thanks for the offer but I'd thought about that one ;) Just not as fun, and these were somewhat notorious for not holding the most accurate time as they would need to be corrected to the master quite regularly.
     
    Last edited: Mar 11, 2011
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    As I recall, there were three wires going to these clocks. One line was common, another line received pulses once per minute UNTIL one minute before the hour. A clock that was accurate switched over to the third line internally. Clocks that were slow stayed on the normal 1 pulse per minute line. When the master reached the 1 minute before the hour point, the normal 1 pulse per minute line went into high gear putting out a long series of pulses. A slow clock would advance to the 59 minute point, at which time it would internally disconnect that line. The remaining line would pulse once at the proper minute point to move all accurate clocks to the even hour point. I don't remember exactly how many make-up pulses were supplied during the one minute period but it wasn't enough to make up a major error in one go. Hope this makes sense.

    Check out page 5 of www.[B]ats-usa.com[/B]/pdf_apnotes/MCMODES.pdf
     
    Last edited: Mar 11, 2011
  6. SgtWookie

    Expert

    Jul 17, 2007
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  7. rogs

    Active Member

    Aug 28, 2009
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    Yes, the type I'm referring to simply neds to receive a short 'pulse' every 30 seconds, to energise the slave clock solenoid, and advance the clock face one half minute postion.

    To set and correct the clock, you have to manually stop and/or advance it as required.

    I'm attaching a copy of the circuit I used for the clock in the video I linked to -- which is a Synchronome clock. It's accurate to about a second a day, using a standard commercial crystal, with no temperature compensation.
    Not that accurate by today's standards of course, but more accurate than the original electromechanical mehanism!

    Not as sophisticated as the type BillB3857 refers to of course, but here in the UK impulse clocks were widely found in industrial, educational and public locations. The one I added the driver to was installed in 1927!

    I say 'added', because I left the beautiful original mechanism as it was -even though it doesn't work!!
     
  8. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I very much appreciate the help everyone.

    BillB, I believe that is the exact situation I am in. So my next issue I guess is how to replicate this Master clock. I don't need to have it automatically set every hour but I'm thinking more of a dial where it either lets it run freely, stops or speeds it up.

    The note mentions an AC voltage needs to be applied to clock correction coil, however it doesn't give the details about this AC voltage and what signals do what to the clock correction coil.

    rogs - thanks for digging that up for me, I'm sure it will come in handy. It seems like though that clock is a little bit more sophisticated than what I need to get going.

    Thanks.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    If you want to use a single once or twice per minute pulse (depends upon the clock), just tie both of the signal lines together. The clock would need to be set manually, of course, possibly by a simple push button to simply add pulses as needed. We had a problem in one of our engineering labs where one clock failed internally and shorted the signal lines together. It really messed up all the clocks in the building. Our answer was to install diodes on each signal line at each clock to prevent backfeed from any failed clock.
     
  10. rogs

    Active Member

    Aug 28, 2009
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    That problem is of course reversed for the type of clock I'm working with. All the clocks, master and slaves are wired in series, with adjustments made to the supply voltage of the 'pulse' generator, to allow sufficient current to flow in what could be dozens of slaves, all connected in series. Problem there is not short circuits, but open circuit solenoids. One open circuit slave solenoid stops all the clocks!!
    The system does have the advantage of being able to operate in the event of a power outtage, with only minimal power required from battery support supply.

    Providing all the clocks are set to show the same time initally, it's a pretty robust system. All clocks will always show the same time as the master, without any remote corrections required.

    Keeping the masters accurate, using electromechanical pendulums, was quite a challenge, but the history shows some pretty ingenious solutions to those problems.

    Not very valid these days, of course......:)
     
  11. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    When you talk about pulses what do you mean exactly? Is there a select frequency/voltage? And what creates the difference between stopping and speeding up? Sorry for the noob questions. I claim not to be slow, but sometimes feel like it! Thanks again!

    edit: So it looks like there is a solenoid or magnet of some sort inside which has 1 wire connected to the live wire from the wall socket and the other side is connected to this extra wire I have. I'm guess then turning this on would speed up the clock? But how to stop it? Does this mean its activated by a pulse of like 12/15VDC?
     
    Last edited: Mar 12, 2011
  12. rogs

    Active Member

    Aug 28, 2009
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    The 'frequency' of the pulse will be once every 30 or 60 seconds, depending, as Bill says, on the clock.
    The 'voltage' will depend on the current requirement of the clock solenoid. If it has a DC resistance of say, 100R, and needs a current of 100mA to activate, then you're going to need a DC supply of 10volts, that can supply 100mA.

    The 'length' or duration of the pulse will either be specified by the clock maker, or you'll have to find out by trial and error. On the circuit I sketched, I included a variable resistor, to allow changing the pulse length of the trigger monostable. 200mS might be a good starting point.

    Edit: of course, I'm thinking about this from the point of view of an impulse clock, so perhap it's not quite the same requirements for 'correction' pulse generators. But the basic principles are the same, I think.

    Edit 2: This article : http://sound.westhost.com/clocks/alternate.html goes into some of the details for different types of clock, and the page has a link near the bottom of the page for further info on synchronous clocks.
    Might have some interesting pointers towards what you need to do??
     
    Last edited: Mar 12, 2011
  13. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Thanks again for the help thus far everyone.

    I have some more info about the clock in question. It is a "SIMPLEX" clock. There is a "Clutch Magnet" inside which is used to control the time. As I mentioned, the clock runs fine without using the clutch magnet, however this is used to correct the time. On the back of the clock the specs for the clutch magnet are as follows:

    Clutch Magnet Volts: 115 V.A. 3 cycles: 60

    So I'm assuming it is controlled via standard wall power. Since one side of the wall power is connected to the one side of the clutch magnet does it make sense that connecting the other side of the clutch magnet to 1 prong will stop it and the other prong will speed it up?

    Thanks!
     
    Last edited: Mar 15, 2011
  14. BillB3857

    Senior Member

    Feb 28, 2009
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  15. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    Thanks. Your support is appreciated

    Looking at pg 25 it seems like the NO connection is what would be delivering the correction signal to the other side of the clutch magnet. I'm guessing this signal would be a pulse from the 120VAC line? Think it would be safe to test around to use a 100ms or so pulse from the 120V line? I really don't want to bust the clock mechanism as I don't know too much about them!
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
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    I'm really not sure exactly what the clutch in you clock does. From the drawing on Pg 25, it looks like it takes 110VAC, just like the regular synchronous motor running the clock. Does it dis-engage the clock motor? Reset the minute had to the 12 position? I couldn't find any description of the action, but to be honest, I really didn't read the entire document, either.
     
  17. Dalaran

    Thread Starter Active Member

    Dec 3, 2009
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    I tried playing with it briefly, I just want to ensure that I don't damage it.

    After pulsing it twice the clock stopped. On the third time it sped up the minute hand until it stopped one minute before the hour. Once the second hand caught up to the hour it began to work normally. I think I'm going to do a little testing... since it sounds like the magnet can handle 110V I doubt I will be harming it me pulsing it like this. I'm assuming that's what the controller board would be doing anyways.

    Thanks again for the help.
     
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