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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details. |
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11th May 2017, 7:40 pm | #1 |
Pentode
Join Date: May 2010
Location: Sandviken, Sweden
Posts: 233
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Synchronous clock loses time
I have a synchronous wall clock that don't keep track with time. It seems to lose about a minute or two per day or thereabout, too much to be acceptable of course but too little to be an easy diagnose. I have several other synchronous clocks in my home and they keep time as they should.
A synchronous motor should not vary it's speed but this is a self-starting movement that can run up to speed unsynchronized and then lock to the mains frequency. So it is possible for it to run slower than intended. The movement is almost hermetically sealed and therefore the whole mechanism is oiled, wheels and all. It looked absolutely clean inside and the oil seemed fresh, despite this it was lagging so I dismantled it, cleaned and oiled it but no difference. The mains cable is new. I have ran the clock in series with a meter while moving the clock in different positions and while tapping the coil to see if there were any anomalies in the current consumption which would indicate an intermittent coil. I have been observing the rotor under the light from a neon indicator too see stroboscope effect, I stared at it for a while (boring) but it kept perfect speed while doing this. I have removed the hour hand and the wheels that drives it so only the minute hand is left, to eliminate these parts from the fault finding. The wheels inside the movement do not seem to bind, they can easily be rotated by hand and they all look like new and have a sufficient axial play. The pivots are shiny and oiled. I am getting quite frustrated Any ideas? |
11th May 2017, 9:41 pm | #2 |
Dekatron
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,864
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Re: Synchronous clock loses time
It looks a good quality item in very good condition.
No ideas at all, I'm afraid, you've done almost everything I would have done already. No doubt someone cleverer will be along soon with some ideas... |
11th May 2017, 9:47 pm | #3 |
Nonode
Join Date: Jan 2010
Location: North Somerset, UK.
Posts: 2,130
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Re: Synchronous clock loses time
Low mains voltage, that is within tolerance for your other clocks, but not for this one ?
A synchronous motor is not normally affected by voltage variations, but as this one can also run asynchronously might be a possibility. Or intermittent low voltage on only the sub circuit that supplies the clock, due perhaps to say a washing machine motor starting. Is the loss of time random or consistent from day to day ? Does it occur steadily throughout the day or concentrated at certain times of day ? |
12th May 2017, 8:32 am | #4 | ||
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
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Re: Synchronous clock loses time
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Most clocks of this sort will run happily in much less mains voltage - say 150 VAC. A couple of thoughts; does the centre arbor (thing holding the minute hand) seem too free? Is the 'slowing down' regular or just at random? Have you another electric clock you can connect to the same socket?
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Mike. |
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12th May 2017, 8:59 am | #5 |
Octode
Join Date: Feb 2006
Location: Bristol, UK.
Posts: 1,042
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Re: Synchronous clock loses time
Just a random thought, is the minute hand secure to the arbour? If it is slightly loose then as the hand sweeps from 6:00 to 12:00 it could drop back slightly under gravity.
Malcolm |
12th May 2017, 2:44 pm | #6 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: Synchronous clock loses time
Does this actually run up to speed unsynchronised and then lock?
I have seen small synchronous motors with lots of poles, that run at only a couple of hundred RPM and can accelerate to synchronous speed in a single cycle - so they keep turning. They won't run asynchronously. Loading the shaft stops them abruptly. But I have also seen motors like you say - basically a shaded-pole induction motor with a permanent magnet on the rotor - which will run asynchronously yet lightly-loaded can lock-in to mains frequency. I can't help thinking that Malcolm might be onto something, and mechanical slippage is the culprit! |
12th May 2017, 7:22 pm | #7 | |
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
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Re: Synchronous clock loses time
Quote:
I still think the centre arbor isn't keeping time but the rest of the train is - ie the friction device, spring or whatever it is will be the culprit.
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Mike. Last edited by Mike Phelan; 12th May 2017 at 7:25 pm. Reason: Further thoughts. |
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12th May 2017, 8:13 pm | #8 |
Retired Dormant Member
Join Date: Dec 2007
Location: Shropshire, UK.
Posts: 3,051
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Re: Synchronous clock loses time
Do you have a camera which can be set to take pictures at, say, 20 minute intervals?
If so, set it looking at the face for 24 hours, then review the pictures, which will indicate either a gradual or a sudden loss of time. |
13th May 2017, 3:25 pm | #9 | |||||
Pentode
Join Date: May 2010
Location: Sandviken, Sweden
Posts: 233
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Re: Synchronous clock loses time
Thank you for the many answers. It was relieving to talk about it and to get some ideas. This is the kind of odd fault that make you wonder if it really is a problem or if it is yourself who are having a 'brain slip' and missed something obvious
Yes I think this is a quality movement, it is from a huge wall clock made by Westerstrand, one of swedens major maker of clocks for public places. Quote:
The clock has no second hand so it is difficult to see when or how it loses time. It is only when the error has accumulated some that it "shows up" on the minute hand. I will anyway try to monitor it and write down the error so I can get a more accurate estimate of the problem. Quote:
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13th May 2017, 11:19 pm | #10 |
Dekatron
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,108
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Re: Synchronous clock loses time
Amazing to think that that the lag is only around 0.14%, but noticeable because we expect major precision from relatively modern pieces.
I would repeat the mention of moving the clock to another power source to exclude any possibility of a 'dirty' supply causing intermittency. i would think that running the clock for a few days at a significantly lower ambient temperature might help to ascertain whether the problem is mechanical or electrical. (Shed?) |
14th May 2017, 4:12 pm | #11 |
Dekatron
Join Date: Nov 2003
Location: Near Leeds, West Yorkshire, UK
Posts: 4,609
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Re: Synchronous clock loses time
Aha! Your picture shows that the motion work is like those on French clocks.
The centre arbor does not slip, but the cutaway part seen on the cannon pinion on which the minute stands is the friction device. Solution: Attach something to the centre arbor to act as a temporary minute hand. If it keeps time then it can only be the cannon pinion slipping; if so a slight squeeze is needed. A common fault in French roulants. There should be no oil anywhere on this part of the clock.
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Mike. |