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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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21st Nov 2019, 3:54 pm | #1 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,102
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Synchronous clock not running
Our kitchen quartz clock stopped running recently, and about the same time I dug out an old Gents synchronous mains clock I had been given which is so handsome and legible that we decided it would nice for the kitchen. ISTR it was donated because it kept stopping, but when I hung it on the wall it worked nicely, but after a few weeks it has stopped and cannot be started (it is not self-starting and has a knob which flicks the motor in the right direction). It may have come from a school and I guess dates from the 30s or 40s.
What would stop such a movement from running? No sign of polymerised grease or mechanical sticktion if you spin the rotor by hand (finger). Should the rotor be magnetised? I can detect no remnant magnetism sufficient to attract a small sewing needle. The coil measures ~6k ohm at DC and I suspect that inductance would dominate over resistance at 50Hz. Besides there is no buzzing from the core.
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- Julian It's good here |
21st Nov 2019, 5:14 pm | #2 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,079
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Re: Synchronous clock not running
I'd expect inductance would be significant. 6kΩ of DC resistance at 240V would imply 40mA. I'd be expecting nearer 10mA.
No buzzing or humming though - what happens if you hold a steel screwdriver next to it? It is possible that the rotor is not magnetised. It could be a variable-reluctance motor, where a toothed rotor. |
21st Nov 2019, 5:33 pm | #3 |
Dekatron
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 5,997
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Re: Synchronous clock not running
That's a good looking clock with a very solid looking movement. I would not suspect the motor as it has been running for a while, much more likely it is too much friction. It will need to be serviced by stripping down, cleaning, and oiling with clock oil but only on the pivots, it doesn't take long to do but take plenty of pics as you disassemble.
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21st Nov 2019, 5:45 pm | #4 |
Hexode
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 387
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Re: Synchronous clock not running
Make sure there is a small amount of rotational movement between the rotor (with the 'coggled' edge) and the plain 'flywheel' adjacent. They're coupled by a lightweight 'U' shaped spring but the flywheel can sieze on the shaft once the lube dries up.
This usually makes starting very difficult. Cheers |
21st Nov 2019, 6:54 pm | #5 |
Octode
Join Date: Nov 2005
Location: Surrey, UK.
Posts: 1,870
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Re: Synchronous clock not running
I have a virtually identical Gents clock with the same movement. The running torque produced by this movement is marginal, so you will probably need to strip it down and clean the pivots and plate holes carefully. A thin oil such as Moebius 8000 works well. These clocks are a bit reluctant to start even when in good clean condition, but mine never stops in normal use.
Leon. |
21st Nov 2019, 9:21 pm | #6 | |
Heptode
Join Date: Nov 2010
Location: Isle of Wight, UK.
Posts: 557
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Re: Synchronous clock not running
Quote:
Use a light grease on the rotor pivots, not oil, or it will be noisy with that synchronous motor 50 hz whiry buzz! Enjoy |
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21st Nov 2019, 10:07 pm | #7 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,102
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Re: Synchronous clock not running
Thanks so much for the observations and advice. It never occurred to me that the 'rotor' was in two parts - I can move them in opposite directions but when I let go they fly back to the same position. I also find there is some slight snagging between the 'toothed' rotor and the pole pieces.
I'll do the necessary by daylight tomorrow. It would be really good to have it running again.
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21st Nov 2019, 10:51 pm | #8 | |
Heptode
Join Date: Nov 2010
Location: Isle of Wight, UK.
Posts: 557
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Re: Synchronous clock not running
Quote:
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22nd Nov 2019, 1:43 am | #9 |
Dekatron
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,337
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Re: Synchronous clock not running
I can recommend using a petrol lighter fluid for cleaning clocks and watches, and the grade of Moebius clock oil that is appropriate for your clock. Expensive, but as only a smear is needed, a 1 oz bottle can last decades (mine has). A couple of weeks ago the much used and battered Lorus wrist watch that my wife wears when gardening stopped. The battery was fine, and as it would have been binned if I couldn't get it to go, I tried flushing the mechanism with lighter fluid, after first having removed it from the case and detached the face. On re-assembly it worked fine. I had only used it on clocks before.
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23rd Nov 2019, 4:21 pm | #10 |
Nonode
Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 2,102
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Re: Synchronous clock not running
I followed all the advice on cleaning and lubricating, photos etc, and was delighted to see it start up happily. I washed out a lot of filth (I used Turpentine Substitute which is a very thin oil) and could see that there were dribbles of oil that had become waxy and thick.
Can't work out the screw threads, do horologists have their own? Measured the nuts at 4.9 and 5.7mm A/F so was able to use 5.0 and 5.5mm nut runners. Also found a serial No: 106400
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23rd Nov 2019, 4:39 pm | #11 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,208
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Re: Synchronous clock not running
Those could well be 6BA and 5BA nuts. BA threads are not uncommon in British electric clocks, telephones, teleprinters, radios, etc.
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