Antique AC clock runs too fast

Thread Starter

Bottleguy

Joined Nov 21, 2020
13
Hello all. I'm trying to find a fix for my old clock (1920's - 1930's, maybe older) It gains about ten seconds every minute. It seems to be a simple induction motor, designed to run off typical house current. If it's not of US manufacture, then the lower frequency (50 hz vs 60) would explain the problem, but is there a solution?
 

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AlbertHall

Joined Jun 4, 2014
10,572
It is a synchronous motor and so runs at a speed determined by the frequency of the AC supply. Gaining 10 seconds in every 60 is about for a 50Hz clock running from 60Hz.
It would not be impossible, but not trivial, to make 50Hz high(-ish) voltage AC supply but note that the frequency should be crystal controlled to allow thw clock to keep decent time.
 

Wolframore

Joined Jan 21, 2019
1,987
Few approaches, a divide by function generator to convert to 50Hz then amplify power.

change the motor

change the pinion gear to same size but less teeth. May be a clock smith can do for you.
 

Lo_volt

Joined Apr 3, 2014
123
I wonder if there are low cost inverters for 50Hz countries that might work in this situation. I'm thinking of a cheap UPS or the like.
 

MrChips

Joined Oct 2, 2009
22,107
AC LINE frequency gives very good long term accuracy.
A solution would be a PLL (phase locked loop) that is locked on to 60Hz LINE frequency but generates 50Hz AC power.
 

bloguetronica

Joined Apr 27, 2007
1,423
I think it would be cheaper to just change the gears to a different ratio, like many said before. AC to AC conversion is tricky and will defeat the purpose in this case, because the line frequency, either for 50Hz countries or for 60Hz countries, is surprisingly accurate.
 

s14rs4

Joined Sep 15, 2016
41
If this is a genuine antique clock then modifying it will detract from its value. Better to generate the correct frequency supply. The current required is tiny, an oscillator and a step up transformer would probably do. It would probably work from a square wave.
 

crutschow

Joined Mar 14, 2008
25,680
It seems to be a simple induction motor
It's actually a synchronous reluctance motor, typical of the type used for line-powered clocks.
A solution would be a PLL (phase locked loop) that is locked on to 60Hz LINE frequency but generates 50Hz AC power.
Normally the output frequency of a PLL is equal to or higher than the reference input.
So one could use the PLL to generate 600Hz from the 60Hz input (with a divide by 10 in the feedback loop) and then divide that by 12 to get 50 Hz.

Thus one could use a 60-50Hz PLL circuit or a 50Hz crystal oscillator, going a power amp driving a small filament transformer (in reverse) to power the clock.
That would avoid any clock modifications.

As s14rs4 note, it would likely work with a square-wave.
But if it's a 50Hz clock, would it be designed for 240Vrms?
 

MrChips

Joined Oct 2, 2009
22,107
It's actually a synchronous reluctance motor, typical of the type used for line-powered clocks.
Normally the output frequency of a PLL is equal to or higher than the reference input.
So one could use the PLL to generate 600Hz from the 60Hz input (with a divide by 10 in the feedback loop) and then divide that by 12 to get 50 Hz.

Thus one could use a 60-50Hz PLL circuit or a 50Hz crystal oscillator, going a power amp driving a small filament transformer (in reverse) to power the clock.
That would avoid any clock modifications.

As s14rs4 note, it would likely work with a square-wave.
But if it's a 50Hz clock, would it be designed for 240Vrms?
or
60Hz x 5 = 300Hz
300Hz / 6 = 50Hz
 

Thread Starter

Bottleguy

Joined Nov 21, 2020
13
or
60Hz x 5 = 300Hz
300Hz / 6 = 50Hz
First, thanks to everyone for your replies. Next, as I try to translate the terms and concepts from Greek to something a total neophyte can understand, I have a very important question...is any of the suggested equipment small enough to fit inside a mantle clock? I've attached a picture to provide scale. The height is 12", the pic is the widest cross section, looking down on the top. I've also attached a picture of the end of the power cord that inserts into the clock, not the wall. Still don't know if it's US made or European. I replaced the original cord years ago but don't remember if the outlet end was bladed or rounded.
 

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Dodgydave

Joined Jun 22, 2012
9,686
Hello all. I'm trying to find a fix for my old clock (1920's - 1930's, maybe older) It gains about ten seconds every minute. It seems to be a simple induction motor, designed to run off typical house current. If it's not of US manufacture, then the lower frequency (50 hz vs 60) would explain the problem, but is there a solution?

As it sounds , your clock is designed for a 50Hz system , and therefore it will run 1.2 times faster on a 60Hz one,,so the only cure is to make a separate oscillator, or replace the innards with a battery module.
 

AlbertHall

Joined Jun 4, 2014
10,572
I have a very important question...is any of the suggested equipment small enough to fit inside a mantle clock?
The extra circuitry doesn't necessarily have to be inside the clock. It could be in a box which has one cable plugged in a wall socket and another cable plugged into the clock.
 

Wolframore

Joined Jan 21, 2019
1,987
I agree and it would be preferred to keep the clock original, there are power phase converters on the market but they appear to be on the expensive side. If your intent is to keep this original because the clockwork is the element of value to you, its the correct approach whether purchased or self built. If the clock face, body and functionality is what’s important to you, it’s easy to change the mechanism to one suited for 60 Hz or battery powered and would be the least expensive route.
 

Thread Starter

Bottleguy

Joined Nov 21, 2020
13
I agree and it would be preferred to keep the clock original, there are power phase converters on the market but they appear to be on the expensive side. If your intent is to keep this original because the clockwork is the element of value to you, its the correct approach whether purchased or self built. If the clock face, body and functionality is what’s important to you, it’s easy to change the mechanism to one suited for 60 Hz or battery powered and would be the least expensive route.
I want to keep the entire clock as original as possible. Is there anything that can be done with the coil...rewind, reduce the number of turns, etc., or is the speed determined only by the line frequency?
 

MrChips

Joined Oct 2, 2009
22,107
Speed is determined by line frequency.

Is that a rotating disc or is it a solenoid coil?
Can you actually observe the wheel rotating very fast?
Can you show the clock movement from different angles?
 
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