ac analog clock motor UK to USA Usage

[Timetips]

Hi,

I have a problem with trying to find a 120 to 240 voltage converter that also changes the Frequency from 60Hz to 50Hz. I know a lot of devices are not unduly affected but these clock motors rely on a stable 50Hz input.

Any ideas or circuit design would be greatly appreciated as I have constant requests from US and Canadian customers wishing to buy these items. I cannot sell to that market unless I can come with the appropriate fix.

Thank you!

 

[KMoffett]

Me guess is that a device (inverter) that will convert 120VAC/60Hz to an "accurate", 240VAC/50HZ is going to cost a lot more than a new clock. Not that it can't be done, it's just going to cost more than people are going want to pay.

A quick Google: 120VAC/60Hz to 240VAC/50HZ inverter

Brought lots of voltage step-up and step-down things, but I didn't see any that converted the line frequency.

Ken

 

[audioguru]

Do people use mechanical electric clocks anymore?

 

[Nigel Goodwin]

Years ago, I had a 2M amateur radio base station - it had a mechanical digital clock - which was 60Hz. For the UK market it was modified with a little inverter to feed the clock motor, consisting of an astable multivibrator and a backwards connected mains transformer. Needless to say, it was so inaccurate as to be completely useless.

What you need is a crystal oscillator, divided down, feeding a couple of transistors and a transformer to feed the clock motor.

 

[crutschow]

This chip https://www.electro-tech-online.com/custompdfs/2009/09/ELM446DS.pdf generates an accurate 50Hz signal from a common 3.58MHz color crystal. You could use that to drive the transistors and transformer as suggested by Nigel.

 

[RODALCO]

Do people use mechanical electric clocks anymore?

Yes, I have about 100 of them and 30 in full time service in my house.

 

[RODALCO]

Lost my text. ok here again

Easiest is to find an identical motor for correct frequency and voltage ( may be the hardest option )

If space allowes in the geartrain see if you can fit a 5/6 intermediate gear to get the speed right.
I have seen that method used in hour counters made for 110V 60Hz converted to 230V 50 Hz.
A series resistor was used for voltage drop.

 

[Timetips]

Thank you!

Hi Guys,

Thanks very much for all of the ideas and input. At least I have starting point to work from now.

To answer the question about are these kind of clock movements still in use, what does the member think runs most of the large clocks on commercial buildings!!

A circuit diagram would have been useful as I am not sure how you block the incoming ac 60 Hz signal and feed in the 50 Hz signal. Also the crystal oscillator and IC seems clever but takes away the electrical generating body regualting these clock movements for you. This is why they are such excellent timekeepers.

Again thanks to all, appreciated.

Timetips

 

[crutschow]

A circuit diagram would have been useful as I am not sure how you block the incoming ac 60 Hz signal and feed in the 50 Hz signal. Also the crystal oscillator and IC seems clever but takes away the electrical generating body regualting these clock movements for you. This is why they are such excellent timekeepers.

The crystal is quite accurate and should be sufficient for most clock purposes (a few seconds a month). You would need a power supply (such as a wall-wort) to convert the 60 Hz to DC. Then use the DC to power the IC and drive the clock at 50 Hz.

An alternate way might be to block every 6th cycle of the 60 Hz to give 50 cycles per second. You could use a counter to send a signal to a solid-state-relay to perform the cycle block. But I'm not sure how well a clock motor will respond to such a signal consisting of 5 cycles of 60 Hz followed by a blank cycle. It may just lock unto the 60 Hz and the inertia would allow it to coast past the blank cycle.

 

[Nigel Goodwin]

Hi Guys,

Thanks very much for all of the ideas and input. At least I have starting point to work from now.

To answer the question about are these kind of clock movements still in use, what does the member think runs most of the large clocks on commercial buildings!!

In which case simply change the gearing to correct it, or replace the motor with the correct type. Presumably one of those options will be astandard feature for such clocks?.

A circuit diagram would have been useful as I am not sure how you block the incoming ac 60 Hz signal and feed in the 50 Hz signal. Also the crystal oscillator and IC seems clever but takes away the electrical generating body regualting these clock movements for you. This is why they are such excellent timekeepers.

You don't 'block' the mains, the inverter generates an entirely separate mains supply of a different frequency. As suggested, a crystal controlled one would give the same sort of accuracy as a digital watch.

 

[Mr RB]

Since you are converting 60Hz to 50Hz, maybe you could use a digital circuit that drops every 6th pulse?

So you have a 120v to 240v transformer, then a digital circuit and triac to drop every 6th pulse. Sounds simple enough, you just need to check that the 50Hz clock motor will still sync and run with a 60Hz 5+0 pulse signal.

 

[crutschow]

Since you are converting 60Hz to 50Hz, maybe you could use a digital circuit that drops every 6th pulse?

Guess you missed my post.

 

[Boncuk]

This is not an electric, but a mechanical problem.

I purchased an eight-track player in the USA and took it to Germany. That player had a synchronous motor for the tape drive.

The problem was solved purely mechanically by enlarging the motor drive disk (belt drive) by the factor 1.2 (60/50). (I actually made a new one on the lathe)

Those clock motors are normally fitted with a "sprocket?" having a defined number of teeth.

Adapting the number will do the change. (probably with a different gear box)

Holding cost for an inverter against cost of a changed mechanical design I guess the mechanics will be the winner. Additionally it won't require extra space.

Boncuk

 

[Mr RB]

Guess you missed my post.

Whoops! You guessed right. Sorry about that.

 

[Nigel Goodwin]

Whoops! You guessed right. Sorry about that.

So how would you do it the oither way?, 60Hz clock used on 50Hz mains

 

[crutschow]

So how would you do it the oither way?, 60Hz clock used on 50Hz mains

Just shows that all solutions aren't symmetrical.

 

[Mr RB]

So how would you do it the oither way?, 60Hz clock used on 50Hz mains

I already solved that one, one of my zero-error bresenham routines will convert 120Hz to 100Hz, or 50Hz to 60Hz (or any Hz to any Hz really) this is from my zero-error PIC timing page and was orig designed so poor people forced to use 60Hz mains freq can still have clock displaying hundredths of seconds;

C code for low-jitter generation of 100Hz from 120Hz mains

	// PIC code, 4MHz xtal, TMR1 at 1:8 prescale 
	// uses 2 variables;
	//   unsigned int bres
	//   unsigned char pulse

	start:

	// wait here for 120Hz pulse
	while(!check_120Hz());	

	// now generate 10 "fake" pulses, each is "1200Hz"
	// which is 833uS. PIC 1Mhz xtal, TMR1 1:8 prescale,
	// we use TMR1L period of 104 = 832uS 
	// note! TMR1L loop is also another zero-error system
	// that we keep subtracting 104 from while retaining
	// its internal error.

	pulse = 10;		// make 10 "fake" pulses
	TMR1L = 0;		// make first pulse immediately

	while(pulse)
	{
		// wait here for fake 1200Hz pulse	
		while(TMR1L.F7);

		// now fix TMR1L and do the main bres event
		TMR1L -= 104;	// subtract 1/1200th of a second

		bres += 100;
		if(bres >= 1200)	// if 100th sec reached!
		{
			bres -= 1200;
			do_100th_event();	// update clock, etc
		}

		// subract a pulse, see if 10 done yet
		pulse--;
	}

	// gets here after 10 "fake" 1200Hz pulses,
	// need to detect a real 120Hz pulse, then
	// do it all again!

	goto start;

The code above behaves much like a digital PLL (Phase Locked
Loop) in that it MUST generate 10 pulses for every real input
pulse (with zero cumulative error), and the output is generated
from that, again with zero cumulative error.

There are other good solutions too, one of the other threads has a couple of hardware approaches using PLLs.

 

[Nigel Goodwin]

There are other good solutions too, one of the other threads has a couple of hardware approaches using PLLs.

Basically a PIC software PLL, but I was wondering if there's some simple method, like the skipping every sixth pulse idea (assuming that even works?).

 

[Mr RB]

What about "injecting" a frequency into the 50Hz so that the beat frequency output is 60Hz?

Considering these clock motors only run about 1watt or 2watt it might be feasible.

 

[Nigel Goodwin]

What about "injecting" a frequency into the 50Hz so that the beat frequency output is 60Hz?

Now that's an interesting idea!

However, it still has the frequency stability problems for the second frequency.