American 60Hz clock - Will it run on pulsed DC?

[Hunts smoothing bomb]

Hi all,

Excuse me if I'm being ignorant here but I wanted your collective opinion, first I'll set the situation...

I am currently looking at an american clock radio for somebody, it's made by Commodore and is a 117v valve set, now the 117v part isn't difficult as I have a suitable transformer that will fit inside the set as there is lots of room, the issue I do have though is with the clock itself as it runs way too slow on 50Hz
Now, my question is this.. If I pulsed DC into the clock winding (also designed for 117vac) at 60Hz would it work? and secondly and most importantly could I do it with a much lower voltage?

Answers on a postcard please!!

Cheers

[Maarten]

Pulsed DC seems like a bad idea. You could probably build a small sine generator and use it to drive a power transformer in reverse to obtain the right voltage.

[broadgage]

Remember also that the inductive impedance of the clock motor winding will be reduced at a lower frequency.
You may therefore need to reduce the voltage to perhaps 100v/110 volts rather than the designed 117/120 volts.

[Argus25]

You can order these with a UK input plug and get your 60Hz 110V power this way:

https://www.kccscientific.com/product/1930/

I have used other solutions too. Often the rotor in the clock is a separate item, available in both 50 and 60 Hz versions, if you are lucky you might find one in a clock on ebay.

In one case for one of my 110V 60 Hz clocks, I disassembled the rotor assembly and Ken Reindel machined a new gear for me (near the output shaft) to alter the ratio to correct it for 50Hz use. He is a master clockmaker:

http://www.kensclockclinic.com

[TrevorG3VLF]

I have seen circuits of a 300Hz oscillator, phase locked to the mains and then this is divided by 5 to get 60Hz or 6 to get 50Hz. This will then need to be amplified to get a suitable supply for the clock.
Pulsed DC could work if the DC was blocked and only the pulses passed but you will need an accurate frequency source. There are invertor circuits to give out AC.
This is a nice little project using CMOS or a microprocessor.

[Nickthedentist]

Similar gadget to the one mentioned by Hugo here:
http://www.electric-clocks.co.uk/Fre...cyconvert.html

[steve102]

I use one of these converters to run a 60Hz Telechron clock from 50Hz UK mains:
http://www.electric-clocks.co.uk/Fre...cyconvert.html

[julie_m]

There is no need to worry about the waveform, just as long as it is symmetrical (for the sake of the permanent-magnet armature). A crystal oscillator and suitable divider chain will do fine; the division should ensure symmetry. Use the Q and Q' outputs from your last flip-flop to drive the gates of a pair of MOSFETs, one drain to each end of the centre-tapped secondary winding of a suitable transformer, the tap to the unregulated supply and the primary to the clock motor.

Small transformers tend to have lousy regulation, so one rated for 18-0-18V from a 230V supply probably will give about the right output with a 12V DC supply. The clock should still run from a reduced voltage.

[PJL]

Originally Posted by TrevorG3VLF

I have seen circuits of a 300Hz oscillator, phase locked to the mains and then this is divided by 5 to get 60Hz or 6 to get 50Hz. This will then need to be amplified to get a suitable supply for the clock.
Pulsed DC could work if the DC was blocked and only the pulses passed but you will need an accurate frequency source. There are invertor circuits to give out AC.
This is a nice little project using CMOS or a microprocessor.

http://sound.whsites.net/clocks/freq-changer.html

Quite complicated though.

[IanBland]

I would be inclined to use a microcontroller as a pseudo phase locked loop, one of the PICs with a zero crossing detector would be ideal.

[Maarten]

When going the non-sinusoidal way, the RMS voltage would be important to get right, too.

[IanBland]

Well, at a fixed, known frequency, a square wave can be made into a very good approximation of a sine wave (better than anything that comes off the mains, heh) with a simple RC filter. Then step it back up with a Class A or AB output stage... ooh, this is actually getting quite complicated isn't it?

with a simple RC filter.

A square wave into an inductor would do the same thing. The inductor being the clock winding.

[Hunts smoothing bomb]

Hi guys,

Thanks for all the replies, I'm unsure yet which way to go regarding this, to buy a ready made unit or to construct from scratch (I prefer the latter I think)

Still, plenty of food for thought.

Thanks again!


Cheers