Need to convert 240v 50Hz - 110v 60Hz (newbie)

Hi floks,
The title says it all,
Here in the uk our domestic supply is 240v 50Hz, I repair clocks for a living and often get asked how to run american electric clocks (110v 60Hz) in the uk, Most people assume that just buying a step down transformer will do, then wonder why their clocks run SLOW ???
I thought it about time i researched this issue and came up with a cost effective answer.
My thoughts so far are to step down transformer to 9-12v, smooth to dc, then using a 555, create 60Hz frequency to be applied to the dc then step up transformer to 110v. Current requirements would be no more than a few watts. Any and all thoughts or possible circuits would be very much apreciated.

Kind regards

Malcolm

 

I'm no expert in this, but it really does not make sense to make a clock that will take the AC frequency to run the timing functions of the clock.

In other words, I think that a step down transformer is what you need. If the clock runs faster, I'm pretty sure it is NOT related to the frequency of the AC...

 

If you use a step down, then your output will be 110v - 50Hz, and if the clock takes the timing from AC, then shouldn't the clock run slower ?

Anyways, your idea might work, but I think that a 555 does not give you precise timing, because you are using capacitors to generate the frequency. You have to use something with a quartz clock.

 

OOPS !!

I am getting confused, YES you are completely correct SLOWER NOT FASTER.
Sorry, Well spotted

Malcolm

 

Odd that you say they run fast; they SHOULD be running slow. Every 60 seconds they would lose 10 seconds.

Older type motor driven US clocks rely on the 60Hz frequency to keep the clock time accurate. There are also quite a few digital clocks that use the 60Hz signal as an internal clock pulse.

Sorry to inform you of this, but your plan to use a 555 timer to generate a 60Hz signal will be woefully inadequate. Even a crystal oscillator won't be good enough. You'd need a temperature compensated or oven controlled crystal oscillator to even get close.

Another possibility could be to take the 50Hz input sinewave, multiply it by 6 to get 300Hz, then divide it by 5 to get a stable 60Hz signal. This method would leave the accuracy of the output up to the power companies.
[eta]
Here's an older article from EDN on using a uC to multiply frequencies:
http://www.edn.com/article/CA45902.html

Here in the States, the 60Hz from the power grid is very accurate. I have no clue how accurate the 50Hz is in other countries.

 

Excellent reply SGTWOOKIE

Thanks for that information, the EDN article will probably be very helpful when i have read it enough times to understand it (newbie)
I am sure you will have read my apology and correction of fast/slow by the time you read this.
I was hoping this would not be too complicated an issue but it seems like it might be, however i will persevere with it as it will be useful in my business to be able to resolve the problem outside the clock hence retaining the originality of the piece. i have considered making a new stator for the motor, to run on 50Hz but as a conservator that is not really acceptable.

 

Sorry my reply was so slow; there were several exchanges between the time when I started writing it to when I actually hit the post button. I was doing some research on clock multiplier circuits for you; the EDN article seemed the most promising.

Attempting to design/build a 220V 50Hz to 120V 60Hz converter is a pretty ambitious project, particularly for a beginner. The learning curve for microcontrollers tends to be somewhat steep, but this would be the best way to approach the problem.

Even then, you'd need a transformer to get the 220V 50Hz down to power the logic and controls, and another transformer that the control circuits could generate the 120v 60Hz output power, and ensure it's regulated. You'd be hard-pressed to build something suitable for under 30 Euros - even if you didnt use a custom circuit board.

 

Chances are that any fix would cost more than a new clock! Unless they are referring to the clocks embedded in microwaves, stereos, etc. In that case, a piece of black electrical tape should do the trick by covering up the display. ;D

--Rich

 

Hi Folks
Sarge, I figure the investment is worth making as some of these clocks are antique and of surprising value. the customer may never run the clock here. if i am restoring it i want to be able to test it at the correct voltage/frequency so i can be sure it is working to spec.

Rich
Unfortunately your sugestion is incorrect, these are clocks from as far back as the 1920s/30s and are considered antique. Although many where made, Many where thrown away so they are becoming rarer, (not ridiculously so but reasonably so) There are some really cool designs especially from the thirties.

Malcolm

 

What about converting a UPS power system ?

For example I have this one that I use for my computer


I looked inside, and if you don't supply it power, it takes power from a 12V battery, and brings it up to 110V 60Hz.

So... all you have to do, is give it a 12V power source instead of the battery...

I don't know how stable is the 60Hz frequency is though...

 

Hi CVMICHAEL

Excellent thinking, I like where this is going. I would like to build my own so i shall now investigate that as an approach. Brilliant many thanks.

malcolm

 

The output from a UPS is simply an approximation of a 60Hz square wave. It is not accurate enough for a clock.

 

OH B-**ER



Malcolm

 

I really do appreciate everyones input on this and thank you for your time and knowledge shareing. I am sure there will be a solution out there somewhere.


Malcolm

 

Haha

I don't know what you said, but it looks very funny

Well, I think the real question is how precise does it have to be ?
I mean, for a clock that was made long ago, at that time, was the AC frequency precise ?

I think it is acceptable if it's off a few seconds per day, but the 50 to 60Hz (10 seconds per minute) is way off the acceptable range...

The question is how far off an UPS frequency would be ? and if it's not precise, can it be modified to be precise ?

 

CVMichael
That was OH B-GGER or OH-BU**ER
I agree a few seconds either way per day is not important.
Malcolm

 

Hi Sgt
This may be getting too involved !!! but is it possible to convert the square wave into sine ??
Malcolm

 

I might be wrong, but I always thought that one of the properties of a transformer is that if you give a square wave at one end, the induced current will be a sine wave at the other end...

The only thing is that you may loose power because not all the current gets induced / transferred from the square wave.

I am a noob too , so I think SgtWookie can give you a better answer.

 

To continue on that...

I think what you need is an H-Bridge to create a sine wave, because if you give a square wave to a transformer, you will get something like (see picture from the link)
http://www.vias.org/eltransformers/lee_electronic_transformers_10_01.html