Frequency Change in Voltage Transformation

[zking786]

I've opened up several transformers and have just found coils and metal (I think Iron) rectangles. The voltage IN is transformed to a different OUT voltage based on the ratio of the number of turns on either end. I'm wondering how frequency is adapted? Does the transformation also alter the frequency? I'm speaking specifically of transformations between 120VAC and 240VAC. The frequencies are different between 120V and 240V appliances, so a simple voltage transformation probably wouldn't suffice? Can someone help in explaining how these frequencies are altered?

[YT2095]

in a 240 to 120 dropper transformer the frequency isn`t altered at all.

take for instance many UK power tools for construction sites, 120 (actualy 110) is used as a Safety measure, lower voltage and also Isolation transformer.

these tools still use 50Hz though

[5614]

As the OUT is a direct consequence of the IN they are both at the same frequency.

 

To vary the frequency some other circuitry is required. Again a 555 ICC could be used. Alternatively look into variable frequency oscillators (VFO), remember that your input is already oscillating as some VFOs require a clean (ie. not oscillating) input.

[Externet]

Hi.

The same transformer that works on 60Hz can be made to work in 50 Hz with a different iron core that will have a higher saturation cohefficient.

Miguel

[zking786]

Externet, please elaborate on your point. I'm a beginning Electricity and Magnetism student and don't understand what you mean by "saturation coefficient".

[YT2095]

yeah, I was going to point out that saturation could be a problem under load, even though it`s only like 12% (or something like that). you Could still get away with it IF you`re not working right up to max tollerance

[Externet]

Hi

In simple words, the core on a transformer (or electromagnet) is capable of absorbing a given amount (the point where it saturates) of the magnetism the sorrounding coil produces.

 

That amount of magnetism takes some time to grow and decay every cycle of the alternating current. Different alloys or sizes of the core allow more (or less) magnetic saturation.

 

That is why an electromagnet to pull automobiles and junk is not the size of a pencil. It needs to be bigger to handle such magnetic field.

 

At 50 Hz, the time a cycle of power lasts is slightly longer than at 60 Hz, thus the core can reach saturation earlier if was designed/calculated for 60Hz, when driven to full power demand.

 

Usually in typical products, that is not always the case, a 60Hz transformer should be capable of handling 50Hz within design tolerances.

 

But by feeding 50 Hz in the primary cannot obtain 60 Hz on the secondary |(nor reverse)

Hope it helps better.

Miguel

[zking786]

That makes sense. So the typical generic transformers don't change frequency, just voltage. Thus a 60Hz appliance will probably run on 50Hz power and vice versa. So they don't really bother too much about the frequency in everyday appliances, right?

[5614]

So they don't really bother too much about the frequency in everyday appliances, right?

Not when it is a small frequency change like this, no.

[Externet]

Right.

Most appliances do not care for the frequency (light bulb, toaster) some are slightly affected but the buil-in tolerances absorb the deficit (radios, stereos, computers) and some other will change its behavior (washing machines, turntables, fans... whatever has synchronous motors)

Miguel

[YT2095]

most clock radios don`t like the change though, many rely on the mains freq as their timebase, and simply divide off that.

older turntables (the non DC motor types) don`t like it either.

[5614]

many rely on the mains freq as their timebase, and simply divide off that.

Really? So if we have loads of radio clocks running off either say 50 or 60 Hz then surely that makes a big difference to the time.

 

If we took 1min: 60sec * 60Hz = 3600 oscillations for a min. Whereas for the 50Hz clock 3600 oscillations would take 72 seconds (= 3600 oscillations / 50Hz). That's a difference of 12secs per minute... that's a massive difference.

 

So how does the clock use the freq of the mains? It cannot be directly.

[swansont]

Really? So if we have loads of radio clocks running off either say 50 or 60 Hz then surely that makes a big difference to the time.

 

If we took 1min: 60sec * 60Hz = 3600 oscillations for a min. Whereas for the 50Hz clock 3600 oscillations would take 72 seconds (= 3600 oscillations / 50Hz). That's a difference of 12secs per minute... that's a massive difference.

 

So how does the clock use the freq of the mains? It cannot be directly.

 

I think it just uses a counter. The power companies keep the frequency right pretty well, because transferring to different parts of the grid efficiently requires it; being off in frequency or phases costs money due to losses. I recall a story, though, of a locality that he let the local frequency drift off by a small amount. After a while some people were getting to work 15-20 min late because of the accumulated error, which is when someone checked and found the problem.

[YT2095]

for the 50Hz a frequency doubler is used to make 100Hz, that then goes through a pair of Divide by 10 counters to give a 1Hz pulse.

and no, it uses that frequency indirectly through the transformer

[5614]

So what if you got 60Hz? Would the clock get way out quite quickly or is swansont saying that it will not happen?

 

I suppose it explains why some clocks always run a bit slow (or fast), it must be the transformer slightly altering the frequency. Obviously it's by a very small amount, but it adds up over time.

[gcol]

I recall a story, though, of a locality that he let the local frequency drift off by a small amount. After a while some people were getting to work 15-20 min late because of the accumulated error, which is when someone checked and found the problem.

 

I remember being told, some years ago, that here in the UK because so many clocks run directly off the mains frequency any deviation over a period of time is corrected by raising or lowering it to bring the clocks back to the correct time.

 

When searching for confirmation, which I could not find, I came accross a south african company which was seeking a change in legislation to allow it to vary its frequency by up to 10%, because of power generation difficulties