Convert AC Mains 240V/50Hz to 120V/60Hz

[Jim44]

Hi

I have a US hair clipper that requires 120V/60Hz. It's power rating is 11W. Tried running the device with a 50W transformer that converted 240V to 120V but the motor makes a huge amount of noise. I guess the vibration dampening was designed to handle the motor working at 60Hz.

Looking around the forum I found https://www.electro-tech-online.com/threads/230v-50hz-to-110v-60hz-frequency-change.97357/ with a circuit diagram for converting the frequency.

The description of that solution is a bit too technical for me and I have some questions. Would that solution work for converting mains power? Is there a simpler way to do this, maybe by butchering the transformer and hacking some stuff into it? I don't understand the jargon, what is a PLL and what is the PLL technique?

If you could help this noob out, my beard would appreciate it

 

[crutschow]

Low frequency PLL's (Phase Locked Loops) normally work with digital (square-wave) frequencies and you need a sine-wave. It's not easy to go from a square-wave to a sine-wave and generate a 120V signal. I think it would likely be cheaper and much easier to just buy a 240V, 50Hz clipper.

One way to do the conversion is to use a 60Hz sinewave oscillator to drive a 25W audio amp and use that to drive a 12V to 120V transformer.

Alternately, you can buy a 60Hz sinewave inverter that operates from 12V and power it from a 12V DC power supply.

 

[picbits]

You'll probably find the "converter" you got has a diode or something in to halve the voltage without giving you a proper sine wave - possibly look at a simple 240v to 110v transformer (a proper coil one rather than a "magic" box of tricks)

60Hz motors will run on 50Hz mains although with larger ones they can get a bit hot and lose efficiency.

 

[dr pepper]

I've seen the 'converters' picbits mentioned, sometimes they are called electronic transformers and are cheap, half wave 50hz into a universal motor in a clipper will shake around quite a bit.
See if you can get a proper wound transformer type reducer, 50hz rather than 60 shouldnt really be an issue, and 50w ones shouldnt be really expensive.

 

[alec_t]

I think it would likely be cheaper and much easier to just buy a 240V, 50Hz clipper.

I agree entirely. Dropping volts is easy: changing frequency ain't.

 

[Jim44]

Thanks very much for all the information. It seems changing frequency won't be worth me pursuing. I'd just like to rule out the transformer as the possible cause of the issue. As I said, the clipper does run, but with almost ear-splitting noise.

The transformer that I bought is quite heavy (estimate 600-700g), which I took to mean that it was using proper coils and such. Is there some way I can check whether it is a legit transformer and not an "electronic converter"?

On the bottom of my (hopefully) transformer. It reads, "Foreign travel AC converter input: 220/240v AC 50W output: 110/120v AC 50Hz/60Hz for electric products up to 50 watts. Radios, Walkman, calculators ,cassettes players, electric shaver, camera, strobes, recargers, AC adaptors"

For interest's sake I opened it up and am attaching the photo. It almost looks like the input is directly soldered to the output, but hopefully I'm misunderstanding the wiring.

 

[picbits]

That does look like a proper transformer type voltage dropper - possibly worth putting a meter on the output just to see what the voltage is (just in case).

Where abouts in the world are you ? Many UK bathrooms and hotel rooms have a "shaver adaptor" type plug on the wall with both 110v and 240v outputs.

 

[Jim44]

That does look like a proper transformer type voltage dropper - possibly worth putting a meter on the output just to see what the voltage is (just in case).

Where abouts in the world are you ? Many UK bathrooms and hotel rooms have a "shaver adaptor" type plug on the wall with both 110v and 240v outputs.

I'm in South Africa. I've seen those adapters in hotels too. But I live here permanently so no such luck in this case

 

[alec_t]

I'm amused by the label which implies that if you put in 50Hz you get 50/60Hz out .

The hair clipper I've got (Wahl) has a reciprocating motor rather than a rotary motor and seems to be mechanically resonant at the mains frequency (50Hz). If yours works that way then the frequency difference is important and could account for the noise. My clipper has a 'Power-Voltage Adjustment' screw on the side and an instruction to 'back screw out if motor makes a noise'. The noise would be caused by the reciprocating part hitting end stops. Does yours have such an adjustment?

 

[dr pepper]

Thats a transformer ok.
I'dve thought the motor in your clippers wouldnt care about a slight change in freq esp lower.
I think in any case new ones might be the way forward as others say.

 

[MrAl]

Hi,

Some of those clippers have an armature that goes back and forth driven by the line frequency AC waveform. If the line frequency is too low it may travel farther than it is supposed to or the coil might be saturating. Even if the head isnt adjusted right it may make a lot of noise, i mean a lot more noise than it should. You could try adjusting the head first and see if that helps. That's the metal part on the top that is held down with one or two screws. It may be designed so that if the head is not exactly adjusted it makes a lot of noise so the user cant use it. You can check if it will cut hair anyway. If it cuts hair then it probably isnt that adjustment. If it doesnt cut hair then it may be that adjustment or it just cant run on a different frequency.

 

[Jim44]

Well it's a WAHL Super Taper II and there is an adjustment screw on the side. I was very hopeful after reading your comment and hooked it up again. After fiddling around, I turned the screw out almost to the point that it's falling out and the noise suddenly stopped! You have saved me a serious wodge of cash, thanks so much! And thanks a lot for all the replies, you're a very nice bunch

Depending where I grip the body of the clipper it gets even quieter so I may be able to learn exactly how to grip/squeeze it for fairly silent operation.

So my understanding from a technical point of view is that the lower frequency causes a higher voltage per cycle. With the higher voltage making the motor knock some internal housing.

 

[alec_t]

Glad to have helped.

 

[MrAl]

Well it's a WAHL Super Taper II and there is an adjustment screw on the side. I was very hopeful after reading your comment and hooked it up again. After fiddling around, I turned the screw out almost to the point that it's falling out and the noise suddenly stopped! You have saved me a serious wodge of cash, thanks so much! And thanks a lot for all the replies, you're a very nice bunch

Depending where I grip the body of the clipper it gets even quieter so I may be able to learn exactly how to grip/squeeze it for fairly silent operation.

So my understanding from a technical point of view is that the lower frequency causes a higher voltage per cycle. With the higher voltage making the motor knock some internal housing.

Hi again,

With the lower frequency the armature magnetic material could saturate and that causes noise even in cores that dont move, or since the armature has more time to dwell at the peak it could be being pushed farther away from center which could cause a physical knocking of materials together.

Without having the device right in front of me though if you are interested in looking into this you could make a white LED strobe light and sync it to the line and view the armature as it is frozen in time in any position with the strobe. This works with musical instrument strings too and you can actually tune the vibrating string with the strobe and see it frozen in any position without any other test equipment. You might want to test it with both 60Hz and 50Hz just to see how different the armature reacts. It may make noise even at 60Hz without proper adjustment.

The other thing to do would be to monitor the current into the armature and look for peaks that rise up suddenly instead of fairly smooth, which would indicate intense saturation.

 

[dr pepper]

Know what you mean mr al about saturation, volt seconds are ever so slighter higher at 50 cycles, and these days everything is designed to be just good enough.

My coffee machine has a pump that has a magnet that just oscillates backwards and forwards, probably a similar idea.

 

[Jim44]

Could you explain further about the saturation and magnetic noise? Is saturation when the magnetic field generated by the conductor is at its maximum?

The one thing I found re magnetic noise is talking about Barkhausen Effect which I'm pretty sure is not what you're referring to.

The other possibility was talking about harmonics generated by interaction of the magnetic flux and the air gap. Is this what you're talking about, if so I'd like to understand what it means.

 

[MrAl]

Hi,

The Barkhausen Effect is something different but it may help here.

A magnetic material is made up of structures called magnetic domains, and they act like tiny somewhat independent magnets. When a current is applied that sets up a field in a given direction, and if that direction is the right direction it causes a domain to 'flip'. Flipping of a domain is pictured by thinking of a tiny bar magnet that is allowed to rotate about an axis. It tries to align itself with the field and when the field reaches a certain level it flips or at least aligns itself with the field. Depending on how much it moves it creates a small current of it's own because it's a magnet who's own field suddenly contributes to the total field (and that's the generator effect) and this is called the Barkhausen Effect here. This helps to understand the domains.

But a given bulk of material only has so much volume, and a limited volume has a limited number of domains. Once all of the domains are aligned, there are none left to flip so the magnetic material becomes much less magnetically active. When a material is magnetically active it means that it can react to a magnetic field set up by say an electric current. When it becomes inactive it no longer reacts to that electric current. When it is active it limits the current (over time) but when it is inactive we only have the air to act as the magnetic medium and air has 1000 times less capacity (or even less) to react to a magnetic field than a true magnetic material. This means once the magnetic metal becomes totally 'used' (all the domains flipped) the only thing left is the air and that doesnt limit the current (over time) as well as the available domains did. That means once this happens the current usually rises and it rises very quickly.
While this is taking place the AC current is causing an interaction between the laminations of the core. Usually these low frequency cores are made up of thin plates of metal which react well to a magnetic field, and they are placed side by side to increase the total bulk of the material and thus elevate it's usefulness as a magnetic core with additional domains. Unfortunately because they are physically different pieces of material, they are attracted to and repelled from each other during the AC cycle, and this causes them to vibrate and bang into each other. Since the higher the current the stronger they attract and repel, the harder they bang into each other and so the audible noise increases. Now normally the increase in current is not enough to cause significant noise in the core or the coil, but as it increases above the design level it starts to make a lot more noise. This is especially true when the plates have not been vacuum varnished because the varnishing partly glues them together and limits the movement somewhat. You dont want to be in the same room as a 10 Killowatt 60 Hz transformer that has not been varnished even if it is not saturating

To explain saturation from the standpoint of inductance, a given coil and core has a given inductance until it partly saturates (some domains flipped) and then the inductance falls to a lower value. If it saturates deeply (most domains flipped) it means that the current goes up in the coil and it could go up very high until the drive element (like a transistor) blows out.
If we look at the equation for an inductor:
V=di/dt*L
and rearrange it a little to solve for di:
di=V*dt/L

we see that if the inductance (L) gets smaller the change in current (di) gets larger. That's how saturation affects the circuit. the inductance falls, the current rises. This equation is linear in L so at first it looks like halving the inductance L will only cause an increase in current of two times, but unfortunately the curve of the magnetic material is very nonlinear such that as the current rises the inductance falls faster and faster, so the current ends up looking like a sharp spike that can rise up much higher than it was originally designed for. That happens because the permeability of the core drops off much quicker and that means the inductance falls fast.

 

[Jim44]

Very cool explanation, thank you! It's interesting how a non-linear reaction suddenly occurs above a particular threshold. Sort of a "if it rains it pours" situation. The shenanigans that conductors can get up to in the presence of a bit of electromagnetism is both delightful and astounding.