50hz vz 60hz and wattage

thelawnet

I have a US appliance, a knife sharpener (contains a motor, powering a spinning wheel). It is labelled:

120V 60HZ 2.1A 125W

I bought a transformer, it is labelled:
220V 50Hz
to
110V 150W

It burnt out on first use.

I'm not sure if it's just a cheap and nasty Chinese transformer that doesn't deliver the rated output, or whether I do need a more powerful transformer.

As I understand it, the lower frequency, 50Hz, against the 60Hz design characteristic, means it runs slower.

But I'm not sure what the correct wattage for my transformer is???

Myser

Using the motor with a 50Hz supply will mean that it does indeed run slower.

I suspect the transformer you had couldn't cope with the peak/starting power of the motor.

Try and purchase a better quality transformer that is rated double the required power.

thelawnet wrote: »

I bought a transformer, it is labelled:
220V 50Hz
to
110V 150W

Also, UK mains voltage is specified at 230V +/- a tolerance. Definately seems like a cheap transformer to me!

brig001

It should have worked apart from starting power as Myser said, and something called power factor. You can google it if you are interested, but basically it means that a motor will take more current than you would expect. The details you gave: 120V 60HZ 2.1A 125W and power = volts x amps = 262W, so I would choose a transformer that can delivery at least 300W.

HTH, Brian.

Ben84

I'm very much against using appliances on electrical supplies they were not designed for. There are a lot of potential problems.

One reason is the wide availability of poor quality and often illegal transformers. I won't go in to all the details, but there are lots of hazards. Some transformers do connect the incoming ~240V supply to the outgoing ~120V directly, which should never happen. They may also be lacking fuses and thermal fuses. Some of them, particularly when used to power up older equipment can lead to very dangerous situations for the appliance and anyone using it. Unfortunately, it's very difficult for most people to tell the difference between a good transformer and a bad one as they probably don't know the difference and rarely can you open the transformer to see what is inside it anyway.

The other issue, which is a major one is that even if you do buy a good quality transformer, it's just not as simple as it seems.

Officially voltage in the UK is taken as 240V, but depending on how close your house is to a substation and the time of day, it may be anywhere from 216 to 253 volts. A rough way to guess your typical voltage is considering how fast filament light bulbs burn out. My house is probably lower on average as light bulbs last me years, but I know some people change them often. Anyway, voltage varies and cheaper transformers may struggle at the higher end of the range.

What does not vary however is frequency (the number of times per second an alternating current changes direction). In the UK it is fixed at 50 Hz and in the US it's 60 Hz. It is essential to the function of many appliances. Synchronous clocks which plug in to the mains use the frequency to control their timing, it also controls the speed of some tape players. The mains frequency is also used at Television Centre and the Granada Studios to time the TV channel transmissions so that when they arrive at your TV, the TV uses the frequency it receives from the mains to time the speed at which the electron beam inside it scans across the back of the screen to produce the picture. Because they should be the same, regardless how far away you are or what power plant is supplying your electricity, it works. So, the mains frequency is fixed (every power plant in the country runs in synchronisation) and is very, very tightly controlled as so many appliances depend on it to function correctly. So, not everything works properly at another frequency and changing frequency is very difficult so most transformers don't do it. The result may be it doesn't work right, or it may damage the appliance through overheating.

You might correctly assume running a 50 Hz appliance at 60 Hz is likely to damage it, but it might incorrectly appear safe to run 60 Hz appliances at 50 Hz as it's lower. This is where things can go wrong. Power supplies and motors may overheat, damaging the appliance and potentially starting a fire. Your knife sharpener must contain a motor and some kind of power supply so it's dubious what will happen.

Some motors are pretty unconcerned about the frequency you feed them, but others like induction motors are greatly affected. They will run, although slower, but another result of lowering frequency is the current they draw goes up and the motor runs much hotter than it was intended to. I won't talk about power supplies as it's less relevant to your question, but they too can overheat at lower frequencies.

Some items, often laptop power supplies state they can accept dual voltage *and* frequencies, so they're fine to use abroad where they match the frequency and voltage with just a socket adaptor, but check the labels on them closely first. As for other items intended for one electrical supply, safest bet is to just use appliances intended for the available electrical supply. If you really must use them with another voltage and/or frequency, buy a transformer from a reputable retailer, accept you may damage the appliance, try to avoid using them for old appliances and never use them for appliances which are left unattended as it's a definite fire hazard if they start to overheat. Appliances you may normally leave safely turned on for hours or even 24/7 like phone chargers and modems are only rated for sustained use at the intended mains frequency.

Myser

Ben84 wrote: »

[STRIKE]Officially voltage in the UK is taken as 240V[/STRIKE]

Not anymore! It used to be 240V but was harmonised with Europe to 230V. The official specification is now 230 volts +10% and –6%. Check UK Power Networks to confirm. No doubt it may read 240V in some areas or even higher. It should not exceed 253V.

Ben84 wrote: »

Some adaptors do connect the incoming ~240V supply to the outgoing ~120V directly

I would not describe a transformer as an adaptor - this will confuse the OP. An adaptor implies no voltage/current transformation. Most people think of travel adaptors which only modify the plug pin type.

Ben84

Myser wrote: »

Not anymore! It used to be 240V but was harmonised with Europe to 230V. The official specification is now 230 volts +10% and –6%. Check UK Power Networks to confirm. No doubt it may read 240V in some areas or even higher. It should not exceed 253V

Oh, when was this? As for 253V, that would be very unusual, but as I understand it an acceptable and possible voltage from a socket in the UK, so anything sold for attaching to a UK socket should be able to cope with this. Some poor quality items however may not.

Myser wrote: »

I would not describe a transformer as an adapter - this will confuse the OP. An adapter implies no voltage/current transformation. Most people think of travel adaptors which only modify the plug pin type.

Fair point. Sometimes I choose not such suitable words in English for things. I will edit my post.

Myser

I believe the specification changed in 1993. In fact, as it was only a change to the specification not the actual supply, it wasn't deemed to have an impact on existing equipment.

I remember doing mains voltage calculations based on 240/250V at school. Of course, now you should use 230V for fuse calculations etc.

People houses' whose mains voltage supply measured 250V and above noticed that they had to replace incandescent bulbs more often and more appliance failures.

keystone

OP just go buy yourself a suitable product rated for UK domestic supplies. Lot less hassle IMHO.

Apart from that how do we know whether a US product manufactured for the US market meets European standards for safety etc?

Cheers

keystone

Myser - you are quite right about harmonisation. More blasted EU bureaucracy.

Cheers

2sides2everystory

I also recall seeing a recent tv piece about matching national grid supplies to demand during 'tv pickup' periods peak kettle boiling periods e.g. just after an Eastenders episode finishes. Whilst the frequency was the parameter they sought to control most particularly, it did go down to 49.7Hz once on poor Simon's watch when Andrew Marr paid him a visit after a promised and evidently imperfectly harmonised 600MW French cross channel electricity link blew a fuse just when he needed it most

That's probably what did for the OP's motor !

Ben84

keystone wrote: »

OP just go buy yourself a suitable product rated for UK domestic supplies. Lot less hassle IMHO.

Apart from that how do we know whether a US product manufactured for the US market meets European standards for safety etc?

Cheers

I might get some negative responses for saying this, but European (excluding UK) electrical standards are not that good and nor from what I can tell are the US ones compared to the UK.

The US and most European plugs don't have fuses, leaving many appliance's flex greatly under protected. Two pin plugs which you can reverse the polarity of the appliance are also common, resulting in a 50/50 chance of having the appliance's switch on the neutral rather than the live. If this happens turning it off stops electricity leaving the appliance, so it appears to be off, but it still has full live potential as the supply is still switched on.

Two pin plugs are often quite wobbly in the sockets as well I found, so they're an arcing hazard too.