uk_grenada

Im living in a place that has uk power standards, but is geographically close to north america. Here people often buy us appliances and plug them into 120 volt transformers. My home has both 230 and 120 volt outlets and a 5kva transformer - but i leave it off - as its too hot to touch if used - and im paying to heat it - in the tropics....

Transformers are to an extent i understand lossy, turning some input power into heat [im told its the eddy currents and a few percent is normal...]

Did i mention we have some of the highest electricity costs on the planet.

So does anyone have insight into what makes a power converter or transformer efficient? I have heard that donut or torroidal transformers wrapped with pure copper are ‘it’ but ?

winston_1

Transformers are actually pretty efficient, probably 97% when used at full load. So your 5kVa one will lose around 150w which will make it hot. There are 2 types of losses, copper losses and iron losses probably both about equal. Iron losses are always there, copper losses depend on load. So your transformer with virtually no load will still lose around 75watts.

Toroidal transformers have lower iron losses but are more expensive.

There are also power converters which use electronic switching. These are more efficient but the output waveform is poor and should only be used on heating appliances, toasters, kettles etc. Certainly don't use them for delicate electronics.

Better still don't buy US appliances.

uk_grenada

I strongly disagree, show me a peer reviewed paper that says an EI transformer can do 97% efficiency, at any load, esp no load where the best ive ever tested was 11% loss.

Whats an iron loss? are you referring to the eddy current result of a twisted field - thats why one main reason torroidal is better.

Torroidal supplies - big ons - are these days not orders of magnitude more than rubbish EI's, maybe ad 30-50% but then compare with cost of losses over time. Every country has manufacturers of them - even america - but amazon has decent chinese ones.

Converter is a non technical term - there are 'converters' that use switch modes that are very unhealthy for electronics but equally there are excellent sine generators available - but they cost.

winston_1

Do you really believe that all those transformers the power companies use to step down from 33kV etc are that lossy?
Efficiency % equals output power divided by input power times 100. So any transformer on no load is 0% efficient. This gradually improves up to full load.
Iron loss refers to the losses in the core, eddy currents (which are minimised by insulating the laminations from each other), and hysteresis (the difference in the power on one half cycle to magnetise the core and the power returned in the next half cycle from the core). Toroidal transformers should have less eddy currents but the hysteresis is still there (maybe a little less due to the compact core).

What would you call the technical term for converter? Sine wave converters are available as you say. I imagine to get the sine wave a filter is added to the output, more losses then.

But as I said, don't buy US appliances. They maybe slightly cheaper, but with all the hassle of transformers etc is it worth it?

uk_grenada

winston_1

I can say that and I did. But anyway I can't believe that a 5kVa transformer consumes 1kW off load. Perhaps you mean 1kVa which is not the same thing as you pay for watts not VA

uk_grenada

winston_1

Have you got a link to this awful devcice?

uk_grenada

winston_1

Interesting, the losses appear higher than I thought. I'm glad he confirms that at zero load the efficiency is 0%.

All the more reason not to source equipment from the US.

uk_grenada

uk_grenada