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Not sure where to ask - POWER TRANSFORMERS

Not sure where to ask - POWER TRANSFORMERS

Old Jan 19th 2018, 12:42 am
  #1  
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Default Not sure where to ask - POWER TRANSFORMERS

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 ?
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Old May 6th 2018, 10:02 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

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.
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Old May 6th 2018, 11:12 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

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.
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Old May 7th 2018, 10:47 am
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Default Re: Not sure where to ask - POWER TRANSFORMERS

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?
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Old May 7th 2018, 12:43 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

No, you can’t say a transformer connected but unloaded is 0% efficient, it is consuming a percentage of its rated capacity which varies depending on design and actual load over time, even temperatures impacting it. You can say it consumes x Watts, eg a 5kva cheap EI device popular in houses here consumes about 1kw off load, an efficient torroidal design about 150 Watts in comparison. The cheap in inverted commas device is costing, here where electrical energy is some of the most expensive on the planet, about 200us a month, when doing nothing. That isn’t 0% of course as it’s likely powering something most of the time, and as it’s losses vary on load it’s not simple to calculate the real loss inless you add a draenetz analyser fur the month.
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Old May 7th 2018, 2:56 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

Originally Posted by uk_grenada View Post
No, you can’t say a transformer connected but unloaded is 0% efficient, it is consuming a percentage of its rated capacity which varies depending on design and actual load over time, even temperatures impacting it. You can say it consumes x Watts, eg a 5kva cheap EI device popular in houses here consumes about 1kw off load, an efficient torroidal design about 150 Watts in comparison. The cheap in inverted commas device is costing, here where electrical energy is some of the most expensive on the planet, about 200us a month, when doing nothing. That isn’t 0% of course as it’s likely powering something most of the time, and as it’s losses vary on load it’s not simple to calculate the real loss inless you add a draenetz analyser fur the month.
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
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Old May 7th 2018, 3:03 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

Originally Posted by winston_1 View Post
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
No unfortunately i mean it, it consumes 20% of its rated power at idle, a bar of an electric heater, its horrible but true. 10% is normal fir better designs of EI’s and if you dont believe me connect one unliaded and see if you can put your hand on the core. Thing is, most of these fixed transformers are always powering something like a freezer or aircon, and so the losses are ignored by those who dont equate heat with cost.
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Old May 7th 2018, 3:33 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

Originally Posted by uk_grenada View Post


No unfortunately i mean it, it consumes 20% of its rated power at idle, a bar of an electric heater, its horrible but true. 10% is normal fir better designs of EI’s and if you dont believe me connect one unliaded and see if you can put your hand on the core. Thing is, most of these fixed transformers are always powering something like a freezer or aircon, and so the losses are ignored by those who dont equate heat with cost.
Have you got a link to this awful devcice?
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Old May 7th 2018, 3:44 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

I dont know if that things made any more but generally just google it - some have axes to grind of course like

https://www.plitron.com/news/toroidal-advantages/

This shows losses compared quite well


Saving energy with the toroidal transformer | OliNo

the absolute truth - compare the example transformers info

Transformers Part 2 - Beginners' Guide to Electronics
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Old May 7th 2018, 4:08 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

Originally Posted by uk_grenada View Post
I dont know if that things made any more but generally just google it - some have axes to grind of course like

https://www.plitron.com/news/toroidal-advantages/

This shows losses compared quite well


Saving energy with the toroidal transformer OliNo

the absolute truth - compare the example transformers info

Transformers Part 2 - Beginners' Guide to Electronics
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.
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Old May 7th 2018, 4:12 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

Semantics, the important point is - teansformers cost you money - better transformers cost you less, stress your electronics less and are greener/quieter.

Frankly i dont care what nationality made them, most of the good ones ive seen are chinese but im sure the right co’s in any country can make them. Actually come to think of it ive used i think boden? American transformers, linear motors and motors that are truly excellent.
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Old May 7th 2018, 4:14 pm
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Default Re: Not sure where to ask - POWER TRANSFORMERS

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