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Old 1st January 2011, 04:50 PM   #1
ZenCow is offline ZenCow  United States
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Default Using 220V transformer on 110V

I am hoping to verify I have this concept down correctly....

If I take a 220V primary, 2 x 35V secondary transformer and connect it to 110V I will have about 2 x 17.5 at the secondaries. Right?

Thanks in advance!
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Old 1st January 2011, 04:57 PM   #2
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Yup!
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Old 1st January 2011, 05:50 PM   #3
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However the output power will be cut in half.
That is:
If we had a 220VA transformer at 220 Volt and 1 Amp.
Then at 110 Volt and 1 Amp we have 110VA.
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Old 1st January 2011, 06:11 PM   #4
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I'd guess you'd be able to draw off more current but regulation wouldn't be as good as a pukka 110 volt one as primary winding will have higher resistance.
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Old 1st January 2011, 06:18 PM   #5
AndrewT is online now AndrewT  Scotland
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no,
cut the supply voltage by half and you cut the VA rating by half.

The transformer windings, both primary and secondary are rated for current. This does not change, even though input and output voltages can be changed.
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Old 2nd January 2011, 01:17 PM   #6
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Well, with all due respect to Andrew, he and I don't agree.
The windings will tolerate more current, but, as I said before, regulation won't be as good.
I'm NOT saying you will get the same rating, but something in between.
I can only suggest you try it and keep an eye on the temperature.
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Old 2nd January 2011, 05:08 PM   #7
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The majority of loss in a loaded transformer is due to winding resistance (copper losses) so the maximum power out is more or less proportional to the input voltage, at least up to the point where saturation comes into play. Half volts in equals (same current) half power out.
Regulation will be worse at lower voltages because copper losses are relatvely higher.

Barry
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Old 2nd January 2011, 05:34 PM   #8
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by barrymagrec View Post
Regulation will be worse at lower voltages because copper losses are relatvely higher.
Which also means the output power will be less than half:
At its nominal voltage, the transformer takes a total P=Pout+Pcu.
The useful output is Pout=P-Pcu.
At half that voltage, the current remains the same and P'=P/2.
Pcu remains the same, therefore P/2=P'out+Pcu, and P'out=P/2-Pcu.
It is easy to see that 2*P'out < Pout:
P-2*Pcu < P-Pcu.
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Old 2nd January 2011, 05:45 PM   #9
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This is true but given that the copper losses are normally a small proportion of rated power, in practical terms it can be ignored. If you run so close to maximum that the extra loss becomes significant a hot day is going to blow you away!

Barry
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Old 2nd January 2011, 06:00 PM   #10
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Looks like some practical testing is called for....
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