Using 220V transformer on 110V

ZenCow · 1st January 2011, 04:50 PM

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!

VictoriaGuy · 1st January 2011, 04:57 PM

Yup!

Speedskater · 1st January 2011, 05:50 PM

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.

toprepairman · 1st January 2011, 06:11 PM

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.

AndrewT · 1st January 2011, 06:18 PM

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.

toprepairman · 2nd January 2011, 01:17 PM

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.

barrymagrec · 2nd January 2011, 05:08 PM

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

Elvee · 2nd January 2011, 05:34 PM

Quote:

Originally Posted by barrymagrec

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.

barrymagrec · 2nd January 2011, 05:45 PM

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

toprepairman · 2nd January 2011, 06:00 PM

Looks like some practical testing is called for....

1st January 2011, 04:50 PM	#1
ZenCow diyAudio Member Join Date: Jan 2006 Location: Denver	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!

1st January 2011, 05:50 PM	#3
Speedskater diyAudio Member Join Date: Sep 2002 Location: Lakewood, Ohio	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. __________________ Kevin

1st January 2011, 06:18 PM	#5
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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. __________________ regards Andrew T.

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1st January 2011, 04:57 PM	#2
VictoriaGuy diyAudio Member Join Date: Dec 2008 Location: Victoria, BC	Yup!

1st January 2011, 06:11 PM	#4
toprepairman diyAudio Member Join Date: Nov 2010	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.

2nd January 2011, 01:17 PM	#6
toprepairman diyAudio Member Join Date: Nov 2010	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.

2nd January 2011, 05:08 PM	#7
barrymagrec diyAudio Member Join Date: Apr 2010	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

2nd January 2011, 05:45 PM	#9
barrymagrec diyAudio Member Join Date: Apr 2010	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

2nd January 2011, 06:00 PM	#10
toprepairman diyAudio Member Join Date: Nov 2010	Looks like some practical testing is called for....

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