Run a transformer backwards?

Richard Ellis · 19th September 2007, 05:16 AM

Can one run a transformer backwards, as in use the secondaries as the primaries?
I made a miscalculation and I need 240VAC for my mains and the wall voltage here is 220VAC....I found a transformer with the following specs.
190/200/208/220/240:220VAC, 500Watt.
If I run it backwards it will be a slight step-up. I know big jumps will bring up issues like insulation breakdown and such , but this is a slight increase. Are there other issues with operating transformers like this?
______________________________________Rick........ ......

cerrem · 19th September 2007, 07:10 AM

First thing ....I need to see a mucho bigger photo of your avatar

To answer your question.....Yes....
You can run this transformer either way...as long as you hook it to the proper voltages.....220 in and 240 out is fine...no difference...

Chris

Tony · 19th September 2007, 07:40 AM

Quote:

Originally posted by Richard Ellis
Can one run a transformer backwards, as in use the secondaries as the primaries?
I made a miscalculation and I need 240VAC for my mains and the wall voltage here is 220VAC....I found a transformer with the following specs.
190/200/208/220/240:220VAC, 500Watt.
If I run it backwards it will be a slight step-up. I know big jumps will bring up issues like insulation breakdown and such , but this is a slight increase. Are there other issues with operating transformers like this?
______________________________________Rick........ ......

by convention, primaries are connected to the power source and secondaries to load..... so as long as voltages are right, it should be no problem.

EC8010 · 19th September 2007, 07:58 AM

Quote:

Originally posted by Tony
By convention, primaries are connected to the power source and secondaries to load..... so as long as voltages are right, it should be no problem.

Not quite. A 1:1 transformer will have (should have) its primary wound from heavier gauge wire to allow for the magnetising current as well as the wanted current. Applying power to the secondary means you pass more current through a thinner wire and are in danger of overheating.

Richard Ellis · 19th September 2007, 11:48 AM

Cerrum:
The beaches here are jam packed with fine ladies come December thru January.
_____________________________________Rick.......
I'll check the wire gauge on the Primaries vs. the secondaries.

Tom Bavis · 19th September 2007, 01:27 PM

It will probably be fine with a slight derating. At 50 Hz, there may not be much margin though... check the current when unloaded - less than 20% of the full load current will be OK. If you get more than this, it's on the edge of saturation.

The rated voltage is under load, so the 220V winding is probably wound for about 230V to allow for resistive loss at full output. So you may not get as much step-up as you think...

Jan Dupont · 19th September 2007, 03:38 PM

Have you actually measured your Mains Voltage

You may be surprised.....

And all transformers put out higher Voltages when unloaded or even half loaded (Voltage given are for fully loaded), so you may be able to use a 240VAC and still get the Voltage out you need...

john65b · 19th September 2007, 03:57 PM

Bigger pic please.

djQUAN · 19th September 2007, 04:00 PM

just curious, what device needs 240V and will not work at 220V?

depending on many factors, your mains voltage could vary a lot.

Tweeker · 19th September 2007, 05:34 PM

If there is built in fusing on the xfmr it may not provide the same protection it normally does.

19th September 2007, 05:16 AM	#1
Richard Ellis diyAudio Member Join Date: Sep 2006 Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.	Run a transformer backwards? Can one run a transformer backwards, as in use the secondaries as the primaries? I made a miscalculation and I need 240VAC for my mains and the wall voltage here is 220VAC....I found a transformer with the following specs. 190/200/208/220/240:220VAC, 500Watt. If I run it backwards it will be a slight step-up. I know big jumps will bring up issues like insulation breakdown and such , but this is a slight increase. Are there other issues with operating transformers like this? ______________________________________Rick........ ......

19th September 2007, 03:38 PM	#7
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	Have you actually measured your Mains Voltage You may be surprised..... And all transformers put out higher Voltages when unloaded or even half loaded (Voltage given are for fully loaded), so you may be able to use a 240VAC and still get the Voltage out you need... __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

19th September 2007, 05:34 PM	#10
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	If there is built in fusing on the xfmr it may not provide the same protection it normally does. __________________ Be sure your foil hat has a good low impedance ground.

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19th September 2007, 07:10 AM	#2
cerrem diyAudio Member Join Date: Jun 2005 Location: San Diego, CA	First thing ....I need to see a mucho bigger photo of your avatar To answer your question.....Yes.... You can run this transformer either way...as long as you hook it to the proper voltages.....220 in and 240 out is fine...no difference... Chris

19th September 2007, 01:27 PM	#6
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	It will probably be fine with a slight derating. At 50 Hz, there may not be much margin though... check the current when unloaded - less than 20% of the full load current will be OK. If you get more than this, it's on the edge of saturation. The rated voltage is under load, so the 220V winding is probably wound for about 230V to allow for resistive loss at full output. So you may not get as much step-up as you think...

19th September 2007, 03:57 PM	#8
john65b diyAudio Member Join Date: Jan 2005 Location: Chicago	Bigger pic please.

19th September 2007, 04:00 PM	#9
djQUAN diyAudio Member Join Date: May 2004 Location: manila	just curious, what device needs 240V and will not work at 220V? depending on many factors, your mains voltage could vary a lot.

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