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Old 11th May 2012, 02:33 PM   #1
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Default Exceeding transformer's voltage rating

I have a transformer with 0-115-230V on the primary and 0-110-230V on the secondary.

If I feed 230V mains on the secondary's 110-230V taps to get 220-0-220V on the primary, how likely is catastrophic failure?

I imagine a power transformer designed for mains use would be build with a healthy dose of headroom. But I still want to live.

On the same topic, what if I connect 2 identical of the said transformer, both primary wired as usual and both secondary wired in series (and in phase) to get 230-0-230V?

Thanks.
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Old 11th May 2012, 02:51 PM   #2
jcx is offline jcx  United States
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put double the rated V on a pwr xfmr winding (strictly speaking its the V*T product) and it will certainly result in core saturation - huge current draw, best case is fuses blowing, breakers popping

the 2 xfmr option can work, if you need higher rectified DC then diode-capacitor doubler topology may work with single xmfr
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Old 11th May 2012, 03:05 PM   #3
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Thanks.

I am using tube rectifier, so I am trying to avoid bridge (lots of tubes) or voltage doubler (capacitor after rectifier).

If the two transformers trick works that would be great as I already have them.
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Old 11th May 2012, 03:08 PM   #4
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Two transformers will work for your application.
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Old 11th May 2012, 03:13 PM   #5
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Thanks again, glad to know that.
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Old 11th May 2012, 08:20 PM   #6
DF96 is offline DF96  England
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Quote:
Originally Posted by Navyblue
a healthy dose of headroom
On the planet where transformers come from, a healthy dose of headroom is considered to be something like 5-10% not 100%. Some cheaper transformers may even have a negative headroom: unloaded they cannot even cope with rated mains voltage but need the primary resistive drop caused by a secondary load to get them under the saturation limit.
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Old 11th May 2012, 09:08 PM   #7
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Thanks for the info, obviously I haven't been to that planet. Glad that I asked.
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Old 11th May 2012, 09:21 PM   #8
jcx is offline jcx  United States
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that's OK some of aren't planning to visit anywhere vacuum tube rectifiers are held in esteem when SiC Schottkys covering the required I,V ratings exist
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