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September 06, 2011


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George Storm

Agreed - but the message needs to be "understand and/or check the full system before committing.
The overdrive can of course be a lot worse than this if the transformer saturates because it is not sufficiently derated to handle this condition - and this used to be relatively common with US (designed-for-60Hz) equipment that was imported into Europe.
On the other hand, if the equipment also includes a capacitor to correct power factor, the peak will be limited only by the drive impedance and the series resistance of the capacitor; it will however be of relatively short duration.
Things can become even more interesting if the transformer is driving a capacitor-smoothed rectifier...

Hans Hammarquist

This explains why, sometimes, when you switch on a toroid transformer (like a VARIAC) it "blows" the fuse. The DC component will saturate the core with excess current as result.

John Dunn

Hello, Hans.

Your point is very well taken. I had forgotten that toroidal transformers are especially prone to this problem.

Thank you for the reminder!

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