It's my fault - but...

[Dave Plowman (News)]

Bought a 1.6VA 22v toroidal transformer from Digikey some time back. Part of an order where I made it up to free postage.

It's labelled Talema - but unlike UK ones has no diagram or other information like spec etc printed on it. So downloaded the PDF from the Digikey site - but was in a bit of a rush when looking at it. And the diagram I saw suggested the primary would be the usual - blue and brown for 230 volt with the other ends of the 115v windings just linked. But I looked at the wrong diagram. Blue and brown was actually one of the secondary windings...

[spuorgelgoog]

That would have been a bit tingly on the output!

Owain

[Brian Gaff]

BigBang then?

Brian

[Andrew Gabriel]

You get quite an impressive bang when you connect a switched mode PSU to the mains, which turns out to be 120V-only input...

[Matty F]

I'm told that you get an impressive bang if you leave the secondary open-circuit on a 5000 to 1 toroidal current transformer. I never dared try it.

[Andrew Gabriel]

It generates a high voltage on the secondary, which comes as a big surprise to people who handle them but don't understand the principles, as the secondary voltage in proper use is extremely low, and safe to touch. I imagine the secondary winding insulation would break down eventually, and then it would get very hot if a single turn shorted out. If it melted through the insulation of the main pass-through conductor, you could get a big bang.

If there's no load for a current transformer (such as a moving iron ammeter), then the secondary output should be shorted out to prevent damage to the transformer and avoid the unexpected high voltage on the terminals.

[Chris J Dixon]

Somewhat different, I was once working on a prototype ac voltage detection relay, with a laminated core. It buzzed unacceptably, so someone suggested a shaded pole. I didn't have a suitable piece of copper to hand, so brazed a short length into a loop, and inserted it into a slot cut into the laminations. I have to admit to being a little skeptical about the change of success.

Confounding my doubts, it worked a treat, but after a very short time, the current flowing in the copper melted the brazing material.

The production version had a section cut off a suitable copper tube, and is still running round the railways.

Chris