Hey, just something I was wondering about transformers.
We know that the transformer has two coils, the primary and the secondary which are not interconnected so the transmission of power comes from the rapidly changing magnetic field right...... well lets suppose there is no load at the output of the transformer and you have the normal 127V AC @ 60Hz connected to input, since the coil is 'electrically common', won't this be a geniune short circuit? causing overheat?

 

Nope. Current in the coil creates a magnetic field. As the field builds, it takes more and more work to keep the current changing, a bit like stretching a spring. The build-up of "back EMF" keeps transformer primaries from becoming a short when unloaded.

Here is a link to our Ebook section about transformers - http://www.allaboutcircuits.com/vol_2/chpt_9/1.html.

 

What happens if I plugged one of those wrongly and it burnt out...smoke went out of it, just a little, is it safe to try to use it again, just wondering cuz they are money suckers....does smoke mean definite short circuit? I know, hello...common sense where are you...

I just want some technical information on it..

 

Smoke usually means that the insulation is questionable. Not safe to use again.

 

Smoke does indeed come from the insulation. It is possible, but not advisable, to continue using a "smoked" component. I once had a DeWalt 18V drill motor which leaked thick yellow smoke. I still got 8 or 9 half-inch dia holes through 2x stock out of it before it stopped altogether. Damaged insulation fails much more quickly than undamaged insulation. I knew I was safe enough at 18V with lots of surrounding plastic. I never would try such a thing at 120V or 240V.