![Burned Section](https://www.experimental-engineering.co.uk/wp-content/uploads/2019/12/IMG_20191209_124228-300x225.jpg)
Well, this is what happens when a Variac rated at 3A is subjected to 15A for a while – a complete burnout. The smell associated with this failure was formidable, it’s a shame I can’t convey odour through photos! Above is the burned section of the winding (it was set for around 115v output from our 240v mains).
![Top Cover Removed](https://www.experimental-engineering.co.uk/wp-content/uploads/2019/12/IMG_20191209_124231-300x225.jpg)
At first the rotor was stuck in position, but a bit of force allowed some movement. The armature holding the brush has melted at the rivets, and the copper tail from the brush is severely heat-discoloured. This got HOT! When brought to me just after failure, it was near impossible to hold onto the outer casing!
![Smoke Residue](https://www.experimental-engineering.co.uk/wp-content/uploads/2019/12/IMG_20191209_124344-300x225.jpg)
Underneath the control knob, there’s white ash, which has evolved from the insulation burning off the windings.
![Shorted Turns](https://www.experimental-engineering.co.uk/wp-content/uploads/2019/12/IMG_20191209_124347-300x225.jpg)
A closer look at the point where the brush was set shows the pair of windings have pretty much fused. The worst of the heating occurred here it seems.
![Windings](https://www.experimental-engineering.co.uk/wp-content/uploads/2019/12/IMG_20191209_132750-300x225.jpg)
The heating has extended down the windings and the insulation has melted all around the top & base of the toroid core. Unfortunately it’s the end of the line for this particular transformer, and it now rests in the Black Museum of Electrical Death.