SMPS transformer windings shorting

[sphinx]

I'm attempting to build a high voltage SMPS and after building two transformers, both developed winding shorts in the bifilar secondary after about 30 seconds of operation. I'm using generic magnet wire with tape between each layer. There aren't any layer-to-layer shorts I can find. It's shorts between parallel wires that are my problem. This is a 1KVp-p winding. Is special magnet wire required at this voltage level? Any other ideas?

[Andrew Eckhardt]

Single layer poly insulation is good for several hundred volts. Bifilar winding is okay so long as they are used as parallel conductors (in your case dragging one finish conductor and tying it to the start for a bifilar series winding will most definitely result in failure.. You may not safely develop 1kV between adjacent turns. You will need single layer builds around the toroid with tape between layers sufficient to withstand the potential developed across the entire layer. Lots of care need be taken as you cross the start wires each time you go around the core. If you do this properly you wind up with layers of insulation that divide off the potential between them as it builds. Because of the difficulty in producing tight insulation layers on a toroid other core formats are usually chosen for very high voltage.

[Rembrant]

You need to find better magnet wire. I tried to wind a brush-less motor one time with Radioshack magnet wire. Talk about a nightmare.