From: "Patrick Turner" To: "Tim" Subject: Re: Winding a Transformer Date: Monday, April 15, 2002 9:10 PM (snip) I just completed using polyurethane for the large trannies. Before poly-u, both were too noisy. After poly-u, one was dead quiet, the other still noisy, so I repeated the process, twice, and then that one shut right up. After all was done, I cleaned off surplus daggy bits of polyurethane, and cleaned it, and painted the lams with matt black house paint. They look right now. 1. Make a can to accept your tranny, about 10% larger than the tranny. Pop riveted galvalised iron will do, sealed with silicon sealant, to prevent any leaks. 2. After testing the tranny without any impregnation, and after establishing what the noise level is without it, get some thick wire to make a temporary lifting handle threaded thru holes in the yokes clamping the lams, but make sure the wire will not come undone, or break, or apply pressure to terminations, windings. 3. Preheat the tranny to 110C, a drop of water on the top of the core will just boil off when its hot enough. If using a frypan to heat a tranny, you may have to set it at 300F to get the tranny core up to 225F ( 110C ). Losses occur, as heat radiates from the iron your're heating. A high temp thermometer place atop the iron with heatpaste around it will do. I used to use a probe I had with a multimeter, until it went phut for no reason. Droppa water has to now tell me what high tech won't. 4. Then the polurethane is thinned with mineral turps about 10%. 5. Work out about how much polyu you would need, and about half fill the vat. 6. carefully lift the prewarmed tranny from the heater pan, and gently dunk into the vat of waiting poly-u. Hopefully the level of poly won't over flow, but top up the vat so the tranny is submerged. It will bubble away for awhile, as air comes out. Leave the tranny to cool within the vat until only barely warm. This will ensure the air that was inside the tranny will have contracted in volume by about 25% at least, and drawn in the poly-u. 7. When cool, lift the tranny out of the vat, leave to drain onto a shallow dish, for about 10 mins. Pour the drained polu back into the vat, and place a board over the top of the vat. Then place the tranny on the heater pan again, and take the temp up about 100C for 4 hours. 8. Test the tranny with an SS diode rectifier circuit, at 30% more DC than envisaged, Use some seriesed light bulbs for a dummy load, 3 will give you 360 volts, so 3 x 100 watt bulbs makes for 300 watts. 9. The tranny should be dead quiet, unless you bring an ear close, not too close, as a shock through the ear might ruin brain, ear, and your life forever. 10. If the noise is still as bad as when you hadn't applied poly-u, repeat the whole process again. 11. Do all this stuff outside, as risk of fire, smell, toxicity is present. I would get a long lead for the pan heater, and have things set up as far away from the house as possible. Poly-u is not as bad as real commercial varnish, which is far more of a hazard, but really the only thing to use with trannies designed to run at high temps. 12. Waxing can be done in the same way, although you would have to keep the wax hot when preheating the OPT or choke. So perhaps preheating can be done on an electric hot plate on a stove, and the pan heater used for the wax and vatting. The soaking of the tranny in the vat should be done for 2 hrs. So your vat needs to be heated by your pan heater. After that, turn the power off, and let things cool. The tranny can be lifted out an be lifted out when cooled down a bit, but before the wax has set solid around the tranny, so that draining occurs. No need to cook tranny for 4 hours after waxing, once pulled out, and drained, its done. (snip)