I have taken a microwave oven transformer and removed the 2nd winding which originally put out 2000 volts. I have rewound the 2nd coil to produce 21 VAC which I then rectify and smooth with 2 large capacitors. I am going to use this transformer to make a variable voltage power supply, but noticed that it gets pretty hot. I have added a large heat sink with multiple cooling fans, and it still climbs in temperature a little more than I like. I decided to check how many amps it was pulling from the mains outlet (120vAC) with no load on the secondary. I was surprised to see that it was pulling just over 10 amps. I know transformers have a no load current on the primary but I did not imagine it would be anywhere near 10 amps. So my questions are... Is this normal for a transformer?
Why is it pulling so many amps with no load?
Is there a way of lowering the no load current without sacrificing useable amperage from the finished power supply?
P.S. I am just a hobbyist who is doing this project mostly to learn things in the process but does plan to use the power supply for simple things around the shop. Please keep in mind when giving very technical answers, that I have no formal education for electronics, so explanations are appreciated.