I need a choke between 3 and 5 H, 400 mA, couple hundred volts ripple. I can't afford to pay $70 for a Hammond 193p, so I want to wind my own. My question is, what size core would be appropriate? Do I need something the size of a MOT, or will something smaller work? Heat is less of an issue since the PSU case will have a fan, so I'm using 23 AWG.
About 2-1/4" square centre peg (1.5" x 1.5") will do. Here's an article if you're interested:
http://geek.scorpiorising.ca/windingchokes.html
http://geek.scorpiorising.ca/windingchokes.html
Aha, I've come across that site, but I didn't connect the name to your username before...
In your transformer winding page you say that up to three laminations can be thrown out. I'm rebuilding a large microwave oven transformer as its windings were welded together and it was buzzing too much. It looks like I'll have to throw out four, maybe five laminations (out of 108 layers total) if I'm to be able to fit the original windings on (and rewinding the thousands of turns of the secondary is beyond what I can do); do you think that will be a problem?
In your transformer winding page you say that up to three laminations can be thrown out. I'm rebuilding a large microwave oven transformer as its windings were welded together and it was buzzing too much. It looks like I'll have to throw out four, maybe five laminations (out of 108 layers total) if I'm to be able to fit the original windings on (and rewinding the thousands of turns of the secondary is beyond what I can do); do you think that will be a problem?
I don't understand why the laminations were welded together, and why they were not interleaved (separate E and I blocks). It doesn't seem to save any construction cost.
I'm using a cap about 135 uF for PFC; I hope it's not too far off as these large ripple AC caps are not cheap. I've seen people use from 20 to 200 uF for MOTs.
I'm using a cap about 135 uF for PFC; I hope it's not too far off as these large ripple AC caps are not cheap. I've seen people use from 20 to 200 uF for MOTs.
Seems easier to me. The air gap between the E and I segments also softens saturation, which is probably just 5% away on those overrated transformers. (Take a bare MOT, monitor primary current with a scope and shunt resistor, then increase primary voltage to maybe 130-140V. Watch the peaks fly by! Now try the same without the air gap (interleaved)...)
Tim
Tim
Interleaved E-I will have a much higher inductance because of the short magnetic path.
Welding of the tranny is faster and creates an energy-limiting "Class-2" transformer. This is needed because microwave trannies are so temporarily overloaded, that your bacon wouldn't be the only thing burning in 5 minutes
Welding of the tranny is faster and creates an energy-limiting "Class-2" transformer. This is needed because microwave trannies are so temporarily overloaded, that your bacon wouldn't be the only thing burning in 5 minutes
Sorry Geek, hope I didn't release too much of our secret evil plans... 
I found an old transformer and ripped out the core. The center E bar is 5x2.9 cm, or just about the area you suggested. I hope 23 AWG magnet wire will be fine for a half amp, as it's all I have. My trouble is figuring out how much of a gap to leave between the E and I sections. I'll either have the choke on the ground side, or on the HV side (couple hundred volts ripple on about 2.7 kV DC). Will about 0.5 mm be a good guesstimate?
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