Electronics > Projects, Designs, and Technical Stuff

Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]

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magic:
OK, thanks for the correction. I got to "primary is a push-pull" and stopped reading there :palm:

If the primary is 10T and the secondaries are 8T each than it's 330/2·0.8=130V indeed. So the diodes are killed by transients or their dubious provenance :P

xavier60:

--- Quote from: magic on July 25, 2019, 07:58:26 am ---OK, thanks for the correction. I got to "primary is a push-pull" and stopped reading there :palm:

If the primary is 10T and the secondaries are 8T each than it's 330/2·0.8=130V indeed. So the diodes are killed by transients or their dubious provenance :P

--- End quote ---
And undamped ringing would come close to doubling that.

Refrigerator:

--- Quote from: xavier60 on July 25, 2019, 08:03:10 am ---
--- Quote from: magic on July 25, 2019, 07:58:26 am ---OK, thanks for the correction. I got to "primary is a push-pull" and stopped reading there :palm:

If the primary is 10T and the secondaries are 8T each than it's 330/2·0.8=130V indeed. So the diodes are killed by transients or their dubious provenance :P

--- End quote ---
And undamped ringing would come close to doubling that.

--- End quote ---

The snubbers on the diodes are another thing i forgot  :palm:
I had them on the crap 150EBU04 diodes.  :-BROKE

Refrigerator:
Took the MOSFETs out and they're both blown.
Cracked one open to check the die size and it's 5.5x5.5 = 30.25mm2, 0.5A/mm2.

magic:
So what actually is the point of having ±65V open circuit secondary voltage for 22V output? Do you expect 33% efficiency under actual load? :-//

I don't know what can be realistically expected from such converter, but 33% seems rather extreme. SMPS work better if transformer ratio is close to ideal and duty cycle close to 50%. Isn't it be better to cut the secondary in half and parallel the two parts for 32V output at lower impedance, still giving margin for 66% efficiency?

PWM surely is magic, but you pay for it right here.

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