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

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Refrigerator:

--- Quote from: magic on July 25, 2019, 02:56:27 pm ---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.

--- End quote ---

I can remove a few turns in the transformer but not now, i still want to test the current setup out.

magic:
Not my circus, not my monkeys :P
Higher turn ratio means lower peak secondary voltage, less primary current and even less resistive losses for the same amount of trafo wire.

https://www.tme.eu/en/details/idw100e60fksa1/tht-universal-diodes/infineon-technologies/

Is this good enough? 600V, 100A and 200W continuous at Tc=100°C. Should be hard to destroy unless you forget the snubber again :P
And you are guaranteed it's not a 1N4148 inside and you get a proper datasheet corresponding to the actual silicon in your hands, no guessing, no smoke, just calculate your power lossess and heatskinking and it works.

Refrigerator:
A little update on the whole project.
I've since blown the welder up two more times.  >:D
Each time getting closer to proper operation.
With the new diodes i have (IDW100E60) and new MOSFETS (IRF460) the welder does power up and survives a trigger pull just fine.
No load with the trigger pulled (operational) the inverter draws 50mA from the mains, which i think is not too bad.
But the MOSFETs popped as soon as the welding wire touched the metal scrap i tried to weld.
I then doubled up on the MOSFETs, previously there were one per side, now there are two per side (a total of four) and also removed two turns off the transformer (10 primary, 5.5 secondary).
Did some tests, everything seemed ok-ish, i then separated a few strands of my negative welding wire and shorted them out to the positive to see how well it melts wire.
It lasted about 30 seconds before blowing up yet again, although a lot more spectacularly than before.

So for once i decided to do some actual research and calculations (groundbreaking stuff, i know).
Couldn't find much info on FBT cores, but Bmax on them appears to be in the range of 2000 to 3400 gauss.
I took 1500 as my Bmax to be extra safe and calcuated a primary of 10.7 turns (rounded off to 10, because generous Bmax estimate).
From that i calculated my secondary, which turned out to be around 3 turns.
I'll rewind my transformer in the same way i did before with the primary between two secondaries, but i'll split the secondary wires to make them bifilar.
So my transformer will be wound with the primary between two bifilar secondaries.

magic:
That's progress :-+

What's the switching frequency, duty cycle, dead time, average input current and primary inductance? Here some math needs to be done: checking if idle magnetizing current of the primary is sane, calculating FET Rds(on) losses.

It seems like your topology shouldn't subject FETs to significant overvoltages because of the clamping action of the opposite FET's body diode, but that's only if everything is laid out tightly and the current loop through the FETs and the capacitor bank is short.

BTW, I have no idea what will happen but you could wrap one turn of cable around the transformer, bring the voltage further down with resistor dividers and hook it up to the scope. It might give at least some approximate picture of voltage waveforms at the working windings.

Refrigerator:
Did some estimates and decided to go with 10:2.5 setup on the transformer.
Also the bifilar thing didn't work out because the wire was too tangled to separate.
With only 2.5 turns on the secondaries it was a bit of a challenge to wind, in the end i decided to loosen the twisted strands of my wire to spread them out, this way it would cover most of the surface. Copper sheet would be best for situations like these.
Anyways, i'll assemble the welder tomorrow and will see how well it works this time.

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