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:
I think the part around the power transformer, primary switches and secondary rectifiers would be more relevant ;)
In particular, secondary diode voltage is something you should know, not guess. What's the turn ratio? How is it rectified?

Refrigerator:

--- Quote from: magic on July 24, 2019, 10:02:02 pm ---I think the part around the power transformer, primary switches and secondary rectifiers would be more relevant ;)
In particular, secondary diode voltage is something you should know, not guess. What's the turn ratio? How is it rectified?

--- End quote ---

I don't quite remember the transformer parameters but they're here in this thread somewhere along with all the other details.
Secondary is configured in a half bridge (center tap ground), primary in a push pull.
Mains is rectified into a capacitor bank with two series capacitors, where the transformer goes in the center, everything is very similar to an ATX PSU.

Refrigerator:
Whew, spent some time surfing through aliexpress, reading all the reviews and found a few gems.


The image is from the reviews and it's quite hilarious, as there's an SMD device stuck into a TO-247 package.

magic:

--- Quote from: Refrigerator on June 22, 2019, 08:50:39 pm ---Open circuit voltage doesn't matter because PWM.
--- End quote ---
:scared:


--- Quote from: Refrigerator on June 22, 2019, 08:50:39 pm ---Also because of the way SMPS PSU works you have to divide your 230VAC peak voltage by 2.
A 10:8 ratio would mean about 17% duty cycle at idle to get 22V.
230*1.41 = 324V(peak)
324*8/10 = 259V
259/2 = 130V
22/130 = 17% duty cycle.

--- End quote ---
Wait, so is the primary 2×10T and the secondary 8T in total, i.e. 2×4T?

Because if not and it actually is 2×10T and 2×8T (or center-tapped 10T and 8T in total) then you got the math wrong. You apply primary voltage to only one 10T winding at a time, but both 8T secondaries react, producing a combined 1.6×Vin across the secondary rectifier.

Is this the circuit you use?

xavier60:
It is the typical half bridge PC PSU topology,

The transformer turns ratio is best calculated from the primary turns divided by the turns of one of the secondaries.

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