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Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]
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Refrigerator:
Getting quite messy but if everything goes to plan i'll have it running today.
With the DTC cranked all the way up i was able to get 4.4A on the output (that's running on 12V) but i toned it down to limit max duty cycle to about 85% just to be safe.
Also came up with a neat way to connect the welding cable to my diode bridge.
My old LPG injectors have a coil resistance of 4Ω, which is going to draw 3 amps from my 12V supply. My 12V supply can handle up to 23.5 amps so that's not a problem but i'm worried the solenoids on those injectors won't last long with 36W going into them.
Good thing the coils are removable so i can perhaps retrofit a coil from a different solenoid such as a solenoid from a washing machine for example.
Refrigerator:
The maiden voyage is going to be tomorrow but all the tests are now complete.
The way i connected my voltage pot meant that if i disconnected it the voltage would be regulated to 2.5V (my reference voltage).
And that's almost exactly what i got at the output when testing on 12V + 100Ω load (because it would max out at 4V with the pot).
This means that my voltage is properly regulated.
All that is left is to finish is the mains wiring (circuit breaker, cable, plug), then i also need to add a resistor to load the inverter output a little for stability reasons.
After that i'll make a driver thingy for the gas solenoid (probably a small MOSFET on a wire) and the welder will be ready to make some sparks (the good kind, i hope).

tautech:

--- Quote from: Refrigerator on July 05, 2019, 09:48:48 pm ---..................
After that i'll make a driver thingy for the gas solenoid (probably a small MOSFET on a wire) and the welder will be ready to make some sparks (the good kind, i hope).

--- End quote ---
Maybe not, this connection needs improvement IMO:



Decent lugs are not that expensive and I have on occasion used small diameter copper pipe crimped onto the welder lead with the edge of a nut as the anvil and squashed tight in a vise.
Likewise the lug flat is formed in a vise and then drilled to requirements.
Refrigerator:
^ to me it looks fine, all the strands were locked in place, the copper plates were cleaned and the M8 bolt was cranked as far as the aluminum would let me.
Perhaps the washer is a little too small but i have mo worries about this connection.
Refrigerator:
It blew up.  :-BROKE
Well, if failure is the best way of learning then i'm in for a whole lot of knowledge.  :palm:
Basically what happened is everything was fine until i blipped the trigger and it instantly blew three IGBT's, two low side and one high side.
Took the opportunity and cracked one apart to see how big the die was and it came in at about 3.5x3.5mm with two bond wires per leg.
Both low side IGBT's completely blew apart, but the one high side IGBT only had a shorted gate.
I'm thinking perhaps the high side IGBT failed first and stayed on then while the two low side IGBT's were turning on the amount of power they had to dissipate was astronomical and they blew up. (that's what my inner Sherlock says anyways)
Now, why would the high side IGBT fail in the first place? Damn voltage spikes i bet.
I'll be remaking the IGBT board to incorporate more protection against voltage spikes and i'll also have to test the remaining IGBT to see if it's still good.
If it's good then i'll still have two remaining IGBT's and will have only one per side, but that should still be enough.
If not i still have some Toshiba MOSFETs that would get the job done as well.
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