Electronics > Projects, Designs, and Technical Stuff
Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]
Refrigerator:
--- Quote from: strawberry on June 27, 2019, 07:41:29 pm ---E65 CF297 2 sets in paralel ( dont know if they are good cores)
--- End quote ---
Well, according to the links below, i think one core should be enough.
http://www.cosmoferrites.com/Downloads/Product/CFR%20Cross%20Reference%20Chart%202011.pdf
https://www.tdk-electronics.tdk.com/inf/80/db/fer/e_65_32_27.pdf
strawberry:
fan 120x120mm 24V 11.3W 3.7m^3/min
air speed approx 5m/s
SK442-100 0.22K/W @5m/s
5kW HB inverter
igbt 0.6K/W
AlO wafer ~0.3K/W
(0.6+0.3)/2+0.22=0.67K/W
IGBT loss 0.66mJ @400V 20A
IGBT 1.6V 32W@20A
IGBT 43W@65kHz
43*2+32=118W
temperature of silicon at room temperature
118*0.67+25=104C
Diode 0.94V@60A trr25ns
Diode 0.9K/W
Rectifier contains 6pcs in total
Rectifier 200A
Rectifier loss 200*0.94=188W
SK442-100 0.22K/W @5m/s
0.9/6+0.22=0.37K/W
temperature of silicon at room temperature
188*0.37+25=94.5C
Refrigerator:
I've got my drive circuitry nearly finished now, it's a mega-bodge on some proto-board but it does work very well.
One problem that i've come into is frequency instability, seems that even small changes in RT make massive difference in operating frequency.
Using a 2n2 CT i get 12 kHz with a 5k1 resistor, 100kHz with a 2k2 resistor and about 50kHz with a 4k7 resistor, i might put a 10 turn trimmer in place of RT to set the frequency more accurately.
So far the gate drive transformer was the fiddliest part to make, finding the right core took longer than i'm willing to admit.
In the end i settled for a core from a common mode choke from the same ATX PSU.
I made it a 1:1 transformer with the same construction as in an ATX PSU, bifilar wound secondary sandwiched between two primaries, 10 turns each.
Gate drive signals look super nice, i used the signal on one of the GDT drive transistor bases as a reference to check if my gate drives were correct.
xavier60:
Does the 5k1 resistor actually measure 5k1?. It seems to be the odd one out.
Refrigerator:
--- Quote from: xavier60 on June 30, 2019, 10:10:47 pm ---Does the 5k1 resistor actually measure 5k1?. It seems to be the odd one out.
--- End quote ---
I've already tossed it in the bin so i can't measure it, but i replaced RT with a 2k 20 turn trimmer and a 3k3 in series and the lowest frequency i can go to is 55kHz, so the 5k1 resistor might not have been 5k1 afterall.
Checked all of the gates of my IGBTs to make sure they're all being driven properly and everything seems fine at 55kHz.
The inverter part is basically finished now, i'll just have to put it all in a box tomorrow.
Next will be the wire feed and speed. I wanted to make a closed loop wire feed mechanism to keep the speed constant but i think i'll do it the easy way with a buck converter.
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