Electronics > Projects, Designs, and Technical Stuff
Homemade IGBT MIG welder with ATX PSU parts. [blown yet again][blown count: 5]
T3sl4co1l:
Some voltage and current monitoring sensors, and protection latches say, might be in order, yet?
Tim
Refrigerator:
--- Quote from: patrick1 on July 24, 2019, 02:40:04 pm ---the idea might corrupt your plan abit, - but away... how about a RC LIPO or LION Pack in paralell with the output.... super caps might be ok too.....
btw i love your ambition ... but its verging on insanity... a home made reliable transformerless? welder.
--- i want too say too, the best arc welding experience i have ever had, is with car batteries, - 24V... it so smooth like butter. so nice.
--- End quote ---
There's no insanity here just a lot of learning (through even more failing).
Also i'd rather not use batteries for welding, good batteries are expensive and bad batteries wouldn't work.
Anyways, i took the diode bridge apart only to find out that just one of the diodes had failed.
One of the diodes in the double diode shorted out throwing the magnetic field in my transformer out of balance and into saturation and blew the MOSFETs right out.
I did some calculations and assuming i get 4V out with 12V in i get a ratio of 1:3, this means that with 340V (rectified 230V) i would see around 113V.
Since it's a half bridge the diodes would see at least double making it 226V that's not including any current spikes so i should take 250V as my bare minimum.
Also digikey came in handy with their filters, with them i can find actual part numbers rather than write "80A diode switching" in the aliexpress search ::)
Ps: cracked the failed diode apart to see what's inside. There are two silicon dies, each 2.5x2.5mm ( 2x6.25mm2 in total) both with two bond wires each.
Two bond wires should be ok at 40 amps, the silicon die has a current density of 6.4A/mm2, in comparison the TO-247AC (150EBU04) diodes were 4.16A/mm2.
Refrigerator:
--- Quote from: T3sl4co1l on July 24, 2019, 03:53:08 pm ---Some voltage and current monitoring sensors, and protection latches say, might be in order, yet?
Tim
--- End quote ---
I had a current sense transformer with current limiting circuit ready but forgot to put the CST onto the power transformer primary wire. :-[
patrick1:
depending on how many transistors you have too burn ;-D.... i would suggest trying to put a motor start capacitor across the transformer primary ... something between 1-10uF. ...
its really hard too protect transistors from this kind of abuse, and im pretty sure a simple diode wont do the job, even a super fast one, - i have never been satisfied with ultra fast dioes for snubbing, - its plain too see on the scope, they only work 80-90% of what you want them too do... especially if you have a fast offtime.
and ferrite inductors are your friend. like the little torroids you have before mains SMP circuits... i would put them everywhere, even one or two turns of your power wires, before and after the transformer, and after the ESR caps, before the arc. stick them everywhere ;-D. - it has got many of my ambitious projects back on track several times...
xavier60:
A schematic would make it possible to follow what is being done.
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