I have a Sunkko 737G which has always worked fine for me. A few days ago, I turned it on, and it worked fine. I turned it off, and then turned it back on about 15 minutes later -- and the fuse in the back blew immediately as I flipped the on-switch. It appears to use a glass 30A fast-blow 5*20mm fuse. I didn't have any but a coworker gave me a 20A fast-blow ceramic fuse. I tried the 20A fuse, and it seemed to last 2-3 seconds before blowing (I think it took a lot longer to blow than the original 30A fuse). It seems there is a legitimately large in-rush current.
I see a couple scenarios here:
1) There's some legitimate problem with the welder. I opened it but didn't see any obvious scorch tell tale scorch marks (there was someone else on here, RustyCaliper) who had a component blow up right before his fuse blew. But I don't see clear evidence of that.
2) The original fuse blew because the large inrush currents eventually wore the fuse out to the point that it blew. The 20A fuse I replaced it with just wasn't enough because, it legitimately needed a 30A fuse. This seems like a poor design to me (that's very little margin on the fuse, and the inrush current is wearing out the fuse?) and I'm wondering if I want a slow-blow fuse, perhaps with a smaller amperage. Ultimately, the line is on a 15 or 20 amp breaker which obviously takes longer to trip than a fast blow fuse -- making me wonder what the point of a 30A fuse is that protects against extremely high inrush currents, but also false blows after a while.
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