Gallery, Projects and General > The Design Shop
Microwave owen transformer spot welder?
PekkaNF:
Ten years ago I read about MOT spot welders and confiscated one MOT from korean owen that was scraped.
Fast forward 10 years: I found that MOT when I was cleaning up garage and desided to find out if it works.
Has any of you build MOT spot welder? How much power you get out of it and what V/A?
I removed secondary and noticed that there are shunts between primary/secondary. Are these shuts good to have?
I put one round of solid copper wire on secondary and got about 1,6 VAC (per round, no load current was 3A on primary). One, two or three sounds of as thick cable I can cram in?
There are estimates on transformer VA-rating vs. core area. Are those estimates any use here or are they out of whack?
Plan is to check if this transformer is any good for small jobs and lab timer circuitry with it. There is a buzz box type welding machine waiting to be butchered for real attempt.
Pekka
vtsteam:
Wish I could help Pekka, I started to build a spot welder from a big transformer about ten years ago. Pulled out the secondary (which was a pain) and re-wound with a few turns of heavy gage cable, but never actually tried it out. It's sitting in a box upstairs. Harbor Freight offered a sale (half) priced spot welder in the mean time, and I ended up buying that. I still wonder how that first one would have worked out. :zap: :loco:
John Rudd:
Pekka,
The mot you generally find are ok for use as a spot welder.....
Have a read here.....http://www.chatzones.co.uk/discus/messages/7/16416.html
You need around 2-3 turns of thickest wire you can fit giving maximum current....
BillTodd:
I've been playing around with a MW transformer making a bandsaw blade welder ( The butt weld mechanism has to be surprisingly accurate - so far I have made two good welds from several feet of blade :LOL: )
Initially, I tried using a spot welder to power the blade welder, but the spot welder is low voltage (~1.7vac - one turn with a 230v primary) .The blade welder needs two or three turns ( I've been experimenting with more but 2-3 seemed to work best)
For a spot welder you'll need to mount the transformer as close to the jaws as possible to keep the resistance down. The current flow is huge: I measured way over 600A from a small hand-held spot welder.
Use the as much copper you can squeeze into the transformer gap (I'd use multiple strips lacquered or taped to insulate them ).
vtsteam:
If I remember correctly I did use some solid copper sheet in the "construction" -- I think I did a search at the time and found that liquid styrene was a good coil dope type insulator, so I made some by dissolving large quantities of polystyrene foam in a small quantity of acetone. Not a recommendation, just an account of my madness in general. :zap:
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