A few weeks ago I was surfing the net and stumbled across the idea of making a spot welder from a microwave oven transformer. The idea sounded fun and so I proceeded to make one. It successfully put a good weld between two 16 ga sheet metal pieces together this evening. I had to hold it on for about 10 seconds for this weld so I think it is probably about the limit for what can be welded. I separately plug in each transformer and so I expect that for lighter gauge metals I will do some combination of holding the push butting down for less time and unplugging one of the transformers.

 

The transformers did not have the exact same windings and so I varied how many wraps I put on them to get the output voltages close together. One transformer had 2 wraps and the other had 3. The final output voltage was 2.32 volts. I also had to switch input spade terminals at one point since the voltages were out of phase and were canceling each other. The nice thing about microwave transformers is that they have "shunts" that limit the current flow and so keep you from blowing your breaker since a spot welder creates what is effectively a "dead short" during normal operation.

 

Not counting a few things I had on hand my total expense was $30. I got the transformers at the scrap yard. People had sold the scrap yard a couple broken microwaves and so I opened up the cases and took out the transformers. They cost me $5 all together. Most of my expense was in the 3/8" round copper bar for the electrode tip and heavy copper wire.

 

This now give me 5 different ways of welding to choose from when working on a project at home. Each has advantages and disadvantages. So depending upon the situation I choose the best one.

• Forge Welding
• Stick Arc Welding
• TIG Arc Welding
• Acetylene/Oxygen gas welding
• Electric Resistance Spot welding

This web site was where I saw two transformers being used. http://home-workshop.com/MOTWelder.htm

I like it!

I saw a guy heating rivets with a spot welder. I would be interested if this spot welder could heat up a 1/4" rivet.

 

brad

It took about 4 seconds to heat up this 1/4" x 3/4" headed rivet.

Nice thanks! I think I may have to build me one of those rivet heaters. I usually save old microwaves to get the magnets from the magnetron but now I have a new use for them.

 

brad

This is very impressive!

 

I tried taking the heating element out of a hair dryer last night and couldn't even put it back together correctly without blowing up that little fan i so desperately wanted to use as my new blower.... :angry:

 

Bravo to you sir!