Instructables

Build a Microwave Transformer Homemade Stick/Arc Welder

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Step 11: Dimmer Control and Welding Thin Wall Tubing

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The welder was too hot for thin-walled tubing frames, I kept melting holes even with the 1/16" 6013 rods. So I plugged the welder into a variac dimmer and turned the power down about 30%.
That gave me very fine control over power. Marc Lander and I did some very nice welds as seen here. After a few we got good enough to do the same welds with 3/32" 6013 rods and no dimmer and not burn holes.
More tricks - I used my left hand to feed a piece of mig welding wire into the weld to add more metal in and soak up the heat. Here's Marc doing that. Any wire is fine for this, coathangers are traditional for muffler work. Sand off the paint first if you don't like fumes.
Stopping to eat lunch helped a lot also. Your welds won't be good when you're shaky and tired.

I got my variac for free, don't buy one for this, they cost as much as a welder.
A solid-state dimmer that's rated for inductive loads does the same thing and costs a lot less.

If you're feeling particularly fancy, you can add in your own scr-based switching circuitry to vary the power, like this guy did.
 
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ddc10114 years ago
How do you tell if a dimmer is solid state and rated for inductive loads. I have checked the website of leviton which is a manufacturer of dimmers sold at home depot as well as the packages and cannot find any references. Thanks
TimAnderson (author)  ddc10114 years ago
This $20 harbor freight "router speed control" is the best deal I know of for a dimmer that works with inductive loads. I bought one to use with the welder, but I haven't tried it yet.
Pagano's hardware here on Alameda has lots of dimmers, but the ones that do inductive loads are $40 or so. The packages there say whether they are intended for inductive loads or not.
Used this speed control. Tested with a 34.4VAC on full. It does vary the voltage readings under adjustment, so I would say it works. Haven't welded with it yet however.
applegeek3 years ago
I think it would be cool if stasterisk added a page on here about how to add taps and switches on the transformer to vary the voltage without buying a special, and probably expensive, dimmer.
ferball3 years ago
Would a standard light dimmer on the 120 v in wire work for power control?
You would probably melt it very quickly. They are rated for only 400 watts and welders use much more than that.
onkelf3 years ago
would it work with a triac regulator ?
Thats the exact variac i have, got it on ebay for 55$ with shipping
Sun Gear5 years ago
where do you find a solid-state dimmer that's rated for inductive loads ?
dman2two26 years ago
Does anyone know what kind of variac dimmer I should use?
Follow the link in step 11 to Dan's Workshop for the details of SCR control. A Variac (a variable autotransformer) bit enough for this job would probably cost as much as a small commercial welder. You'll also find Dan's big welder, built around *eight* microwave transformers.
Leffe5 years ago
i dont want to be rude or something but its not a really nice weld tho :) u went too fast in the middle (becoming a flat weld and creating a track instead of nice weld rings) and ur start and end is too slow wich gives those bumps

but nice work on the microwave oven conversion tho