spot welder made from a microwave transformer

[lilshawn]

I kind of crapped my idea on another thread with my project...

So, thought i'd post some pictures in a new thread. I'll be building another one (and documenting the other steps) once I source another microwave, but in the mean time. I'll post up my current standing.

I have started building a spot welder. There comes a time when you have a need for something like this, and it's not worth spending +200 bucks to buy one. It's actually really easy to do, and the most dangerous part is where the 110 AC goes in, the output is low voltage so it's safe...just don't touch it with your metal ring or watch. I'll be covering this portion, so there won't be any accidents with it.

It is really easy to build. The old microwave i got the transformer from was free. the wire and whatnot I already had. Basically an hours time, a hacksaw, a chisel, and a punch, and a chunk of heavy wire was all it took.

I don't have any pics of the disassembly, but i unscrewed the cabinet and took the transformer out. I cut the high voltage coil off the transformer and wound my own wire on there.



i managed to get 2 loops through the transformer. it was pretty tight. I used about 2 1/2 feet of heavy 2 gauge 600 volt grounding wire and some copper lugs and bolts. Copper is IMPERATIVE to use. It has the best conductivity of all the metals next to silver. the reason spot welding works is because steel is only about 10-15% as conductive as copper. therefore, the steel heats up due to resistance. if i had used aluminum lugs or steel bolts, they would heat up and burn off.

after plugging it in i decided to test the voltage output (meager 2.2 volts AC) but also, about how many amps this thing was putting out. after a few fuses (the biggest of which was an 80 amp fuse) and couple of melted bolts and framing nails later, I pulled out the clamp meter.

The meter i have is a Fluke 87 mark III and a 80i-600A AC Current Clamp. It's rated to acurately measure up to 600 amps AC continuously (2000 for short periods of time) it's a 1000:1 ratio transformer...meaning if i place my 87 meter on the milliamp scale, the reading in milliamperes is what the clamp is reading in AMPS.

So, I did what any good technician would do, I dead shorted the lugs with a pair of vice grips and powered up the transformer...



That's 1360 amps. good thing this clamp meter can take up to 2000.

the next step is to make a wooden set of arms to hold the wires in place with a box to hold the transformer and switches.

[drventure]

Very cool.

You've got my vote for "Most dangerous thing in the arcade" 

 

[DaOld Man]

I like this, I dont think Ive seen it done before. Please keep us updated, im about ready for a new microwave anyway LOL.

[kahlid74]

You have a welders mask and full protective electrical gear right?  That would scare me greatly working with it.

[Nephasth]

Clean up that workbench!

Looking forward to the results!

[lilshawn]

it's really not a big deal. you are making a weld using the materials you are attaching together. the tiny spot between the electrodes heats up red hot. the pressure you apply squishes the red hot metal together forming the weld.

The reason you get arc with other forms of welding is because you use high voltage. because this is so low voltage (2.2 volts AC) the voltage doesn't have enough "omph" to jump a gap. there is no arc (or next to none) it's perfectly safe to use. In fact, it's safe enough that if you accidentally touched both ends of the output, no harm would come to you. there isn't enough "omph" to push through the great resistance that is the human body.

SHOCK HAZARD: As defined in American National Standard, C39.5, Safety Requirements for Electrical & Electronic Measuring & Controlling Instrumentation: A shock hazard shall be considered to exist at any part involving a potential in excess of 30 volts RMS (sine wave) or 42.4 volts DC or peak and where a leakage current from that part to ground exceeds 0.5 milliampere, when measured with an appropriate measuring instrument defined in Section 11.6.1 of ANSI C39.5.

because this project's output is under 30 volts RMS AC, the output is not considered a shock hazard.

If the skin is wet or damaged, the resistance through the body will be greatly reduced, and a much lower voltage may be lethal.

so really, it's POWER not either amperage or voltage that can kill you. it depends highly on excessive amounts of both to get to the point of lethality. It also depends of the path of conductivity. a lethal power isn't likely to be lethal if it's conducted only through your hand. but would be if it went from one hand to the other. (across the heart) or through your head.

Any electrical device is capable of killing you under the right (wrong?) circumstances, and as always, precautions should be taken when operating them. This goes especially with items that are home made, or retail items that are modified.

You can't see in the photos I posted, but the core of the transformer is  grounded and the input is fused. Should the insulation on the transformer primary short out, the ground and fuse will help prevent serious injury or death. The output, because of it's ridiculously high output current, is un-fused. Failure of the secondary would likely be plainly obvious. The likelihood of coming into contact with 110v AC from the input on the output side of the transformer is highly unlikely.

[yaksplat]

This scares the crap out of me.  I love it.

[lilshawn]

Clean up that workbench!

Looking forward to the results!

yeah no doubt 

it's even worse now.    i'm currently procrastinating cleaning it as I type this.

[yaksplat]

I'm guessing that won't do aluminum welding 

[lilshawn]

I'm guessing that won't do aluminum welding 

I haven't tried, but  the resistivity of aluminium is 65% higher than that of copper. (much much higher than steel) It could in theory work... but you'd probably need in the area of 15 or 20,000 amps to do it. you'd need a bigger transformer though.

[selfie]

This scares the crap out of me.  I love it.

My thoughts exactly

[Dervacumen]

This is gonna go over real well with my wife when I ask her if she knows anyone with an extra microwave.

[lilshawn]

as long as you agree to immediately dispose of the remaining parts as soon as it's disassembled, she shouldn't  have a problem.

it's when you take the microwave apart, and the hulk is sitting in the middle of the living room for 4 days.... 

[ChadTower]

4 days?  That thing would be on my front porch for 4 months.