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Author: Subject: Spot Welder
elementcollector1
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[*] posted on 2-10-2016 at 13:46
Spot Welder


So, in my quest to assemble a metal reactor for high-temperature distillation, I noticed that I really needed a welder of some sort if I wanted this thing to hold up. With that aim in mind, I began constructing a spot welder. It's heavily based off of Grant Thompson's (aka the King of Random) version from a microwave oven transformer, with two safety switches, a plug, and of course the new secondary and solid copper tubing added to the transformer itself.

http://www.instructables.com/id/How-to-Make-a-Spot-Welder-fo...

However, upon testing my prior iteration, I found that the transformer had somehow managed to spontaneously stop working between yesterday and this morning. Go figure. I've got a new transformer now, but I just want to make absolutely sure I've got the theory right. So, could someone check over my setup and make sure I've got it right, at least from a theoretical standpoint?

-The live (black) wire leading from the plug goes through two safety switches (both rated for high current and voltage), before connecting to one of the primary coil's terminals.

-The neutral (white) wire goes to the other terminal on the primary coil.

-The ground (green) wire connects to the transformer block itself.



[Edited on 10-2-2016 by elementcollector1]




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Oscilllator
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[*] posted on 2-10-2016 at 18:29


Microwave oven transformers are very simple in construction and quite robust, so it is unlikely that one just broke on you. Check that the safety switches aren't burned out and that the insulation isn't melted.
Your wiring sounds correct. It makes no difference which wire (live/neutral) is attached to either end of the primary coil. I assume the primary coil in this case is the one with more turns to it?
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elementcollector1
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[*] posted on 2-10-2016 at 18:46


Quote: Originally posted by Oscilllator  
Microwave oven transformers are very simple in construction and quite robust, so it is unlikely that one just broke on you. Check that the safety switches aren't burned out and that the insulation isn't melted.
Your wiring sounds correct. It makes no difference which wire (live/neutral) is attached to either end of the primary coil. I assume the primary coil in this case is the one with more turns to it?


The primary coil is the one with less turns on it... I think. Either that, or I've made a horrible mistake with which coil I decided to dremel into oblivion.

I checked with the multimeter, all the switches work perfectly. The transformer I used previously may not have been a MOT, as it had four output wires at each coil. No idea what that was about, but I had figured out which wires weren't connected to each other and assumed those were the 'terminals'.

Well, if nobody else steps in saying "Halt! You've forgotten such-and-such!" then I'm going to go ahead and wire this thing up again. Hopefully this time I'll also remember to make it look safe, as the staff at think[box] were none too happy to see my strange contraption plugged in.




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[*] posted on 2-10-2016 at 19:04


When looking at an unmodified MOT, the primary will have fewer turns of relatively thick wire while the secondary will have more turns of relatively thinner diameter wire. This is contrary to what you'll typically find in other transformer because the MOT is a step up transformer.

The winding that must be hacked away is the more turns/thinner wire one (the secondary). Also, if you're using copper tube with no insulation, you're probably shorting out the secondary. Buy a few feet of 6 or 8 gauge THHN wire from your nearest big box store and experiment with # of turns you need for the secondary. As a very rough guide, you can expect around 1V/turn (open circuit) but that will drop under load.




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elementcollector1
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[*] posted on 3-10-2016 at 15:54


Quote: Originally posted by m1tanker78  
When looking at an unmodified MOT, the primary will have fewer turns of relatively thick wire while the secondary will have more turns of relatively thinner diameter wire. This is contrary to what you'll typically find in other transformer because the MOT is a step up transformer.

The winding that must be hacked away is the more turns/thinner wire one (the secondary). Also, if you're using copper tube with no insulation, you're probably shorting out the secondary. Buy a few feet of 6 or 8 gauge THHN wire from your nearest big box store and experiment with # of turns you need for the secondary. As a very rough guide, you can expect around 1V/turn (open circuit) but that will drop under load.


Oh, thank goodness. That was indeed the one I completely destroyed.
Don't worry, the secondary's insulated. In fact, I wish it was insulated just a little less, because it's rather hard to form into the transformer coil. Oh well.

Schoolwork's picking up again, so I may have to slow down on this project until the weekend. Hopefully some pictures will be posted soon!




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[*] posted on 6-10-2016 at 11:12


It works! Just welded together two washers. It also tripped the circuit breaker every time I used it, but that's an easy fix.

Now let's see how well it works on steel pipes...




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[*] posted on 6-10-2016 at 18:47


BTW - if you want to try copper tubing as a super-heavy conductor, slip it into polyethylene tubing for an insulator.



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[*] posted on 6-10-2016 at 21:11


Don't weld titanium for more than a moment, and wear safety glasses :) it will tack quickly in air with no flux, or eject burning metal if left going too long. Good mechanically and electrically. About 1 second max with the MOT core and new 1.5 turn secondary. Used large braided copper wire; Red, white, black +ground main box supply line for homes. Just strip the three shielded wires (+ bare ground) and twist all four together on each end for a decent equivelant single braided copper cable.

At least that was my experience. also note it was poor for tacking 5 cent nickels together even with borax flux(around edges of overlap, not between) . Though never tried with zinc chloride. They were weak mechanically, never got a decent electrode made as they kept separating.

I stopped experimenting when it became apparent good pressure helps alot. Couldnt allocate time to make a suitable lever press. Was hoping to make something akin to a hand press bottle capper ( think rootbeer). It was fun though, and I have a nice fiberglass rod ~1" dia. been saving for lever arm... One of these days




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[*] posted on 7-10-2016 at 03:44
elementcollector1


" It also tripped the circuit breaker every time I used it, but that's an easy fix."

when you modify a MOT

if you knock out the magnetic shunts, current is limited only by resistances,
so it is easy to pop a breaker.

if you leave the shunts in, then there is automatic current limiting,
the breaker pops less often.




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[*] posted on 7-10-2016 at 09:12


Is the shunt a part of the MOT itself?



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[*] posted on 7-10-2016 at 09:15


arc-welder-triac-controler.jpg - 33kB



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