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Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
I have two MOT's at my disposal and I am in need of a spot welder, both have between 40 - 50 turns on the primary. I looked up some designs on the internet but I don't like them because each one varies a lot. I was wondering how many turns I should use on the secondary and whether or not I should keep the shunts in. Also, should I use the second MOT as a ballast so I don't run the risk of tripping a breaker?
Oh one other thing: as long as the MOT is grounded via the ac plug, I can hold the metal while I am welding, correct?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I need the ability to weld too! ive got 8 Mots for various purposes, 2 of which i can permanently assign to this project. What type, method, circuit will you use? id like something more than just a "spot" welder, mostly for simple welding of sheet steel.
As you have said, im not that impressed with the crap others have come up with.
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
I think I will do some experimentation. I already have a mig welder so I just need a simple spot welder to weld sheet metal and stuff, but it would be nice to have variable power. There are several different inputs on the primary so I am thinking of doing some experimentation on which produce the highest and lowest amount of current for welding. Thus I will have variable power. Otherwise I might do some research on a tl494 controlled spot welder.
Once I have all that set up and my MOT runs then i will see if it starts drawing excessive current. If it does then I will just use the second MOT to ballast it. I have seen a lot of videos on youtube of MOT arc welders, might be worth a shot.
As for the electrode design I think I will go with this: Because I have plenty of 8awg wire but not much strong copper pipe
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Camp Badger wrote ...
I have two MOT's at my disposal and I am in need of a spot welder, both have between 40 - 50 turns on the primary. I looked up some designs on the internet but I don't like them because each one varies a lot. I was wondering how many turns I should use on the secondary and whether or not I should keep the shunts in. Also, should I use the second MOT as a ballast so I don't run the risk of tripping a breaker?
Oh one other thing: as long as the MOT is grounded via the ac plug, I can hold the metal while I am welding, correct?
You are going about this rather backwards. Instead of asking if your MOT can work as a spot welder, you need to determine what your requirements for the application are. For example, how thick is the steal that you want to spot weld? How many amps would it take to do the job, and how large should the electrodes be? Without knowing all that, you really won't know if you can make a suitable spot welder with your MOT. Based on what I know about spot welders and MOT's, You will probably be only able to make a spot welder that will handle VERY LIGHT gauge metal. If you are planning on spot welding a steal car body (for example) then there's no way that your MOT will be able to produce enough current to weld that thickness of steal.
MOT's have a primary winding that run on 120V AC, and the secondary outputs around 2KV. You would need to completely remove the secondary winding, and replace it with ONE TURN of very heavy gauge copper wire. You also need to make some sort of clamp device that will hold the electrodes on each side of your work piece during the weld, and for some time period after the electric power has been removed. So, not only will you have a challenge electrically, but also mechanically!
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Thanks xray! Yeah I knew from the start that it would be for thin sheet metal, no thicker than say a butter knife. Ah I should have known it would be 1 turn because that would provide the highest amperage. Do you think 8awg would be alright for the secondary? It's the lowest I have. I have the clamp device designed though. I will get started on it tomorrow
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Camp Badger wrote ...
Thanks xray! Yeah I knew from the start that it would be for thin sheet metal, no thicker than say a butter knife. Ah I should have known it would be 1 turn because that would provide the highest amperage. Do you think 8awg would be alright for the secondary? It's the lowest I have. I have the clamp device designed though. I will get started on it tomorrow
I really couldn't tell you if 8 awg wire would work. It might be too heavy to wind around the core of your MOT. The number of turns on the secondary will determine the open circuit voltage, and the thickness of the wire will determine the max current that it can source. And of course the primary winding also is a big factor in the overall power that the transformer can provide to the welded joint. If you want to weld metal that may be dirty, or if it has a coating of rust or corrosion, you should of course clean all surfaces in order to provide as low weld resistance as possible, but you may need to go with more than one turn on the secondary for more voltage to get the weld started. So, you might need to experiment with different secondary turns. If you find that you need to use a lot of pressure on the welder electrodes in order to get the weld to start heating, then you should add a turn or two and try again. Wityh a little more voltage, you will find that your welds will start easier. But if the voltage is too high, you may get too much sparking and splattering.
You can make a simple resistance spot welder with an old soldering gun. They usually have between one and five secondary turns, depending on make and model. Just remove the usual soldering tip, and mechanically fasten your resistance welding electrodes to the prongs. You should be able to spot weld light gauge sheet steal or stainless steal with it!
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Well I built the spot welder in a day and it turned out quite well! Removing the secondary was a real pain in the ass but after it was out I found that 2 turns on the secondary was optimum. I used 8awg and it heats up a lot! If you have a lower gauge then use that instead. I used copper grounding wire for the electrodes.
Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Camp Badger wrote ...
Well I built the spot welder in a day and it turned out quite well! Removing the secondary was a real pain in the ass but after it was out I found that 2 turns on the secondary was optimum. I used 8awg and it heats up a lot! If you have a lower gauge then use that instead. I used copper grounding wire for the electrodes.
Here it is:
AWESOME! Good job!
Could you show us an example or two of your spot welds?
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Thanks you! I will tomorrow after I find some steel, I tried some miscellaneous sheet metal in my garage earlier but it was aluminum so the welds wouldn't hold. I am also planning to install a couple "helping hands" to hold smaller sized metal while it is being welded.
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