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Arc Welder from MOT

Discussion in 'Members Lounge' started by Menticol, Dec 18, 2009.

  1. Menticol

    Menticol Active Member

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    Hello!

    I'm making an arc welder from Microwave oven transformers. The procedure is theoretically simple: Replacing the secondary (high voltage) winding with 7 meters (24 foot) of 10 AWG wire, coiled in 20 turns. Apply the procedure on two MOT's, then wire their inputs in parallel and their outputs in series

    [​IMG]

    Picture credits from: Build a Microwave Transformer Homemade Stick/Arc Welder

    My problem is, my 10 AWG wire comes with an very thick PVC isulation, and is impossible to wire it on such small space. The store where I bought it stole all my money, so discarding it is not a good option.

    I had an idea: Replace the old jacked (white) with a new one made of electrical PVC tape, as shown in this example

    IMAGE ATTACHED

    Do you think it's enough for avoiding arcing or shorts?
     

    Attached Files:

    Last edited: Dec 18, 2009
  2. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Actually if you can get a can of cheap enamel spray paint and can hang your wire someplace where it can hang from end to end you can make your own cheap version of enameled wire.
    Your still likely going to get awful welds though! Your going to have a very short weld time before the transformer over heats and it going to have horrible arc characteristics as well.
     
  3. Menticol

    Menticol Active Member

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    Well you are our resident welder, I trust in your advice. Still, some people seem to have improved the concept. This guy added capacitors for power factor correction, another added a choke in series with the transformer output to stabilize the arc:

    This is the cap's guy

    Mega Buzz Box 100 Amp Welder*

    Here is the choke, in the floor of the golf cart
    http://www.instructables.com/files/deriv/F7K/MOKZ/FG9V4FXI/F7KMOKZFG9V4FXI.MEDIUM.jpg

    Look the results he claims... is that feasible with this equipment?
    Portable Homebuilt Electric Generator*

    PS: I suppose that my electrical tape idea is ruled out. It's a shame, I liked it because tape seemed harder to scratch than enamel during rewiring. But when you talk about temperature...
     
    Last edited: Dec 18, 2009
  4. dave

    Dave New Member

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  5. Willbe

    Willbe New Member

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    Last edited by a moderator: Dec 26, 2013
  6. Menticol

    Menticol Active Member

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    Last edited by a moderator: Dec 26, 2013
  7. Hayato

    Hayato Member

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    Why not use the High voltage side as the primary?
     
  8. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Its not that it wont work it more of a problem with getting enough power for long enough periods to be able to do anything practical with it. A portable 100 amp stick welder is nearly useless for any level of welding. I have had a few and they where not all that impressive.

    The problem with the tape is that it has a low melting point and running 100 amps through #10 wire is going to warm it up fast! Your tape will melt out rather quickly and short out your windings.

    A real welder transformer has a variable output adjustment. The rectifying it and then running it through a capacitor and choke will give you a fair DC welder equivalent but with only one range.
    By the time your done with all the finding parts and building it your financially into it further than had you just bought a good used one. I have picked up good used portable stick welders for under $30 a few times.

    If it just to try and build one its a fun project to learn from but if you need to do any real welding that has to serve a purpose your better off with a factory made one.

    Here is the actual factory schematics for the old Lincoln SP-100 series wire feed welders. Basically all you need is a heavy duty 2 KVA or a set of smaller transformers with a 18 - 24 VAC secondary and a heavy choke for the power supply side. It can also be modified to work with other output voltages or functions as well. If you just use the voltage regulation part is fairly easy of build.
    Change the voltage feedback loop to a current feedback and use a higher voltage transformer and it can work as a basic adjustable stick welder power source too. They are based on a nearly identical power control circuit.

    Its just a thought!

    SP-100 Schematics.png
     
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  9. 420God

    420God New Member

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    I dont know if it will work but with a large capasitor and charge circuit like a camera flash you might more uni form welds and lessen the risk of burning out the transformer
     

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