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  1. #1
    Join Date
    Nov 2017
    Indiana, USA

    Default Hello from Indianapolis, IN, USA

    Hi Everyone,

    I put quite a bit of information in my profile that will give you my background and interests. One I left out is welding, so I guess I can talk a little about that. I purchased a Harbor Freight DC MIG Welder a couple of years ago, but haven't had the time to do much with it, or master how to use it effectively. I wished I would have just bought a regular stick welder because I have some experience using those. So I went back to HF (Cheap Chinese Tool Retailer in USA) and bought a small AC (90A) welder for $90. I'm in the process of following a few YouTube videos that detail how to convert it into a serviceable DC welder by using a large SCR and bridge rectifier, a large choke, and capacitor bank, and already have some parts ordered on eBay.

    I do contract engineering work from home, and I'm working on a new product development for a company on the east coast of the US. One of the design elements I'm using is a P-channel MOSFET as a replacement for the reverse polarity diode on the +24Vdc supply input to make it dummy proof.

    It occurred to me that I could use the same concept on the welder project. And instead of using a standard bridge rectifier, I could use the "Use a MOSFET as an extremely efficient reverse polarity diode" trick instead of the bipolar PN junction diodes used in most rectifier bridges. You can look this up on Google, but basically you use P-channel MOSFETs with low RDS values as substitutes for silicon diodes, which includes bridge rectifiers. At 90Amps 220VAC RMS, you eliminate about 90A x ~1v(per diode) x 4 = 360 Watts of waste heat + heatsink + fan. Since I design PCBs as part of my job, I will probably do that for this project and then have some green boards made to use for other projects, like the DC motor conversion on my Enco mill, and maybe sell some on eBay.

    Let me know if there is any interest down there.


  2. #2
    Join Date
    Jan 2004
    Mackay North Qld


    Hi Tim,
    Welcome to the Metalwork Forums,

    You will fit in here just fine. Our members have a wide range of interests as you will see as you navigate around the sub forums.

    There are many experienced and helpful people in their particular spheres of interest.

    Look out for a pm with some links of how to operate within the Forums.

    Welcome again


  3. #3
    Join Date
    May 2013
    Rockhampton, QLD


    Welcome to the forum Tim.

  4. #4
    Join Date
    May 2011
    Murray Bridge S Aust.


    Welcome to a TOP Forum Tim. Your project sounds very interesting, not that I know anything about elctronics, but I do know about welders.
    To grow old is mandatory, growing up is optional.

  5. #5
    Join Date
    Aug 2011


    Welcomd to the forum Tim!

    Wrt your DC welder conversion, i would be very interested in your ideas. I posted a thread only a few weeks ago about doing a similar thing with an old AC welder i have although had not considered using MOSFETs.



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