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Thread: Idealarc Roundtop Rectified Problem

  1. #1
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    Idealarc Roundtop Rectified Problem

    I have a 1957 Idealarc. The rectifier was arcing and burnt up a couple of the plates. This old design doesn’t look like anything I can find online. 1) Can I just eliminate the two plates that are burnt up? 2) Or can I move plates that are on the end to where the burnt plates were? 3) Or can I just replace the entire rectifier with the modern diode style.
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  2. #2
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    Re: Idealarc Roundtop Rectified Problem

    Here is the wiring diagram
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    Re: Idealarc Roundtop Rectified Problem

    I would go with new stud diodes. Just be sure you build a heat sink assembly for them. The newer idealarcs all have that sort of arrangement https://weldingweb.com/vbb/showthread.ph...-diode-upgrade
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    Re: Idealarc Roundtop Rectified Problem

    This post gives some pics of what the newer diode assembly looks like: https://weldingweb.com/vbb/showthread.ph...p-Please/page2
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  5. #5
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    Re: Idealarc Roundtop Rectified Problem

    That is a selenium diode assembly, common in old equipment. Only choice is to replace with the newer stud diodes.
    You can use copper or aluminium plates for the heat sink. stud diode of the size needed have about a 3/4 inch threaded stud.
    Come in standard polarity and reverse. Depending on your heat sinks you will use either 2 of each or 4 of the same polarity.
    The idea is to make a full wave bridge diode. with 2 AC connections and DC+ and DC- connection points. look up on line full wave bridge diode.
    Should get several diagrams, pictures and heat sink set ups. also will find 20 amp blocks with 4 terminals.
    Diodes have an anode and a cathode. The anode is the triangle the cathode is the line the triangle points to.
    Some weld diode bridges use two plates, uses two diodes of each polarity, same polarity on each plate. with 3 plates you can use all the same diodes.
    On this site is a thread with good pictures on a idealarc 250 retro fit and upgrade on the diode assembly. search it out.

  6. #6
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    Re: Idealarc Roundtop Rectified Problem

    Tried to get a recommendation for a replacement rectifier from Lincoln but they have no ideas. Said it was too old, 1957. I hate to junk it over this issue but I only paid $100 for it. I'm not going to put a lot of effort into repairing it. You would think that the theory behind the rectifier would be the same for any similar sized machine and there would be one on the shelf for replacement. But that doesn't seem to be the case.

    I just bought another Idealarc round top yesterday. A 1986 model that was clean as a whistle inside. I'll save the other for parts. The fan is worth more than $100. So if anybody needs any Idealarc round top parts, I have some. There are still a lot of good rectifier plates too. Only 2 burnt up.
    Last edited by WFM; 11-23-2019 at 08:26 AM.

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    Re: Idealarc Roundtop Rectified Problem

    I don't think it is hard to repair that round top, really. generic 150 amp diodes (4 total, handles 300 amps). Check the first link I posted, he was in the same boat. you can make the plates/heat sink from any old aluminum plate you have or can get from the scrap yard.
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  8. #8
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    Re: Idealarc Roundtop Rectified Problem

    Quote Originally Posted by Louie1961 View Post
    I don't think it is hard to repair that round top, really. generic 150 amp diodes (4 total, handles 300 amps). Check the first link I posted, he was in the same boat. you can make the plates/heat sink from any old aluminum plate you have or can get from the scrap yard.
    Thanks, I'll look into it. Maybe I can save it.

  9. #9
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    Re: Idealarc Roundtop Rectified Problem

    If you look around you can also find pre-built bridge rectifiers that will work in your welder

    https://www.ebay.com/itm/290-AMP-SIN...HUlQHCz-2JQj2A
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  10. #10
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    Re: Idealarc Roundtop Rectified Problem

    what this guy does is overkill for a welder, but you can see he is slinging together 4 $40 diodes.
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  11. #11
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    Re: Idealarc Roundtop Rectified Problem

    Search eBay for "MDQ300A 300A bridge rectifier". 300 amp rectifier for about $20 - $25. Don't know how you'd heat sink it and how well it would hold up, but it should work OK at moderate welding currents.

    Selenium rectifiers and silicon rectifiers have slightly different properties (voltage drop). In some circuit applications, it may make a difference.

    DO NOT BREATHE THE SMOKE from a burning selenium rectifier!

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