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  1. #1
    Join Date
    Feb 2020
    Location
    Albury
    Age
    58
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    90

    Default Welder rectifier (AC->DC)

    Turn you old AC transformer style (Buzz box) welder into DC with this bridge rectifier.

    It is capable of 140A continuous current with repetitive peaks to 700A. Up to 600V

    Here is some reading on AC vs DC welding.

    The box is 300x200x150, with most of the space inside taken up by heat sinks. Weight is about 2kg.

    The guy that built it was using it to weld Aluminium with his AC stick welder.

    It's free to a good home. I'm happy to ship anywhere in AU if you pay for the shipping cost.

    IMG_5844.pngIMG_5845.png

  2. #2
    Join Date
    Aug 2011
    Location
    Melbourne
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    4,779

    Default

    I was nearly going to make my own version of that. All it requires are bridge rectifiers. The more you gang together the higher the current capability.

    In the end I just bought a DC inverter welder. I went from a 180A welder the size of 2 milk crates weighing 60kg to a 200A welder the size of a shoe box weighing about 8kg!

    Still I would have been interested to see how it went.

    Nice offer BTW!

    Simon



    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  3. #3
    BobL is offline Member: Blue and white apron brigade
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    Feb 2006
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    Perth
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    7,182

    Default

    I was given one a couple of years ago. It was in a large cobweb filled 450 x450 x 200 mm steel plate box and had large Al heat sinks. It was mostly empty but it still weighed a fair bit and took up a lot of space. I pulled it apart as all I wanted were the diodes to make a smaller high current dc power supply. Now I need to look around for a beefy, say 24V tranny.

  4. #4
    Join Date
    Oct 2007
    Location
    Alexandra Vic
    Age
    69
    Posts
    654

    Default

    Quote Originally Posted by simonl View Post
    I was nearly going to make my own version of that. All it requires are bridge rectifiers. The more you gang together the higher the current capability.

    You would be better to fabricate a bridge rectifier from 4 discrete diodes that can handle the required currents. Paralleling lower current bridge rectifier modules does not control the current sharing between modules so the device with the lowest losses carries the bulk of the current, and the device with the highest losses carries very little. Eventually the one doing most of the work packs in and leaves the rest to fight it out, and the cycle repeats with the new most efficient one doing all the work etc. Eventually they all die from being overloaded, possibly with less than a second between the first and the last giving up. It's just the way of semiconductors, overload them and they die faster than anything can protect them.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  5. #5
    Join Date
    Mar 2011
    Location
    Southern Flinders Ranges
    Posts
    1,536

    Default

    Quote Originally Posted by BobL View Post
    I was given one a couple of years ago. It was in a large cobweb filled 450 x450 x 200 mm steel plate box and had large Al heat sinks. It was mostly empty but it still weighed a fair bit and took up a lot of space. I pulled it apart as all I wanted were the diodes to make a smaller high current dc power supply. Now I need to look around for a beefy, say 24V tranny.
    I carted a 27kVA 28V secondary winding transformer off to the skip at work a couple of weeks ago.. No idea what it was used for and can’t fathom any application requiring almost 1000A at that voltage.

  6. #6
    Join Date
    Aug 2012
    Location
    Greenmount, W.A.
    Age
    70
    Posts
    272

    Default

    Good Evening,
    I will take it off your hands - if it has not already gone.
    I will use it to produce a 24 volts DC supply to drive some DC motors I have. They will be powering a tapping chuck in an old drill press I have. Voltage regulation - I can still remember how to do it, as I too was once an electrical engineer - but it is fading fast!
    PM about to be sent.
    Regards,
    Alan.

  7. #7
    Join Date
    Jul 2007
    Location
    Perth
    Posts
    332

    Default

    Quote Originally Posted by racingtadpole View Post
    I carted a 27kVA 28V secondary winding transformer off to the skip at work a couple of weeks ago.. No idea what it was used for and can’t fathom any application requiring almost 1000A at that voltage.
    As a guess 28v DC is commonly used in the aviation industry at least, as a ground power source and if the amperage rating is high, then engine starting probably. Alan.

  8. #8
    Join Date
    Mar 2011
    Location
    Southern Flinders Ranges
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    1,536

    Default

    Wrong industry. Aircraft are not normally the sort of thing I see underground.

  9. #9
    Join Date
    Aug 2011
    Location
    Melbourne
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    4,779

    Default

    Quote Originally Posted by malb View Post
    You would be better to fabricate a bridge rectifier from 4 discrete diodes that can handle the required currents. Paralleling lower current bridge rectifier modules does not control the current sharing between modules so the device with the lowest losses carries the bulk of the current, and the device with the highest losses carries very little. Eventually the one doing most of the work packs in and leaves the rest to fight it out, and the cycle repeats with the new most efficient one doing all the work etc. Eventually they all die from being overloaded, possibly with less than a second between the first and the last giving up. It's just the way of semiconductors, overload them and they die faster than anything can protect them.
    Hi Mal,

    Yea that's correct. I had forgotten about that. So the component that carries the higher current gets hotter and then further reduces it's resistance further increasing the current flow. A thermal runaway until the magic smoke comes out!

    Simon

    Sent from my SM-G970F using Tapatalk
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

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