Sorry - Need help with 90A HF mod toroid
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  1. #1

    Sorry - Need help with 90A HF mod toroid

    Brand new to the site so please be gentle. I am doing the mod to your basic HF 90A AC welder to DC. Got 200A rectifier, and a 100,000uf cap, connectors and 8AWG flex wire and also a transformer to run the wire feed motor through the trigger relay. The question I can't seem to get an answer to is about the induction coil or choke. I started asking this on an EE forum site here.

    Naturally the EE folks got very VERY technical and wanted me to calculate the inductance of the coil etc. All I want to know is if I wrap a stripped down toroid core from a power amp with as many wraps of 8AWG wire as I can will that be a worthwhile improvement and is there any reason I should not? I was about to just not do that part of the mod then I somehow happened onto this site which seems a little more user friendly (not that they weren't friendly) for a woodworker like me.

    Yes, I could just buy another welder but where's the fun in that?

    Any help would be much appreciated.
    Last edited by Andybb; 02-01-2019 at 10:35 PM.

  2. #2
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    Re: Sorry - Need help with 90A HF mod toroid

    Wire welders are meant to be a constant voltage output. Capacitors work on voltage, inductors work on current. So in MIG welders you see large banks of capacitors and in constant current machines like stick welders you see large inductors as filters. For what you are doing, I would put a small inductors or none at all. I definitely would not put a big honking inductor/choke in there.
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  3. #3
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    Re: Sorry - Need help with 90A HF mod toroid

    Back when I had the HF 90A welder I was considering the same mod as you. There are several threads on doing the mod in the HF forum and I remember reading lots of discussion on the if/how to use a choke. Have you done a forum search? I attached a link to one of the discussions below.

    https://weldingweb.com/showthread.ph...-to-DCEN-Redux
    Last edited by jrporter; 02-01-2019 at 11:32 PM.
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  4. #4

    Re: Sorry - Need help with 90A HF mod toroid

    Quote Originally Posted by jrporter View Post
    Back when I had the HF 90A welder I was considering the same mod as you. There are several threads on doing the mod in the HF forum and I remember reading lots of discussion on the if/how to use a choke. Have you done a forum search? I attached a link to one of the discussions below.

    https://weldingweb.com/showthread.ph...-to-DCEN-Redux
    Yes, but the jury seems to be out on if it's a good idea or not, however the thread you linked to said he had a definite improvement. Seems that even if you can't get to the ideal inductance, some is better than none?

  5. #5
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    Re: Sorry - Need help with 90A HF mod toroid

    Are you doing this because you like to tinker, or are you doing this to save money? If the latter, what is your time worth? I really do think you would be better served by one of these. https://www.harborfreight.com/weldin...put-64804.html
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  6. #6
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    Re: Sorry - Need help with 90A HF mod toroid

    The inductor is needed on the output, if you don't have one, it is like welding with car batteries.
    I can measure the one on a small Hobart welder, but how you would measure and translate it to what you have ?
    You might look for inductors added to batteries for some ideas.

  7. #7

    Re: Sorry - Need help with 90A HF mod toroid

    Quote Originally Posted by Louie1961 View Post
    Are you doing this because you like to tinker, or are you doing this to save money? If the latter, what is your time worth? I really do think you would be better served by one of these. https://www.harborfreight.com/weldin...put-64804.html
    Just like to tinker so I thought I'd give it a try and try and learn something in the process. If it doesn't work I'd probably grab a new Lincoln or Hobart.

  8. #8
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    Re: Sorry - Need help with 90A HF mod toroid

    Just like to tinker
    That's cool. I would pull down the owners manuals for some lincoln and miller MIG welders then..they have the schematics and the parts lists. you might be able to see what kind of inductors they used in their designs.
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  9. #9
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    Re: Sorry - Need help with 90A HF mod toroid

    The old early model Harbor Freight Migs came with a good sized inducter in the torch circuit, at least mine did, what it was missing was a capacitor(s)
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  10. #10
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    Re: Sorry - Need help with 90A HF mod toroid

    I don't have that machine but what 455dan said. Get the caps and bridge rectumfrier. Your reactor (coil) was designed for that size of machine, don't mess with it. Design of inductors depends on wire size ( gauge), number of turns, diameter of coil and a formula. I may have left something out but that's the basic. Mig is a constant voltage process and needs the caps to keep the voltage stable/constant. I can't understand why they even make a mig machine with ac only.

  11. #11
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    Re: Sorry - Need help with 90A HF mod toroid

    As near as I remember, the AC wire feeds don't have a choke or reactor coil.

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