125 flux core
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Thread: 125 flux core

  1. #1

    125 flux core

    First post It has been a long time since I have done any welding and never did much. So just a newbie.

    After doing lots of research I think that the HF 125 Flux Core with the modifications described on this site and various other websites and on you tube will suit my home hobbyist needs. I am going to buy a new one. They are on sale for $90 and after a 20% off coupon my price should be $72. Can't beat it.

    My question concerns the capacitor. Is there a formula that determines how many mfd's the capacitor should have? I have seen a wide variation in what is recommended. In looking on fleabay I can across a listing for a Miller capacitor. 60 volt 16000 mfd's part number 163535. Don't know what model it was for. The mfd's on this Miller capacitor are a fraction of what is being recommended. I would think that Miller would spec the right size capacitor. And prices for capacitors increase rapidly as the mfd's increase. Don't want to buy a larger capacitor than I need but don't want to buy too small either.

    Thanks for any assistance you can give me.

    Chuck

  2. #2
    Join Date
    Jan 2009
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    Sonoma County
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    630

    Re: 125 flux core

    Long ago you could apply a coupon on welders. Not any more. I paid $72 for the 10-years-ago version of that one.

    My advice on the capacitor is measure the space where it will go, first.

    I don't think there is a precise formula for specifying capacity because you will use the welder at various output levels. (and anything above original output will stress the internals more). Rather, whatever is used on a similar welder should be about right.
    HF MIG-180 with all the mods.
    Grizzly H8153 Stick/Tig Pulse 130/160.
    Wards PowrKraft AC-230. Stick & carbon arc.

  3. #3
    Join Date
    May 2009
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    Re: 125 flux core

    It seems to be calculated so it would end up about 40,000uf per 100A.
    If space is a problem two smaller capacitors can be paralleled to give the proper value.

  4. #4

    Re: 125 flux core

    In searching I found this http://www.skillbank.co.uk/psu/smoothing.htm which seems to be what I am looking for. However I can't get the numbers to work out anywhere close to what people have used. The diagram looks to be the same basic circuitry as in these HF welders. I must be using the wrong numbers.

    Thanks for the suggestions

  5. #5
    Join Date
    May 2009
    Location
    Wyoming US
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    3,232

    Re: 125 flux core

    A formula that calculates it as percentages and a 37-63 ratio seems to most resemble what many of the welder designers use.TC= R*C.
    For instance 120A@20v=.166ohms of resistance
    At .1666ohms and a a time constant of .00833 seconds or 120hz you would need 49890mfd or about 50,000mfd per 120A.
    So it would end up about 40,000uf per 100A.
    That seems to be the way the manufacturers figure it.

  6. #6

    Re: 125 flux core

    Picked up a new 125 yesterday, $90, and ordered a 150amp bridge rectifier, $17.

    Looking at capacitors and trying to decide between a 63v 50000uf, $34
    https://www.ebay.com/itm/1pc-SPRAGUE...19.m1438.l2649

    or two 50v 27000uf, $37
    https://www.ebay.com/itm/LOT-OF-2-UC....c100022.m2048

    or three 63v 22000uf $10 from China.
    https://www.ebay.com/itm/Dimension-3...19.m1438.l2649, $10.

    The single cap would be easiest to mount. I am leaning toward the single cap.

    I am going to relocate the fan as this guy did, http://forum.driveonwood.com/t/modif...ady-own-one/64, and maybe move the transformer back 2 inches to create more room for the rectifier and the caps in front of the transformer.

    I am also thinking about adding a choke. Trying to figure out how I could make one and where to mount it.

    Any and all suggestions would be appreciated.

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