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Millermatic 35 repair

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  • Millermatic 35 repair

    Bought my Millermatic-35 back in the mid 90s from a guy down the road.
    It worked but never seems to work right.
    While welding, it seems like the power supply was surging. It would be normal for abt a sec, then almost stop welding for another second, then back to normal for a sec and so on. It was impossible to make a good looking weld.

    I let unit sit until just recently. Today I removed the cover and took a look around. I found the 4 diodes near the fan. Disconnected the wires and measured 9-10 ohms in one direction and open in the other direction. I guess they are OK.??

    Pulled the 6 large caps. The are rated at 9000uf and 35v.
    Checked them with my Fluke meter set to 10,000uf and it read "OL" on all 6 caps.

    Checked around the net and found some "computer" grade caps with the correct ratings and screw terminals. Not so sure I need "computer" grade caps but that's all I could find. Will they work??

    WIll bad caps cause the "surging" I was seeing??

    Am I barking up the wrong tree here??

    SN= HJ153419

    Thx in adv for any help

    John C

  • #2
    Found a ref to a thread on weldingweb.com where I learned modern theory dictates 40,000uf/100amps for the weld caps. I decided 6 ea 10,000uf caps should do the trick since my welder it rated at 150 amps.
    The vendor (tedss.com) didn't have 6 of the 10,000uf caps available but did have 11,000uf caps (50v) on sale for $18/piece so I went with that ( Oh boy, caps are going up!!)

    I asked the vendor abt the "computer grade" terminology. He says that term simply means large can electrolytics.

    Still not real clear on the what the symptoms of bad caps are other than "there will be a change".

    I also discovered that you can change one character in the owners manual address and get an earlier version.
    Eample:
    http://www.millerwelds.com/om/o1301q_mil.pdf
    Change to http://www.millerwelds.com/om/o1301c_mil.pdf

    When the document opens it will say what serial# it starts with and the year of manuf.

    We'll see what happens when I get the caps installed and the power cord replaced.

    Comment


    • #3
      I let unit sit until just recently. Today I removed the cover and took a look around. I found the 4 diodes near the fan. Disconnected the wires and measured 9-10 ohms in one direction and open in the other direction. I guess they are OK.??

      OK, I've got a couple of new diodes (same machine spec) in resistance ohms I get 6.4 meg ohm in one direction and 133 Kohm in the other so you must be using the diode test function which would be 0.425 volts and infinate in the other direction

      Pulled the 6 large caps. The are rated at 9000uf and 35v.
      Checked them with my Fluke meter set to 10,000uf and it read "OL" on all 6 caps.

      Your getting that OL, cause the caps still have a charge in them, best to stick a resistor on the poles and drain them completely. I don't suggest using a screwdriver across the poles like I do to discharge them.

      Comment


      • #4
        OK, you have a Millermatic 35S, not the norm MM35, so its an old 1978 model. Usually what happens is the caps become loose on the rails, especially if the caps are hanging like yours are. Were any loose, when you attempted to check them individually.

        Comment


        • #5
          Originally posted by cruizer
          OH, and it says on the sides of the individual caps what they are, so I looked it up and sure enough they are 20,000 microfarad @ 35 volts. Soooooo, the new ones you ordered, if installed will go off like a firecracker from ****

          They say 9000uf on the old caps. The manual that covers my serial# says they are 9000uf ( http://www.millerwelds.com/om/o1301c_mil.pdf ). From what I have been reading on this site, the later models went to 20,000uf caps.

          The caps haven't had power applied for at least 7 years and I did short them with my needle nose and then did a DC voltage check before I connected my brand new Fluke cap meter. Plus I figured since they were 35 years old, they need to be replaced anyway.

          In regards to the diodes, I was using an old Simpson meter I got off Craigslist recently, I'm not that familiar with it and I may have had it set to diode check. I'll find my old trusty Fluke multimeter and retest them.

          Assuming the caps are bad, would that explain the surging I was experiencing??

          Comment


          • #6
            Originally posted by cruizer View Post
            OK, you have a Millermatic 35S, not the norm MM35, so its an old 1978 model. Usually what happens is the caps become loose on the rails, especially if the caps are hanging like yours are. Were any loose, when you attempted to check them individually.

            No. They were all tight..

            Comment


            • #7
              I would guess that the surging may be more related to gun liner/contact tip issues. I would buy a new liner for the size wire you are running. I had a minor issue with surging in my Bernard gun recently and dug into it. Turns out I had a liner for .045 wire in there and am now running .035. The wire would zig zag inside the liner, then spring out.

              Comment


              • #8
                They say 9000uf on the old caps. The manual that covers my serial# says they are 9000uf From what I have been reading on this site, the later models went to 20,000uf caps.

                You said you had a MM35, but it was really a 35S, so I changed my post to verify that you have the 9000 Microfarad caps. True they do wear out so changing them wouldn't be a bad idea, never the less its unlikely that they are you problem on the surging issue. What would happen is that you would drop output power.

                Walker has a better solution.

                Comment


                • #9
                  This what it looks like on the front:
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                  Here's a pic of the gun. Any input on this?
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                  Just noticed this. This can't be good for welding steel:
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                  If the liner was bad, could/would it still feed wire smoothly when not welding?

                  Could the argon gas be causing the surging issue??'

                  I bought the rig from a guy that built and restored small aircraft. Must have had it set up for welding alum.
                  Last edited by John C; 10-23-2012, 11:26 PM.

                  Comment


                  • #10
                    The wire surging issues are generally caused by too loose of drive rollers, bent liner, (yes the wire will appear to go through nicely cold) Not so much when welding though. It's difficult to say if the bottle is wrong, but as C-25 gas, often just says Argon on the bottle. The machine simply won't weld right, surging, probably not. what wire and polarity are you using. I see you have a spot panel, covering up the "S" after 35. That may be a problem too..

                    So change the bottle to C-25, change your liner, and change your tip. Tighten your drive rollers so that the wire curls up nicely in the palm of your hand without slipping.

                    Comment


                    • #11
                      Got a bottle of 25/75 mix yesterday. Also picked-up a liner and tip. Had great fun installing the liner.

                      Finally got in there and fired-up the beast.
                      I ran out of time but was able to run a quick bead. Seems to be working much better now. Instead of the popping and stubbing, I get a smooth bacon frying sound and significantly more heat.


                      While re-wiring the main power connector, I discovered the 35 yr old insulation isn't looking real good. Looks like a new power wire will be needed soon, very soon...

                      Comment

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