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handler 120 low on power

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  • handler 120 low on power

    I have a hobart handler 120, currently it is low on power - welding on setting #4 is like #1 or #2.

    Not too long ago I replaced the big cap because the top terminal had come loose, overheated, and messed up the threaded insert. Also, for reasons I don't recall, I also replaced the diodes (with factory replacements from local airgas). This was some time ago...I suspect what happened was I replaced the cap, power seemed low, so I replaced the diodes...power is still low. It has been many months since I've looked at it, so fuzzy on the details.

    Have a good 246VAC input. Checked the OCV and get 14v, 16v, 17v and 19v on settings #1 2 3 & 4 respectively.

    Checked both diodes out of circuit and both are open one direction, and read ~480 the other direction, which I assume means .480v.

    Running open circuit, I have 21VAC coming from each of the heavy xfmr leads (where they connect to the diode lugs).

    The odd thing is running open circuit, I measure 41 VAC at the output (in conjunction with 19VDC OCV on setting #4).

    Should there be any measurable AC at the output?

    Is 21VAC into the diodes acceptable?

    Depending on the answers to the above, where do I look next?

    Have used this welder for 10+ years, always flawless until the terminal on top of cap loosened and fried. Hasn't been right since.

    Also....what it the 3 terminal disc shaped component located just behind the rectifier? Appears to tie into each diode's input then have 1 (red) output wire.

    Thanks for any suggestions.

  • #2
    You should have 20Vac from each transformer lead at the diodes to the negative capacitor terminal(transformer center tap) and 40Vac from diode to diode on the transformer leads. The DC output on range 4 should be 28Vdc and yes there will be an AC component because of the DC ripple.

    Hopefully you have a misprint on your input voltage as should be 120Vac.



    • #3
      Thanks for the reply; it is a 230VAC model, the owners manual shows both a 120 and a 230 model. Mine has always been wired and run on 230.

      Sounds like I have the right input (21VAC each) at the diodes. I will double check the AC across the diodes, but suspect with correct individual voltage, the combined will be correct.

      Assuming everything going into the diodes is right, and the diodes are new (and check good), what else can cause low OCV? The diodes are indeed "pointing" the right way (towards the heatsink) according to the markings on them.

      I suspect if there was a problem with the cap, it would blow up (seen that before).

      Would it be safe to check OCV with the cap disconnected? I realize the output would not be "clean", but I think that would show if the cap was dragging it down?


      • #4
        What is the SPEC number of your unit? The early 230V(Handler 150) units had two output caps not one. Might be your problem.


        • #5
          Originally posted by allpinball View Post
          ...I suspect if there was a problem with the cap, it would blow up (seen that before).
          Not necessarily. As an HVAC technician, blown capacitors are among my most frequent repairs. Maybe 1/4 of them have any visual signs of failure.


          • #6
            spec # 7144 as seen in attached picture.

            it is indeed a 230v machine.

            I did some further testing.

            43vac across the diodes.

            no difference in DC OCV with capacitor disconnected - so I know the cap is not somehow "dragging it down".

            measured DC voltage while welding on setting #4 - jumping around but typically 10-15 V

            If I've got 21 and 21 V at the diodes and only getting 19VDC out, then it has to be bad diodes, yes?

            I checked all the bolted connections and don't see anything questionable. Resistance from either diode lug back to the center tap is 4 ohms each.


            • #7
              Odd, when I search the manuals page for "handler 120/150", in the results, nothing near my serial number comes up.

              When I search the manual page for my serial number, nothing at all comes up.

              Any of the manuals that do come up under "handler 120/150" look just like my machine.

              Not too concerned a bout it, but curious what I have if it's not found in those searchers.


              • #8
                These older units on not available online. OCV should be
                Range1 20Vdc
                Range2 23Vdc
                Range3 25Vdc
                Range4 27Vdc
                I included other tests in regards to the drive as well.
                Handler 6969_7144voltage tests.pdf


                • #9
                  Also. Your unit only needed one cap of 53,000 uf 30Vdc.