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Cleaning, Testing and Splicing Transformers

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  • Cleaning, Testing and Splicing Transformers

    I bought a used Thunderbolt AC/DC stick welder (s/n KF853364) for a great price ($40) because the former owner had not read the part in the owner's manual about "duty cycle". The transformer lead to the AC High terminal had been badly damaged at the terminal end. I'm replacing the terminal post, and I had a couple of questions:

    1. The transformer wire is 1/4" square profile aluminum wire. It is now too short to reach to the terminal post. I was thinking of running 4 AWG copper stranded wire as a splice between the terminal post and the transformer wire, but I don't know a good way to splice the copper wire to the aluminum transformer wire. Does anyone have recommendations?

    2. Can anyone recommend a good electrical test for the transformer? I have a megger, but it only goes down to 250 volts and I'm worried about putting that much voltage on the secondary (low voltage) side of the transformer.

    3. The iron core laminations are very rusty. My usual practice on non-electrical rusty iron is to use Ospho (a phosphoric acid + binders solution), but I don't know if it would attack the varnish between the laminations and short them out. What's the best way to get the rust off the laminations before re-spraying with insulating varnish?

    Thank you for all the help!

    Dave Doerschuk

  • #2
    In order:
    1.Splice with a 'split bolt' connector, available at electrical supply houses, tell them what you are doing, they will give you the right size.

    2. Meg the high side, 'smoke test' the low side.(only kidding)
    Check for shorts to core on low side with neon test light, with secondary isolated.
    Use regular 120volt circuit to energize ONE SIDE of secondary, other wire connected to test lamp. If lamp lights when remaining lead is touched to case, transformer is toast.

    3. Wire brush works well enough for this.

    I hope this is helpful.
    As always if you find yourself uncomfortable with any of this,DON"T DO IT. This is what I would do in these conditions, what you do is up to you,don't get hurt, and then say I told you to do it.
    work safe, always wear your safety glasses.

    Edward Heimbach


    • #3
      I'd procede in the following sequence;
      1, use the megger to test for insulation problems. Since Meggers check for insulation breakdown between the winding and core, I don't understand your hesitation to use the instrument on a transformer.
      2, if the windings pass the megger test, splice the wire to the transformer winding, using either a hi compression splice sleve, or U bolt connector, and use sufficient antioxidant on the splice.
      3, forget about the rust on the laminations, and use the machine.
      The rust will have little to no effect on the operation of the machine.


      • #4
        Thanks! Brand of Hi Compression Splice Sleeves

        Ed and Franz,

        Thank you both very much for your answers. I'm headed off to get to work on the welder.

        Franz, I was intrigued by your reference to Hi Compression Splice Sleeves. Do you happen to know of a manufacturer that makes a product that would work well with a square aluminum 1/4" transformer wire, and a copper 4 AWG stranded? If so, I'd really be glad to know it; Kerney (sp?) nuts and split nuts are pretty hard on soft aluminum.

        Thank you both again for the help!

        Dave Doerschuk


        • #5
          Nicropress sleeves and tool will work but I would use solid not stranded wire as it isn't going to be moved a lot. Tool is too expensive for one use so call around to find someone that will spice it. Tool looks like small bolt cutter having thick section with hole halfs instead of cutting edges. Electric supply sells them.

          The split copper bolt has groove down middle middle of bolt to take wire. Nut has saddle that rides in the groove. They are sized for wire.

          Clean oxide from aluminum wire carefully then apply anti oxide grease. Can do same for copper but not as important. Then splice. Wrap with electrical tape.


          • #6
            This would be a good application for RTV (silicone sealer) and heatshrink tubing. Along with the anti-oxidant grease, this would make almost any possibility of oxidation nonexistant.

            Allen T.


            • #7
              Insulink, the same splices electric utilitys use, would be my choice, but I have a drawer full of them, so it's an easy choice.
              If I didn't have sleves, I'd probably make one by boring a piece of steel rod.
              As far as crimping is concerned, you want to use a hydraulic crimper.
              Be real careful using Silicone RTV, most over the counter RTVs outgas acid as they cure, and that wouldn't be nice to aluminum.


              • #8

                Senior moment - I should have been more specific. The RTV I've used for that type stuff came from the electrician up the street. There are more breeds of RTV than welding rods .

                Allen T.