Murex Miget-Carrying on where Pauly left off.

  1. baldy Member

    Messages:
    276
    kent uk
    Was that with fresh wire or the old stuff? my bro used to coat the wire in anti splatter spray to stop it rusting.wash the liner out and try some fresh wire.
     
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  2. Mattycoops43 Member

    Messages:
    116
    Location:
    Newport, South Wales
    Right. We are finally getting there.

    I started with the old wire, but then I wondered if the holes were being caused by the anti spatter spray which is still wet in the reel so I swapped to a brand new 15kg drum. No difference. I then had a good look at the Euro torch and why my MB36 wouldn't fit. The gas connection on the Murex torch is 5.72mm dia and the new MB36 is 5.95, so designed for a 6mm fitting. Fortunately the socket on the Murex is plastic, so I just used a brand new 6mm drill and ran it into the hole by hand to scrape it out and hey presto, a nice tight sliding fit.

    At the same time, while it was on the bench I got my tester out to confirm the wiring of the rectifier, and it was definitely feeding EN?? NO idea why, unless it was specced that way from new for some reason, it is not a home conversion as the wire to the transformer, which then feeds the earth cable is red, and the black cable goes directly to the torch.

    First off I rebuilt the rec, with the plates swapped over, top and bottom. (I kept the same pairs together). This in my mind should have worked, but when I tested it it was giving the same polarity, so I have misunderstood something there. In the mean time, I have swapped the cables over, but I have had to use a 2" bit of earth cable to extend the neg wire as it doesn't reach the top of the rectifier. It works fine, but I want to do a tidier job, so if someone can explain how I change the polarity of the rec I would be grateful.

    Back together, correct polarity and new torch and it is AMAZING! Like a new machine. Power 4 is more than ample for welding the box section stuff I do trailer repairs with, I can use 5 for short bursts, but it trips the mains after a couple of minutes.

    While it was in bits, I measured the WFS and Voltage at different settings to get an idea. Interesting, the WFS is almost an exponential curve, the difference between 0 and 1 is almost nothing, and the difference between 9 and 10 is about 200f/s!!!! :D this is fine, an now I have measured the output I know how to use the control knob to get into the ballpark.

    Main noticeable difference when welding? I could get the SIP to weld nicely, but the WFS was highly critical, the tiniest increment out would stop it welding properly at all. The Murex seems to be far less sensitive, half a notch either way it still welds fine. I guess it's just a far more stable feed speed.

    Anyway, I got it set up. then did a job I had waiting. Just adding a drawbar to a grotty old boat trolley so they can use a gator to drag a small boat out of the water, but the way it welded a rusty bit of scrap 2x2 to a galvanised trolley gives me high hopes for it's performance.

    I'll add some pics in a separate post from my phone.

    Matt
     
  3. Mattycoops43 Member

    Messages:
    116
    Location:
    Newport, South Wales
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  4. Mattycoops43 Member

    Messages:
    116
    Location:
    Newport, South Wales
    So, just to clarify with the rectifier. One pair of plates is marked with a Neg stamp on each outer surface, and one pair is stamped with a Pos on each outer face (To show which way the diodes are working?) I took it apart and reassembled with the neg pair and the pos pair swapped over, thinking it would change the output voltage polarity, but it made no difference, and definitely did not put it back the same way by mistake, as I had marked up the outputs neg and pos on the plates.

    Any ideas?
     
  5. baldy Member

    Messages:
    276
    kent uk
    You could do a Dinse plug conversion like the new oxford i bought where you can spec the pos or neg torch.you could then run gasless wire too.Maybe it could be time to fit a new rectifier. it did weld well when my bro had it, quite why the recitfier is wired in reverse?, heaven knows.I think id source it from technical arc rather than the bay.See the oxford section for my review.
    Also i take it youre using a multimeter to ensure correct polarity?

    OXFORD review
     
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  6. Mattycoops43 Member

    Messages:
    116
    Location:
    Newport, South Wales
    Yes, using a multimeter.

    I like the idea of a Dinse conversion. Solves the problem of tidying up and more usability in one go.

    Why would you change the rectifier? it's working perfectly.

    Matt
     
  7. baldy Member

    Messages:
    276
    kent uk
    I would change the rectifier as its old,relatively inexpensive and you may find a new one which is working defo 100% may weld better, also i did think of adding some smoothing capacitors whilst in there.The new oxford has the caps, and it does weld nice.
     
  8. baldy Member

    Messages:
    276
    kent uk
    You could put the rectifier thru an osciloscope test to see if its working 100 %. dont forget new technology may well be more efficient.
     
  9. eddie49 Member

    Matt, to change the polarity of the rectifier: mount it upside down ( the whole thing ). Then the pair of plates that are stamped "-" will be at the bottom, and connect to the red wire ( = ground clamp ), and the pair of plates that are stamped "+" will be at the top, and connect to the black cable that goes to the torch ( positive ). The wires will be in the same places, and so length will be OK.
    With the rectifier upside down, the AC input connections ( the U-shaped metal bridges that join the pairs of thin flat plates with rounded ends ) may be swapped left-for-right, but that doesn't matter - since AC swaps backwards and forwards 50 times per second anyway!
    You may have to shuffle the central stud downwards in the stack of plates, so that there is enough free stud to bolt to the mounting bracket at the bottom.
     
  10. baldy Member

    Messages:
    276
    kent uk
    A complete mystery why it was built that way !
     
  11. Mattycoops43 Member

    Messages:
    116
    Location:
    Newport, South Wales
    Hi Eddie.

    Thanks for that, but I can't flip it over as the input tabs for the ac current will then be on the wrong side and the wire won't reach again (they come out on the corners) , I effectively did the same thing by taking it apart, the only difference is the inner pair of plates have become they outer pair.

    Interestingly, the wire going to dc+ is red and the wire going to dc- is black its just that the red wire is the earth lead. I was surprised that all the switching and transformer etc are on the earth side, the electrode side is straight off the rec.
     
  12. baldy Member

    Messages:
    276
    kent uk
    buy some suitable cables and connectors and rewire it correctly .It shouldnt be difficult.
     
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