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  1. #1
    Join Date
    Jun 2009

    Default Connecting Miller Porta-Mig to PowCon 400SMT

    Iím hoping some of the Miller experts on this xlnt site can help me connect a Miller Porta-Mig wire feeder to a PowCon 400SMT power supply.
    The manuals for these machines can be found at and

    Some details:

    The Porta-Mig manual calls for a 4-pin x 14-pin connector cable that runs from the 4-pin socket on the control box inside the Porta-Mig to a welding power supply, presumably something blue w/ a 14-pin receptacle. (Early versions of the connector cable had a pair of Hubbell twist lock ends, one male and one female, instead of an Amphenol-14.) My variant of the 400SMT has an Amphenol 17-pin connector. And, so, OK, Iím going to make cable. According to the manuals, here are the pinouts:

    MILLER 4-PIN PINOUTS (Wire Color as Shown in Porta-Mig Schematic)
    1 -- Black -- Hot 115vac (goes to pin I on the other end of a Miller 14-pin cable)

    2 -- Red Ė Hot 115vac, just when gun trigger is on (J on a Miller 14-pin)

    3 -- Green -- Safety Ground (K on Miller 14)

    4 -- White Ė Neutral (G on Miller 14)

    Referring to Fig 8.1, pg 26 of the Porta-Mig manual, Pins 1 and 4 supply 115vac from the welding power source to the primary of the Porta-Migís control transformer; its 24v secondary supplies the MIG gun. Pulling the trigger energizes contact relay CR1, which connects one terminal of the gas solenoid to Pin 1. Since the other solenoid terminal is wired directly to Pin 4, gas flows on trigger pull. Pin 2 is also wired to the Black terminal on the solenoid, and thus Pin 2 is hot when, and only when, the trigger is on.

    B -- Control Board Common. Used with remote control devices.

    E -- Contactor Input. Will energize the welding power source when a dry contact closes to pin B.

    G -- Chassis Common. Safety ground.

    J -- AC Return. The PowCon control transformer can supply 30 or 115 volts. This pin is the return for both.

    H -- 115VAC with respect to J. Max 5A, protected by front panel breaker.

    S -- 30v with respect to J. Max 10A, protected by front panel breaker.
    Notice that the Miller 14-pin and Powcon 17-pin letter assignments differ. Also, the 400SMT has some additional pins of its 17-pin connector wired, but these arenít a factor here.

    Now we come to my problem. On pg 9 the 400SMT manual calls out in bold capitals,


    This warning concerns meóit sounds exactly like what the Porta-Mig plans to do with its Pin 2 if I let it. I donít want the 115v contactor close signal to fry a $600 Powcon board.

    Please see the generic Wiki-diagram of an SPDT relay attached below. (The terminal numbers are arbitrary and donít reflect Miller or PowCon practice.)

    The only way I can see all this working is to:

    Replace the 4-pin Porta-Mig connector with a 5-pin version.

    i) Mount the new relay in the Porta-Mig. (The PowCon manual suggests it can be located inside the 400SMT, but thatís a pretty crowded box.)

    ii) Replace the 4-pin receptacle in the Porta-Mig control box with a 5-pin version

    iii) Wire Pins 1, 3 and 4 of the new control box receptacle like they were in the 4-pin version.

    iv) Connect the SPDT relay coil across the Porta-Mig gas solenoid so that it would energized on trigger pull.

    v) Connect the relay output common, Terminal 30 in the Wiki, to Pin-2 of the new receptacle and the Normally Open relay output, Terminal 87, to Pin 5.

    Next, Make a 5-pin x 17-pin cable.

    i) Connect Pin-1, Black, to PowCon Pin-H, 115vac; Pin-3, Green, to PowCon Pin-G, Safety Ground; and Pin-4, White, to PowCon Pin-J, Neutral.

    ii) Connect Pin-2 to Powcon Pin B, Control Common, and Pin-5 to Powcon Pin-E, Contactor Input. B and E would be connected through the relay on trigger pull and the 400SMT would supply welding current to the feeder.

    iii) Finally, Iíve got some 16/5 cable on hand. Eyeballing an ampacity chart indicates this is good enough for 25 ft at the 5 amps 115vac the Powcon can supply. Is this amperage sufficient for the drive motoróthe Porta-Mig manual doesnít call out its requirement?

    One point I donít understand is why the PowCon manual calls for a SPDT relay; it looks to me like a normally open single pole single throw(SPST) relay would work.

    Does this sound right, gentlemen? Am I missing something important? Any advice about how to proceed would be most welcome. Thank you in advance.
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