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  1. #1
    Join Date
    Oct 2012
    Location
    Portland, Oregon
    Posts
    6

    Default RFC-E foot control clips set peak amperage

    Has anyone had problems with their RFC-E foot control producing less than the set peak welding amperage?

    I bought my Miller Foot Control model RFC-E to use with a Maxstar 91 years ago, but rarely used it, replacing it with an RFCS-14HD because I liked the heel stop on the newer pedal. I brought the RFC-E out of storage and attached it to my Miller Dynasty 200 DX recently and find I can not produce the top amperage set when welding; for example if I set the peak amperage to 55 amps, I can produce only about 28 amps while welding with the pedal floored.

    After several frustrating runs, I measured the resistance of my old trusty RFC-14, the RFCS-14HD, and the RFC-E. The RFC-14 and RFCS-14HD produce a resistance range of 0 to 1K ohms while the RFC-E produces 0 to about 700 ohms. I took the RFC-E apart and adjusted its internal gear on the potentiometer by a tooth then put it back together and tried it again. Now the arc comes on too hot, but does go all the way to full set amperage.

    The RFC-E's trouble appears to be a design problem. The full travel of the pedal does not rotate the potentiometer through its full 0-1000 ohm range.

    Is anyone aware of a recall on this product or a repair kit that corrects this problem? The owner's manual does not show internal parts. Elsewhere on the web I found a post saying this model foot control was OEM'ed by Miller from Linemaster Inc. Any truth in that?
    Last edited by jpcallan; 10-17-2012 at 07:14 PM.

  2. #2
    Join Date
    Oct 2004
    Location
    Edmonton, Alberta
    Posts
    7,733

    Default

    It's an old 1993 style pedal, that apparently never caught on, so it was discontinued. Maybe its just worn out,

  3. #3
    Join Date
    Oct 2012
    Location
    Portland, Oregon
    Posts
    6

    Default The RFC-E is virtually new

    Hello Cruizer and thank you for your interest and advice on my problem.

    The RFC-E is virtually new. When I had trouble getting full amperage on the Maxstar 91 years ago, I put the RFC-E aside and fixed the problem with money by buying an RFCS-14 (that I disliked until I upgraded it to a RFCS-14HD), but at least I did get full output and was able to finish the field job I was doing at the time. My Miller factory rep offered to buy back the RFC-E at the time because he said there were known problems, but I decided to hang on to it because I liked the its small form factor and sturdy cable (which the replacement RFCS-14 didn't have).

    I've been chasing the problem with an ohmmeter, comparing the signals from my RFC-E to both the RFCS-14HD and RFC-14 -- they don't match. I used the description in the Miller Owner's Manual of the pin-out and I found a handy description you wrote up on building a 14-pin extension cord that was easier to understand. I cut/pasted it just below:

    .....Anyhow a basic cable your after would be a 16/6 SOOW

    .....A - 24vac
    .....B - Contactor Control
    .....C - Control pot input
    .....D - Control pot common
    .....E - Control pot wiper
    .....G - 24 Vac common

    .....This will be your basic all round cable

    C->D resistance is 1075 ohms. The internal pot is marked 1K ohm and is a Clarostat type J. Clearly the pot resistance is about 8% too high.

    I don't know which pins the welding power supply is reading E->C or E->D. Is the welding amperage proportional to the resistance or inversely proportional to the resistance?

    On the RFC-E I'm measuring E->C, which is 1070 ohms with the pedal in the off position and 170 ohms with the pedal floored, E->D, which is 3.6 ohms with the pedal in the off position and 965 ohms with the pedal floored.

  4. #4
    Join Date
    Aug 2008
    Location
    Orange, TX
    Posts
    1,214

    Default

    Quote Originally Posted by jpcallan View Post
    C->D resistance is 1075 ohms. The internal pot is marked 1K ohm and is a Clarostat type J. Clearly the pot resistance is about 8% too high.
    I believe you'll find the tolerance on that pot is +/-10% in which case your 1070 would be within spec.
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  5. #5
    Join Date
    Oct 2012
    Location
    Portland, Oregon
    Posts
    6

    Default More about Miller 14-pin foot controls

    Well I have certainly learned a lot more about Miller and Miller-compatible foot controls than I thought I would ever know investigating how exactly a foot control signals the welder's amperage control circuits.

    Thank you to everybody that took time to offer advice. The folks at Linemaster Switch Inc and Miller were both very forthcoming with help and advice.

    Linemaster did in fact manufacture the RFC-E foot control for use mainly with the Miller Econotig. It uses a white plastic rack to drive a pinion gear on the Clarostat 1K ohm pot. After carefully measuring the resistance between pin C (10V reference voltage) and pin E (potentiometer wiper signal sent back to the welder; 0V= min amperage, 10V=max amperage), the trouble is cause by the RFC-E rack and pinion gears not rotating the pot shaft though its full rotation. The RFC-E's control of the welder's output amperage (tested on a Dynasty 200, and Synchrowave 350) is not perfect, but is much better. By shimming the heel end of the plastic rack to travel a little farther toward minimum output, and adjusting the pinion gear set-screw on the pot shaft using the ohmmeter to zero ohms when the pedal is floored to maximum output; it now starts a little hot when the pedal is just depressed, but does reach full welding current output when the pedal hits the floor.

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