On the right track? RFCS-23 for use with a Dialarc HF

[sscherin]

2 part question

I found a great deal on a Miller RFCS-23 foot pedal ($50) with the 5 pin connector.

I have a DialArc HF TIG welder (Well it's an Airco but it was made by Miller for Airco. I've checked.. It's a Dialarc HF-P under that orange paint)

Now I know that its supposed to take a RFC-23 pedal.. From what I read in the manual the only difference is the resistor..
The RFCS-23 uses a #030-051 130w 1000ohm and the RFC-23 uses a #030-0651 130w 15 ohm..

Should I be able to simply swap to the 030-0651 resistor and have it work on the Dialarc?

Do I even have to? Looking at the circuit diagram it's just a simple voltage divider circuit that limits a 30v DC feed to a winding in the transformer that controls output. Any way I do the math a 1000 or 15 ohm pot set up as a divider will output the same voltage range. They are both rated for 130w

Now to part 2.

Now I know I still have to deal with the plugs.
Years ago the welder was used for a remote training setup and all the twist lock remote sockets were removed and put in a remote panel that I didn't get.
So my welder is sockletless. at the moment.. I have to buy 2 twist locks and receptacles or I was thinking I could order the 5 pin panel mount socket and use the existing plug on the RFCS-23.. . Miller PN #035-523



Any thought on this plan?

[duaneb55]

Sent you a Private Message.

[martikat]

Does anyone have a verdict on this? I'm in the exact same boat.

[Aeronca41]

Haven't seen Duane on here for along time, but here's my two cents worth.

Yes, you have to change the resistor. The current flow through a 15 ohm resistor vs 1,000 ohms will be dramatically higher, all else in the circuit being equal, making it run a LOT hotter. Power dissipated by the resistor increases as the square of the current; double the current and you get 4 times as much heat generated. I don't have time right now to look into the machine's internal resistance in this circuit, but going from 1000 to 15 ohms is dramatic. Enough to toast something, more than likely. But, the biggest reason it won't work well (if at all) is that a voltage divider has to be looked at as an overall whole; if you dramatically reduce the ratio of the resistance of the pedal to the resistance inside the machjine, that will give it far less control over the current. Thus, from pedal full up to full down, you are going to have very, very little control of the heat. Not gonna work. Need to change the resistor, in which case all should be well. As to the sockets, do what he said--that will work fine.

[martikat]

Thanks Aeronca. I don't fully understand how the voltage and current coming out of the pedal control the current coming out of the transformer, but it makes sense that you'd need the current coming out of the voltage divider to be what the machine is designed for, not just the voltage that you'd get with either resistor. My plan right now is to buy a used RFCS-23 with the 1000 ohm resistor and the 5 pin plug, and convert it to an RFC-23 by swapping the resistor to a 15 ohm and the 5 pin plug to 2 twist locks, the 3 prong for the remote amperage control and the 2 prong for contactor control, which would be about $100 in new parts on top of the pedal unless someone has a better suggestion or an idea why this wouldn't work. Thanks for your explanation.