El-Cheapo TIG pedal

[shenion]

Oh forgot to mention the connections:

Blue - T1 goes to the negative side of the bridge (also one side of the big rheostat.)

Orange - Goes to the wiper of the rheostat. Note this allows you to set the max on the unit and footpedal is 0-max.

Red - Negative side of the rheostat.

Brown - output, connects to external current control input.

The 6-pin connector I used is a Jones type. I did not have the Hubbel connectors for the welder and easier to use 1 connector. I ran the contactor through it also. The footpedal also has an LED to show it is connected and the unit is set to remote. The diode gets rid of a dead spot in the first part of travel.

I do think I'll redo it with pulse-width control and a constant voltage mode to run MIG.

 

[wilton]

tig control

The Miller board I am talking about is part# RF-10, model # 041 111
it is an interface board that goes into the welder that is supposed to substitute for the 15 ohm 150 W pot , and allows you to use a fingertip control with small pot, or a foot pedal with a small pot. There is a schematic of it on the Welding Web site , but no parts list.

 

[wilton]

Tig control

No, I was wrong it isnt 041111 its called Mic4. Its an interface box which goes between the miller and either a fingertip control or a foot pedal. The guy at miller sent me the schematic, and it looks pretty simple , an SCR, a 741 opamp and other assorted parts. Shenion, are you trying to make your airco do tig and mig? If so doesnt the mig welder have to have constant voltage?

 

[shenion]

Yes, I saw the schematic of the MIC-4.

The Airco is the same as the Dialarc, Miller made both. They are constant current (CC) power sources. It can do spray-transfer MIG. I have used it in short-circuit mode. It works ok once set up but requires maintaining a constant torch distance (also relies on the arc start feature) and wire feed has a very short speed range before the wire breaks into an oscillation of short, burn to tip, lose arc, restart.

I had a Lincoln Idealarc R3S-300 CV machine 3-phase (until today.) I looked at the schematic to see how to run it on 1 phase. I did and managed to test it on 1P before selling it.

What I realized is both the Lincoln and Airco work the same way. They use saturating inductors to limit current. Two, many-turn field coils around the same core allow it to be saturated with a low current. I.e if 10 turns at 500A on the sense winding would saturate the core, 5000 turns on the same coil can saturate the coil with a 1A control current.

The Airco is a CC machine while the Lincoln was CV. The only difference is the Airco uses a fixed coil current while the Lincoln has a control board to vary the coil current to maintain a constant voltage.

This works fine. The only issue is the voltmeters will read the full voltage until a load is applied. There is also a minimum current (5A for the Airco.)

So, I will make a board that measures the arc voltage and varies the saturation coil control current to maintain a constant voltage (similar to what the Lincoln does.)

 

[wilton]

Fixed Coil Current

So what do you do? maybe put some kind of DPDT switch arrangement to switch the fixed coil out, and switch in the CV control board in, effectively creating a combination TiG/ Mig welder? If thats the case sounds like a winner to me!

 

[shenion]

The welder has an remote current control plug. I would connect the board to that. The board itself would have a CV/CC switch to select between the MIG voltage control or the TIG foot pedal.