Question about MIG output voltage

I am resurrecting an old MIG I made by Chicago Electric, I got it free.
The voltage selector switch is no longer available. The switch was labeled from
left to right 2 , 1, OFF, 3 , 4. There is a diagram on the front of the machine
showing thin to thick materials showing switch position 1 as the thinnest and
finally position 4 as the thickest.
I am using a SPST and two SPDT 20 amp toggle switches to replace the old cam
type selector, this way I get an actual off switch. The original cam switch is
badly burned and would not operate correctly nor could I figure out its
operation because somebody else had been inside befor me.
Now to the question. I need to know if the output voltage of the MIG gets higher
as the material to be welded gets thicker? OCV readings go from 27.3 to 46.6
depending on the switches. I am thinking the lower OCV should be labeled 1 or
Low and the higher OCV should be 4 or High, does this sound correct? Maybe use
A, B, C and D with A being lowest. This is one of those "hard to get it right in
your head" things.
Anyone know how to make a "HOT" mig gun cold? I know I could use a contactor in
the ground circuit but I am not sure of the contact amperage with the D.C.
voltage levels. The specs say this thing outputs 28 to 84 amps, but the specs
also say the OCV is 22 to 34 volts, I would think these are "typical".
Finally, anyone know what brand the mig gun is on these old Chicago Electric
Thanks for any help.
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Yes, the voltage will go up as you ask for more heat. Put the contactor in the primary circuit, lots less amperage to switch there.
Myself, I have no idea where you'd get another gun except from another similar welder. Check ebay, that's always a good start.
Make sure the feeder isn't all broke before you get too far, it'd be bad to get it all working and then find the feeder is too broke to deal with.
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You can use a Binzel Gun to replace the old one. They have adaptors to fit anything! I think their HO is in Frederick MD. and their website is something like
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Check the price of a whole new Chicago Electric MIG unit before you go spending money on parts and a gun. You may be investing more than it's worth.
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Chicago Electric is a Harbor Freight brand. Chicago Electric welders are built off-shore, e.g. China. The gun, therefore, is likely to be a brand you and I have never heard of.
Sounds like the design is similar to some of their current product line. Voltage is determined by which of two small boost coils on the secondary side of the transformer are switched in. In at least one, they use two single pole, double throw switches to do this. I would suggest you do the same. Check out the product manuals on the Harbor Freight site. They have schematics that should help.
OCV may be as high as 34V but the voltage when you are actually welding with is going to be more like 20V. So pick a contactor accordingly. Or you could replace the diodes in the rectifier circuit with SCRs and add an appropriate circuit to trigger then when the trigger is pushed on the gun.
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