Bit of a puzzler...

[Wedg1e]

I've been sorting out an old Romarc 200 MIG that I recently acquired from another forum member. On the front panel is a toggle switch and a 2-pin socket. The wiring to these is configured such that throwing the switch disconnects the wire feed motor and instead applies its current (essentially 12 to 24v DC) to the socket.
I'm struggling to understand what it would be used for; after all the motor is only powered when the torch triger is pressed, so what would you plug in that would need power instead of the wire feed?

Baffled of Teesside

 

[the snooper]

foot switch ?
maybe connecting the 2 pins again will run the motor

 

[shenion]

Sounds like a connection for a spool gun.

 

[Wedg1e]

Sounds like a connection for a spool gun.

Hmmm, I did wonder that at one stage, but never having played with one I couldn't see why you'd use one on a MIG set - it's already feeding wire, after all. S'pose if the gun was loaded with alu wire it'd save a lot of hassle changing liners etc.
The spool gun would have to have a Euro connector of course, to collect gas and weld current... sounds feasible then

 

[Wedg1e]

foot switch ?
maybe connecting the 2 pins again will run the motor

Er, no. Connecting the two pins would blow the PCB!

 

[shenion]

Yes, many have spool guns that connect to MIG feeders for aluminum wire. Mine came with one but it hard wires in. Never tried it as it has 8 wires and no docs are available on how it connects.

I have tried aluminum MIG on mine, it is hard to feed on a 12' torch. Not easy to use. I may see about getting the spool gun working so i can just plug it in and use it.

 

[pedrobedro]

Probably an external wire feed unit could be used with it.

 

[Wedg1e]

OK, a quick rummage on Ebay turns up any number if spool guns with a Euro connector and separate trigger lead... sounds like it may be worth reinstating the wiring on this MIG then

It's yet another product of our mates Technical Arc in York; badged as a Romarc 200 although the spec. of the main power devices suggests it may not be quite as poky as 200A - I'll hang a clamp meter on it and find out.

I've got it working; there were a few issues with it mostly down to age, damp etc., but the wire feed circuitry had been bypassed with a triac and a pot. I thought I'd rip that off and fix the original circuit to start with; after a bit of thought re. transistors etc. that's now working fine. One of the other glitches (and perhaps the reason the original speed control was bypassed) was a blown logic IC. Bit daft really; two gates of this 40106 are used, one to trigger an off-board relay that pulls in the main contactor and the other to fire an on-board relay that connects the variable voltage to the drive motor. In the rest position this relay shorts the motor to ground. With you pressed the trigger it was pulling-in the offboard relay and hence the contactor, energising the main transformer which produces a secondary of 12-24v to drive the motor according to the requred Amps... but the blown logic gate was leaving the onboard relay in its deactivated position so it was shorting this voltage straight to earth, taking out the pass transistor in the speed control!

Add in the corroded wiring and grubby switch contacts (it has two switches giving 16 steps), corroded transistor legs, previous repairs etc. and it was looking a bit sorry for itself, but I think there's fundamentally a good (albeit 27 year old) machine under there.

Now for the other unit I acquired, a Portamig wire feed (built guess where: York!). Wondering if I can adapt it to run from my SMP TIG set (another Tech Arc product!) to give me a combined MIG/TIG/stick system...