Wednesday, August 08, 2007

The light of a 1000 suns..or just 1.5?

Ok a little slow on updates. Its not like I am getting paid to write, and with comments turned off I have no visibility on hits, so I might as well be speaking to a vacuum.

So I turned comments on.

I built the heat treat oven, but it has no door. The control box hasn't been wired either, but I have all the parts. I am going to use two solid state relays instead of one, need to cover both LIVE poles of the 220V outlet, since the heater coils will be electrically hot otherwise, even when the oven is off. I need to get working on the damned door, its where the thermocouple mounts as well.

The Arc welder is finished, and finally there is light! I welded a crappy bead on a large bolt I had laying around with 1/8" 6011 rod, first I had the power turned all the way down so it was just sparking and sticking to the bolt. I cranked it up to max and burned through most of the rod - worked like charm. It was hot wearing full jeans, a buttoned up jean shirt, leather gloves, and that arc helmet out in the humidity, but the proof of concept is over. Time to mount the rectifier bridge I made and wind the choke, which will put me into the area of DC welding.

I have actually been custom designing the voltage-controlled variable wire speed circuit for the MIG welder portion, I originally made a PWM circuit thats just knob speed controlled, but since my power supply CC not CV, I need some way of regulating the voltage, MIG being a CV process n' all. Arc voltage to high, feed wire faster. Arc voltage too low, feed less wire. Now I have a knob for the target voltage (10-35V for MIG) and the wire speed will vary to obtain that voltage. In theory.

In essence I am designing a closed feedback loop system, but since I slept through "Elements of Control" in college, I am flying blind. Although I am not worried about oscillation, mainly at pulling a clean DC voltage signal off of the arc with some sense wires at the gun. The circuit looks good on paper, but I imagine some RF will ride in on those wires - I may have to wind some chokes and clip on some ferrite beads to block it. Since my measuring circuit is analog (opamps) optoisolation is way too complicated. Anyways, the opamps do the comparison, shift the level a bit, and provide a DC voltage to the PWM section which is voltage-controlled.

I'll have to test it at some point to see if the circuit goes apeshit or not when its measuring a real arc.

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