How to limit welder current (heat)?
Hi All, I admit to being electrically dumb, well one step above dumb, I'm a software engineer not electrical engineer, but I don't even know enough enough to be dangerous yet:) I'm going to be converting an ac welder to dc. It's a harbor freight 90 amp flux wire job, comes from the factory as AC for some unknown reason, but should be DCEN for FCAW welding. There are several walk throughs availabile online. I don't know the rules for linking to other forums, so I won't post a link, but you can google 90 amp welder dcen conversion if you want details. I attached an image of the circuit I got from a post by bluecatfish onweldingweb. I'll be taking the transformer output, running through a full bridge rectifier to convert to rippled DC, using capacitors to remove ripple, and lastly running through a torroid inductor. Another problem with this welder is it only comes with high/low power settings. The low is still too hot and burns through thinner metals. I want a way limit current further, but maintain voltage for a stable arc. I'll be adding a bleeder resistor to drain the caps, which gave me an idea. At first I thought to use several more resistors in parallel with the bleeder to reduce current. I imagine this might work but be horribly inefficient. It would still use all available power from the supply, just converting some of it to heat, leaving less power for the arc. I've read that adding resistance in series will reduce current, but won't that drop voltage available for the arc? Then I was thinking, I have a motor speed control for a router. I believe this is a pwm. Could it be used to chop the mains input (120v 20a) to the transformer and reduce overall output without effecting voltage(I've read this is 38v 80a in the factory state before my mods)? since I'm adding capacitors downstream, will they just discharge too fast leaving me with ripple/pulsing? If so, how would I slow the discharge rate? (I'm looking at 3x or 4x caps 22,000uF @65v in parallel on a bus bar, so 66,000 or 88,000uF total). Sorry if in not making sense, as I said in the intro, I have a lot to learn, and right now, the more I read, the more confused I get.
Edit: After more research, and to hopefully use correct terminology, I think I'm talking about using a current divider when referring to multiple resistors in parallel to the welding leads. I think I'm referring to a switching regulator when I suggested using a pwm to chop the transformer input.
Can either of these work like I'm hoping? Is there a better way, that is relatively simple?
Thanks in advance for your patience and help.