Thoughts on this used welder?

[joshuabardwell]

A capacitor will do a lot to absorb spikes, but a varistor in addition will likely be needed if there is any real electronics involved.

You know, I'm showing my ignorance here, but now that you mention it, that thing I was calling a capacitor is probably a varistor. Capacitors are usually cylindrical in shape, although I think they sometimes come in the dime-shaped package that my welder has got. But more fundamentally, the dang thing says "varistor" on the side. I was trying to look up replacements for it the other day, in case it was messed up, and I could not figure out why it didn't have a Farad rating printed on it. I looked all over the Internet for "Varistor Capacitor" trying to track down who the manufacturer or part number was. James, this may explain why the results I got from my multimeter didn't look anything like a capacitor should look.

But if it's a varistor, where's the capacitor to go with the inductor/choke? I thought they usually came in pairs.

Another thought: if it's a varistor, then isn't it consumable? Won't it eventually lose its ability to protect against spikes, like a power strip?

Every time I look dumb, I learn something new. After all these years, you'd think I'd stop looking so dumb so often.

 

[k0ua]

Yes Varistors "wear out" eventually. I have been going back and looking at your photo's and I don't see a cap anywhere so far, I do see a little MOV (metal oxide varistor). When a MOV wears out... they are generally are "open" and ineffective. They sometimes fail catastrophically and short, but mostly they just "go away"

Yes caps and inductors are often used together in power supplys . But sometimes only one componet is used. In this case I am thinking since this "power supply" is high current, it would take a large cap to do much good, and the inductor is more effective in this case. This may or may not be true, but it is what I think, perhaps a design engineer could weigh in here.

James K0UA

 

[CNC Dan]

But if it's a varistor, where's the capacitor to go with the inductor/choke? I thought they usually came in pairs.

In a power supply for an electronic circuit, yes. But at the current a welder puts out they wouldn't do much good unless they were huge(expensive).

Another thought: if it's a varistor, then isn't it consumable? Won't it eventually lose its ability to protect against spikes, like a power strip?

depends on its rating, and how big the spikes are. Cheap power strips are made diferent. Often the varister is after a fuse and when it gets a big spike it conducts hard and blows the fuse, saving the down stream circuits. If you replace the varister in the welder, get a big one.

 

[CNC Dan]

Sorry, doubble post.

 

[joshuabardwell]

Yes Varistors "wear out" eventually. I have been going back and looking at your photo's and I don't see a cap anywhere so far, I do see a little MOV (metal oxide varistor). When a MOV wears out... they are generally are "open" and ineffective. They sometimes fail catastrophically and short, but mostly they just "go away"

Yes. Some of the power strips that I have, when they stop protecting (the MOVs wear out), they stop conducting power too. But I have the impression that many power strips keep conducting power, and are just not protecting anymore. This must pertain to a difference in the wiring of a power strip vs. my welder, as opposed to any quality of the MOV itself. Good to know. If the DC output on my welder ever fails entirely, it could be because the MOV has been consumed and will show "open".

Yes caps and inductors are often used together in power supplys . But sometimes only one componet is used. In this case I am thinking since this "power supply" is high current, it would take a large cap to do much good, and the inductor is more effective in this case. This may or may not be true, but it is what I think, perhaps a design engineer could weigh in here.

Seems like CNCDan agrees with you.

Thanks for the info, guys. I love learning new stuff like this.

 

[k0ua]

Good to know. If the DC output on my welder ever fails entirely, it could be because the MOV has been consumed and will show "open".

Look at your schematic, the MOV is across the DC output. If it fails open you will never know it. It does not carry any current.

James K0UA

 

[joshuabardwell]

Look at your schematic, the MOV is across the DC output. If it fails open you will never know it. It does not carry any current.

Sheesh. You're right. How would I even know if it had failed?

 

[joshuabardwell]

I did some more practice tonight. I had planned on welding up a small frame for the hand truck that I use to move my welder around on. Just a square base-plate basically, to allow me to tilt the truck back and move the welder around without having to have the welder ratchet-strapped to the cart like I do now.

At this point, I figure 1/8" is about the thinnest material I can try to weld, so I got some 1.5" angle iron, 1/8" thick. I actually have another piece of flat, 1/8" scrap that I had laying around my barn, so I shined it up and ran some practice beads. I had previously run some beads using 1/8" 6013, and I thought those were a little thick for what I intended to do, so I got some 3/32 rods at Tractor Supply when I bought the angle iron. Having gotten good results with 6013, and knowing that 6013 is a low-penetration rod (so less chance of blow-through), I wanted to get 6013, but they didn't have anything smaller than 1/8" so that was out. They had 3/32" in 7014, so I got that. They had something even thinner, but it was about twice as expensive as the 7014, so no dice.

I started out using the 1 amp per mil rule. 3/32 = 0.09, so start out at 90 amps.



WHOAH. Way too hot. Lots of spatter, a "pancake" at the end of the weld, and the puddle was like 2" long. So I turned it down maybe 10-15 amps.



Still way too hot! Part of what was confusing me was that I was having a little rod sticking and a tiny bit of difficulty starting the arc, so I was thinking my power was on the low side of what the rod needed. But really, I bet it is just that my work metal was not as clean as it needed to be since it had been sitting outside for a couple of moist days. Finally, I dialed the welder down all the way to its lowest setting, about 40 amps.



Much better.

Oh, and about that frame for the welder? Well, upon further investigation, I discovered that the hand cart could be reconfigured to ride on four wheels like a push-cart, and the baseplate could be flipped ninety degrees so it didn't block the DC lugs on the welder any more. So the frame I was going to make is kind of unnecessary. But I have the metal all cut up, and I may go ahead and weld it up anyway just for the practice.

 

[joshuabardwell]

Today's small welding job: fixing a pair of hedge clippers. They are double-jointed, and a pin fell out of a joint. You can see two other pins in the photo that are still in place. I'm honestly not sure what's holding them in. They kind of seem to have been peened at the end, but of course that'd only hold them in from one direction. I previously tried JB-weld, but it gave up nearly instantly. I figured I would probably want some relatively hard metal, so I cut the head off a bolt, stuck it through, put two tack welds on either side of it, and ground it all down.



BTW, I am aware of the hazards of welding galvanized steel. In this case, it was, like, literally four total seconds of welding, so I just kept my head out of the fumes and held my breath. If it was a larger job, I would set up a fan blowing across the work location to carry the fumes away.

This was a $30 pair of hedge clippers. The way I see it, I get to count that against the cost of the welder. At this rate, I'll be MAKING money in no time!

BTW, in case you care, I used 1/8" 6011 at about 110 amps.

 

[k0ua]

I figure that old AC buzzbox I started welding with doesn't owe me a dime, I kept an old lawn mower pieced together after if fell apart so many times from use and abuse mowing 7 acres before I got a tractor and finish mower. I reckon any repair on some of your stuff that you would have thrown away otherwise does really subtract from the price of your welder. And beside that you are gaining skill, a valuable skill to use now and in the future.

James K0UA