Modifying my $90 HF FCAW welder to be less of a spattery piece of junk

[freedom_in_4low]

I was watching YouTube videos on making better flux core welds and kept being told that I needed to set the polarity on my welder to DCEN, or DC Electrode Negative. I didn't see any provision on my machine for that so I got to looking into it and learned that it, and possibly other low budget, entry level type welders like my Chicago Electric Flux 125, are basically just a big transformer in a box and supply AC to the ground clamp and electrode, and this supposedly reduces the amount of heat you can put into the material as well as causing more spatter. The fix for this, to make it a "real" flux core welder, is to use a bridge rectifier to flip the bottom halves of the AC wave up to the top, then as much capacitance as you can cram into the box to smooth the big wave into a ripple.

There are tons of instructional YT videos on this mod, but many are not very detailed on the actual parts necessary (like, I had these capacitors left over in my garage kind of stuff), and very few have any sort of wiring diagram which I don't like.

So for DCEN, you want the electrode going to the negative output of the rectifier, and the ground clamp going to positive, with the capacitor bridging across in parallel, + to +, - to -. What's missing from that diagram is the bleed down resistor. The capacitor will hold voltage after you've stopped welding, and though the voltage isn't something that's going to kill you, it's not going to feel good either. You want a resistor that can handle the wattage it will be dissipating, have a high enough resistance not to be a large parasitic loss on your machine output, but low enough to bleed down in a reasonable amount of time. P=IV and V=IR apply, and it simply wires across the terminals just like the capacitor so that when you shut it off, there's still a complete circuit for the capacitor to discharge into the resistor.

I even thought about giving myself the capability to easily switch to DCEP, but then I'd have to have a gun capable of a gas connection and I figure at that point it'll just be time to buy a real MIG welder and set this one aside for when I want to weld in the wind and only have 110V available.

I've ordered most of the components, just need to shop around locally a bit for some of the odds and ends like hardware. Most of it is cheap chinese junk, because why would I buy expensive made in USA stuff for a cheap chinese junk machine? But I understand why the welder is what it is, because these parts add to the cost to the point that it becomes close enough that you could just buy a used 110V mig on craigslist. But since I already have this one, I might as well try to squeeze some more use out of it (yes I'm aware of the sunk cost fallacy) and work toward getting a weld that I won't be embarassed to have showing on my rig (no one will ever see my exhaust mount).

1. 150A bridge rectifier. Want this to have some margin against the welder output, which is 125. https://www.amazon.com/dp/B07B4YL29S/?tag=wranglerorg-20
2. heat sink for rectifier https://www.amazon.com/dp/B01N9GGAX9/?tag=wranglerorg-20
3. thermal paste for heatsink-rectifier interface https://www.amazon.com/dp/B00M5G6AHY/?tag=wranglerorg-20
4. capacitors - I'll come back and link this when they come in and I know for sure they'll fit. The output of the welder is supposed to be around 38V so I ordered a pair of 50V, 47000 µF for a total of 94000µF. I'm not an electrical engineer so I have no idea how to size the capacitance but it lined up with the size somebody pulled out of a Lincoln that actually came with capacitance built-in.
5. bleed down resistor - the easiest availability come in packs of 2 and I wanted 50-100Ω so I got a pair of 50Ω, 50W. Using both in series 37V/100Ω=.37A and 0.37A * 38V = 14W total so plenty of headroom and will discharge the capacitor to <5V in 10 seconds. Or I could just use one resistor and get it bled down in half the time and still be at only 29W, but also robs twice the current from the output...not really likely to matter. https://www.digikey.com/en/resource...version-calculator-capacitor-safety-discharge https://www.amazon.com/dp/B071P29LYP/?tag=wranglerorg-20

The rest is somewhat optional and flexible but the ground cable on this is annoyingly short so I'm gonna make a new one and use some of the existing cable for my new wiring.
6. cable https://www.amazon.com/dp/B07KBCZLLN/?tag=wranglerorg-20
7. dinse connector so i can remove it if I want and use it on another machine (even though I don't currently have one) https://www.amazon.com/dp/B011LLG4F6/?tag=wranglerorg-20
8. higher quality ground clamp https://www.amazon.com/dp/B07L4N1TCJ/?tag=wranglerorg-20

the rest is just odds and ends like some angled brackets and fasteners to mount the rectifier and heat sink, copper terminals to make the wire connections, etc. If I can get away from work for a bit I'll try to run out and get some of this stuff so I can at least get the rectifier done tonight and post progress as I do it.

@Chris if we get that shop equipment/tools subforum, this is the kind of thread I was thinking of for it.

 

[Chris]

You got your forum

From now on shop and tool related threads go in this forum. If you find any other threads that belong in here, tag me in them and I'll move them over.

 

[freedom_in_4low]

Well go figure, the last thing to deliver is going to be the thermal paste, which prevents me from final mounting the rectifier and heat sink. Looks like tonight will just be mockup

 

[freedom_in_4low]

rectifier is in and the AC is wired to it; and the wires for the electrode and ground clamp are extended and ready to cut to to length once I have the capacitor mounting figured out. I mounted the rectifier up in the top thinking I can put the caps in the bottom, and it just barely hangs down in front of the fan so it should get some air to the heat sink. If I have room I may add a Folgers fan shroud so that hot air doesn't just recirculate around the fan; that might help that 20% duty cycle by getting more air to the transformer but I'll need to put a little scoop under the heat sink to pull air up into it if I do that.

The terminal in the far right is the back side of the dinse/euro ground cable connector. If that copper lug looks ugly, it's because it's handmade out of soft drawn 1/4" copper tubing. I cut it to length, smashed the bolt end flat, drilled an appropriately sized hole, installed it on the wire using vice grips to clamp it to the wire as tightly as humanly possible, and then soldered it. This is how I'm doing all of the larger wiring connections in this thing because I didn't want to go hunting for overpriced lugs. There's a home made copper tubing butt connector inside that blue heat shrink, which is how I extended the wire that previously ran from the transformer secondary directly to the electrode.

Apologies for this next photo being garbage, I didn't notice it wasn't focused and now the machine is in my garage to keep my kids out of it.

The capacitors are supposed to be delivered today...fingers crossed they'll fit. Otherwise I'll have to find a higher quantity of smaller ones to get the capacitance I'm looking for (which as I mentioned is somewhat arbitrary, I just borrowed it from what somebody posted on a weld forum that their Lincoln had...I think that may have been a stick welder but the intent is still to smooth out the voltage).

For good measure I went ahead and ordered a new auto darkening welding helmet. Nothing fancy, just a Hobart that has a 50% larger window than the HF one I've been using. I shopped around a bit to find it, because the entry level Hobart/Miller/Lincoln masks all had the same lens size as the HF, but Hobart has an upgraded one for just a bit more. Seems like Miller and Lincoln want you to spend $350 to get anything more than a 1-3/4" tall lens. I saw a reasonably priced one from Yeswelder with a huge viewing area, but there were more reviews than I wanted to see about going to bed with itchy eyes because it would randomly flash them while in use.

 

[freedom_in_4low]

This ground clamp is so overkill but it'll be nice to have one that makes more contact with the workpiece than a few points in the clamp teeth. The one it came with is basically a clamp from the cheapest jumper cables you can find.

Upside is its rated to 300A so it will be the last ground clamp I ever have to buy.

 

[bucky]

That clamp will hold better and outlast your welder.The repurposed cheap jumper cable ground clamps that come with lower priced welders are pieces of shit.

 

[freedom_in_4low]

I spent way too much time last night playing 3D tetris trying to fit those capacitors in. I was really hoping to just zip tie them together an tie their terminals together but there just wasn't any way to make that happen, so one of them is going to have to be lying down and the other upright, next to it. That also means I'm out of wire unless I cannibalize about 18" out of my ground cable, which I guess I can do since it's 10' long.

I have some cleanup to do, still need to wire the second capacitor and the resistor, secure some wire so it doesn't get caught up in the fan, and try to insulate some more of the open copper so I don't end up striking an arc inside the machine cabinet (like the little piece of naked copper peeking out from the split in the blue heat shrink).

The second cap is upright, behind the circuit board.

Credit to my wife, who's been patiently watching Ozark while I do all this at the kitchen table.

 

[freedom_in_4low]

Final product.

There's a capacitor sitting upright on the left edge, and if you look down next to it you can see the bottom of the other one, laying down.

The gold colored thing in the bottom, to the right of the transformer with the yellow/red wire is the bleed down resistor.

On the other side you can see the top of the capacitor laying down on the right. The rectifier is hanging from the top, with the aluminum heat sink protruding down into the discharge of my Folgers brand fan shroud. The fan was previously in the open air, which is a horrible fan arrangement. It should actually move air through the cabinet now instead of just recirculating around the fan itself. I haven't actually used it enough to be able to perceive any improvement in the duty cycle, but my in laws sent the Folgers can home with my kids to play with in the dirt and I had the welder open, so why not.

I'd like to know where to make my submission for the "10lbs of shit in a 5lb bag" award. I'm gonna wait for tomorrow when it's warmer out to fire this thing up, because I'm gonna do it in my driveway just in case it explodes or bursts into flames.

 

[freedom_in_4low]

I used the welder today and it didn't burst into flames.

I definitely seem to be putting in more heat and less spatter. Don't have an oscilloscope so I can't say what the waveform looks like, but this looks better than the last job I did.

I'm working on a weight to approximately equal a 3" section of TJ frame so I'm welding strips of 1/8" x1.25" bar into a block. I started by laying two together, offset by 1/8", to do a lap joint. Flipped it over and welded the other side, then added another strip with a lap joint and then had a single bevel edge joint on the other side (the bevel being formed by the bead of a previous lap joint). Repeat until I had 5 layers and took a break for dinner.

My first lap joint had spots that were ok, but a spot where I moved too quickly.

My last edge joint (on the right, below) looks pretty decent to me.

What this is all for is I'm going to put together a strap to go around the frame and attach this to it so I can mount it on the passenger side behind the t case skid; to see if the weight of 3" of frame has any affect on the oscillating driveline vibration I've had since regearing. That's for another thread. I know there would be easier ways to do this but none that require me to do this much welding so I chose this way to make myself get some practice.

 

[freedom_in_4low]

In video form