stabilizing the DC output of a cheap mig welder?

I bought one of those cheap chinese mig welders, It splatters alot and is alittle unstable. I removed the case to find only a transformer and two diodes. Im thinking of adding a inductor in the + dc line, most good dc welders have atleast this. Is there any other improvements i could do to stabilize the output? Would filter caps help?

Reply to
tucker
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A capacitor would make the spatter worse (big changes in current for small changes in arc resistance). I think an inductor is a fine idea. It tends to keep the current stable over a half cycle, even if the arc is shorted momentarily by a drop of molten metal.

I added one to my buzz box and it allowed me to do some very nice welds on thin material at low current. It takes some big wire, though. I used 1/8" by 1/4" wire for mine.

Reply to
John Popelish

I can't remember exactly where I got the laminations, but I had a stack of E's about 4 by 6 inches in size. I made two stacks about 2 inches high and epoxied the laminations together. Then I drilled a pair of quarter inch holes near the ends of the center legs, to make a section that would saturate first, so the inductance would sag, gracefully as the core approached saturation flux.

I made a wooden coil form with a block the size of the center of the E stacks with sides bolted on. I premeasured a length of 1/8 by 1/4 wire and placed the middle of the piece along the bottom of the form, and would two coils, side by side, so the ends were on the outside. A made 6 or 8 of these coils and bound them with glass tape and epoxy. I placed either 3 or 4 of these coils on the center leg of each E stack, with a quarter inch of space between the stacks for cooling. I overlapped the adjacent ends of the coils and soldered then in series (one set on each E stack, so I could connect the halves in series for low current, or parallel for high current).

I put the open ends of the E's together on a 1/8th inch spacer (just sat on on top of the other). I hooked the two halves in series, used the inductor for some low current work, and have never tried it with the parallel connection. I do very little thick section welding. I made this 15 or more years ago, and have since collected an inductance bridge. One of these days I should measure what I made.

I have one kind of rod (I don't remember exactly what they are) that blast molten iron and slag all over the place when used with AC, but with DC and this big inductor, I get very smooth welds covered with a puddle of slag that slowly curls up at the ends and falls off the weld, as the metal cools. Almost as little clean up as if I were using a tig torch. The neat thing is the sound the inductor makes each time a drop of molten steel bridges between the electrode and the work. Instead of the pops with metal splatter and flux all over, the inductor just gives off a brief "unng".

Reply to
John Popelish

length

in current.

machines to reduce

I can see how real current regulation would ruin the automatic arc length feedback needed for stable MIG welding. So the optimum inductance for a MIG welder may be lower than for a stick welder.

Reply to
John Popelish

John, how did you make the inductor?

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Reply to
Ignoramus21405

A MIG welder is designed for constant voltage, not constant current. The arc length becomes self regulating becasue small changes in voltage cause a large change in current. Having said that, variable or fixed inductors can be found in some MIG machines to reduce splatter.

Reply to
Rick

length

change in current.

machines to reduce

Yes, you're probably correct. And as this is a cheapo unit I don't suppose it has any provisions for setting an output voltage, just wire speed. Not a whole lot to lose by trying one, that's for sure...

Reply to
Rick

Hello Mr Tucker, I have been down a similar road, buying a cheap welder and then trying to make it work better by doing the sort of improvements that you are talking about. I wasted a lot of time and effort.

My advice to you is take it back and spend more money on a machine similar to these in this link below

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Stay away from 115V machines. Too small.

Here is the link to the Lincoln 175T manual.

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Page 54 shows the transformer and choke assembly made with flat ribbon wire. You can see the capacitor also. These 93,000 microfarad caps are very expensive. About $100 as a spare part here in Australia. Maybe cheaper in your part of the world. Schematic is on page 43 What I like about this model, if you look at the schematic, is the voltage taps are done on the secondary of the transformer. A cheaper, not so good method, is to tap the primary winding of the transformer.

Here is a link to the Miller 185 manual

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Page 38 shows four capacitors of 30,000 microfarads. Four separate caps is better than one big cap. Lower ESR The schematic is on page 24.

From the schematics of these manuals, you may get some ideas what to aim for if you do decide to try and improve your cheap welder. There is also a how to weld tutorial and problem solving pages that may help with the spatter problem you are having.

Another option is to use your electronic repair skills to fix a broken machine or a machine that has been written off beyond economic repair because some component is no longer available. Use you skills, get round that problem and maybe pick up a bargain on an older high quality machine.

Just for fun on your cheap welder. Try adding a choke to the "work" lead. You don't even have to cut the work lead. Just connect the large alligator clip/clamp (that normally goes to the job) to the "add on" choke and use another "work clamp" from the choke to the job.

You can make a choke. Make two or three. Find some old discarded microwave ovens. Salvage the large power transformer.

Remove the "I" piece of the "E" and "I' core. and knock the windings out of the "E" section of the core. To remove the "I" section in one piece. Slightly hacksaw about 1mm into the weld. Use a "brickies bolster" or wide blade chisel and gently tap into the hack sawed cut. The "I" section will come off easily in one piece.

It would be nice to use proper winding wire or ribbon but just for fun use whatever heavy insulated cable you can get your hands on and fill up the window. Probably only several turns. There has to be a gap between the "E" and "I" pieces of your core. Start with an excessive gap of say 2 to 3 mm and use whatever clamping method you like to hold the "I" piece in place. Tack weld it back on if you like, or get fancy and make it adjustable with brackets and screws.

Make a few chokes like this and you can experiment adding one or all three to the "work" lead and see if your welder works better.

Later on you can adjust the gaps of your chokes a bit nicer to get maximum inductance for the operating current you are interested in. No point in having a huge gap where the choke does not saturate until 200 amps flows through it when you are only interested in say 100 amps. No Point in having a small gap and the choke saturates with only 30 amps flowing through it.

So while you are just experimenting for fun, err on the big gap side. Then close it up later.

Some time ago, I was sucking the brains of an engineer from Lincoln Electric in regard to building chokes and how to set the core gaps and he got the s**ts with me and said, "We make f****ng welders here, not electronic power supplies, we experiment by trial and error until the machine welds correctly"

So from the horses mouth, experiment and have fun. :-)

I enquired on this group years ago about setting the gap for a particular current. There were a few methods involving power supplies/banks of capacitors and using an oscilloscope to look at the pulse shape across a low value sense resistor. I didn't quite understand what I was supposed to look for.

This was the other method suggested which I used to find the current at which the core saturates with a particular gap.

Variac on very low setting (several volts) ? AC stick welder primary

Welder O/P --> 100 amp shunt --> choke under test --> Welder O/P

That is, across the welder output terminals connect your choke under test in series with a 100 amp shunt.

The 100 Amp shunt acts as a sense resistor so a digital voltmeter can indicate the current flowing. For example on my shunt 60mV equals 100 Amps. An oscilloscope is placed across the shunt and shows a nice sine waveform. Turn up the variac on the primary side AC stick welder. Warning! Keep input voltage low, several volts only, because the secondary has almost a dead short across it. As the current increases through the choke and shunt you will see the AC waveform begin to distort slightly. Note what the current is just before distortion. If it is around 100 amps you are laughing. If it is only 40 amps then you will have to increase the gap between the E and I piece and try again.

I'll bet this machine of yours does not have a proper wire speed controller that works independent of the output voltage settings. This is another improvement you can make. Pulse Width Motor Speed controller. Google for those. Here is the one I used. It works well.

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Be warned, I spent more time experimenting/making test welds trying to improve a cheap machine than I did welding up proper jobs and projects. The cheap welder improvement project takes over. Isn't that correct Igor? Home built Welders become an Obsession! :-)

Regards, John Crighton Sydney

Reply to
John Crighton

Thanks for all the replies, i found a junked 3 phase dc welder and salvaged a stack of three inductors, they dont look that big so i guess it dosent take as much inductance to filter 3 phase as single phase. I plan on trying one then series adding two then three to get enough inductance. My question is can i put the inductor in the ground lead or do i have to put it in the hot lead. I have a 225 amp buzzbox for heavy stuff, i got this cheap Mig to help with thin metal. It doesnt have a wire speed control just a Hi/Lo switch so i also plan on adding a reostat to help control wire speed.

Reply to
tucker

How about changing a plan and restoring the junked 3 phase welder? Depending on how good it is, it could be a great welder!

I also have a 3 phase dc welder:

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Reply to
Ignoramus16356

Yes experiment with various combinations.

Electrically it makes no difference. Much easier for you to simply add your experimental chokes to the the "work lead" ouside the case of the welder. (Lets call it a work lead incase pedants get upset and start panicking ;-)

WoW! Is this a three phase machine.

I did the same thing also but my elcheapo mig was useless on carbody thickness as well as

1/8 of an inch thickness for general purpose.

After mods, concentrating on car body thickness only of around 1mm or 40 thousands of an inch my modified mig works well compared to a good brand welder such as Lincoln 170T on car body thickness.

I used the existing choke in my cheap mig welder as a choke input filter DC supply. I added 60,000 microfarads of capacitance in a separate external capacitor bank outside the welder. This made for a stiffer DC supply. I mean a supply with better regulation. I hate to use terms like regulation when we are talking about crap but you get my drift. Because the DC voltage I have to work with is now well below what it used to be due to the choke input filter, thin metal such as car body stuff is all it can do. But the voltage on this DC supply is better regulated, stiffer, better stabilised, use whatever term you like, better welds are now produced. Heaps better and that nice crackle fried bacon sound is produced. Not a hissing spluttering noise that it made before while running a bead. Beads that melted right through and almost fell out the bottom. Now the weld bead looks more like the tutorial manuals and I don't burn through as easily as I did before.

But I had to have another choke This is the choke that makes the mig welder work as a mig welder. The choke that you have to have. And you say your machine is so cheap that it doesn't have a choke at all. Incredible! For me this choke is simply added to the work lead outside the case of my cheap welder. There is no room inside the case. I just experimented until the magical crackling sound was obtained.

In my cheap Mig welder, I measured the highest DC voltage that was applied to the motor about 30V. That is with welding wire running out of gun but not welding. While welding the voltage on the motor was all over the place jumping above and below 12V so the wire speed was varying greatly. This is a bad ... bad .... bad...

I built my wire speed motor control box external to the welder on a long cable so that I can have the control box near my left hand so that I can adjust the wire speed knob while welding. To get that magic crackling noise.

This box contains a small power transformer for a 2 amp DC regulated supply of around 22V DC. Just turned out that way because that is what I had to hand. This speed control I told you about earlier works nice.

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I added a delay circuit also. Motor starts a few second after the trigger is pressed to make sure shielding gas is well and truly flowing. Didn't make a lot of difference but I liked the idea and did it for fun. I added a relay to short out the motor connection terminals after the power is removed from the motor. This is electrical braking and it did work, so I now clip off one inch of protruding wire off the end of the gun nozzle instead of two inches, before making a new weld. The real welders have a control called "burn back" which saves wasting wire by having to clip so much off the end of the nozzle. You should still clip the wire anyway before continuing the bead. The sharp point helps make a good quick starting arc. Anyway this "burn back" control just delays the power being removed form the gun after the trigger has been released. Motor speed runs down and welder keeps welding for a small preset time to use up the wire.

I think you would waste a lot of time trying to find a rheostat, It would be expensive. Then you still have a motor that varies in speed while welding because your motor is running off the welders output supply. You are only slightly better off. Your cheap mig welder sounds crappier than mine was. Mine had a choke and a crappy speed control you have less to play with.

Built a proper pulse width modulation motor controller. It is easy, cheap and will work nicely straight away with no messing around. You would have to buy a bunch of 10 watt or

20 watt 2 amp rheostats to find one of the correct value to put in series with the motor to get the required motor speed. Bad idea.

Lets hear how you got on with the chokes that you found. I am keen to know.

Regards, John Crighton Sydney

Reply to
John Crighton

I have a problem with my inductor, its a high current RF choke made with # 6 or 8 square copper wire (same size as the round alum wire on my transformers output so i know its heavy enough) however its air core so i need to add some kind of core to raise the inductance. The problem is its 2" I.D. is round, i cant think of a core except for a solid steel rod, or stack ( I ) sections in it from a old transformer, i thought of making a pvc donut from elbows and filling with steel BBs sense i dont have powdered iorn. Second its hard to insert the choke in the hot line going to the migs flexible feed hose, so for experimenting would it be the same if I put the choke in the ground lead ?

Reply to
tucker

The core will likely saturate, causing all sorts of problems.

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Many thanks,

Don Lancaster                          voice phone: (928)428-4073
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Reply to
Don Lancaster

I bought some powerded iron some time ago for doing a similar thing. It may have been Edmunds Scientific. Best to try to partially insulate the particles.

greg

Reply to
GregS

Need a GAP or SLOT in the thing.

greg

Reply to
GregS

You might put a stack of ferrite beads in the middle of the coil, like the LFB360230-200

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Or the wound ribbon core from a soldering gun.

That puts more voltage on the work piece.

Reply to
John Popelish

You can do that by mixing them with a slow cure epoxy, until the mixture is about as stiff as modeling clay.

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Reply to
John Popelish

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