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Author Topic: Convert Your AC Stick Welder to DC - For better welds?  (Read 11310 times)
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K1JJ
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« on: June 08, 2005, 03:25:03 PM »

I've gotten to the point where my AC stick welds are as good as
they're gonna get. They're "OK", but not as flowing and
smooth as I'd like.

Like many of us, I've got a standard "Lincoln Welder" unit
with capacity for maybe 250A. Someone suggested to
put in a standard full wave bridge rectifier rated for 300 Amps
to convert it to DC. They said the spitting stops and the welds
come out tremendously better.

I've used rented TIG [aluminum welding] and MIG units before,
but never did DC stick. Seems like a cheap fix.

Has anyone had actual experience comparing AC to DC stick
welding? Also, does the bridge rectifier sound like a good idea?

Tnx.
Tom, K1JJ
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« Reply #1 on: June 09, 2005, 09:52:53 AM »

I have a friend who converted his Lincoln to DC with 4 huge rectifiers and reported good results. It's probably worth a try. I'm not sure what polarity your work will require so you will probably need to do some experimenting.
Keith
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Chuck k3xu
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« Reply #2 on: June 09, 2005, 10:29:44 AM »

For D.C. stick welding you use reverse polarity.
For TIG welding you use straight polarity.
Using reverse you have 60% of the heat on the welding rod 40% on the base metal.
You need this to consume the rod.
With TIG welding you don't want the tungsten to consume so you have the heat on the base metal.
With AC. welding you are limited to the rod you can use.
6011, 6013 and others have a arc stabilizer added to the flux (potassium salt)
Still  welding with these rods is very sputtering and low grade.
Changing to DC. you will be able to run low hydrogen rod 7018 to get stronger welds.
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WA1GFZ
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« Reply #3 on: June 09, 2005, 11:14:48 AM »

Tom,
Back in LaPointe days I helped a guy build a big bridge with high current
diodes to convert his stick welder. A high current bridge can drop 2 volts
so at 250 amps that is 500 watts steady state. A good sized heat sink
also required.  Check your open circuit voltage at 250 amp setting to determine diode voltage. You want to be at least  2X but 10 X would be better considering transients while blowing slag.
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KE1GF
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« Reply #4 on: June 09, 2005, 12:14:54 PM »

Tom Vu, why don't you give Frank KB3AHE a call, I think he's a nuke welder...

One more question, did you build an oven for your sticks to keep the moisture out of them?

I have a 100A buzz box here, not much of a welder but if I need to throw down a bead on some thin stuff I've got it...
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K1JJ
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« Reply #5 on: June 09, 2005, 02:34:31 PM »

Tnx for the info, guys.  

I didn't know about reversing the polarity for DC work, Chuck.

So, if I continue to use my 6013 rods, will I see any advantage to the welding process, or do I need to use the 7018 rods to make it worthwhile?  I have lots of the older rods left.

Wish I knew about this before I welded a lot of stuff out there. But, I really over-killed the AC welds to make sure they were strong.

BTW, I fould TIG welding aluminum to be quite easy, like soldering. Many guys say it's harder, but I think the years of soldering experienece made it a breeze.

Looks like a big heatsink is needed for the conversion, Frank.

T
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« Reply #6 on: June 09, 2005, 04:25:23 PM »

Tom,

Like you I have a Lincoln 225 amp AC stick welder, it does a great job and even today is pretty cheap ($250 at Home Depot). Never had any of my welds break so it does the job for most stuff a non pro needs. However my welds never look as good as those pictures you see in welding books where the weld looks looks like coins laid on top of each other sideways with next to no splatter.

When we took a drilling rig to Turkey we had a new Onan generator/DC welder for the rig since we had to fabricate and repair our own stuff. Not cheap at 3K but when I first used it I couldn't believe it. My welds looked like the ones in those books. Basically I just did what I do with the AC welder but the welds look great and next to no splatter. DC holds a better and more uniform arc, and it's easier to do than AC welding. I was using 6013 sticks like I do for most stuff. I heard that reversing the polarity is useful for welding upside down, but I've never tried that.

Anyway going to DC will sure make your welds look better and with less skill than running AC. It's worth a try if you have some big rectifiers around. I think Lincoln's AC/DC stick (225/125) runs $450, so they are charging $200 for the rectifiers to get DC.

73

Marty WB2RJR
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Chuck k3xu
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« Reply #7 on: June 09, 2005, 04:29:19 PM »

Tom, you can use dc with E-6013. your arc will be very smooth and you will have better results.
The 6013 electrode is "60" thousand psi tensile strength, "1" is all position ,"3" is high Titania potassium( flux coating)
The 7018 electrode is "70" thousand psi tensile strength "1"  all position "8" iron powder,low hydrogen.
The rods need to be cooked in a rod oven before you use them to dry out the hydrogen (water)
If It was me I would keep the AC buzz box and buy a high frequency converter so I could do TIG aluminum with it.
A 150 amp air-cooled weldcraft brand Tig torch is cheap.($150?)
The high freq units, Dayton electric has one for $300 bucks in the grainger book.
Then I would find a used 250 amp gas drive welder,miller,lincoln hobart for $500 to $800 bucks
for my DC welding needs.
You can drag it out to your towers if need be.
 Also use it as a generator when the power goes out.
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WA1GFZ
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« Reply #8 on: June 10, 2005, 08:57:41 AM »

high frequency welder. Does anyone know how high the frequency?
Use your class e transmitter as a tig welder. Climb up the tower and
unhook the coax and attach the stick. Just need to remote key the rig.
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« Reply #9 on: June 10, 2005, 09:17:22 AM »

Quote from: WA1GFZ
high frequency welder. Does anyone know how high the frequency?
Use your class e transmitter as a tig welder. Climb up the tower and
unhook the coax and attach the stick. Just need to remote key the rig.


I once read a review of a large solid state audio power amp where they fed the thing with a tone and used the output to weld. Or so they said.
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K1JJ
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« Reply #10 on: June 10, 2005, 11:22:56 AM »

Quote from: WB2RJR
Tom,

When we took a drilling rig to Turkey we had a new Onan
generator/DC welder for the rig since we had to fabricate
and repair our own stuff. Not cheap at 3K but when I first
used it I couldn't believe it. My welds looked like the ones
in those books. Basically I just did what I do with the AC
welder but the welds look great and next to no splatter.
DC holds a better and more uniform arc, and it's easier
to do than AC welding. I was using 6013 sticks like I do
for most stuff.

Yep, that's what I was hoping to hear!  I will definately
look around for some big surplus rectifier "spark plugs"
to mount on a heat sink.

It's taken me many welds to get good at AC arc welding.
I think it was great basic training with crap equipment and
now with good stuff,  the welds will look real good like you
found with DC..

A high freq system sounds interesting too, though might
as well buy a cheaper  combo MIG/TIG system with the
shielding gas and do it right.  The DC converter is just an
intermediate step.

Thanks again for the info.

T
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KE1GF
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« Reply #11 on: June 10, 2005, 11:30:28 AM »

Quote from: WA1GFZ
high frequency welder. Does anyone know how high the frequency?
Use your class e transmitter as a tig welder. Climb up the tower and
unhook the coax and attach the stick. Just need to remote key the rig.


Frank attach the Torch, with TIG you hold the stick in your hand, kind like gas welding only with a squarewave driving an arc...

I suppose that you could make an power-transformer less H-brige forward converter that would put out a ton of current in square-wave form, I think the chips from unitrode (TI now) will control up to about 75kVA...
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Chuck k3xu
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« Reply #12 on: June 10, 2005, 11:52:34 AM »

Check this link out !
http://www.deltaschooloftrades.com/
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WA1GFZ
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« Reply #13 on: June 10, 2005, 12:19:00 PM »

The transformer inside a welder is an interesting device. think about the short circuit when the stick gets stuck to the metal. Current is limited and you don't blow the primary breaker. This is a cool trick in the transformer design to limit current without killing primary inductance. A solid state design in current mode would do the same thing if it is fast enough to protect the hardware. I wouder if you could just drive the primary of the lincon at a higher frequency??
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« Reply #14 on: June 10, 2005, 05:12:32 PM »

Those AC buzz box I think use a core that moves in and out of the transformer or inductor.  I think the series inductance changes when you spin the knob around.  It's been a while since I opened mine up and cleaned it out.  You will see if you open yours up.  If you don't tighten the knob down the core will go in in an effort to find the maximum reluctance like a solonoid.

Tom,

I have 4 very big dual diode modules mounted to a heatsink.  I can hook you up with a fan braket too if you want.  You supply 115 or 230 fan and away you go.  Maybe some rc snubbers around the diodes to tame the noise some. I think there's about 400amps worth of full bridge rectifier.  I also got some very nice Eutectic rod around here for welding up aluminum.

Boss wanted me to weld some big aluminum so he gave me all this stuff.  Boss took off and project got cancelled, so just taking up room in shack.  I was going to build a Boeing 747, but other projects got in the way so it's yours if you want.

Not sure of switching frequency, but I think most BIGGER welders probably using Igbt's so probably below 20kHz, and yes, similar technology used in welders as switching audio amplifiers, motor drives, UPS, and that amazing High Frequency Resonant Zero Voltage Switched Full Bridge Phase Shift Modulator  that I built - The one without the meters.  The Unitrode solution would probably work, but if you are serious do yourself a favor and pay a few grand and buy a welder off the shelf. A monumental task to get one of these full bridge things runnning good.  I'm not sure but maybe there is really a dc current with just some HF riding on top of it.

Regards,
Bob
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K1JJ
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« Reply #15 on: June 10, 2005, 08:54:59 PM »

Quote from: N9NEO
Tom,

I have 4 very big dual diode modules mounted to a heatsink.  I can hook you up with a fan braket too if you want.  You supply 115 or 230 fan and away you go.  Maybe some rc snubbers around the diodes to tame the noise some. I think there's about 400amps worth of full bridge rectifier.  I also got some very nice Eutectic rod around here for welding up aluminum.
Bob


Hi Bob,

Yes!  I would like to try those big Mo-Fo rectifiers. It will be fun to weld with DC.

BTW, those aluminum rods will weld aluminum w/o using a shielding gas?

I often wondered what they were doing inside with that crank to adj current limits. Mine is real hard to turn, so it'd be a good excuse to take it apart and install the rectifiers and oil it up.

T
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Do you use crocodile clips in your shack?
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« Reply #16 on: June 10, 2005, 09:37:22 PM »

Ok, I will find a fan bracket and look around for rod.  I also have some very large EI core inductors that you may want to take.  I seem to recall that I was looking at inductors on the dc side for some reason.  Probably to reduce current ripple and get nice weld.

Yes on the Eutectic Castolin 4021  They will weld ok no sheild.  I think DCRP too.  Project called for welding 3/4", so I needed big amps.  I suspect that it might be possible to gas weld with these rods too.  They will tell you no you can't, but what do they know.  I tried to preheat aluminum and gas weld, but stick wouldn't stick to Al.  Kept rolling off.  It was an 'Unweldable aircraft Alloy" Maybe they are right.

link below to thread on converting buzzbox to dc.

Just say NEO!

http://groups-beta.google.com/group/sci.engr.joining.welding/browse_frm/thread/84cd6a805446e865/8815240faa95d0a7?q=n9neo&rnum=1&hl=en#8815240faa95d0a7
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K1JJ
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« Reply #17 on: June 11, 2005, 01:00:27 AM »

Bob,

I read a lot of that old buzz box conversion thread. Looks like there was a lot of discussion about it.

OK on using the inductor. Sounds like a good idea to maintain the arc and reduce ripple.

Let me know when ya get everything together, OM.

Tnx.
73,
T
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« Reply #18 on: June 13, 2005, 08:04:34 AM »

An inductor will limit input current and cause a big voltage spike as the rod is removed. I'm not sure if this will help or hurt. Might want an output cap. Yes the coupling in the transformer is key in limiting current.
Variable coupling in the transformer
I think they are called magnetic shunts if I remember from constant voltage transformer design days.
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Chuck k3xu
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« Reply #19 on: June 14, 2005, 11:09:04 AM »

Tom(k1jj)  What shade lens do you use when you weld ?
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K1JJ
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« Reply #20 on: June 14, 2005, 12:15:04 PM »

Hi Chuck,

Gee, I'm not sure.  I bought the accessories years ago as a
package and the guy told me what to use.

I can say that it is on the edge of darkness where I can see
what's going on, but any darker and I would have a problem
seeing. So guess it's OK for AC arc welding.


I also have a set of goggles used for brazing that restrict less,
but would be too little for welding.

I'm curious, why do you axe?

T
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« Reply #21 on: June 14, 2005, 02:35:30 PM »

The shade lens you use is just was important as the rod you use.
Most welding helmets come with a shade ten lens.
This is OK for light stick welding jobs (80-90 amps)
Tig welding you should use at least a shade 11 and darker.
 Welding with a shielding gas(Mig) the arc is brighter shade 12 - 13 needed.
Higher amp welding like 1/8 flux core, 5/32 7018  you should use a shade 13 lens.
I like the gold plated shade 13 lens. It blocks %100 of the UV to your eyes
and the welding is in color. blue arc, red weld puddle, orange sparks
very easy to see if your getting slag inclusions.
A shade 5 is used for  hot wrench work.
Plasma cutting shade 8 to 10.
I know welders that have made the move to a darker lens and there skills improved allot.
They would be blinded by the arc light and missed seeing more of the puddle.
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« Reply #22 on: June 14, 2005, 02:44:41 PM »

Tom,

What a pain, can't see crap until that arc is striked. My friend who runs a welding/machining shop uses one of these......

http://weilerwelding.com/shopsite_sc/store/html/EQChelmets.html

God, these are great, you can see perfectly, and when the arc hits they go immediately dark. You don't have that deal where the weld starts an inch off of where it should be because you couldn't see anything with the helmet on.

Start a welding business so you can write off all this stuff.

73 Marty WB2RJR
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Chuck k3xu
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« Reply #23 on: June 14, 2005, 03:08:34 PM »

Some of the higher end auto dark hoods have a shade control on them.
I never liked the auto dark ones because I would get a small flash of arc light before it would darken.
I would run 1/16 metal core 6 wire (high bred mig wire)at around 300 amps running in 3/4 Filet welds.
At this amp setting a small flash would give you sand paper eyes at 2AM.
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« Reply #24 on: June 14, 2005, 03:16:56 PM »

Tnx for the info, Chuck.  I printed it out to save.

I checked and found my shade is a 10 and the welder is set at about 100A... so guess I'm OK.  I'm using 1/8" rod, 6011 right now.

If I go to the DC welding I wonder if I should move up to that gold 13 lens?


Marty:  Yes, I have looked at the electronic ones, but at $200+ I figured I didn't weld often enuff. I also wondered about the attack time Chuck mentioned of these, since nothing is instantaneous and with light, it goes pretty fast...:-)

Boy, starting your own metal fab/welding shop appears to be a good money maker. The guys I know have done very well, but are good.  I'd enroll in a tech school course if I were to take it seriously, but just a hobby thing when I need it for now.

73,
T
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