Converting Stick Welder from AC to Full Wave DC

[Rick V]

Converting Stick Welder from AC to Full Wave DC

I’ve got a cheap ($77 Canadian 'special' from Princess Auto) 117 volt imported AC stick welder. It’s OK – I want to convert it to full wave DC. Why? I saw a fellow at work welding with a new model massive Lincoln welder using DC+ on 3/32 inch 7018 rod. To show me where I might be going wrong with my technique, he welded at 85 amps then dropped to 65 amps – the same amperage range as my machine. Compared to my welder:
a) - He struck the arc easily (not like me having real sticky problems starting a new rod),
b) - The weld arc was smooth (mine always sounds angry and darts here and there),
c) - The weld went down beautifully (mine welds like to go down in lumps), and
d) - The thin slag layer just peeled off as he lightly stroked it with the chipping hammer (I have to beat chunks mine off with the hammer then really wire brush well.

Wow, I said – that’s wonderful, so what’s it like on AC?
So he switched to AC and – guess what?
a) - He had trouble striking the arc - sticky problems starting a new rod,
b) - The weld arc was rough, sounded angry and darted about,
c) - The weld went down somewhat lumpier, and
d) - That thin slag layer; he had to beat chunks off with the hammer then wire brush the weld.

Conclusion: DC is way better than AC!
Lesson Learned: I want to convert from AC to DC.

How to do it – cheaply?
My small 117 volt welder runs on 30-40 amps input (Yes, that high.) I turn a knob to adjust welding current/voltage; inside the welder this slide one part of a two-part transformer into or out of the other part. I measured the output using twin-carbon arc to simulate welding with rod. The welder outputs a variable AC welding current from about 40 amps (at about 22 volts) to 85 amps (at 42 volts). The open circuit voltage is 62 volts.

In order to convert AC to full wave DC, I need to make up a full wave bridge rectifier - cheaply. (We all like that concept.)

Option 1: Use 4 big amperage diodes and make up a rectifier bridge.
Best buy I could find was on MOTOROLA MR1265FL RECTIFIER rated 300 PIV 650 amp; it looks like a two-inch diameter, 2 inch white ceramic puck on a 3 x 3 inch flat metal base plate.
Best Price (new) was $17.50 US dollars from Fair Radio out of Lima Ohio at web site http://www.fairradio.com/rectif.htm
Let’s see: 17.50 x 4 = ~$72 plus shipping…. Say $100 Canadian.
What do I get?
300 PIV (peak inverse volts) will handle my puny welder's 62 open circuit volts with ease.
650 amp rating will handle even my short circuit output current of say absolute max of 150 amps.
Two hassles:
- Wiring up to these massive diode pins and diode plates will not be easy.
- Complicated mounting: the electrically conducting plates must each be on a heat sink but each set of two diodes must be separate heat sinks and the two sinks insulated from each other. Also, these things are big, they will not fit inside my welder; I would need to build a separate box to house the diodes. This means extra external cables with connectors ($ expense) to go from the welder to the diode box.

Option 2: Use several smaller amperage bridge rectifiers in parallel to reach the current needed.
Best buys I could find were:
International Rectifier GBPC3510, 35 amps at 1000 PIV for $2.62 Canadian dollars each, or
Some other manufacturer MB3510, 35 amps at 1000 PIV for $2.86 Canadian dollars each. (Prices from e-sonic in Toronto Canada)
To go up even 5 amps in capacity, like to 40 amps, costs too much. The price decrease to drop from 35 amps to 25 was 10 cents. To drop the PIV from 1000 down to say 400 saves about 20 cents. So, let’s stick with bridges rated at 35 amps and 1000 PIV.

I’m not so certain of running diode is parallel, so I want a bit more capacity that the 150 amps in option 1; let’s go for about 200 amps. At 35 amps per bridge, this means 6 bridges in parallel for 6 x 35 = 210 amps. This will cost me 6 x 2.62 = $15.72 Canadian plus shipping, say $20 – Cheap!

Neat thing about the bridges, at the temperature rises; the specifications indicate that their current carrying capacity goes down. So, if one bridge heats up from carrying more current than its parallel neighbours, the hotter bridge automatically carries less current…. Cool!

Wiring will be easy since I can use multiple short runs of #10 wire and female spade connectors - heavy duty versions of standard auto connectors. I think that I can also mount all 6 bridges on a copper bar just in front of the rear fan - inside my welder. I would have to remove the cover to change polarity. If I want to externally change polarity, I would need to install welding cable joiners external to the welder - that would cost more than $20 worth of bridge rectifiers.

So, that’s where I am with my thinking at the moment.
Any flies in this soup?
Comments? Suggestions?

Rick V.

[MAC702]

You'll want more than just the rectifier set-up. You'll want a choke to smooth out the current, or it will still be going to zero at 120Hz (or are you on a 50Hz system? In which case it will still go to zero at 100 Hz.) With just rectifiers, instead of the sine wave, you'll get humps from zero to maximum, but always positive. A capacitive/inductive choke will smooth it out and make it much more pleasant for welding. There are plans and parts available on the Internet for the searching. Others here may know more as well. I've always had a DC machine. My dad did have a homemade bridge-rectified AC machine when I was a kid, but I don't really remember much except it, except it was a Hobart the size of a refrigerator.

[Rick V]

An update on diodes in parallel...

I had a look inside my Canadian Tire MIG/Flux Core Wire Feed Welder - actually a Campbell Hausfeld WG206000AV 115 Volt input with 70 Amp DC output.

Hey, it uses a bridge of 8 diodes - like a conventional bridge rectifier set up 4 diodes but with two diodes in parallel in place of each diode in a conventional bridge.
IMPORTANT POINT: Commercial welding equipment is using diodes in parallel - in this case it looks like two 35 amps diodes in parallel to achieve the 70 amp output.

Some observations:
1 - The diodes are all button-type with integral metal housings (cans), each the size of a ten cent piece. The can is serrated and simply pressed into a hole in the heat sink.

2 - There are two style of diodes, 4 with +ve metal cans (black epoxy centers) and 4 with -ve metal cans (red epoxy centres).

3 - There are two flat-plate aluminum heat sinks - one with holes holding the 4 diodes with +ve cans and another sink with holes holding the 4 diodes with -ve cans.

4 - Each set of 2 parallel diodes are on mounted with an inch of each other on the same heat sink.

5 - There are no power resistors connected to the diode pairs to balance current; the diodes are just connected in parallel - period.

Thus, using diodes in parallel can be done - as is done by welding suppliers.

Rick V

[awright]

Yes but the manufacturer is probably sorting his diodes by forward voltage drop and assembling them in matched pairs. The more welders you are selling and the more diodes you are sorting, the closer you can afford to match forward voltage drop. Since we, as home brewers, usually do not have access to either large batches of diodes or equipment to match forward drop at high current, I would not recommend use of pairs of diodes to achieve desired current handling as a practical approach at home. After all, how much effort in matching diodes is worth the modest price advantage? It is, however, worth the cost if you are selling thousands of units.

Some high current diodes actually do have two or more matched diode pellets inside the package, unbeknownst to us unless we study the manufacturer's spec sheet. But in that case, the manufacturer has matched the diode chips very closely, probably at high speed using automated equipment on the assembly line. Additionally, the multiple diode pellets are inherently very closely matched in temperature due to proximity inside the package.

Have you explored the various surplus houses for high current stud-mount diodes? Here again, for home brewers, I think stud mounted diodes are MUCH easier to properly mount than hocky puck diodes unless you use the manufacturer's mounting hardware for preloading the pellets inside the hocky pucks to the proper clamping force. Proper clamping force and mounting surfaces meeting the flatness and smoothness specs of the diode manufacturer are vital for proper current handling by the diode. The pellet is actually loose inside the hocky puck and the extermally applied clamping force is the only thing creating the proper contact between the pellet and the mounting surfaces of the puck. Insufficient force and you risk losing current capacity. Too much force and you risk fracturing the pellet.

I seem to remember recently coming across some high-current stud mount diodes being offered by surplus houses. I wasn't interested because I have gathered some high current stud-mount diodes over the years for my own welding current rectifier (as soon as I get a round toit). Try Industrial Liquidators on Hawthorne Boulevard in the LA area or Triangle Machinery in the San Jose area (sorry I don't have their web addresses handy, but they should be easy to find). The reason I am suggesting these is that thole are the only surplus electronics places I've been to recently where I might have seen the high current stud diodes. The nice thing about getting diodes that have enough current capacity in a single package is that no matching is required when you build up your bridge.

I agree with MAC702 that a stabilizer coil in the DC welding circuit will be advisable to smooth the arc.

Have fun, and let us know how it works out.

awright

[MotoFab]

Originally Posted by Rick V

An update on diodes in parallel...

I don't want to dissuade you from your rectifier project Rick, but this Harbor Freight 80ADC inverter is on sale for $119.99. It might be easier to buy a complete box in the long run, but I know how it is once I get the scent of a project. Anyway . . .


I have one and it works real well. It is made in China, but it is the GYS brand in other markets. It has the Dinse cable connectors, and a cast bronze work clamp. Pretty nice by any standard. It is quite happy with 3/32" 7018 DC+. And uses a 20A circuit and is good with a 50ft 12AWG extension cord.

You can parallel multiple units and make a lotto amps. 160A for $240. Same goes with that HF 130A DC 220VAC TIG/Stick product. Just parallel the front panel pots and you have 260A for under $400 on sale. I mean since you are electrically industrious.

- Jim


http://www.harborfreight.com/cpi/pho...1199/91110.gif

[Rick V]

awright - thanks for the insider info on the diodes - very well informed.

MotoFab - ye make a lightweight (inverter) argument with strong output!
Amazing... the idea of paralleling two inexpensive inverter welders opens whole new possibilities for creating almost ripple free DC - at very high efficiency!

A couple of those 130A DC 220VAC TIG/Stick you mention could serve as the 'POWER SOURCE' - pure ripple free DC for not only stick and TIG but for a MIG gun as well. We are talking totally variable 0 - 260 amps output here - that costs well over $2,000 in any MIG machine I have seen.

At this price, we may be hearing the first 'gong' of the death knell for conventional 60 cycle-transformer/rectifier/choke welders.

Great input fellows... thanks
Rick V

[MotoFab]

Originally Posted by Rick V

awright - thanks for the insider info on the diodes - very well informed.

MotoFab - ye make a lightweight (inverter) argument with strong output!
Amazing... the idea of paralleling two inexpensive inverter welders opens whole new possibilities for creating almost ripple free DC - at very high efficiency!

A couple of those 130A DC 220VAC TIG/Stick you mention could serve as the 'POWER SOURCE' - pure ripple free DC for not only stick and TIG but for a MIG gun as well.

Great input fellows... thanks

You bet. Here's something Rick. You may or may not know but I'm just puttin' it out there.

From a certain perspective, the 'Constant Voltage' part of the CV supply of a typical MIG transformer-based supply doesn't really exist.

CV is more of an 'artifact' than any actual electronic hardware. How it works is, as a byproduct of driving the wire, the DC drive motor is controlling the voltage. The motor leads are connected between the torch and work clamp leads, and is powered directly from the welder output.

Sure, there is a variable voltage knob to add or subtract an 'offset' to the motor speed. But the motor is driven by the voltage in the arc gap. And here's something else, it has 'closed-loop' control that also doesn't really exist.

I mean, there is no actual 'closed-loop control circuit'. The 'control and feedback voltage' it is a physical phenomenon of the arc.

* * * * *

The closed-loop Constant Voltage supply works like this . . . If the arc gets longer the voltage increases and the motor speeds up and shortens the arc. If the arc gets shorter the voltage decreases and the motor slow down and lengthens the arc.

Visualize this. The most experienced Stick welders have a Constant Voltage control built-in to their hand and arm. Using their arm, they control the arc voltage via arc length control. The most experienced Stick welders have a tightly controlled arc length just like a MIG wire feed.

* * * * *

So, the MIG transformer is actually a Constant Current supply. It's current is unregulated, but it is constant current just the same. Sort of like a battery is an unregulated constant voltage supply.

All welding supplies are Constant Current. The front-panel-switched multiple taps of a MIG transformer are functionally identical to a transformer-based Stick supply with selectable amperage.

Also functionally identical are the 'infinitely adjustable' Stick transformers and the MIG transformers with a 'lamp dimmer' installed on the line-in to the transformer primary.

* * * * *

Well, if the MIG supply is Constant Current just like TIG and Stick, what turns the MIG into a Constant Voltage source? The drive motor operating from the arc voltage.

If you think about this, you can easily imagine adding a wire feeder to either a transformer-based or inverter-based TIG or Stick supply. You just have to get the arc voltage divided right to set the desired arc length.

* * * * *

You know what Rick, since you are so industrious, you could try making an AC MIG machine. The arc would be AC alright. But a low-amp bridge rectifier and capacitor connected between the output leads will make enough DC amps to drive the motor. Or even easier, a 'universal' brush-type motor will operate from AC or DC. Maybe there's one in your machine.

- Jim

[awright]

Whoa, there, Hoss! Slow down a little bit!

Motofab, I think you are going to confuse lots of guys out there with your "clarification" of constant voltage/constant current supplies. While I can agree with some of your analyses of the feedback mechanism in MIG supplies that use the arc voltage to control the wire feed speed, don't forget that many MIG machines out there do not use arc voltage to control wire speed - they use constant, manually selected wire feed speed and the arc length adjusts itself to consume the wire at the speed it is fed into the arc (within the limits of machine capability).

There are most certainly distinctly different types of welding power supplies, although they are generally not purely one or the other because the current from CC supplies does vary somewhat with conditions in the external welding circuit and the voltage from a CV supply does vary somewhat with welding circuit conditions. The deviations from "ideal" CC or CV characteristics arise from both intentional design to create the desired feel and response to the welder's manipulation of the torch/electrode and from the cost, difficulty, or impossibility of achieving the pure form of either design.

The transformer version ot these two types of machines are generally constructed quite differently, although it may not be obvious from outside the covers. A transformer-type CV machine generally has an ordinary type of transformer with magnetic flux always fairly tightly coupled to both windings (primary and secondary). This means that the secondary voltage tries to stay constant, with secondary current increasing in response to reduced load impedance. Some slope or self-limiting of output current may be built in to avoid destructively high secondary currents in the event of a short between electrode and work. There is also usually an inductor in the AC circuit prior to any rectifier and/or a smoothing coil in the torch loop downstream of the rectifier. These add desirable characteristics, such as slope or arc stability and smoothness.

Conversely, a transformer-type CC supply will often have a transformer that provides for a large and adjustable amount of leakage flux. That is, not all of the magnetic flux induced in the magnetic core by the primary is coupled to the secondary, with the amount that is not coupled being manually or automatically adjusted to get the desired output current. This adjustment may be achieved by moving the primary and secondary windings apart physically, thus decreasing magnetic coupling between the two, or by inserting a magnetic shunt into the core of the transformer between the two windings. This shunt acts as a variable magnetic short circuit, causing some or much of the magnetic flux to be diverted around the secondary, thus limiting current output. Some machines use an electronically-controlled, saturable magnetic shunt to accomplish the same function automatically.

Take a look at the volt-ampere curves on page 11 of the MillerMatic 251 constant voltage MIG machine manual and on page 11 of the Miller Econotig constant-current machine manual (arbitrary examples that I happened to be referring to recently). The CV curves for the econotig are nearly vertical (nearly constant-current) over much of its operating range, and the CV curves for the MillerMatic are very nearly horizontal (constant voltage) over much of its operating range. Those are the characteristics built into the machines that define the type of machine. That fulfills my definition of, "... actual electronic hardware..."

Motofab, I think I vaguely grasp what you are getting at in your comments about constant voltage and constant current machines, but I fear that the way you are stating it will not assist the understanding of the process by many new welders.

I find the discussions of power supply design in, "Welding Power Handbook," by A. F. Manz of Linde Division of Union Carbide (1981), and, "Welding Processes and Power Sources," by Edward W. Pierre (fifth printing, 1981) to be very helpful in understanding welding power supply design. I picked them up in my local independent used book stores.

awright

[Rick V]

Hey - this is great stuff.
MotoFab and Awright, I see you-all helping CoachGeo (George) too.... My Gosh - scary stuff! Still, if George doesn't fry himeslf with those darn AC welders (instead of DC ones), he may provide the answer of high power DC MIG at low cost.

Motofab - quote
You know what Rick, since you are so industrious, you could try making an AC MIG machine. The arc would be AC alright. But a low-amp bridge rectifier and capacitor connected between the output leads will make enough DC amps to drive the motor. Or even easier, a 'universal' brush-type motor will operate from AC or DC. Maybe there's one in your machine.
...then
Awright - you recall I said my Canadian Tire (CTC) Wire Feed Mig Welder (Campbell Hausfeld-CH) with 70 amp DC output used a bridge of 8 diodes (not 4), using pairs of 35 amp diodes in parallel? You said the manufacturer's can sort many diodes to attain matching characteristics and pair them up.

Well, things changed this week. Thursday, I got authorization from CH to return the welder to my CTC store and I did - got a full refund. I then went out to BOC welding supply to look at Lincoln SP-175T and Miller equivalent. I crawed around inside the SP-175T because it was 'on special' for $900 Canadian (~800 US I guess). Friday night the CTC flyer arrived... yikes..the MIG-PaK 15 was on sale for $200 off - sale price $550! I couldn't resist; I bought one.
So... MotoFab, I won't be building an AC MIG machine.
So..Awright, my MIG-Pak 15 uses a bridge of 16 diodes! - apparently in pairs of pairs! (Thought you would like that! You know double-double ???.)

Interesting inside the MigPak 15. On the outside and user accessible space (wire rollers, main external connections), the MIG-Pak 15 is identical to the SP-175T I saw two days ago. Inside where the electrics live, I am willing to bet, it is identical too - exact same power output rating of 130 amps at 20 volt with a 30% duty cycle .... and for almost 1/2 the price, I can live with a different plastic front name plate! (Oh, I am short only a gas regulator and hose - the gas solenoid and liner are installed.) I had the regulator and hose - so was up and running fast!
(Well after calibrating the machine for wire speed and my gas regulator [# turns to produce a given flow rate in cfm] with that specific machine.)

Filtering:
Where my Campbell Hausfeld used a choke input filter - after the rectifier bridge, the Lincoln uses a capacitor input filter (in parallel) followed by an inductor (in series) with the +ve output.

Rick

[MotoFab]

Quitter ! Heh heh

Nice deal on the machine.

Rick, were you experimenting with 100% CO2 shield gas?
You were getting a good price for it from a Paintball store or something?
Looks like straight CO2 is okay by Miller.

Anyway, check out pages 24 and 25 of this Manual that AW pointed out.
http://www.millerwelds.com/om/o1326x_mil.pdf

Or pages 22 and 23 of this Manual (nearly the identical manual from Jan '04)
http://www.millerwelds.com/om/o1326p_mil.pdf

- Jim

[awright]

One clarification and a comment:

In my, "Whoa, there..." post I carelessly used "CV" in two different ways. While that post is ancient history by now, let me clarify what I was referring to for posterity.

I used the term in the conventional usage in discussing Constant Current (CC), and Constant Voltage (CV) machines through most of the post. Then, in discussing volt-ampere curves, I carelessly used "CV" to refer to the volt-ampere curves in the Miller manuals, in this case using the term as "Current-Voltage" curves. My bad.

Rick V, it would be interesting to know if the SP-175T is identical inside the case to the MIG-PAK 15, especially if they also use 16 diodes in their rectifier. Paralleling four diodes in each leg of the rectifier bridge as a cost-saving method seems a little extreme to me They must have gotten a real deal on small diodes to make that worthwhile. Those press-in diodes were originally developed for automotive alternator applications and are probably cheap as dirt in large quantities due to volume production for the auto industry. Additionally, pressing them into holes in heat sinks is probably a very cheap assembly technique.

Hope you enjoy your welder.

awright

[Rick V]

MotoFab and Awright - thanks for great background info and suggestions.

RE MotoFab - "Rick, were you experimenting with 100% CO2 shield gas?
You were getting a good price for it from a Paintball store or something?
Looks like straight CO2 is okay by Miller. "
Yes - I have two 20 oz tanks. (Since 1 lb CO2 = 8 cf, 20 oz = 10 cf)
Each tank holds 10 cf of CO2, so at 15 cf/h I am good for ~40 minutes welding/tank. A tank fill costs me $2.50 on Fridays.
I don't do a lot of continuous welding nor leave the welder set up. So the portability, low entry cost, fill anywhere, low fill cost and no rental fees works for me. I already have one straped to the back of my new Lincoln - about the maximum weight in a portable - guess about 60 lbs.

RE Awright - "Rick V, it would be interesting to know if the SP-175T is identical inside the case to the MIG-PAK 15, especially if they also use 16 diodes in their rectifier. "
Yes - tell ya what. I'll go to BOC and ask to see the insides of that SP-175T. Now I'm curious. I'll report back!

Rick V

[MotoFab]

Originally Posted by Rick V

MotoFab and Awright - thanks for great background info and suggestions.

. . . A tank fill costs me $2.50 on Fridays.

You bet, And heh heh, and at a gas store an additional $20 for the hookup fee

Please, call me Jim

[Rick V]

Originally Posted by Rick V
Awright - "Rick V, it would be interesting to know if the SP-175T is identical inside the case to the MIG-PAK 15, especially if they also use 16 diodes in their rectifier. "
Yes - tell ya what. I'll go to BOC and ask to see the insides of that SP-175T. Now I'm curious. I'll report back!

Reference: MIG Pak 15, MIG-Pak 15, MIG-Pak-15, MIG Pak-15, MIG PAK 15, MIG-PAK 15, MIG-PAK-15

Hi, I just returned from the welding supplier, having looked carefully at the innards of a Lincoln SP-175T.
Is the Lincoln SP-175T the same as a Lincoln MIG-PAK 15?

The answer - Absolutely Identical In Every Detail! (Except the name plate on the front.)
Same fan housing, rectifier bank (yes, the same 16 diodes on the same configuration heat sink), same transformer, choke, power capacitor, circuit board, circuit breaker, gas solenoid, off/on switch, power-selector switch and rheostat wire feed adjuster. They don't come anymore identical!

There it is - Final Answer? Yes, that is my final answer -
The Lincoln SP-175T is absolutely identical to the Lincoln MIG-PAK 15.

Rick V

[popeyeus]

Go to the junk yard and find a old three phase dc welder and take out the 3/4 inch stud diodes and or single phase diode bridge assembly from a old gas generator welder. Maybe take out a reactor coil from some other old welder and capacitor for your choke filter reactor coil. Maybe you be in luck and find a whole welder that still works, but has a loose wire or burn of connection, most common problem with welder that are thrown away. I found a old forney welder that way for 17 dollars scrap price. I also bought a scrap lincoln 225 welder that just need cables and a plug in connector on the end of the 220 line. Wire brushed it and spray painted it. Looks like new. Bought a old scrap trindl 125A welder for 10 dollars. Needs cables. It is wired for 125 volts but has a double primary winding connected in parallel for 125 volts and could be wired for 250 by putting the two primary windings in series in the proper phase with each other. The maximum output with this welder is 100 amps drawing 25 or 30 amp on 125 volts and about 15 amps wired for 250 volts. I want to build a portable dc converter with filtering to be used on any buzz box welder. I would like to make them for sale. That would be fun to do. And with how many hundreds of thousand ac welders out there, there could be a market for them. I thought i remember years ago, that sears had something like that.

[daman]

Or just go buy a AC/DC off CL for $200 and call it a day!

[Bluewelders]

He probably did whatever he was going to do 4 years ago.

[daman]

Originally Posted by Bluewelders

He probably did whatever he was going to do 4 years ago.

I read the date,,,i was commenting on someone else's attempt to do this..

[Rick V]

My, my, my - My 4-year-old post Resurrected from the Dead!

He probably did whatever he was going to do 4 years ago. - Bluewelders

Not quite - I still don't have an AC powered DC stick machine of about 150 amps.
(Although I did get into 200+ amp DC welding with car batteries and a home-made arc stabilizer.)

Or just go buy a AC/DC off CL for $200 and call it a day! - daman

Yep Good Point! - that's what I have been doing the last couple of weeks.
See my recent (April 21, 2010) post, "Lincoln-Anyone know the Model # and Specs?"

At the moment, I'm weighing two used machines on Craig List:
- Used AC/DC 225 Lincoln asking $265
- Used Miller Thunderbolt AC/DC machine asking $295 (similar specs as the Lincoln)

Hey I'm 4 years older, retired on a pension and now consult. I have more spare $ and less ambition = the idea of building instead of buying now holds less appeal.

Thanks for the Resurrection!
Rick V.

[daman]

Originally Posted by Rick V

My, my, my - My 4-year-old post Resurrected from the Dead!


Not quite - I still don't have an AC powered DC stick machine of about 150 amps.
(Although I did get into 200+ amp DC welding with car batteries and a home-made arc stabilizer.)


Yep Good Point! - that's what I have been doing the last couple of weeks.
See my recent (April 21, 2010) post, "Lincoln-Anyone know the Model # and Specs?"

At the moment, I'm weighing two used machines on Craig List:
- Used AC/DC 225 Lincoln asking $265
- Used Miller Thunderbolt AC/DC machine asking $295 (similar specs as the Lincoln)

Hey I'm 4 years older, retired on a pension and now consult. I have more spare $ and less ambition = the idea of building instead of buying now holds less appeal.

Thanks for the Resurrection!
Rick V.

I found a used but like New Hobart AC/DC the other day but was already gone by the time i called on it $200,good deals out there but you gota jump on them.

[Rick V]

Right again daman! You gotto be FAST, yet you got to be prudent too.

It gets more complicated when you can't find aything locally but do find items in towns and cities 1 to 2 hours drive out of town.
e.g. Will you be the first guy to arrive with the cash in hand?

Also, I have seen good deals vanish - stamped sold but then re-appear a week later ???
What gives with that? Buyer didn't show? Buyer offered too little money on the spot?
Or... maybe the buyer found something wrong with the welder... the most scary one.

Can you trust those 'Resurrected Old Ones'?

Rick V