Portable Welder




Introduction: Portable Welder

About: At 50, I have a vast array of experiences that cover many interests and technical domains. I started programming at 16, 1984, on an Atari 800 computer. I've been around, and actively involved, for most of the …
  • Automotive and Motorcycle: [WON RUNNER UP!]

I was interested in a "portable welder".  I started investigating and I found a few gas and propane driven models from $699+

I then found a great Instructable that started me thinking in a different way: http://media.nbcmontana.com/id/SpoolGun/

Instead of a gas generator powered welder, I could use a 24V DC battery powered welder system; based around a spool gun.

I currently own a Lincoln 175HD 208V [220V AC circuit] welder which can weld aluminum via its push-wire gun, but it requires changing out a liner in the gun's cable so that the wire doesn't "birds nest" [bunch up] in the feed tube.  Needless to say, it raises the threshold of "what's worth the trouble" of switching everything out.  Lincoln now makes a separate spool gun that works with the newer models of Lincoln welders, but not with my 175HD.  I found a great "retrofit" website on how to wire the spool gun for use with my welder.  Having a spoolgun that I would use for aluminum welding, and the push-wire gun for other wire types, would lower that threshold, and I could also use the spoolgun for my portable welder idea.

So while Tim Anderson's great Instructable is based around a generic spoolgun that he found on ebay [priced in the $135-$150 range], I decided to go with the Lincoln Electric Magnum 100SG Spoolgun [priced in the ~$222 range] so that I could use it with both my existing AC powered welder and the DC welder that I had in mind.

Complexity:  Intermediate, requires:
  • knowledge of welding
  • knowledge of DC electronic circuitry
  • experience with High Amperage vehicle batteries

Safety: *Special precautions*
  • I am not a professional certified welder nor electrician, so understand that you (like I did) assume all responsibility and liability for attempting to [re]create this project.
  • Not going to get into the whole Edison vs. Tesla debate of the safety of DC vs AC, but for this specific project, DC is relatively safe.  Relatively in that you won't get "shocked", but the arc from high amperage DC current releases various gasses, radiation, and produces enough heat to seriously burn, even maime.
  • While welding, make sure you use protective gear and cover your skin.  A DC arc can generates molten metal slatter, enough ultraviolet radiation to give you a sunburn, and can permanently damage your retina if viewed with the naked eye.  Be cautious of any spectators/bystanders

Step 1: Parts List

Lincoln Magnus SG100 Spoolgun $222.00
Stanley FMST20261 FatMax Metal and Plastic Toolbox with Drawer [Limited Quantity Remaining] $51.45
50' of 1/0 Welding Cable [25'red/25'black] $130.00
Positive & negative set battery ring insulated junction post terminal block stud $15.00
NEW waterproof DC/DC Converter Regulator 12V Step UP to 24V 72W 3A $24.99
NEW waterproof DC/DC Converter Regulator 24V Step down to 12V 120W 10A $19.99
Bussman DC Circuit Breaker 150 Amp Surface 181150F Auto $31.99
[20 total] Solder Pellet Solder Slug for 1 Awg wire Pink $13.00
[8 total] Solder Pellet Solder Slug for 1/0 Awg wire Black $6.80
[4 total] Anderson SB175 Connector Kit 1/0 Awg ~$28.00
[2 total] Anderson Power Poles connectors PP120 $2.35
12V 40A SPST Premium Relay & Socket 4Pin 4P 4 Wire For Car Auto $4.99
S18884 HOSE NIPPLE $4.65
T9078-3 THUMB SCREW $1.35
20A-350A Contactor $98.00
Circular Connectors - Contacts > SA3349/1 $12.95
NOT CHEAP, but was exactly what I wanted!      Total ~$750.00

* These come in a selection of colors which are interchangeable EXECEPT for the yellow ones. The yellows plugs only fit other yellow plugs
* I was unable to find the specific connectors that fit the PP120s. I was able to grind down two of the connectors from the SB175s to fit, but it would probably be best to just buy another set of two of the SB175 connectors (for a total of 6).

Step 2: Schematic

The schematic is actually quite simple.

Two 12V automotive batteries, wired in series, generates the necessary 24V high amp positive/negative inputs/outputs for welding.

The circuit uses a high amp contactor (think of it is a very high amp relay; 150AMP in our case).  These are now used extensively in electric cars; it was through an electric car parts website that I found one.

The contactor is controlled through the trigger of the spool gun, so that the tip isn't always hot, as was the case in Tim Anderson's original Instructable.  This makes the whole thing much safer, as it's very easy to fumble around with the gun when using heavy welding gloves.

There is also an additional relay that controls the drive motor in the spoolgun that advances the welding wire.  The motor in the Lincoln spoolgun is labeled at 24V, but the contactor I ordered uses a 12V coil.  The manufacturer of the contactor that I'm using, Gigavac, has 24V coil models, which would simplify the circuit, but the supplier I ordered from only offered the 12V coil model.  I also like the idea of using the two voltage-regulator power supplies so that the voltage to the spoolgun motor would be regulated.  Possibly overkill, but better safe than sorry.

The trigger is basically the 12V+ supply to the two relays (contactor and drive motor relay).  These two relays supply 24V+ to the spoolgun tip [unregulated] and the drive motor [regulated].  The tip is supplied raw/unregulated 24V+ 150amp from the batteries, and the motor is supplied with a regulated 24V+ 3amp from the secondary power supply.

Step 3: Connectors and Cables

I decided to go with Anderson high amp connectors throughout this project.

First, I wired one of the connectors to my vehicle batteries.  I'm currently running with two 12V batteries that I normally run in parallel.  One is a regular starter battery; the other is a deep-cycle battery that I have connected to some small solar panels mounted on the roof of the vehicle.  I can change the wiring configuration from parallel to series when I need to use the welder.
Photos of my setup are not included because you'll have to decide how you want to configure the connection to your battery configuration.   If you don't have the space for two car batteries under the hood, then you'll want to install them in the trunk or elsewhere.  I am not going to cover that here, as there's just too many possible configurations.

Vehicle Battery: SB175
Cable: SB175-->SB175
Welder: SB175

Second, you'll want to create a connection cable to connect from the batteries/vehicle to the welder itself.  I went with two 5ft lengths of 1/0 welding cables with an SB175 connector on both ends.  One thing I learned: all the SB175 colors are interchangeable except the yellow ones.  I originally used a yellow connector for my vehicle connection, but when I ordered more, I decided to try the other colors, which is how I discovered that yellow connectors only connect with other yellow connectors.  In the end this worked out OK, as the cable I made had a yellow connector on one end and a grey connector on the other.

Working with the 1/0 cable is actually very easy. The 1/0 cable may be overkill!  You could use 2 gauge or even 4 gauge wire, throughout, to save some money, but when using longer "runs" [lengths] of cable, it is recommended to use lower gauge wire.  My plug-in 208V AC to 24V DC 175amp Lincoln Welder uses only 4 gauge wire, for example.  Whichever gauge you choose, go with a "welding wire", which uses very fine copper strands vs. wire with larger (more solid, less flexible) copper strands.

Once everything was soldered on (but before clipping the contacts into the SB175), I wrapped both cables in 1" Heat Shrink Wrap. With the 1/0 wire it was a very tight fit and required two people to get it slid on. It is not required for anything but aesthetic.

Step 4: Connectors on the Welder Box

There are a total of six connectors that make up the welder itself.
  1. Anderson SB175 24V 150amp supply
  2. 3/8" MIF connector for the sheild-gas regulator
  3. 1Anderson PP120 "ground" wire connector
  4. 24pin female connector (trigger and spoolgun motor)
  5. port for the spoolgun conductor block
  6. (not shown) a 10amp fuse port
1 If I make another, I will just use another SB175 connector, instead of the single PP120.  I thought they both used the same internal copper contacts, but the PP120 uses a smaller contact.  I had to use a grinder to make the SB175 contact fit the PP120 housing, because I could not find a supplier for the copper contact used specifically for the PP120 housing.

2 Unfortunately, these connectors didn't come with pins installed, so I had to purchase the pins separately, solder them to supply wires, and then epoxy the whole thing together.  I went to this trouble, because I wanted to use the male plug that is already connected to the spoolgun (a Lincoln Electric proprietary receptacle) so that it's interchangeable with my Lincoln AC welder.

Step 5: Supply Connector

To install the main 24V high amp supply connector, trace the outline of the plug onto the metal sidewall of the toolbox, then drill a hole large enough to insert a jig saw to cut an inverted U shape, leaving the bottom uncut.  Bend the piece of metal inward, making a small shelf for the inside section of the plug to mount to.

I then used an L bracket to secure the top of the connector to the metal side wall.  I used rubber gasket washers to mount the L bracket and then used hot glue to seal where the plug contacts the cut metal.  The toolbox isn't water tight, but I wanted it to resist water where it was most likely to corrode. 

With the lower shelf formed by bending the metal inward, the L backet, and the hot-glue, the plug is surprisingly stable.
  • In the photo, you'll also notice the input for the shield-gas regulator.  I'll cover that in a later step.  
  • In the second photo, make note of the fuse for the power-supply/regulators. This is a 10amp fuse as that's the maximum rating for the larger of the two regulated power supplies.  This was a basic glass tube fuse holder that I had on-hand, but originally purchased from Radio Shack.  You can use the blade style if you like, but installation of the glass tube fuse holder was a simple round drill hole to mount to the toolbox sidewall.

Step 6: Spoolgun Connectors

On the side opposite the supply, I mounted the three connectors used by the spoolgun itself.
  1. The "ground" wire connector.
  2. The trigger/motor connector.
  3. The spoolgun conductor block connector.
1. If I did this again, I would just use another SB175 connector, instead of the single PP120 connector.  The reason being that the internal copper contacts for the PP120 are not the same size as the contacts for the SB175, which meant I had to grind down the contact to make it fit.  The connector is called the "ground", but it does not always carry a negative charge.  With flux-cored wire, the "ground" cable is actually carrying a positive charge, while the spoolgun tip is carrying a negative charge.  With non-flux-cored [Mig] wire, using a shield gas, the polarity is reversed.  We'll cover this more when I show you the internal wiring.  I mounted the PP120 by drilling a round hole just large enough to squeeze the PP120 through, then sealed the whole thing with Sugru™.

2. The trigger/motor connector mounts through a small round hole drilled into the sidewall, which is then secured with some self-tapping screws.  I would use a bolt with a smaller head if I did this again.

3. I'll cover the conductor block in more detail in the next step, but you'll want to cut the hole in the side wall a good bit larger than the size of the conductor block hole.  I recommend isolating the conductor block so that it's not making contact with the toolbox's metal side wall.  I tried mounting the block a couple of different ways before I found one I liked; the easiest way being to make the hole in the side wall a few sizes larger then the conductor block,and then use rubber washers and electrical tape to insulate.

These connections look kind of bad in this blown-up image, but they actually look pretty neat IRL.

The third image represents the bulk of the parts that you'll need to order directly from Lincoln Electric (through a distributor such as weldingsupply.com).  The thumb-screw is not shown in the image; you'll see it installed in the second image.  I did not order the middle bolt used to connect the electrical cable to the conductor block, as I had one that would fit.  It is a 1/4-20 x .375 bolt, with washer and lock washer.

Cut off everything from the mounting bracket except for the cube that the conductor block slides into.  Then use a few foam/rubber washers [Harbor Freight - Item 67667] to isolate the metal of the block from the metal of the side wall.  I used a hard rubber washer, the type used to seal a garden hose, as well as some of the larger foam washers.  For added protection, I used electrical tape to cover the "edge" of the hole I cut into the sidewall of the toolbox, just to make sure there would be no contact.  With DC, if the conductor block were to make contact with the metal of the toolbox it wouldn't hurt anything, I was just being extra cautious.

I then bolted through from the outside into the plastic mounting "cube" with the exposed part of the conductor block facing the front of the tool box.  You'll see a detail of this in the fourth image.

Step 7: Lincoln Four-post "square Flange Female Receptacle"

That leaves the proprietary Lincoln Electric four-post "square flange female receptacle".  To be honest, this was the most difficult part of the whole project, both in finding the parts and in assembling them.

Since I wanted to use the spoolgun for both my existing Lincoln welder and the welder that I was building, I decided to go with replicating the female connection for the male plug that is installed on the Lincoln Magnus SG100 spoolgun.  If you decide not to use this specific spoolgun, or don't specifically need to use the attached proprietary connector, you might want to use a different connector type all together.  You could easily use a four-pin din male/female connector set, for example.

I was able to order the receptacle from Lincoln, but it came WITHOUT the actual contacts installed.  I was able to find contacts that would fit (see the part list under digikey), but they had to be soldered to wires, and the contacts had to be epoxied into the flange.

I accidentally deleted the image I took during this step of assembly, which makes it difficult to communicate.

I'm more than happy to answer any questions about this step; unless you specifically need to match the Lincoln Spoolgun connetor  it would be easier for you to use a whole different connector type if possible.

Step 8: Electrical

My system uses two relay circuits.  One controls the 24V 3amp to the wire motor in the spoolgun, and the other is the 24V 150amp contactor that provides the power for welding.  Both of these relays have 12V coils.  It would have been possible to purchase 24V coils, and have all the circuits be 24V, but 12V was what I had access to.

I wanted a regulated voltage for the spoolgun motor as it's designed to be used in an AC/DC welder, where the voltage is regulated, and I also wanted regulated so that the speed of the wire motor would be constant.

I looked on ebay and found some very nice regulated DC-DC power-supplies:
  1. 24V to 12V 10amp [link]
  2. 12V to 24V 3amp [link]
These provide rock stable voltage to both the relay coils, and the drive motor.  Probably overkill, since the voltage coming from the batteries would not have a great range (causing speed fluctuations in the drive motor), but I wanted something very dependable.

I mounted both of these onto a spare heat sink that I had, that clipped nicely into the inside of the toolbox, but if you don't have a heat sink, you can mount them directly to the metal sidewall of the toolbox, as the current draw isn't anywhere near their limits, so even just the heat dissipation through their case should be fine.

I also installed a 1x3 board that I cut to size that would wedge into the tool box where I would mount the connections.  I used 2 two-position terminal blocks from Radio Shack.  One is 12V for the coils, and the other is 24V for the drive motor.  I also used two large high amp terminals that represented the positive and negative charge.

For welding the charge is used in two different configurations.  When using a flux-core wire, the "ground wire" actually carries a positive charge, and the spoolgun carries a negative charge.  When using a shield-gas mig wire, the polarity is opposite.  Having the terminals allows changing the charge to the "ground wire" and the "conductor block" with ease.

The negative wire (within the toolbox) connects directly from the SB175 input connector [-], to the final negative terminal, as all the various switching is done via the positive wire.  The positive wire connects from the SB175 input connector [+], to a 150amp circuit breaker which is connected directly to the contactor with a small piece of steel that I cut to size.  The contactor then connects to the final positive terminal.  I made the mistake of attaching the contactor to the toolbox before figuring out the best placement to accommodate the 1/0 gauge wire, so you'll see in the picture that my positive wire from the supply connector has an S curve to it, because trying to size the 1/0 custom cable length to the exact size would have been tricky.  If I had waited to mount the contactor in the last step, I could have had more flexibility in sizing the cable lengths.

  • Note that the supply for the two regulated power supplies is connected prior to the 150amp circuit breaker (smaller 10g wire shown in image 3), as they are supplied through their own 10amp fuse.

Step 9: Shield Gas for Mig Welding

All of the various DC welders I found online were specifically for flux-cored wire based welding, that doesn't require the usage of a shield gas.  Since I'm using both a Lincoln gas enabled Spoolgun and connector block, adding support for full MIG shield-gas welding was very straightforward.

It was just a matter of finding a female gas connector that would fit the gas regulator that came with my original AC powered welder. For me that was a 3/8" female FIP connector that I purchase in the plumbing department of Lowes.  Best to just take your regulator into Lowes with you and find the female connector that fits. Since I was mounting this into the sidewall of the toolbox, I purchased a 3/8" female FIP connector, with a 3/8" male connector on the other end, so that I could use a female/female connector inside the toolbox to snug the connector securely to the side wall.  I then purchase a male-2-barb fitting, and used  a semi-rigid airline that I also purchase from Lowes.  

The other end of the hose connects to the nipple that screws directly into the Lincoln connector block.  I used small hose clamps to tighten everything down.  The PSI on the connection is not high.

  • If you don't already have a regulator, they can be purchased seperately, but I'm not going to cover that.  Happy to answer any questions, but outside the scope of this instructable.
  • These parts are not listed in my parts list because they are going to be custom to whatever regulator you have.
  • The gas will be ALWAYS-ON.  I did not go to the trouble of adding an electric gas valve connected to the trigger, so you have to turn the gas on/off at the tank.  I will probably be doing mostly flux-core welding, so adding an electric gas value would have been overkill for me.  If you plan to do mostly aluminum welding, then you might want to consider adding such a valve so you're having to manually control your gas flow.
  • For MIG welding (using a shield gas), the "ground wire" should be connected to the negative post, and the conductor block connected to the positive post; the inverse of the connections when welding with flux-cored wires.  

Step 10: Final

I have tested the welder on a major project, and I believe it actually welds better than my original 220V AC welder!

Possible additional components:
  • A potentiometer to control the speed of the wire feed, as it's a bit faster than I'm used to welding with.  If you have a lot of experience with welding, it may be perfect for you, but I prefer it a bit slower.
  • An amp rheostat to modify the amperage/heat of the welder, when welding small gauge metals as the "default" may be too hot.  I don't have enough experience with High Amperage DC current modulation to tackle it just yet.

I plan to add a quick video demo for low gauge wire soldering, but want to go ahead and publish this Instructable before then.

  • This is my first Instructable, so be gentle.  
  • Any constructive feedback is great.  
  • Any negative or blatantly inappropriate comments will be deleted out-of-hand!

Hope ya like it!
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    Reply 9 years ago on Introduction

    Thank you very much! This was one of the few projects that moved from experiment to project on the first try! Plugged it in, pulled the trigger and it welded! :)


    Reply 6 years ago

    Would love to see a video of it welding.

    Ryan Gable
    Ryan Gable

    3 years ago

    This is most impressive! Would love to see some of your other instructables if you're still making them. I know I'm late in finding this but what a cool read.


    6 years ago

    Hi, Nice set up. Studying the schematic, I'm curious if you could reduce the overall cost of this by using a golf cart solenoid, like this: http://www.ebay.com/itm/SOLENOID-RELAY-BATTERY-ISO...

    in lieu of the specified contactor? Also, is it possible to eliminate the step up transformer altogether by feeding the motor relay from the primary side of the step down transformer, and use the stepped down 12 volts to the trigger only to actuate the relay & solenoid (your contactor)?


    6 years ago

    or further, eliminate both transformers and use a 24 volt contactor & 24 volt relay? Is the trigger switch only rated for 12 volts?


    Reply 4 years ago

    The issue is that the contactor required 12v for switching, so that's why the 12v bit of the circuit. but it looks like they now have a 24v contactor.


    7 years ago

    You've had this set up for a good bit of time now. Have you made any interesting mods to the original design? I'd be very interested to hear


    8 years ago

    can we see this running ? like a video or something. Im a student in a welding class and my teachers are pretty interested by your way of making a portable welding machine


    Reply 8 years ago

    I'll see what I can do this weekend.


    9 years ago on Introduction

    Any estimate on run time with a fresh or fully charged pair of batteries?


    Reply 9 years ago on Introduction

    I went through 1/2 lb of wire with no discernible drain on the battery. I wired them back in parallel and started the engine right away. I use a series of solar panels (just 45watta) to keep the batteries topped up. Haven't had a need to weld any longer in one go.


    Reply 9 years ago on Introduction

    Very cool, thanks for the reply and fantastic instructable.


    Reply 9 years ago on Introduction

    Thanks! I'm a computer programmer (started in computer engineering, so have some basic electronics knowledge), and my father is a retired machinist and welder. He taught me the basics.

    I consider myself a Zac-of-all-trades, so pretty fearless about trying new things. Only had one all-out DIY failure (water cooling a computer of all things, but I tried for WAY too much for my first such project).

    I've got a few Instructables planned for the year. I reworked and updated an older Instructable: Survival Kit Shotgun, I just have to get it recorded.

    I'm also going to start some extensive mod'ing of my hummer H2, and a possible HUD for my motorcycle helmet now that transparent OLEDs are coming down in price.