DIY-Welder - Build your own Arc, MIG and TIG welder Page hits:

What does it take to build your own welder?

You will need to be mechanically inclined. Electrical knowledge helps but is not critical.

The main components for stick welding are:

  1. A gas or electric motor. 12HP or better for gas, 10HP for electric.
  2. A 120 amp or larger alternator that can be easily modified for an external regulator. Or alternators in parallel.
  3. A control board to set voltage and current.
  4. A reactor core
  5. A current sense resistor
  6. A frame to mount the motor, alternator and controls.
  7. A filter capacitor
  8. Suitable connectors, wire and welding electrode holder and clamp

Start with a riding mower for a big engine.

I'm amazed how available these are. I have picked up 4 over the last year. Many appear on Craig's list; owners let them sit, they wont start and they just buy a new one and give the old one away. The most I paid for the 4 was $150 and that was because it was identical to one I was fixing up. There are many at $100 or less. One I got for free with a dead engine. I bought 2 more for the engines at $80 each.

Note: Use what you need off the rider; the rest is worth money. I have sold transaxles for $50, wheels for $20/ea. A dead engine will have a carb, coil, starter and muffler that people will pay for. Every riding mower I have bought ended up costing me nothing as I sold the parts I did not need. Smaller stuff will go on Ebay, bigger parts are easier to sell on Craigs list as you don't have to deal with shipping. If the deck is still good, it is worth a lot as they rot out and the spindles are expensive to replace.

When you are done, all the leftover metal can be taken to recycling. I got about $20 for what was left. Remove all non-metal parts and you will usually get a better rate for "Clean" steel.

A Craftsman, MTD or Murray 38" will have a 10 to 14.5 HP engine. It will include all wiring, pulleys, and a frame precut for the motor. You can even remove the deck and install the alternator on the same pulley. That will give you a "Riding welder" like the first prototype. The second prototype was the front half of a Craftsman 38" mower frame and some angle iron. The main drive pulley and idlers make it easy to install the alternator.

I have found the Craftsman riding mowers easiest to modify and far better quality. Others I have seen are usually rotted out by the time an owner gives it away.

If the engine does not smoke or knock, it should be fine. Check the oil for water and make sure there are no knocking sounds. The OHV engines are better and likely newer. They often need a valve adjustment to run smooth. I find vertical B&S engines tend to give a small puff of smoke when starting then run clean.

Most often the carb gets gummed up. Common starting problems are dead batteries, loose connections or a bad starter solenoid. Carb rebuild kits are easy to find on Ebay. If the float is dirty, the engine will fill up with gas. Should be ok as long as it has not been run that way long. A worn engine is usually not worth repairing. The first rider I bought (actually it was free), was run all day with little or no oil. It still ran but there was a pile of parts in the oil pan; all kinds of things were chewed up. Anything beyond a new gasket, carb cleanup is usually not worth fixing.

A horizontal or vertical shaft engine will do.

An electric motor will do also. 8HP would be a minimum. These can get expensive, but if you have one, use it. A Motor/alternator setup is easier to build and control than winding your own transformers.

The Alternator

These are a bit harder to find. Most cars these days have 60 amp alternators. Just any one will not do. The ideal alternator is a surplus military or aircraft 24V 200A alternator. These are hard to find and usually fetch a premium.

The "boom box" car craze has people putting huge stereo systems in their cars. These require heavy-duty alternators. So, sellers on Ebay have many 150 amp and up alternators available. Many are remanufactured but still have a warrantee. I would suggest a 160 amp or above. For thin metal MIG work, a 120A will do. You will not get the rated output for welding. Automotive alternators run at 13.8V. Since we will be welding in the 18-30V range, output can be expected to be less. The control board is efficient and will help. I expect the 200A to top out at about 150A

I chose a Motorcraft 200A alternator that was designed for a late model Mustang. I chose it as the regulator mounts on the back of the alternator. It was easy to remove the regulator and attach wires to the brushes for the project. It also was easier to mount as the bolts were parallel to the shaft. If you use a horizontal engine, it might be easier to use one that has bolts perpendicular so both engine and alternator could be bolted down to a frame or plate.

Another option is to parallel two alternators. Connect the fields together and the outputs together. This works well and can use more common alternators. It has the benefit of running two belts; reducing the problem of burning out belts.

The Control board.

The board is shown in the menu. It provides the Constant Voltage (CV) and Constant Current (CC) control needed for welding. It will be offered for sale at as low a cost as possible. The digital version is an expensive board right now. I am working on simplifying it.

There is also be a simplified board without the smarts and load/save capability. Just two knobs to set voltage and current and switches for contactor, power and remote control. Will do MIG and stick welding; TIG will work also but will not have automatic controls.

More info as the boards are finished.

Other components:

Reactor: This is needed to stabilize the arc and also to provide current smoothing needed for MIG welding. They can be made with some heavy wire and a steel core. The Auto-Powered Arc welder has plans to make a reactor (referred to as an arc stabilizer in the article).

Capacitors: At least one to protect the alternator from surges. An AC motor start capacitor will do. For MIG welding, a large bank of computer-grade capacitors will really help the alternator handle the surge currents that short-arc MIG generates. It will also help starting the arc in stick welding but hurt stability without a significant reactor added.. 20,000uf/75V or more will help. The first prototype used a 160uf motor start capacitor. It worked great for arc welding. The second used two 23,000uf/75V caps in parallel. This helped MIG welding. I have 3 more of the large capacitors, to add but don't have much room.

Current sense resistor: There are two ways to measure the current. The best is a resistor in line with the work lead. However, this will need to handle the full current. In the first prototype, I used about 4 feet of #6 wire. It worked ok. There are 200A 0.020 ohm shunts (resistors) available but are usually designed for accurate lab testing and are expensive. I used the reactor coil resistance as a sense. The board filters out the high-frequency spikes generated by the reactor.

The second method of measuring the current is to put a resistor in series with the alternator field. That will measure the field current that is proportional to the output current. This is easier although there is a small "minimum current". The second prototype uses a 0.1 ohm resistor in series with the power to the field.

Welding wires and connectors: Welding wire is expensive as it is a lot of copper. For 200A #2 wire will do for short distances. I used some #1 wire designed for the car stereo. Works well and is flexible. Don't be surprised if 100' of welding wire is your biggest expense. A 50' roll will allow a 20' ground lead and a 30' work lead.

You will need a ground clamp and electrode holder. Easily found on Ebay; usually for about $20.

Adding MIG Welding

MIG welding can be done as long as the control board supports constant voltage control. A wire feeder is needed. A burned out cheap MIG might do to use the feeder out of.

There are separate wire feeders on Ebay. I picked up one a while back. A 120V feeder is easier to power as you can plug it into an outlet (or run off a small UPS or inverter if remote.) These are older units that need AC power and have just a relay output to control the welder. The old 120V feeders are also cheaper.

Newer wire feeders run on 24V or 42V AC. They can be used, but you need to find a way to power them. Many require considerable current (7A at 24V) so a transformer gets expensive.

Or you can build your on wire feeder. Not that difficult if you can find a geared motor, gas solenoid and have machining tools (a lathe is a big help.) A speed control circuit will be posted soon.

MIG guns are not that expensive. Many are on Ebay or buy a Parweld one new for about $100.

A contactor will add safety and better starts. When the trigger is pulled, the alternator has to build up the field and output current. This takes time especially if you have large smoothing capacitors on the output. This makes the wire stutter when starting a weld. Adding a contactor will allow the alternator to pre-charge the capacitors and also adds a safety of less chance of a "live torch" when not welding.

You will need a supply of MIG gas (Argon/CO2 or just CO2) and a regulator and some sort of flow control..

TIG welding

Scratch-start TIG welding will require a torch, a gas solenoid, a supply of pure argon and a regulator. A foot control is helpful and can be built easily.

A foot control helps scratch starting. You can start with the current at a minimum to scratch start then increase the current.

The simplified control board will work. It will not support a long post flow on the gas; that can be done by pulling the torch away and still holding the trigger. That will allow the tungsten to cool and not get contaminated. It defaults to a few seconds of post flow; that should be enough for low-current welding.