How to Make an Onboard Welder OBW Weldernator

I have an ’89 F-250 with a externally regulated alternator. I researched weldernator conversions and I wanted to get some first hand experience before I altered my charging system. I collected some parts and built an alternator welder powered by a lawnmower (see my blog for details). It worked well enough for me to justify converting my F-250.
I picked up a large project box from Radio Shack, a double throw switch, an automotive battery disconnect switch, a choke/throttle cable and a 200 volt DC gage from ebay. I had some 6 gage wire, jumper cables, 110v outlet and a 60 amp winch disconnect plug laying around the garage. I made my welding cables from the 6 gage wire. I used the jumper cable clamps for the ground and electrode clamps. I used some scrap 5/16″ copper tubing to make some butt connectors to attach the wire to the winch plug. I fitted the volt gage, outlet and double throw (DT) switch into the project box. I used the studs on the volt gage as the junction for all of the wires. The battery disconnect switch breaks the connection between the alternator and the battery to prevent overcharging. The center post of the DT switch is wired to the “field” post on the alternator. One of the remaining switch posts is connected to 12v+ and the other post is connect to the “field” wire from the voltage regulator. The switch allows you to by-pass the voltage regulator and full field the alternator by sending 12 volts to the field post on the alternator. Most guys use welding disconnects to attach the wire to the control box, but I had the winch plug so I used it. I was going to use welding ground clamps and electrode holders, but I wanted to be able to reverse the polarity if needed. The welding plug prevents me from plugging the wires in backwards so I used the jumper cable claps as the ground and electrode holder. They can easily be switched from ground to electrode and the price was right (free). The 110v outlet is wired to the positive and negative posts on the back of the volt gage. It can be used to power an 110v AC tool that has brushes (saws all, grinder, drill etc). It can also power anything that uses a transformer like a cell phone charge and incandescent light bulbs. The choke / throttle cable is needed to bump up the engine rpm’s and generate the voltage needed for welding or operating the power tools. I swapped my large alternator pulley for the smallest one I could find. It spins the alternator faster and lets me keep the engine rpm’s lower while welding. I upgraded the positive wire from the alternator to 6 gage wire. It runs to the positive post on the volt gage where it connects to the positive side of the winch plug, 110v outlet and the battery disconnect switch. The battery disconnect switch is connected to the positive side of the battery. The negative side of the volt gage is connect to alternator with 6 gage wire. It’s also connected to the negative side of the 110v outlet and the negative side of the winch plug.

The first step to using the welder is to turn off the battery disconnect switch separating the battery from the alternator. Plug in your welding leads and flip the DT switch from charging to welding. Pull the choke cable until the engine reaches the desired rpm’s. My large body Ford alternator generates about 70 volts at 2,000 rpm’s. I get good penetration in 1/4″ steel at that setting with a 3/32″ 7018 rod. I was worried about overloading the 6 gage wire and the winch plug, but they were not hot after burning through 3 rods. The alternator was warm, but did not seem to be too hot. Make sure to switch back to charging mode before you reconnect the battery to the alternator.

If you have an alternator with an internal voltage regulator or do not want to modify your charging system you can add a bracket for a Ford alternator to your engine. You can search the junkyard for a bracket to modify or make one from scratch. If you do not have room under the hood you can simply remove the second alternator when you are done welding and store it inside the vehicle.