Onboard welder using a GM Delco 140 Amp alternator

out of a '94 Chevy Camaro

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Why did I need it?

I learned how to weld out of necessity when I needed to fabricate a rear bumper that can accommodate tow points. I didn't have anybody to teach me so I bought a couple of books and borrowed a 110V Lincoln WeldPac wire-feed welder and set out to practice until I felt comfortable with the basics. Welding is something that one needs to DO to learn it. It's mostly experience. The first day of the first big trail ride event I attended ended with and all-night welding session as several rigs lined up front of the welding truck to have various broken bits repaired. I got to love melting metal and saw how useful this could be on the trail to do some quick emergency repairs.

So with this in mind I began to research how to construct an onboard welder. Again there are a couple of options:

• Battery welder - Most likely everybody who has ever disconnected/reconnected a car/truck battery noticed the healthy sparks that the battery can generate. While the 12 volts from a single battery is not really enough to weld, take 2 or 3 batteries connected in series producing 24 or 36 volts and you got a dandy 100% duty cycle power source usable for welding. Connect some #4 or #2 welding leads with ground clamp and electrode holder and you're ready to weld. For a couple of minutes... You also need to make sure that you weld well away from the batteries to reduce the risk of explosion due to the fumes generated by the heavy load on the batteries. It is also quiet cumbersome to carry 2 or 3 batteries on the trail. So, onto the next option.
• Alternator welder - This is it. The alternator is a simple wonder. Once freed from its automotive restrictions and hooked up to a suitable motivating force it can generate all kind of power suitable for welding. And not just any kind of power but high-frequency power. Why does it matter you ask? The standard household current powered welders have low frequency (60Hz cycle) which means that in an AC arc welder the current switches direction 60 times a second which agitates the weld puddle at that speed producing a cleaning effect. The faster the agitation the faster and better the cleaning producing better and stronger welds given the same power input. In the alternator welder the current level cycles up and down and produces frequencies in the hundreds or thousands per second! It makes a 100 Amp high-frequency alternator welder equivalent to a 140 Amp ordinary AC arc welder. You have to see it to believe it! So this is what I was after.

The basics...

There are a few write-ups on the web on this topic and they all use or recommend the use of the older style externally regulated alternators. It makes sense since on these alternators there is a ready field power input connection that can be simply hooked up to the battery through a relay giving it full field voltage. With an internal regulator it's a more complex matter. We need to remove the regulator and the exciter or voltage sensing diode pack from inside the alternator. This requires careful disassembly and identification of all the components. Here is the basic diagram of an externally regulated automotive alternator circuit:

The regulator can be inside the alternator too but the connections are basically the same. The next picture illustrates the connections to be eliminated:

This leaves a 12 volt connection to the rotor field brush - by using a 30A automotive relay and a 10A fuse - and a direct ground connection to reduce the chance of damaging the engine electronics. The welding leads are connected to the battery output terminal and to the direct ground as illustrated:

This illustration assumes an internal AC/DC rectifier. Obviously the rectifier needs to be able to handle the high voltage generated by system (rated at least 30A at 200V, 50A is better) so if yours is not up to the task (kind of like mine) then you need to hook up an external rectifier (easier) or swap out the diodes on the internal one (more difficult).

Rectifiers come in many shapes and sizes from OEM replacement parts to specialty heavy-duty units in their own cooled boxes. A good source for parts is Transpo Electronics at www.transpo-usa.com. They have hundreds of different models with specs available and they also have the boxed heavy-duty units. Replacing the factory mounted diodes that are usually soldered on requires that you heat the heatsink with the mounted diodes on a hot plate just until the solder melts then replace them with the new ones with some solder applied and allow to cool. Since it requires special equipment it was out of the question for me.

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