BUILD A $20 PORTABLE DC ARC WELDER

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Considering that the parts for the project are almost all scavenged, the welder is amazingly versatile. For one thing, DC capability is often preferred for smooth sheet-metal work, and our lawnmower unit can have its polarity reversed for changing the penetration and spatter qualities of its arc! There are, however, a few limitations to the tool's capabilities. First, the maximum heat of the arc is about 50 amps, so the device won't penetrate more than about 1/4" into steel. In addition, it's best not to use the welder for more than about 20 minutes at a time . . . to avoid overheating the alternator (the thermal overload switch shown in the schematic drawing automatically tells you when enough is enough).

And finally, the unit's low-voltage DC current presents both an advantage and a disadvantage over conventional AC power. Because the voltage of a circuit determines the distance a spark will jump, the rod used with our portable welder must be held steadily close to the surface of the work to maintain an arc. But, because it is a direct-current welder, there's little tendency for the rod to become stuck.

Of course, the most astounding thing about Dennis's welder is how little it cost. The only components that our researcher was forced to buy were the resistors, which he located at the nearest auto parts store. And — even if your storehouse of valuable discards doesn't equal MOTHER's — you should still be able to purchase the resistors, wires, switches, pulleys, and V-belt for less than $20. When you think about it, a $20 DC arc welder, with a built-in dolly, might be the workshop bargain of the year!

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