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Build a Portable DC Arc Welder for $20

November/December 1980

By the MOTHER EARTH NEWS editors

The completed portable DC arc welder looked like this.PHOTO: MOTHER EARTH NEWS STAFF

Given a choice between adding either arc or gas welding to the workshop, most tinkerersfind a small AC arc unit to be an inexpensive andimpressively versatile piece ofequipment. However, for those occasional remote outdoor chores that come up aroundmost farmsteads, gas is just about the only practical choice. (Of course, there are portableelectric welders available, and one coulduse a shop unit and tote along a generator ... buteither approach represents a considerable investment, especially if the devices will beused only to accomplish infrequent in-the-field repairs.)

As it happens, MOTHER EARTH NEWS' researchers run into a fair number of remotewelding jobs out at our Eco-Village propertyfrom tacking together a windplant frameto sealing a hydroplant pipe that are just plain inaccessible to the Lincoln automaticfeed unit that they prefer. Therefore, it didn't take long for one member of our team to getso fed up with the hassle of loading both a generator and an arc welder into a pickuptruck that he began combining some odds and ends around the shop to make his ownportable DC arc welder.

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Experimenter Dennis Burkholder decided that after scrounging up an old powermower, a set-aside Delco-Remy automobile alternator, and a weary but serviceable 12-volt deep-cycle batteryhe had just about everything he needed to build a portable,intermittent-duty, low-voltage, welder. Sure enough, after trying a couple of differentcombinations of the scrap components, he came up with what must be the least expensive

(and strangest looking) arc welder ever assembled.

Essentially, the welder is powered by the roughly 50 amps that the Delco-Remyalternator is capable of producing . . . and is adjusted by varying the speed of thelawnmower engine. But the 12-volt battery is needed to balance out those surges thatoccur when the arc is struck or broken. Furthermore, Dennis found that the setup workeda lot more smoothly with two 1 1/2-ohm, 8-amp resistors placed in series with the field ofthe alternator, to cut the field voltage to about 6 volts. (In fact, withoutthe two resistors,striking an arc would nearly kill the 3-HP Briggs & Stratton engine!)

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 thepenetration and spatter qualities of its arc! There are, however, a few limitations to thetool's capabilities. First, the maximum heat of the arc is about 50 amps, so the devicewon't penetrate more than about 1/4" into steel. In addition, it's best not to use the welderfor more than about 20 minutes at a time to avoid overheating the alternator (a thermaloverload switch tells you when enough is enough).

And finally, the unit's low-voltage DCcurrent presents both an advantage and adisadvantage over conventional AC power. Because the voltage of a circuit determinesthe 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 itis

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 onlycomponents that our researcher was forced to buy were the resistors, which he located atthe nearest auto parts store. And even ifyourstorehouse of valuable discards doesn'tequal our 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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