How I Turned Car Batteries Into A Welder [Video]

Makeshift tools for the post-apocalypse

If we’re lucky enough to survive Armageddon, our precious electrical grids won’t. But we needn’t pine for energy as we build a new civilization from the scraps of the old one. Inside every abandoned car is a lead-acid battery just waiting to power a makeshift arc welder.

Saws, drills, grinders, and lathes may be more precise tools, but welding devices are unmatched for their versatility and brawn. Arc welders work by melting steel with a blinding electrical discharge. They can both sever thick beams and fuse pieces of metal together in ways that other tools can’t. Amid their showers of sparks, a pile of scrap can become a house or a boat—or even an arena for postapocalyptic blood sport.

A single car battery lacks the juice to sustain a metal-melting arc between the tip of a welding rod and a piece of steel. (Zombies holding your supply hostage? Welding rods can be made from coat hangers, silica gel, lye, and paper.) So to build my welder, I wired three car batteries in series, then clamped a set of jumper cables between the negative lead of the first battery and a chunk of steel. With another set of cables, I linked the last battery’s positive lead to a welding rod.

By scraping the rod against the steel, I was able to strike an electric arc. The batteries provided a flow of electrons powerful enough to melt steel in the rod and base metal and merge them, creating a weld. My rig has a maximum output of 300 amps, which is plenty to cut or combine thick steel. Yet it is adjustable, so it can also weld delicate sheet metal; I routed the batteries’ current through a dining fork, which provides some resistance and limits the flow of electrons.

If you can make a welder and get good at using it, you’ll have an unstoppable tool for building after the end-time. When you run out of electricity, charge the car batteries with a bike generator [see “Rebuild,” March 2014] and get to work assembling your very own Thunderdome.

Warning: Do not attempt until lawyers no longer roam the Earth.

Hackett is Popular Science’s intrepid DIY columnist.

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Photograph by Ray Lego

This article originally appeared in the July 2014 issue of Popular Science.