Make Your Own Emergency Power Plant

If you have a car, a moderate tool collection and good tinkering abilities, you can make your own emergency power plant.
January/February 1985
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If you're anything like the folks here at MOTHER'S Eco-Village, you're probably swamped with nagging little chores that require some drilling here, some grinding there and a bit of cutting somewhere else. Trouble is, all these work sites somehow manage to be nowhere near a source of 110-volt power — so, unless you're particularly fond of hand-tool labor, you've got to either spring for a portable generator or resign yourself to a ramshackle existence.

Curiously enough, nearly everybody owns — and uses most every day — a reliable and generous source of electrical energy without even knowing it: the modern automobile! Yep, if you drive a car or truck manufactured between the middle 1960s and the present, it's possible to modify that machine's charging circuit to make it deliver 110 volts of 20-amp (or greater) DC service at the flick of a switch. With that amount of power, you'd be able to run lights, power tools, pumps, resistance-element appliances or just about anything that doesn't use an induction (AC only) motor or a transformer. Here's what you need to know to build your own emergency power plant.

"Alternative" Energy

Around 1963, you see, the major auto manufacturers started to equip their products with alternators, which not only made the cars more reliable, but opened up a whole world of possibilities to tinker-types like us.

Actually, the design of an alternator is somewhat opposite to that of a generator: Rather than current being extracted from an armature rotating within a wound stationary field, an alternator's output is drawn from three stator coils fixed around a spinning multipole rotor containing the field windings. This produces high-frequency AC current, which is then rectified, through diodes, into the direct current used in automotive charging systems.

Now, since an alternator's output voltage increases as its rotor RPM is boosted, a regulator is included in the system to sample that output and compare it to a desired reference provided by a Zener diode. If the output is too great (or too little), a transistorized circuit controlled by the Zener adjusts current flow to the field rotor to keep the alternator's output voltage within acceptable limits (between 12.5 and 13.5 volts).

Two Simple Circuits

All that's fine, of course, for charging car batteries, but we wanted to move on to bigger and better things, so we turned researchers Dennis Burkholder and Robyn Bryan loose on a staffer's 1978 Ford pickup to see if they couldn't coax it into giving up 110 big ones without damaging the stock equipment. What they came up with is a pretty ingenious use of about 50 dollars worth of over-the-counter and junkyard parts, a hookup that comes close to duplicating the convenience and performance of commercial converters that are considerably more expensive!

The concept is simple enough: By switching the regulator (and thus the battery charging system) out of the circuit and feeding 12 volts directly into the alternator's field windings, you can get that tiny dynamo to eat enough Wheaties (in the form of current) to put out about 85 volts at a reasonable engine speed (roughly 2,800 RPM).

But we wanted 110 volts, and with the standard 40-amp alternator, this would have required revving the engine higher than we cared to, so we found ourselves a 2 ¼ -inch General Motors double-grooved alternator pulley that increased the standard 2.45-to-1 crankshaft-to-alternator-shaft ratio to a steeper 3-to-1 gear-up, which ultimately allows the DC dynamo to produce 110 volts for extended periods without damaging the truck's six-cylinder engine.

Using this setup, it's theoretically possible to get over 4,000 watts' worth of power from the machinery already under the vehicle's hood. But to be on the safe side, we've been limiting our demand to 2,200 watts, or about 20 amps — still a heck of a lot more current than even the heftiest power tools would draw.

By referring to our pictorial schematic in the image gallery, you'll be able to get a pretty good idea of how our system's wired and plumbed. But let's walk through it just once to eliminate any confusion.

We can ignore the charging circuit, because that remains essentially unchanged. But once the 4-pole, double-throw master switch is thrown into the "on" position, the remote power system is activated, and the alternator's output goes through a pair of 16-gauge wires (almost a 12-gauge equivalent) to a set of 12-volt, 10-amp fuses and on through a pair of "extra insurance" automotive diodes mounted in an aluminum bracket. After running through an inexpensive ammeter, the current travels into a 1,000-watt resistor (simply a non-immersion heating element from a mobile home water heater fastened inside a 15-inch length of 2-inch CPVC pipe) and into a weatherproof receptacle, the opposite legs of which are grounded to the truck.

Additionally, a DC voltmeter is grounded through one of the ammeter terminals but requires a 150k-ohm resistor to multiply its existing 0- to 15-volt scale by a factor often. Also, a solenoid vacuum switch (normally open) taken from an eight-cylinder Jeep is wired in parallel with the 1,000-watt resistor coils.

The plumbing's been added to provide vacuum to a choke pulldown diaphragm snitched from a Motorcraft two-barrel carburetor. In conjunction with the Jeep's solenoid-operated vacuum switch and an aquarium air-supply valve, this sweet feature allows remote-control operation that's adjustable to suit a particular job. Put another way, the vehicle's engine will remain at normal idle speed until there's a demand on the system of 100 watts or so (prompted at the moment a tool or appliance is switched on). Then, as current passes through the resistor, the parallel-wired solenoid "borrows" enough to kick the open valve closed, activating the pulldown diaphragm and speeding up the engine by means of a beaded chain fastened to the throttle lever with a miniature collar clamp.

(The one drawback of this inexpensive remote-control setup is that as current demand increases, the resistor element gets warmer, diverting excess voltage to the solenoid, which could cause it to fail over an extended period. To circumvent this possibility, we've included in our design an optional switch that cuts both the resistor and the solenoid-operated vacuum switch out of the circuit so that heavy-duty tools or appliances can be used as long as the alternator maintains its output. An air control valve placed in the solenoid vacuum line allows engine speed to be controlled manually.)

The adjusting screw on the rear of the choke pulldown device provides an upper limit which can be used to preset maximum RPM and, thus, voltage. Similarly, the aquarium valve can be used to fine-tune output below that limit by decreasing the vacuum pull on the suction-sensitive diaphragm. Also, to prevent the diaphragm from yanking the throttle open too quickly and causing hesitation, the exposed inlet of the aquarium valve should be soldered shut, then redrilled with a No. 68 (.031-inch) bit, to allow a small amount of buffering air bleed.

Naturally, when the remote power system is switched off, it doesn't interfere with the charging circuit or the foot-operated throttle. And when the aquarium valve is closed completely, the calculated vacuum leak is eliminated for normal driving.

Some Helpful Tips for Building Your Emergency Power Plant

We're not suggesting that everyone should have an emergency generating station under the hood. But if you feel comfortable working with automobiles, you might want to give this setup a try. Remember that we were experimenting with a 40-amp alternator and that a higher-output unit (from an air-conditioned car or a commercial pickup) can provide high voltage at a lower RPM, in which case you might not need to find (or machine) an extra-small pulley for it. Keep in mind, too, that the combination of high voltage and amperage produced by this modification is every bit as lethal as the AC socket in your house wall, so treat it with the same respect! (You can avoid any low-voltage equipment damage, as well, by disconnecting the positive terminal of your battery cable while making the wiring modifications.)

Should you plan to run your vehicle over an extended period of time as an emergency power source for the household (which is an admittedly fuel-consumptive practice, considering that the alternator only requires about 6 horsepower of the 100 or more provided by the engine), be aware that the car's radiator may require a greater rate of airflow, which can be provided by replacing the four-bladed fan with a multibladed type.

If you use the setup as it was intended to be used — and that's as an occasional source of temporary power when none other is available — you'll be sure to appreciate what a little bit of tinkering can offer!

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