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!
