Build a Wind-Powered Battery Charger

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Kelly inserts an old and dying battery into Breezy's battery box to be recharged . A close-up (Far above) shows Breezy's recharging mechanism with its rubber-band drive attached to both the four-inch cap and the shaft.
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Mechanical details of Breezy's construction.
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Breezy can breathe new life into your dying radio and flashlight batteries.
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All the equipment and parts you will need to build Breezy.

Imagine using the wind to breathe new life into dying
batteries. Most battery chargers require electrical power
derived from the burning of fossil fuels. But what if you
could capture the power of a breeze and turn it into power
that could be stored until later, when you need it? Talk
about self-sufficiency and recycling rolled into one! If
you like soft energy paths, and want to break the
“throw-away” battery cycle in your home, here’s a project
for you ….

Some Background

The concept of harnessing the wind to do work isn’t new.
Our ancestors frequently utilized wind power to pump water,
saw wood, and grind grains. In fact, the design and
implementation of useful windmills dates back hundreds of
years. While the burning of fossil and nuclear fuels
dominates world-power production, environmental concerns
prompt us to now look seriously at “green” energy sources.
Wind is clean, free, and abundantly available. So why not
simply substitute wind power? Energy experts are quick to
point out the fact that our modern per-household power
consumption is usually much greater than the wind alone can
provide. Does that mean that wind power won’t work? Quite
the contrary. Rather, our challenge is to “catch, store,
and utilize” energy from as many different sources as
possible. A little here and a little there saves money,
worry, and the Earth.

Building Breezy

By following these simple instructions, you should easily
be able to construct this windmill in one afternoon, and be
recharging AAA through D-size batteries by evening. So
gather up your supplies (see Parts List in the Image Gallery) and follow the
instructions below.

Breezy’s body is constructed of 1″
diameter, schedule 21 PVC pipe. Plastic pipe was selected
for its ruggedness, availability, and especially, its cost.
You may choose to substitute schedule 40 PVC pipe for
additional durability, but it is not necessary.

PVC pipe, normally used for plumbing, is easy to cut and
put together. Begin by cutting the 1″ diameter PVC pipe
into the various sizes noted in the parts list. You can
mark the appropriate lengths right onto the pipe with a
pencil. (Avoid making unnecessary marks that you’ll have to
clean off later.) Cutting the pipe is simple, and can be
done with a hacksaw or handsaw; make the cuts as straight
as possible. You may want to use some fingernail-polish
remover or acetone (in a well-ventilated area) to clean off
the ink labeling from the pipe. The materials needed for
Breezy are commonly available, but feel free to substitute
materials on-hand where necessary and applicable. For
example, you may choose to use different diameters of PVC
pipe. If so, you’ll have to change the size of

Also, keep in mind that if you decrease the pipe’s
diameter, you must scale down the overall size of the
entire unit. Next, sandpaper both ends of each previously
cut piece of PVC pipe to ensure a clean fit. Then,
following the diagram, temporarily assemble the
precut pieces of pipe with the appropriate fittings. Start
with one side and assemble the sail members. Don’t push the
pipe pieces completely into the fittings; instead, gently
slide each piece part way into the elbow, tee, or end cap
with a back and forth motion. Next, assemble the members
and fittings of the other sail. Notice from the diagram
that this sail frame is oriented in the opposite direction.
This is critical in the function of the unit because
Breezy’s sails work by “catching” the breeze and then
letting it “spill” off the back edge of the sail. With both
sail frames assembled, it’s time to put together the center
vertical member and the
top and bottom cross members. (Refer to Breezy Mechanical
Detail in the Image Gallery). Drill a hole in the “tee” separating
the top cross members. This hole should be X” in diameter,
and can be easily drilled with 3/4″ spade bit. (Separate
the tee from the assembly before drilling it.) Also, use a
vice when drilling such a large hole; the drill bit might
grab the tee from your hand. This 3/4″ hole will provide
rotor stability by allowing the mast (steel rod) to
protrude through it. Center this hole perfectly so the
windmill won’t be off balance.

Making and Assembling the Sails

Breezy’s sails can be made from any lightweight, but
durable material. (I sacrificed a sheet for mine.) If you
purchase new material, launder it first to avoid shrinkage
later. Then cut it into two identical pieces, 40″ wide x
38″ long. Turn one of the newly cut pieces wrong side out,
and fold it in half so it is now 20″ wide by 38″ long.
Stitch the two edges (opposite the fold) together to form
what looks like a pillowcase with open ends. This seam
should be run f” in from the cut edges. When cutting the
seam-thread, leave it longer than normal (approximately six
inches). Next, turn the material right side out and stitch
a 1/2″ hem (as you would with pants) on both ends. These
hems will increase the life of your sails.

Repeat this procedure with the other piece of material.
You can now glue the various pieces together. First,
recheck your prior assembly for proper fit and symmetry. If
satisfied with the temporary structure, start disconnecting
the tee (on both sides) that connects the top cross member
to the top sail members. This is necessary for sliding the
sails onto the vertical sail members; if you don’t, you may
find yourself with no means to attach the seamed sail. Once
the sails are in place, begin disassembling, gluing, and
reassembling the structure one piece at a time. Use PVC
Cement, available at your local hardware store. It may drip
when applying, so protect your work surface with newspaper.
I swab the cement inside the rim of the fitting, and then
insert the piece of pipe with a quick twisting motion.
Pre-check your alignment before each insertion.
When you finish gluing the assembly, set it aside.

Recharging Mechanism Assembly

This is the part of Breezy that allows for the conversion
the wind’s mechanical power into stored, electrical battery
power. Breezy is self-starting, always turns the same way,
and doesn’t care from which direction the wind is blowing.
Again, temporarily piece together the mechanism to check
for proper fit. Take the earlier cut pieces of pipe and
assemble as indicated in the mechanical detail. Keep in
mind that the elbow (motor shroud/enclosure) must face
toward the 4″ ABS cap (rotor pulley), and be even with

This is so the rubber band, acting as a belt, can have one
end around the motor shaft and the other around the 4″ cap.
This simple pulley arrangement has a step-up effect, which
greatly multiplies the rotor speed (40:1), and applies it
to the motor shaft. Next, remove both end caps, and with a
3/4″ spade bit, drill a hole in the top center of each one.
Using a 1 1/4″ spade bit, drill a hole through the center
of the 4″ ABS cap, and then check all three holes for
proper clearance.

The two end caps will easily slide over the main mast
(steel rod). The 4″ cap should just fit around the 1″ PVC
pipe. You can now begin gluing the pieces together,
starting with the pipe piece fitting into the bottom of the
four-way fitting. Next slide the 4″ cap, open-side down,
over this glued piece of pipe. Apply a ring of glue around
the drilled hole in the ABS cap to secure it to the bottom
of the four way. The piece to follow should be a coupler;
glue and attach to the bottom (under the cap) of the same
piece of pipe. By pushing the coupler up against the 4″
cap, you’ll secure the various pieces into a solid rotor
pulley mechanism. Make sure the 4″ cap rotates with the
windmill assembly, and doesn’t slip. Finish by gluing
another 2″ piece of pipe into the bottom of the coupler,
and following it with an end cap having a pre-drilled 3/4″

Only a few remaining pieces need PVC cement. In the
mechanical detail, study the portion of the mechanism just
below the pulley assembly. First, glue the tee into place
on the 48″ piece of 1″ diameter PVC pipe. This piece of
pipe is called the support mast, and provides the vertical
support for the entire assembly. It is important that the
motor enclosure be even with the rotor pulley (4″ ABS cap),
so the rubber drive band won’t be misaligned. The only
portion not requiring cement is the motor
enclosure (elbow). Last, attach the battery box opening up
to a 6″-long piece of 3/4″ PVC pipe. (This is the only part
of the assembly that requires 3/4″ PVC.) I found that a
plastic outlet box (located in the electrical section of
your hardware store) and cover will work nicely to
waterproof the recharging batteries.

If you use this type, check the size of the opening in the
box and adjust your 6″ piece of PVC to the appropriate
diameter to perfectly fit the opening. As far as the
matching cover, if you can find only one with either a
light switch or two plug-in plate, don’t worry. You can use
diagonal cutters to enlarge the opening to a 2.5″ by 2.5″
square (approximate measurements) to allow easy access to
your batteries. Attach the cover to the box so it opens
upward, providing more rain protection.

The wind-power converter or “generator” is simply a DC
motor which is held in the top of the 5″-long PVC pipe by
several wrappings of friction tape. Wind several inches of
tape around the bottom of the motor case to allow the motor
to extend from the pipe end. Test fit it in the pipe, and
continue the process until you’re sure that the motor will
stay in this position. Detail the motor enclosure elbow
(see Detail) with a 3/4″-long horizontal cut on both sides
of the horizontal segment. This will allow the drive belt
(rubber band) to extend from the motor enclosure without
touching the sides, which would make Breezy less

Cut these out with a hacksaw or on a mill so they are
slightly larger than the width of the rubber band. Next
comes the cutting and drilling of the bearing. The most
efficient material I have found for this application is
UHMW, (Ultra-High Molecular Weight) plastic. This
relatively new plastic is self-lubricating, wear-resistant,
and doesn’t need to be oiled or replaced like a
ball-bearing would. The bearing should be cut from a 2″
diameter UHMW rod, and should be 1″ thick. Also, a 3/4″
hole must be drilled through the center, so it can move
freely around the steel rod, or mast. This completes the
basic mechanical construction part of Breezy.

Electrical Circuit

The simplest form of charging system for Breezy could be
formed by directly connecting the motor/generator to the
battery through a diode. With this system, the diode allows
power generated by the motor/generator to be applied to the
battery, but blocks any power trying to return from the
battery. Without the diode, the battery would rapidly
discharge itself back into the motor during times of low or
no wind. However,

I don’t recommend this charging system. With the 40:1
step-up mechanism attached to the motor/generator, voltages
as high as 10 volts can be created in high-wind conditions.
These high voltages would overcharge the 1.5 volt batteries
and could possibly damage them. Instead you will need to
add a couple of other components to limit the amount of
power made available to the battery. Refer to the Breezy Mechanical Detail in the Image Gallery, and notice the motor/generator is connected through the 1
N4007 diode and the 51 ohm, one watt resistor, to the
battery holder. These parts are available from your local
Radio Shack store. In
addition to the diode and resistor, a special type of
transistor (Field Effect Transistor) is utilized to limit
the amount of power in the circuit. When the windspeed
increases above the optimum level needed for charging, the
motor/generator output voltage increases above three

The Field Effect Transistor senses this voltage increase
and begins to dissipate the extra electrical energy as
heat. Additionally, the 51-ohm resistor limits the amount
of charging current applied to your batteries to keep them
charging properly. If the wind gusts strongly, the
transistor will continue to clamp the charging voltage
harder and harder until it eventually “slips” the rubber
drive band temporarily. This action will not harm the unit,
but rather acts like a governor on the system. The LED
(Light Emitting Diode) is an option that you can add to
Breezy that gives you a visual “OK” indication. Building
the circuit is easy. Using a small soldering iron, simply
connect the various parts. Keep your work neat and remember
that you will need to install the circuit in the battery
box later. Remember to use red wire on the positive side, black on the negative.
If not, you might uncharge a battery and damage
it. Using a small voltmeter, check the polarity of your
motor/generator. With the wind blowing, the rotor turning,
and the motor/generator outputting a voltage, determine
which lead or terminal is positive, and which is

If you don’t connect the positive side to the diode, the
unit won’t charge; double-check this on your Breezy.
Congratulations, you’re now done with the electrical part
as well.

Final Assembly

At last, Breezy is ready to be put to the test. Secure the
sails before taking your windmill to your chosen site.
(Move Breezy from time to time to test various sites around
your place.) Use 20-pound fishing line to hold the sails in
the proper position. This strength of fishing line provides
a high-wind safety mechanism. If the wind is too strong,
the line will break and stop the windmill from spinning. To
begin the final assembly process, drill four holes (W” in
diameter) through the top and bottom end caps. Locate the
holes, one per top and bottom, for both sails. These holes
will hold the sail in the correct position. You may need
someone to hold the sail up while you fasten it.

With a needle, thread some 20-pound test fishing line from
above, through to the bottom of the top end cap. Continue
with the line down through the inside of the sail (along
the seam), through the top hole and out the lower hole on
the bottom end cap. The fishing line should be slightly
loose to allow some give in the sail, and must be knotted
on the top and bottom end caps. I knotted the line around a
small washer to help hold it in place.

Next, with the same needle run a small bit of fishing line
through the sail material and over the top elbow in order
to hold the sail up on this end. Repeat the procedure to
properly position the opposite sail.

Using Breezy

Take Breezy to the
operating site and begin by driving the X” rod into the
ground about 18″. Be careful not to “maul” the top of the
rod too badly; the main rotor assembly must slide over the

With the rod in place, use a carpenter’s level to make sure
the rod is perfectly vertical; Breezy must be vertical to
operate at maximum efficiency. Using a ladder, slide the
support mast assembly over the top of the rod, and push it
into the ground approximately 4″. Drop the UHMW bearing
into place atop the support mast. Then, slip the rubber
drive band around the rotor pulley and ease the main rotor
assembly over the top of the rod. With the rotor assembly
resting atop the support mast and UHMW bearing, work the
rubber drive band over the motor/generator shaft. Position
the motor enclosure elbow so that the rubber drive band
operates smoothly. Guy (or steady) Breezy using “clothesline” wire and tent stakes at a ground radius of
approximately eight feet. The guy lines should hold the
support mast firmly, and keep Breezy from moving from side
to side as it rotates. I like to use three guy lines, but
you may be more comfortable with four. Well, that’s it just
select a battery to charge. With a light breeze, my Breezy
takes about eight hours to fully charge a D cell that is
completely run down. Smaller C, AA, and AAA batteries will
take even less time. Experiment with your unit to determine
what works best in your area. Good luck with your Breezy
and congratulations-you’ve broken the “throw-away” battery
syndrome and made the world a better place.

Editor’s Note: Kelly Isaac is a high school teacher and
neo-naturalist specializing in applied biology, chemistry,
and physics.