wood103.pdf

Dan Bartmann

& Dan Fink

The Wood 103 was built mostly of wood in just a few hours, with very little number crunching.

Producing 100 watts in a 30+ mph wind ain’t bad for a weekend project!

he initial goal of our project was to

build a functional, permanent magnet

alternator from scratch, primarily out

of wood. When the alternator was

together and working, it became clear

that wind was the logical energy source

for it. This unit (we call it the “Wood

103”) is not intended to be a permanent

addition to a remote home energy

system, but a demonstration of how

simple it really is to produce energy

from scratch—and to be a bit silly!

Many homemade wind generator designs require a fully

equipped machine shop to build. Our wooden version,

built in a day, can be made with mostly local materials

and simple hand tools in any remote corner of the

world. The alternator design is well suited to

hydroelectric, human, or animal power. We plan to use it

for a series of magnet and electricity demonstrations at

local schools, and for future experiments with different

energy sources, windings, cores, poles, and rotors. This

project will cost you only US$50–75, depending on what

you pay for magnets and wire.

Alternator Basics

Electricity is simply the flow of electrons through a

circuit. When a magnet moves past a wire (or a wire

past a magnet), electrons within the wire want to move.

When the wire is wound into a coil, the magnet passes

by more loops of wire. It pushes the electrons harder,

and can therefore make more electricity for us to

harvest.

The magnetic field can be supplied by either permanent

magnets or electromagnets. All of our designs use

permanent magnets. In a permanent magnet alternator

(PMA), the magnets are mounted on the armature (also

sometimes called the “rotor”), which is the part that

spins. It is connected directly to the wind generator rotor

(the blades and hub). There are no electrical

connections to the armature; it simply moves the

magnets. Each magnet has two poles, north (N) and

south (S). The magnets are oriented in the armature so

that the poles alternate N-S-N-S.

Home Power #88 • April / May 2002

Wind Power

The other half of a PMA is the stator,

which does not move. It consists of

an array of wire coils connected

together. The coils in our stator

alternate in the direction they are

wound, clockwise (CW) and counter-

clockwise (CCW). The coils and

magnets are spaced evenly with

each other. So when the north pole

of a magnet is passing a clockwise

coil, the south pole of the next

magnet is passing the counter-

clockwise coil next door, and so on.

The coil cores are located inside or

behind the coils, and help

concentrate the magnetic field into

the coils, increasing output. The

cores must be of magnetic material,

but also must be electrically

nonconductive to avoid power-

wasting eddy currents. The air gap is

the distance between the spinning

magnets and the stationary coils

(between the armature and the

stator), and must be kept as small as possible. But the

spinning magnets must not be allowed to touch the

coils, or physical damage to them will occur.

The Wood 103 has three, 2 foot, hand-carved blades,

creating a swept area of 12.5 square feet.

The more loops of wire that each magnet passes, the

higher the voltage produced. Voltage is important, since

until the alternator voltage exceeds the battery bank

voltage, no electrons can flow. The sooner the alternator

voltage reaches battery voltage or above in low winds,

the sooner the batteries will start to charge.

Permanent Magnet Alternator

CCW

Increasing the number of turns of wire in each coil

allows higher voltage at any given speed. But thinner

wire can carry fewer electrons. Using thicker wire allows

more electrons to flow, but physical size limits the

number of turns per coil. This also explains why

enameled magnet wire is always used in coils. The

enamel insulation is very thin, and allows for more turns

per coil than does thick plastic insulation. Any alternator

design is a compromise between the number of turns

per coil, the wire size, and the shaft rpm.

CCW

Shaft

The electricity produced by an alternator is called “wild”

alternating current (AC). Instead of changing direction at

a steady 60 times per second like standard AC house

current, its frequency varies with the speed of the

alternator.

Armature:

Holds magnets,

rotates

CCW

Since we want to charge batteries, the wild AC is fed to

them through a bridge rectifier, which converts AC to

DC (direct current) for battery charging. The alternator

may produce much higher voltages than the battery

bank does, but the batteries will hold the system voltage

from the wind generator down to their normal level when

charging.

CCW

Magnets:

Polarity alternates

Stator:

Holds coils,

stationary

Coils:

Winding direction alternates

Home Power #88 • April / May 2002

Wind Power

Design

We had successfully converted AC induction motors

into PMA wind generators before. But starting from

scratch was truly a first-time experiment. Our design

choices for wire size, number of windings, number of

poles, blade pitch, and other factors were intuitive rather

than calculated.

Materials Used

The materials we used are not hard to find:

• Wood, the harder the better. We used pine since

it was locally available.

Every wind generator, waterwheel, and alternator we’ve

built has produced usable energy, no matter how

strange the design. The trick is matching the generator,

rotor, and energy source. You can do a lot of study and

calculation to get there. But if the design is quick, cheap,

and easy to build, why not just make adjustments by

observing the unit’s performance?

• Copper magnet wire, about 100 feet (30 m),

enameled #22 (0.64 mm diameter).

• Eight surplus neodymium-iron-boron magnets,

four with the south pole on the convex face, and

four with the north pole on the convex face.

• Dirt (magnetite sand).

• A 10 inch (25 cm) piece of 3 / 8 inch (9.5 mm) steel

shaft with a nut on the end to hold the hub on.

•Two, 3 / 8 inch by 2 inch (9.5 mm x 5 cm) bolts, but

these are optional.

If you try this project and change the wire size, magnet

type, rotor design, and stator cores, you’d still be

making usable energy and have a great starting point

for further research. Just change one thing at a time

until the unit performs to your satisfaction. We’re aware

that many design improvements could be made to the

Wood 103—and we hope that others will experiment

with variations.

• Bridge rectifier, rated for least 15 amps, 100 volts.

• Other supplies—glue and linseed oil.

Wooden Alternator

The biggest problem with building most wind generator

designs at home is the need for machine tools—usually

at least a metal lathe is required. Headquarters for our

business, Otherpower.com, is high on a mountain, 11

miles (18 km) past the nearest utility line. We are lucky

enough to have basic tools up here, but many folks

around the world don’t. That’s the main reason we used

so much wood in this design.

Wood 103 PM Alternator: End View

Series Connections:

Increase voltage

It’s possible to build human-powered

woodworking tools in almost any location. With

some patience, only simple hand tools are

required for this project. If you want to

build it in a day, though, a lathe, drill

press, band saw, and power planer can

be very helpful!

Armature:

3 7 / 8 in.

Shaft:

3 / 8 in.

Rotation

Building the Armature

The key to the Wood 103’s armature

is the neodymium-iron-boron

(NdFeB) magnets. They are the

strongest permanent magnets

available. Ours are surplus from

computer hard drives. They are

curved, and measure about 1 3 / 4 by

1 3 / 8 by 1 / 4 inch thick (44 x 35 x 6

mm). Eight fit together in a 3 7 / 8 inch

(9.8 cm) diameter ring. That’s why

we chose this particular diameter for

the armature.

Magnets:

Rare earth,

poles alternate

Stator:

Stationary

Windings:

#22 enameled copper wired,

wound in alternating directions

The magnets are available with

either the north or south pole on the

To Parallel Connections:

Increase amperage

Home Power #88 • April / May 2002

Wind Power

Safety Warning!

The large NdFeB magnets in this project are

extremely powerful, and can be dangerous. They

are brittle, and if allowed to snap together from a

distance, they can break and might send sharp

shrapnel flying. They are powerful enough to cause

painful damage to your fingers if you allow them to

pinch you, and can cause malfunctions in cardiac

pacemakers if brought too close.

The wooden armature holds eight NdFeB

(neodymium-iron-boron) magnets arranged

in alternating polarity around its perimeter.

Use safety glasses, gloves, a firm grip, and Zen-like

concentration when handling these magnets. Do

not get them anywhere near televisions, computer

monitors, floppy discs, videotapes, credit cards, etc.

They are not toys, and should be kept out of reach

of children!

convex face. For this project, you will need four of each

configuration. Don’t start tearing your computer apart to

get these, though! They are from very large hard drives,

and you won’t find any inside your computer. Check the

Access section at the end of this article for suppliers.

stack up to 1 3 / 4 inches; 4.4 cm) are 1 / 4 inch (6 mm)

smaller in diameter than the rest. Once assembled, the

armature will then have a recessed slot for the magnets.

Otherwise some means of “lathing” the slot will have to

be devised. It could be done on the alternator’s pillow

blocks with a sanding block mounted below, or in a drill

press. It would also be wise to first drill a shaft hole into

each plywood disk, and then assemble, glue, and clamp

all the plywood disks together on the shaft before

turning.

To construct the armature, we laminated plywood circles

together with glue. The 3 7 / 8 inch (9.8 cm) diameter

wooden cylinder is 3 3 / 4 inches (9.5 cm) long, with a 1 3 / 4

inch (4.4 cm) wide slot cut into it 1 / 4 inch (6 mm) deep to

tightly accept the magnets. To assure that the magnets

would be flush with the armature surface, we cut the

plywood disks a bit oversized, and turned them down on

the lathe to the proper diameter. The same procedure

was used to cut the magnet slot to exactly the right

depth.

Building the Pillow Blocks

The pillow block bearings were made from pine, since

that’s the hardest wood we have available up here on

the mountain. Certainly hardwood would be much

better. First we drilled a hole slightly under 3 / 8 inch (9.5

mm) diameter in each pillow block. Using a gas stove

burner, we heated the shaft to almost red hot, and

Using a firm grip, we carefully press-fit and epoxied the

magnets into place. Remember that these magnets

come in two different configurations—north pole on the

convex face and south pole on the convex face. The

magnets must have alternating poles facing out, and

this is how they naturally want to align themselves.

Pillow blocks support the armature. Charred wood

creates “carbon” bearings for the shaft to spin on.

Next, we drilled the shaft hole through the center of the

armature using a lathe, though it could certainly be

done with a hand drill if you are careful to align it

perfectly. We roughed up the surface of the shaft with a

file before epoxying it into the hole. It should be a very

tight fit—we had to gently tap it through with a hammer.

This may not be strong enough, and it might be wise to

actually pin the armature to the shaft. Time will tell!

Construction without a Lathe

We did cheat by using a lathe to shape the armature,

but a coping saw and sandpaper would work just fine. If

a lathe is not available, our suggestion is to first cut out

the disks, making sure that some of them (enough to

Home Power #88 • April / May 2002

Wind Power

forced it through the holes. This gave a good tight fit,

hardened the wood, and made a layer of carbon on the

inside for better lubrication. We drilled a small hole in

the top of each pillow block, down into the shaft hole, so

the bearings can be greased.

Stator Construction

After pressing the hot shaft through the pillow blocks,

we were very pleased with how freely the armature

turned and how little play there was. In a slow

waterwheel design, wood/carbon bearings would

probably last for years. This wind generator is a actually

a fairly high-speed unit, and real ball bearings would be

a big improvement. Such bearings could be easily

scavenged from an old electric motor of any kind.

Wooden bearings were certainly simple, fast, and fun

though!

Building the Stator

The stator, on which the coils are wound, is made up of

two identical halves. Each half is made from 2 by 4 inch

lumber, 6 inches long (5 x 10 x 15 cm). A semi-circular

cutout with a 5 inch diameter (12.7 cm) was made on

each half. The tolerances are pretty tight, but this allows

more than a 1 / 2 inch (13 mm) to fit the coils and core

material inside.

On the sides of the 2 by 4s, right over the cutout, we

glued thin ( 1 / 8 inch; 3 mm) U-shaped plywood “half

disks,” which have an inner diameter of 4 inches (10 cm)

and an outer diameter of 6 inches (15 cm). They have

slots cut large enough to accept the coils. These were

made with a hand saw, 3 / 8 inch (9.5 mm) drill bit, and a

rat tail file. The coils are wound in these slots, and the

space inside and behind the coils is filled with the

magnetite core material. There are four coils on each

half of the stator, and they must be evenly spaced.

of this type is often available from electronics stores or

electric motor repair shops. Each stator half contains

four coils. Each coil is 100 turns, and every coil is wound

in the opposite direction as its neighbor. It’s important to

wind the coils neatly and tightly, using a wooden dowel

to carefully press each winding loop into place.

Most common alternators use thin steel laminates as

cores, to help concentrate the magnetic field through

the coils. Magnetism in motion pushes the electrons

around in the steel too. The laminates are insulated from

each other to block these eddy currents, which would

otherwise waste energy.

Our twin stator halves are wound with #22 (0.64 mm

diameter) enameled copper magnet wire. Magnet wire

The two stator halves—one wound with 100 turns

per coil, and one ready to be wound.

These laminates are difficult to make in a home shop,

so we chose dirt as our stator core—actually magnetite

sand mixed with epoxy. It is not as effective as real

laminates, but was very easy to use, and available for

free by separating it from the dirt in our road. We mixed

the magnetite with epoxy and simply spooned it into the

open cores. If the cores were left empty (an “air core”)

the alternator would still work, but with much less power.

Magnetite is a common mineral, a type of iron oxide. It is

a byproduct of some gold mining operations, and can

sometimes be purchased. As an alternative, we simply

dragged a large neodymium magnet (just like the ones

we used for the armature) around on our local dirt road

on a string for a while, attracting all the ferrous sand,

which stuck to the magnet.

Home Power #88 • April / May 2002

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