This is an AC electric generator which lights up a tiny
incandescent light bulb. The generator is made from a hollow-ended
cardboard box with a nail through the center. The box has many turns of
varnished thin copper wire wound around, with four large magnets clamped around
the nail. When the nail and magnets are spun fast by hand, the little
light bulb lights up dimly.
I wrote this article because I found lots of projects for making a simple
electric motor, but nobody gave the secret for making a generator. Well,
here it is: use strong magnets, lots of fine wire, and a special light
bulb which only needs 1/2 volt.
Also, don't bother making a "commutator," just hook the wires directly to the bulb. It's much simpler that way, but
the generator will produce AC (alternating current).
Before you start, here are some notes: DON'T USE DIFFERENT PARTS.
You must use a special light bulb. Normal flashlight bulbs will not work.
Also, you must use the large, strong magnets shown in the parts list.
Smaller magnets won't work. Use thin wire with varnish insulation. The
wire must be #30 gauge or smaller. Also, you can
improve the generator if you buy lots of extra kits of wire and wind it on the cardboard, since the bulb will light
up even when the generator spins slowly. Three kits of Radio Shack wire is
expensive, it's cheaper to mail-order just one or two
Open-frame box solenoids, but you'll, need vise-grips pliers to pry apart
the steel frame and remove the spool of wire.
First make the hollow-ended box. Score the cardboard strip like so:
| 8cm | 3.5cm | 8cm | 3.2cm | 7.7cm |
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|8 | | | | |
|cm | | | | |
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NOTE: this page must be displayed in COURIER FONT, otherwise
these pictures will be wrecked and unreadable. Most browsers
do this automatically.
|\ 7.7 | \ 3.5
| \3.2 | \
| | 8 |
| | |
| | |
| | | Fold it like this and tape
| | | it securely.
| | |
| | |
| | |
| | |
\ | |
|\ | \
| \ | \ Use the nail to poke a hole
| \______________|___\ perfectly straight through the
| | /| center of the box, going through
| | \ / | both sides and all three layers
| | \ / | of cardboard. Then pull the nail
| | \ (hole) | out and use it to widen all the
| | \ / | holes slightly, so when you put
| | O | the nail back through, it will
| | / \ | be a bit loose and able to spin.
| | / \ |
| | / \ | ( You can find the exact center
\ | / \ | by using a ruler to draw an "X"
\|___________________| from the corners. )
At this point you should let your four magnets clamp themselves
around the nail, and give
it a spin. This guarantees the box is large enough. The nail and
magnets should spin freely. The corners of the magnets should NOT bump
the inside of the box as they spin. If the box is a bit too small, start
over and make it a little bigger. Either that, or try a thinner nail.
And be sure to use the right magnets. Smaller ones won't work.
[YES, you can build the box from plexiglas or thin wood instead if you
wish. However, don't make it any larger than shown above. You want
the wire to stay very close to the spinning magnets, so keep the box
as small as possible. And don't use smaller magnets.]
Pick the spool of number-30 varnished wire from
_______________ the kit of spools. This is the thinnest.
_|______________ \ Tape one end of the number-30 magnet wire
|\ | \ to the side of the box, then wind all of
| \ | \ the wire onto the box as shown. It's OK
| \_____________|___\ to cover up the nail hole. Pull the taped
| | | end of the wire out, then tape down both
\ | | of the wires so the coil doesn't unwind.
\\ | | You should have about 10cm of wire left
\\\====================| sticking out.
/ | ==================== \
/ | | | \ Use sandpaper or the edge of a
| \ | | | knife to scrape the thin plastic
| \|__________________| | coating off 2cm of the wire ends.
| Remove every bit of red coating,
so the wire ends are coppery.
(note: the five lines of wire shown above are not real, that's
the 'equals signs' I used to draw with. The real wire can just
be wound up in a big wad in the center of the cardboard box.)
|\ | \
| \ | \
| \_____________|___\ Spread the wire away from the
| | | nail hole and tape it in place.
\ | | Stick the nail back through the
\\ | | holes and make sure it can spin.
\\\====================| Take your four magnets, stick
\\\========---=========/___ them face to face in two pairs,
|\\========(\\)========/ \ Then stick the two pairs inside
-----+-\==========(_)=======/ \ the box and on either side of the
/ | ==================== | nail so they grab the nail. Push
/ | | | | them around until they are some-
\ | | | what balanced and even, then spin
\|__________________| | the nail and see if they turn
freely. If you wish, you can
push 2cm squares of cardboard
between the magnets to straighten
them. If you wish, tape the
magnets so they don't move
around on the nail.
|_____| |_____________| 2 magnets
=================|| NAIL |_____________|
|_____| |_____________| 2 magnets
SIDE VIEW OF THE
NAIL AND MAGNETS VIEW FROM THE END
TWIST THE WIRES TOGETHER TO THE BULB
Make sure that each end of the generator's wires are totally cleared of
red plastic coating. If there is a bit of plastic left, it might act as an
insulator which turns off your light bulb circuit.
Twist the scraped end of each generator wire securely around the silver
tip of each wire from the small light bulb. (If necessary, use a knife to
strip more plastic from the ends of the light bulb wires.) One generator
wire goes to one light bulb wire, the other generator wire goes to the
other light bulb wire, and the two twisted wire connections should not
touch together. In the twisted wires, metal must touch metal with no
plastic in between.
Spin the magnet REALLY fast and the bulb will light dimly.
If it doesn't work, try spinning it in a dark room so you don't miss
the dim glow. If needed, adjust the position of the magnets so they don't
hit or scrape the cardboard. This thing has to spin *fast*, and if the
magnets whack the cardboard and slow down, you won't see any light.
(IF IT DOESN'T WORK, SEE "DEBUGGING" BELOW)
Once you get it to work, try clamping the point of the nail into the chuck
of a hand-crank drill. Spin the magnets fast with the drill and the bulb
will light brightly. Don't go too fast or you'll burn out the bulb, or
maybe fling magnets all over the room. You can try this with an electric
drill as well, although electric drills don't spin as fast.
Note: your generator produces Alternating Current, not Direct Current.
The output voltage is about 2 volts max, so there is no electric shock
hazard at all.
All metals contain a movable substance called "electric charge". Even
uncharged wires are full of charge! After all, the atoms of the metal are
made half of positive protons and half of negative electrons. Metals are
special because their electrons don't stay connected to the metal atoms,
instead they fly around inside the metal and form a type of electric
"liquid" inside the wires. All
wires are full of electric fluid. Modern
scientists call this the "electron sea" or "electron gas." The fluid
charge is movable, and this lets metals be electric conductors. The
movable charge-stuff is not
invisible, it actually gives metals their silvery shine. The electron gas
is like a silvery fluid. Sort of.
When a circle of wire surrounds a magnetic field, and
the magnetic field then changes, a circular "pressure" called Voltage
appears. The faster the magnetic field changes, the larger the voltage
becomes. This circular voltage trys to force the movable charges in the
wire to rotate around the circle. In other words,
moving magnets cause changing magnetic fields which try to create electric
currents in closed circles of wire. A moving magnet
causes a pumping action. If the circuit is not complete, if there is a
break, then the pumping force will cause no charge flow. Instead, a
voltage difference will appear at the ends of the wires. But if the
circuit is "complete" or "closed", then the magnet's pumping action can
force the electrons of the coil to begin flowing. A moving magnet can
create an electric current in a closed circuit. The effect is called
Electromagnetic Induction. This is a basic law of physics, and it is
used by all coil/magnet electric generators.
Generators don't have just one circle of wire.
Suppose that many circles surround the
moving magnet. Suppose that all the circles are connected in series to
form a coil. The small voltages from all the circles will add together
to give much larger voltage. A coil with 100 turns will have a hundred
times more voltage than a one-turn coil.
Now for the light bulb. If we connect the ends of the coil together,
then whenever the magnet moves, the metal's charges will move and a
large electric current will appear in the coil. What if we instead
connect a light bulb between the ends of the coil? A light bulb is
really just a piece of wire. The charges of the light bulb's filament
will be pushed
along. When the charges within the copper wire pass into the thin light
bulb filament, their speed greatly increases. When the charges leave the
filament and move back into the larger copper wire, they slow down again.
Inside the narrow filament, the fast-moving charges heat the metal by a
sort of electrical "friction". The metal filament gets so hot that it
glows. The moving charges also heat the wires of the generator a bit, but
since the generator wires are so much thicker, almost all of the heating
takes place in the light bulb filament.
So, just connect a light bulb to a coil of wire, place a short powerful
magnet in the coil, then spin the magnet fast. The faster you spin the
magnet, the higher the voltage pump-force becomes, and the brighter the
light bulb lights up. The more powerful your magnet, the higher the
voltage and the brighter the bulb. And the more circles of wire in your
coil, the higher the voltage and the brighter the bulb.
Disconnect one wire from the light bulb. Spin the magnet. While
still spinning the magnet, have a friend touch the wires together
so the bulb lights up again. Is the nail still as easy to spin?
Keep spinning the magnet while your friend connects and disconnects
the bulb. Do you feel any differences in how hard you must spin the nail?
Also try spinning the magnets while your friend connects the generator
wires directly together (with no bulb connected.)
When you crank the generator and make the lightbulb turn on, you are
working against electrical friction in order to create the heat and light.
You can FEEL the work you perform, because whenever you connect the bulb,
it suddenly gets harder to crank the generator. When you disconnect the
bulb, it gets easier.
Think of it like this. If you rub your hands together lightly, the skin
stays cool, but if you rub your hands together hard, your skin gets hot.
It takes more effort to rub skin hard so that it heats up;
it takes work. And in a similar way, it's hard to heat the lightbulb
filament, it takes work. You twist the generator shaft, the generator
pushes the wire's charge through the tiny filament, and if you don't keep
spinning the magnet, the magnet will be slowed quickly.
FEEL THE ELECTRONS
When your hand spins the magnet, you can feel the extra work it takes
to light the bulb. This happens because your hand is connected to the
flowing charge in the bulb, and when you push on it, you can feel it
push back on you! How is your hand connected to the flowing charges?
Your hand twists the nail, the nail spins the
magnet, the magnet pushes the invisible magnetic fields, the fields
push the movable charges, the charges flow slowly through the light
bulb filament, and the tiny filament causes friction against the flow
of charge and heats up. But then the reverse happens! The charge
can't move much because of the tiny filament, so it resists the
pressure from the magnetic fields, which in turn resist the pressure
from the magnet, which resists the twisting pressure from the nail,
which resists the twisting pressure from your fingers. So, in a
very real way, you can FEEL the electrons in the light bulb filament.
When you push them, you can FEEL their reluctance to move through
the narrow filament!
TURN OFF THE FIELD
Try changing the magnets' position. Remove the magnets, then tape them
around the nail so that the two stacks are clinging side by side, rather
than stacked up in a line. Spin the magnets. Does the light bulb still
light up? No. This happens because The N pole of one magnet stack is
very close to the S pole of the other, and vice versa. The magnetic field
is now stretching between the two stacks of magnets, and isn't spreading
outward. Most of the field is trapped between the neighboring opposite
poles, so the field doesn't extend out through the coil. When magnets are
side by side like this, they form one larger but weak magnet. On the
hand, when you make a single stack of magnets instead, the field extends
outwards for many inches. The stacked magnets form a larger but very
strong magnet. If you spin the single magnet stack, the
field cuts through the wires and pumps their electrons
MEASURE THE VOLTAGE AND CURRENT
If you can get a Digital Voltmeter or DVM, you can make some measurements.
(Once you can see some numbers, you can perform some professional science
experiments. This is great for science fair projects.) Spin the magnets
to light up the bulb, then connect the meter leads across the light bulb
connections. Set the meter for AC volts. Spin the magnets and see just
how high a voltage your generator produces.
How high can you make the voltage just
by using fingers? Or using a hand drill? Try spinning the magnets just
fast enough to barely light the bulb in a dark room. How small a voltage
is needed? Also try
light bulb, then measure the AC voltage across the two ends of the coil.
Can you tell if it's still the same as when the bulb was connected? Hint:
to spin the magnets at a constant rate, use an electric drill with a
fully-charged battery. Or perhaps hook the nail to an electric motor and
connect the motor to a DC power supply with settable voltage.
Note: The light bulb has around 50 ohms resistance. Also, 250ft of #30
wire has around
21 Ohms resistance. Because of the wire resistance, the
generator can only create around 60 milliamps current at most (0.06
amperes.) If you wind extra #30 wire onto the generator, it will increase
the maximum voltage, and maximum power. But since this adds more
resistance it WON'T increase the maximum possible current. To increase
the maximum possible current, either spin the magnets much faster, replace
the #30 wire with thicker wire, or use a stronger type of magnet material.
There is a simple way to convert your generator into a
motor. It involves using paint or tape to insulate a spot on one side of
then using a 6V battery and using the generator's wires,
touching the nail to form a switch. The rotating magnets turn the nail,
which turns the coil on
and off at just the right times. Can you discover the trick?
MAKING DC, CHARGE A BATTERY
You can change this generator so it makes DC rather than AC. The voltage
is still very low, so it's not very useful. If spun very fast, you might
be able to recharge a tiny 1.2v rechargeable battery. (Maybe you could
add lots more turns of wire to the coil to increase the voltage?)
Convert to DC:
The hard way: add a spinning "commutator" switch
sliding metal "brushes," so that each time the magnets turn half way, the
switch reverses the generator connections.
Easy way: Add a one-way valve! An "electricity valve" is called a diode
or rectifier. If you connect a diode in series with one of your motor
wires, it will
only let the charges flow in one direction. It will change the
Alternating Current into one-way flow (called "pulsating direct current.)
Try diodes from Radio Shack such as 1N4000 or 1N4001. Unfortunately a
diode needs about 3/4 volts to force any charges through, and this voltage
subtracts from your generator output. If your generator only puts out one
volt, then the diode will reduce this to 1/4 volt. So if you want to add
a diode, try doubling or tripling the amount of wire on
your generator. Also try using a special "Schottky" diode with lower
voltage than 0.7V, such as 1N5819 from digikey.com
HISTORY OF "ULTRA SIMPLE" GENERATOR
While running the tech shop at the Museum of Science in Boston, I was
working on new ideas for exhibits for the Electricity Hall in 1988. I
knew that the Exploratorium had an electric generator exhibit where the
museum visitor would yank a plastic-embedded coil plate through a row of
huge magnets (magnetron horn-magnets from a military radar.) Doing so
would light up a small bulb. I just knew that there HAD to be a way which
uses more common magnets. So I stacked up a pile of 3" loudspeaker
magnets (those black donut things) and waved it past various coils.
Finally I wound about five pounds of #26 wire around a ring of nails
pounded into a board, hooked up a #49 light bulb, then moved the stack of
speaker magnets in and out. This easily lit up the bulb.
Around 1994 I was thinking about the ultra-simple electric motor which
later became known on internet as the "Beakman Motor." Wouldn't it be
cool if kids could also make an electric generator that simple?
But it should be possible with parts from a Radio Shack store, since Radio
Shack had the special light bulb as well as magnets and spools of
electromagnet wire. After a few hours of experimenting I fould that I
could just barely light up the 20 milliamps bulb by using a single spool
of #30 wire from radio shack. But the wire had to be VERY close to a fast
spinning magnet, and the magnet had to be composed of four powerful
ceramic magnets in a stack.
To impress all the Physics Teachers, I tried to make the parts be easily
available, and the cost as low as possible. To make a popular project, I
made sure no tools were needed except scissors. I refused to use ball
bearings or plastic parts. So I made my own cardboard box for the
coil, and used a nail for the spinning shaft. To avoid extra parts, the
nail is just clamped by the powerful magnets. If anyone else wants to try
to make a cheaper or simpler electric generator, they have to do better
than I did!
WARNING: Keep the magnets away from computers, disks, videotapes, color
TV sets, and from wallets and purses containing credit cards. Try this:
the generator far from your color TV, turn on the TV, start spinning the
nail so the magnet is spinning fast, then bring the generator about 2ft
away from the TV screen. DON'T BRING IT CLOSER!!! Keep spinning the
magnets, and you'll see a cool wobbling effect in the TV picture, along
with some color changes. The field from the magnet is bending the
electron beam that paints the picture on the screen. Be careful, if you
bring the magnet about 15cm away, the iron sheet inside the TV picture
tube will become magnetized and the distorted colors will be permanent.
DON'T USE DIFFERENT PARTS. If the light bulb won't light, usually it's
becaused different parts were used. Follwo instructions.
If you changed the magnets, it won't work. So
don't use different magnets. If you used a different bulb, it won't work.
Use the parts in the list, don't make changes. If you're not using #30
varnish-coated wire, then it won't work. So don't use different wire.
Don't use different parts. Before testing anything else, ask yourself if
you used the parts in the parts list? If you used different parts, the
generator will fail. Notice: it's very important that you use the parts
listed, and don't use substitutes.
SPIN IT FAST, IN THE DARK. Sometimes your generator is working fine, but
you're not spinning it fast enough. Or perhaps the dim glow of the light
bulb is being missed in a brightly lit room. So, go into semi-darkness.
Then spin the thing REALLY FAST. Try cranking it with an old-fashioned
drill. (Electric drills don't turn very fast.) Or try gluing a tiny
wheel to the nail, then rub the wheel on the spinning tire of an
bicycle (don't go too fast or the bulb will burn out.)
ADD LOTS MORE WIRE. If your coil has more than 250
then the bulb glows much brighter. The Radio Shack wire is 200 feet long,
which gives about 250 turns. If you could wind more turns on your coil,
then your bulb would light up at lower magnet speed. Buy two kits of
wire from Radio Shack, then use both spools of #30.
Scrape every bit of the red plastic coating off all the wire ends. Then
end of the new spool to the end of the old one. This creates a single
longer wire. Be sure to wind the extra wire in the same
direction as before.
Better source of wire: buy a large "Solenoid"
from a mail order company, then use Vice-grip pliers to pry open the metal
bracket. The hole in the solenoid goes through a square steel plate, and
pry the rest of the steel frame outwards, you can remove the square plate
and take out the wire spool. Peel off the tape, and
wind 600 turns on your generator. Try this one:
DON'T USE OTHER MAGNETS, use the large 2-inch rectangular
magnets sold by Radio Shack,
#64-1899. Or try
They cost about $2 each, and have no holes through the center.
Don't use the smaller 1 inch Radio Shack magnets. Most other magnets are
way too weak and will not work unless you spin the
magnets incredibly fast, at thousands of RPM (revolutions per
USING SMALLER MAGNETS If you can't wait for mail-order of the correct
magnets, instead you can use twenty of the Radio Shack 1" magnets 64-1879.
Glue them together to form two large magnets.
Here's how I did it. First I formed two magnet stacks: I glued ten
in two separate stacks of five magnets each. I used 5-minute epoxy.
Before the glue hardens, adjust the magnets so the sides of each small
stack are flat, and wipe off the excess epoxy. (To make the sides flat, I
laid each stack down on aluminum foil, pressed them down to align the
magnets, then peeled off the foil when the glue was hard.) Next, glue two
of these 5-magnet stacks together side by side so the stacks are repelling
each other. See the diagram below. Glue the narrow side together, so the
block will be 2" wide.
Then hold them together until the glue hardens. That way the
N pole of one stack is near the N pole of the other, and S is near S.
N _________ N _________
|_________| <-----> |_________| Making a 2-inch block magnet
|_________| Glue |_________|
|_________| Together |_________|
Do the same with the other ten magnets. This gives you two large rectangle
magnets, each made up of ten small ones. Each magnet should have two holes
on each flat pole face. Clamp the two magnets on either side of your nail
as usual. They should attract together and grab the nail. These aren't as
powerful as the four "high energy" ceramic magnets, so you'll need twice
as much wire for your generator.
DON'T USE A DIFFERENT BULB. This generator cannot power a normal
flashlight bulb, it needs the special 25-milliamp, 1.5-volt bulb sold by
Radio Shack. Also try using a red LED. Don't use a normal flashlight
bulb, since that kind of bulb
requires way more energy before it starts to glow. If you simply cannot
find the Radio Shack 25mA bulb, you can use a 1.5V 40mA bulb, but add
twice as much magnet wire to your coil (buy two of those kits of magnet
wire.) The generator needs more than 250 turns wrapped
around it. Five hundred turns is better, that way you won't have
to spin the magnets so fast.
STACK THE MAGNETS SO THEY STRONGLY ATTRACT. Make sure the four rectangle
stacked to create two strong poles, otherwise the generator won't work.
Do this: stack
four magnets so their widest faces are clinging together. Then jam the
nail through the crack in the middle of the stack. Then take this
apart, and re-assemble it inside the generator in the same way.
CLEAN THE WIRE ENDS THOROUGHLY.
If the generator refuses to work, inspect the spot where the wires twist
together. The coil of wire has a very thin red plastic coating, and you
must clean ALL of this coating off the last half-inch of the wire ends
before twisting them to
the light bulb wires. Also, the tips of the light bulb wires must be
stripped clean of all plastic. The metal part of the light bulb wire
must touch the metal of the coil
If there is any plastic between the metal of the generator wire and the
bulb wire, the circuit will be "open" and no charge will flow.
Be sure to follow the instructions and diagrams. You MUST wind the coil
so the coil goes across the side of the box which has the nail hole. If
you wind it so no coil is crossing the nail-hole side of the box, then the
magnetic fields won't cut across the wires, and no electric voltage will
Also, don't wind the coil over the open end of the box, otherwise you
won't be able to get your fingers inside to make changes to the
If you cannot spin the magnets fast enough with your fingers, try a
"twist drill" or hand-crank drill. Clamp the nail in the end of
the drill and spin the magnets as fast as you can. An electric
drill may work too, but most electric drills don't move as fast as
the hand-cranked type.
AC VOLTMETER. If you have an electronic voltmeter, set it to measure two
volts AC, then connect it to the generator wires and spin the generator.
The light bulb needs a bit more than 0.50 volts AC in order to light
dimly. At 1.0V it lights brightly. If your generator's voltage is lower
than 0.5V, you need to spin it much faster, or you need strong magnets, or
you need to add lots more turns of wire.
DON'T SUBSTITUTE THE MAGNETS OR THE LIGHT BULB WITH A DIFFERENT TYPE. It
needs strong magnets and a low-voltage, low-current incandescent bulb.
If your generator doesn't work, check the parts again and make sure you
have the right type of magnets and the right type of light bulb. Don't
use fewer magnets. Weaker magnets may work in theory, but you won't be
able to spin them fast enough by hand, and a high speed motor will be
required in order to spin them. Don't use an LED. A red LED could work
in theory, but you need at least 1-1/2 volts to barely light one up (the
green or blue kind need even higher volts.) The light bulb is better
because it lights up at less than 1/2 volt. (If you really must light up
an LED, use the red kind, and also add about three more spools of #30 wire
to your generator coil.)
Perhaps your luck is bad and you got a dead light bulb. To test it, get
any new, fresh 1.5V battery (the size doesn't matter.) Take the bulb off
the generator, then touch one wire form the bulb to the top of the battery
and one wire to the bottom. The light bulb should light up brightly. If
it stays dark, the bulb is bad.
The generator can be improved by using more turns of wire. You used only
the spool of #30 wire. With more wire, the magnets don't have to spin as
fast to light the bulb. Connect the thinnest of the remaining spools of
wire to one end of the wire that's already wrapped, making sure to scrape
the wire ends totally clean before twisting them together. Make sure to
wind the extra wire in the same direction as the rest of the coil.
Or, if you want to light your light bulb REALLY bright, buy a second kit
of wire, hook the second #30 spool to the coil you have already made, then
wind all the wire onto the coil. Be sure to clean all the red plastic off
the ends of the extra wire that you've added.