A Tesla generator spins magnets past windings of copper wire, which induces a magnetic current. This current can be used to produce electrical voltage, which can be used to do work - anything from lighting up a lightbulb, to charging a cellphone, to charging a battery. The spinning magnets are called the rotor. The set of mounted wire windings, which are held stationary above the rotor, are call the stator. The rotor magnets and stator windings never touch each other, but they are held in close proximity in order to get the strongest results. The path of the spinning magnets should be at right angles with the wires of the coils, passing right below their center, in order to induce the most current. Here is an image of an alternating current generator similar to the one I've built:
In a micro-hydro generator like this one, running water is used to spin the rotor. The generator transforms mechanical energy, which is the physical spinning of the rotor, into electrical energy. The electrical energy, which begins as alternating current, runs through copper wires into a series of diodes, which rectify the current. Rectification of alternating current turns it into direct current, which the item being powered, called the "load," is then able to use. This is needed because alternating current reverses direction periodically, and the load uses current that only flows in one direction. Here is a diagram of a diode rectifier:
Anything that spins the rotor can be used to generate electricity by this method. You could use compressed air to spin this rotor, or, if the rotor was connected to a handle and crank, the energy of your own arm.
The principles may seem complex at first, but a generator like this one is inexpensive to build. The parts needed can be found at a hardware store and an electronics store. If you already have a drill, a dremel, an old CD case and some CDs you don't mind repurposing, the rest of the materials cost about $30.00.
What Materials Do I Need To Build a Tesla Generator?
Image by Steven Jackson
9 Compact Discs
One Spindle-Type Compact Disc Case, 3" high
One 9" Plastic Platter
One-Pound Spool of Enameled 24 AWG Magnet Wire
Six ½ inch x 1/8 inch Neodymium Rare Earth Magnets
Two Bridge Rectifiers
One Capacitor Rated at 200 Volts and 470 microfarads
One Electronics Breadboard
Ten 1/8" Nylon Spacers
One Plastic Ice Cream Scoop
One Brass Bolt with Nut
One Hose
One Hose Clamp
Four Pop Rivets
Two 2" Diameter Wooden Discs
One 1" Bolt with Nut
One 1/2" Nylon Spacer
One Small Water Pump (Optional)
One Large Rechargeable Battery (Optional)
One 5-Gallon Bucket (Optional)
These are the tools and adhesives I needed:
One Tube E6000 Glue
One Roll Clear Tape
Dremel With 1/16" and 1/8" Drill Bits and Router Bit
This video explains how to generate alternating current through magnetic induction. In this example, we use a Tesla micro-hydro turbine. This turbine and stator can also generate electrical current when spun by other methods.
Warning:Use eye protection at all times, preferably goggles; bits of plastic will be flying everywhere while you dremel holes in your components. Plastic may melt if dremel speeds are too high; stop the tool if this begins to happen and let the plastic cool. Protect all surfaces from spilled glue, dremel bits and drills; we covered our tables with cardboard. Magnets can be very dangerous if you use larger magnets than we recommend: you can pinch your fingers badly if they get close to each other and suddenly snap together while your hand is in the way. Do not let children play with magnets. Magnets are dangerous if swallowed. E6000 glue is also unsafe for consumption, and we recommend good ventilation while the glue is wet.
Step 1. You will need to drill holes in eight old compact discs. This will be your stack of platters, which running water will flow across. The flowing water will make them spin, and the holes are for the water to rush through. The water will enter from the side of the CD case and drain out the bottom. Each CD needs three holes, which will be about an inch long and crescent-shaped, and fairly near the center of the discs. Space the holes so that the CD will maintain its structural strength; if the holes are close together the plastic may crack. Use a workbench with a hole in the center, and attach the dremel to it from underneath. Drill a starter hole in each section with a drill bit, and then move the CD over the dremel to cut out the larger shapes with a router bit. Making a jig out of a flat CD case is helpful; you can spin the CD on the center mount, allowing you to create smooth crescent shapes with the dremel. To do this, you will need to drill a hole in the bottom of the CD case in the correct location, which the dremel bit will protrude up through so it can cut into your CD. Try to adjust your speed so that the friction does not simply melt the plastic; if it does, remove melted bits from your tools before continuing to drill or cut.
Image by Oluwa Jackson
Step 2. Next, drill a large hole in the side of the CD case, and six large holes in the bottom of the case to make your water’s inlet and your outflow. The hole at the side should fit the hole you will drill in the plastic ice cream scoop you’ll use to funnel the water into the case. Keep a flap attached to the side of the hole that you can use to mount a screw through it; this will go through the top of the ice cream scoop to hold it securely on the case.
Image by Oluwa Jackson
Step 3. The CDs you’ve made into platters will need spaces between them about as thick as a CD. That’s because the surface area of each CD needs to be exposed to the rushing water; the water will cling to the surface of each CD to make it spin. This is due to adhesive, cohesive, and boundary layer forces, which are properties of water made possible by the polar structure of water molecules. To make spaces between the CDs, we used nylon spacers that we bought at the hardware store. Make sure that the spacers don’t cover up any of the holes you’ve drilled. Rough up the spacers with sandpaper, and use E6000 glue to attach each spacer to each CD, except for the bottom spacer: the bottom CD needs to spin freely upon the spacer attached to the base of the spindle, which should still be smooth. Make sure that the holes you drilled in the CDs line up with each other as you glue the stack. Make sure not to get any glue whatsoever on the upright spindle of the CD case, as the CDs will need to spin rapidly on it.
Image by Oluwa Jackson
Step 4. Next you will need to attach the plastic ice cream scoop to the rotor. You may need to use a belt sander to shape the scoop to fit snugly against the curve of the side of the CD case. Drill a hole in the base of the handle big enough to fit a hose into, and a hole through the curved inside surface of the scoop down into the handle. Fit the scoop against the side of the CD case, and determine where to drill to attach a screw to the flap you left in it. Drill your holes, and counter-sink a brass screw such that the head of the screw will be set into the plastic flap and curved inner surface of the scoop, and the nut will hold it onto the outer surface of the scoop. Once the scoop and case are screwed together, use E6000 glue to seal all holes around the edges where they meet to attach them more securely together and prevent water from leaking out. Let the glue dry overnight.
Image by Oluwa Jackson
Image by Oluwa Jackson
Step 5.Now you have built the piece that will spin. You still need to attach the part that will generate current: magnets. We used six ½ inch x 1/8 inch neodymium rare earth magnets. These will be glued, evenly spaced in a hexagon, to the top CD of your platter. This is the 9th CD, and it doesn’t have holes drilled in it. The magnets must be arranged so that they alternate polarity; for example, if one magnet has the south pole facing up, then the two next to it need to have the north pole facing up. We used E6000 glue to attach our magnets, marking their polarity on the tops with a permanent marker. Magnets with the same pole facing each other repel each other, and magnets with the opposite poles facing each other will be strongly attracted to each other. Test your magnets this way to determine which sides need to be facing upwards. Once you have your magnets attached, glue the top CD to the spacer at the top of your stack, being sure to leave enough room so that the CD case isn’t touching the tops of the magnets; they need to be able to spin.
Image by Oluwa Jackson
Congratulations: you have finished building your rotor! Now for the next step: the stator.
How To Build a Stator
A stator is made by making windings of copper wire, called magnet wire, in a trapezoidal shape. We made six windings of 200 turns each. Your windings must all have the same number of turns. They must fit directly over the magnets without the windings touching each other, so plan your dimensions accordingly. We used nearly a pound of enameled 24 AWG magnet wire. The windings must be wound tight, and held together securely so they don’t unwind; there should be no gaps between the wires. We used tape wrapped around the straight sides of the trapezoids to hold the windings together before we glued them down. Leave about eight inches of wire loose at the beginnings and endings of the windings, because you’re going to need to attach the windings to the rectifier. Use a piece of tape to mark the wire at the beginning of the winding.
Step 1. You will need to wind your wire around a form, so determine the size of the trapezoid you need and use pop rivets between two small wooden discs to make the corners. The wooden discs should be held half an inch apart by a small-diameter nylon spacer in the middle of the discs, glued onto only one of the discs. Pop rivets will allow you to attach and remove one of the discs, so you can get your windings off the form once they are wound. A screw and nut threaded through the center of the form will hold the form together while you are winding the wire.
Image by Oluwa Jackson
Step 2. Leaving eight inches free, start winding your wire around the form, keeping it tight and counting the turns. This will take two people: one to turn the form, and one to hold the wire taut. Once you have 200 turns, carefully remove one of the discs from the form, taping the end of the wire down to keep it tight. Slide tape under the winding, and wrap a piece securely around each side before removing the winding completely from the frame. Leave eight inches of wire free at the end of the winding, then snip it free of the spool. Make six such windings. Mark the beginning end of each wire with a "+", and the finishing end of each wire with a "-", so you will know which ends to attach to which side of your rectifier later.
Image by Oluwa Jackson
Step 3. You will need to glue your windings to a plastic platter. We improvised and used the lid of a food container. It needs to be larger than the diameter of your generator, because it is going to sit on top of it with the windings over the magnets. Like the magnets, the windings need to alternate polarity. So if one of your windings is wound counterclockwise, the two next to it need to be wound clockwise. Just flip the winding over to get the correct spin direction, tracing it from the start of the winding which you marked with tape. Once your windings are evenly spaced over the magnets, and you have made sure they are alternating spin direction, glue them to the plastic platter with E6000 glue. After this dries, apply more glue all over the windings to help keep them wound together, making sure none of your loose wires get glued to the wires from a different winding. The loose wires should all face the outside edge of the platter. You can use superglue for this if you prefer.
Image by Oluwa Jackson
How to Test Your Generator with a Water Pump
To prove that your generator works, you need to make it spin. A freestanding test appropriate for a science fair is a bucket of water with a water pump, which you will attach to your generator. Home use will most likely involve attaching your generator to a faucet while you fill up your sink, pool or bathtub, and it will not require a battery or a pump. To use a water pump to test your generator, you need bucket with two holes in the lid. One hole is for water to pour into from the bottom of the generator; it should be big enough to leave the holes you drilled at the bottom of the CD case exposed, but small enough to hold up the generator. The second a hole is for the water pump to draw water through. Rather using than a lid, you can hold your generator over the bucket with a pair of small planks, but if you do you must be careful not to drop your electronics into the water.
Image by Oluwa Jackson
Step 1. Attach a hose between the outflow of the water pump and the intake of the generator, using a hose clamp. Dip the other end of the water pump into the water in the bucket (at least a gallon), making
sure the inlet is not blocked in any way, nor resting with the inlet directly downward on the
bucket's bottom.
Image by Oluwa Jackson
Step 2. Attach the water pump to a large rechargeable battery, using alligator clips on the positive and negative leads.
Image by Oluwa Jackson
Step 3. Turn the water pump on. This will pull water into your turbine and make the CDs spin. That will rotate the magnets under the stator coils, and generate a current. This video demonstrates the spinning in action:
Video by Oluwa Jackson, music by The Chemical Brothers
Step 4. Hook your stator wires up to a digital multimeter (DMM) see how much voltage you are generating. To do this, set the DMM to alternating current. Then tie all your positive wire ends together, and all your negative wire ends together, and hook them up to the DMM test leads. Once you determine the voltage your generator is outputting, you can determine the specifications of your capacitor and voltage regulator.
Troubleshooting: What do you do if your test fails and your generator doesn't spin? We have encountered four potential problems:
Insufficient water force.You can address this by narrowing the turbine's water inlet, forcing the water into a stronger and more concentrated stream. We used putty.
Water flow is poorly aimed at turbine stack.Experiment with different angles of water flow until you find one that creates a spin.
Turbine housing is too tight.Make sure nothing stationary touches your magnets. Also, make sure nothing stationary touches the sides of your discs as they spin.
Too much friction between spindle and turbine.Make sure there is no glue or tacky material rubbing on surfaces that need to move smoothly past one another.
How to Hook Your Generator To a Load
You must now convert the alternating current (AC) you are generating to
direct current (DC). To do that, attach your loose stator wires to a
bridge rectifier, test it to discover its output, and then choose an
appropriate capacitor and voltage regulator as I will discuss below.
Step 1. A bridge rectifier has four pins, which you insert through four holes in a breadboard. You will need two bridge rectifiers, placed next to each other. They have a positive and a negative end, so find where these are marked and line them up with each other, with the positive ends on the same side. The next step is to add the red positive and black negative wires leading from the breadboard to the load, so it's time to prepare the positive and negative leads to be soldered. Cut a ten inch length
of insulated red wire, and a ten inch length of insulated black wire, and
strip 3/4 of an inch of the insulation off the ends. Twist the bare wires, and tin them
with solder. This holds the exposed wires together with a conductive
material. The red wire will be soldered onto the positive ends of the
bridge rectifiers, and the black wire will be soldered to the negative
ends; the proper ends are marked in the rectifiers. Note that each wire
connects to both bridges; you need to make sure you strip enough length of wire so that it reaches between them. Your stator wires are be soldered between
them, only connected to one bridge each. This is how your breadboard will look from the back: note the soldering iron at a center pin, where the magnet wire is being attached.
Image by Oluwa Jackson
Step 2. To
connect them to your stator, first prepare the ends of your stator
wires by tinning them with solder and burning off the enamel coating for
about half an inch. Twist together a positive and negative wire that
are two windings apart from each other and solder them together. This is
where having marked the beginning of the winding with a "+" and the end
of the winding with a "-" becomes very important. "+" always connects
to "-". The idea here is to connect the three windings that spin
counterclockwise to one another, and then to a bridge rectifier. Then,
connect the three windings that spin clockwise to each other and to the
second bridge rectifier next to the first. To connect to the bridges,
leave two pairs of wires free: that leaves two wires from clockwise windings, one marked with a "+" and one marked with a "-", connected to one bridge rectifier, and two wires from counterclockwise windings
connected to the second bridge rectifier. The free wires are connected
to your bridge rectifiers by being soldered to the middle pins. The middle pins are marked with a sine wave, which represents alternating current, and either "+" or "-" can be attached to either of these pins: what is important is that the "+" and "-" wires from the same winding direction are soldered to the same bridge rectifier. From
there, the bridge rectifier will connect your stator to the load,
carrying electricity to whatever you want to power. Now that you've soldered your windings to what is called a "full bridge rectifier package," your AC current is transformed to DC
current. This is how your breadboard will look from the front: note the two bridges, and the magnet wires marked with "+" and "-".
Image by Oluwa Jackson
Step 3. Now test your output with either a DMM or oscilloscope. This will help you determine the specification of your smoothing capacitor. A smoothing capacitor reduces fluctuations so that current is steadier; otherwise the waveforms are humped waves and drop to zero periodically, which would interrupt the flow of voltage to your device. The capacitor has two pins that you will push through the breadboard. The positive end of the capacitor attaches to the positive end of the bridge using the red wire, and the black wire attaches to the negative end. This carries the rectified current through the smoothing capacitor, and then to the load, with red and black wires as before.The capacitor pictured below, which is appropriate for our generator's output, is rated at 200 Volts and 470 microfarads.
Image by Steven Jackson
Step 4. Attach your output to a load. The load can be anything that uses electricity at the voltage you are outputting. You can test your output with a lightbulb first to make sure it's safe. A generator like this can charge a rechargeable battery; it could charge a cell phone, or power a small blender. In this video, we attached our generator to an oscilloscope with the red and black wires so we could measure the voltage output it generated. We spun it on a Dremel tool at varying speeds, proving that it was generating current by the waveforms you can see on the oscilloscope, though you can also test your output with a DMM:
Video by Oluwa Jackson, music by Skrillex
You’re all done! Now you can attach your turbine to a faucet to generate electricity whenever you wish to power a small electronic device or charge a battery.
Our first test was to determine whether our turbine actually spun when we hooked it up to a water pump. At first, it did not. We had to use putty to reshape the water inlet so that the narrower opening increased the pressure of the water shooting into the turbine. After a few tries, we finally got the turbine to spin. The rate was decent, but we weren't able to sit the turbine housing (a repurposed CD case) clicked onto its base the way we'd originally intended, and water was exiting from the sides as well as the bottom of the case. We ended up prying the nylon spacer off the base, and sanding it down so that there was more headroom in the turbine. This improved our situation slightly. We were still suspicious that the turbine stack was grazing the sides of the case enough to cause slowness and inefficiency. We were also not happy with the amount of friction between the turbine stack and the spindle it rotates around, and the turbine stack and the bottom spacer. We tried silicon lubricant, but once it was wet it actually got stickier and made things worse.
Test 2: June 1, 2016
On this day, we tested our turbine again, and tried adjusting the size of the outflow holes at the bottom of the case by changing them from six round holes to three large crescents. Result were worse. We ended up taping over the mod to narrow it back down a bit. Once we got the turbine spinning (slowly with the water test, unfortunately), it was time to work on the stator. We wired up our coils to a full bridge rectifier, and attached that to an oscilloscope to see whether we were actually generating current. Then we spun our rotor on a Dremel tool underneath the stator, so we could vary our speeds and determine maximum DC voltage output. At first, results were promising, as waveforms did appear on the oscilloscope. It's alive! At top speed we got about 4 Volts. We had also planned to try measuring our output with a DMM, but before we got the chance, disaster struck. One of our team turned the Dremel to a higher speed than before, and a magnet flung itself loose from the top of the rotor, shattered the side of the turbine housing, and disappeared into the lab - only to be found with difficulty in a box on the table with the oscilloscope. Thankfully no one was struck, and the only equipment that was damaged was our turbine.
Test 3: June 8, 2016
We completely reworked our turbines. We used the shattered casing to house a waterwheel turbine, with a rotor like the original version. The blades are cut from an aluminum can and glued to a CD at the top and a nylon spacer with ridges dremeled into it at the bottom.
We taped the housing together with duct tape, and kept the water inlet the same. This worked fine. We tested it with the pump circulating water from a bucket, just as we did with the other tests. The waterwheel spun very nicely. We hooked a DMM to the stator, and found that at the speed the pump was running we were generating 2.2 mV. This is not enough energy to power a typical device, but it's proof that we were indeed generating electricity with our turbine!
We took our original Tesla turbine and housed it in a spiral-shaped housing made of acetate film glued between two pieces of acrylic. The turbine spins on bearings, which are screwed into the top and base of the housing. We are using the same rotor and stator that we'd had in the original housing.
We glued the pieces together with E6000. Water enters through an ordinary gutter pipe and drains through holes drilled in the base. The magnets are very close to the top of the housing, for maximum interaction with the stator, but there is about half an inch of room between the rotor and the base of the housing.
For our test, we dumped 7 gallons of water into a tub that was taped to our drainage pipe; we had about 7 feet of head. Our turbine only spun for a few seconds, as the water drained through very rapidly, but we were able to verify that our rotor works! It spun much more quickly than it had when we did the test with the water pump, but not nearly as fast as when we'd spun it on a dremel. Our DMM read 2.9 mV at top speed. I feel that this is definite proof of concept, but if we want to generate usable electricity we're going to need to up the scale, as in more and stronger magnets, on a wider rotor.
There was little water leakage from the side of the housing, which is a better result than we had with the original housing. The rotor had been packed in so tightly that we actually had friction problems from the CDs being too close to the housing's sides. More room helped the water flow correctly, and the CDs spin more rapidly.
Looking to the Future
We will need to cut our stator windings off their current mount and move them further apart, and then remount them so that the sides of the windings are all exactly the same distance from each other. Then we can mount 12 magnets to a larger rotor instead of 6, and they will all be pushing electrons simultaneously.
Another design issue is that we have a steel screw in our housing too close to our magnets; it interacts with their magnetic field and slows the spin down slightly. We can replace it with brass.
