Shake Flashlight





Introduction: Shake Flashlight

About: We are a supplier of neodymium, rare earth magnets. We also love to conduct experiments with our magnets and build unique projects with them! We have several engineers on staff who are always thinking of new...

How can you generate electricity without batteries? With magnets of course! In this Instructable, we will show how a magnet and some electrical components can make a simple shake flashlight that never needs batteries! This type of flashlight is great for hiking, camping, or emergency situations. Taking away the need for batteries means this flashlight is already ready to go and can last a long time!

Materials needed: Small cut of PVC pipe, magnet wire, neodymium magnet, LED's, 4 diodes or 1 diode bridge, capacitor, resistor, wire, breadboard, and electrical tape.

Step 1: Cut PVC and Wrap Wire Around It

The first step is to cut a piece of PVC pipe (or other non-magnetic material). The inner diameter of the pipe will determine the size magnet you need to use. We used a pipe with a 3/4" inner diameter, schedule 40, and cut it to 6.5" length. The length doesn't matter as much, but keep in mind that you want the magnet to have a short distance to travel when you shake it. We used a 3/4" magnet, our part DCX0 to go inside of the flashlight.

After cutting the PVC, it is time to wrap the wire around the tube. When doing this, make sure to leave the end out at the start and an end when finished. These ends will later attach to other wires. We used thin, 30 gauge wire, our product MW30-4.

We used a drill to spin the tube around while holding the wire and wrapping it back and forth in the center of the tube. How many turns? We forgot to count, sorry! A couple hundred should do the trick. The output voltage generated is directly related to the number of turns. Doubling the turns should double the voltage (in a perfect system). I would say around 300 turns. Turning slow can help you get a nice, tight coil. We simply used some tape to hold the ends down so it didn't unravel.

Step 2: Wire Testing

Before spending the time creating a circuit, we wanted to test the system to make sure it would work. LED's, like all diodes, only allow flow in one direction. So in this simple circuit, we used two LED's to test the coil assembly to see if it makes any electricity.

Using our breadboard, we hooked up the power supply (the coil) and the two diodes in parallel. We connected the wires from the coil to insulated wire, which we then inserted into the breadboard.

Check out this very informative Instructable on using a breadboard if you are having some trouble.

If you are confident in your wiring abilities, you can skip this step and head right to making the circuit!

Step 3: Create Your Circuit!

Now, let's add a few more things to our circuit to transform the blinking light into a steady, usable light source.

Step 4: Add a Diode Bridge

This diode bridge will take the alternating electrical output of our coil and get it flowing in one direction. You can make a diode bridge out of four individual diodes, but we chose a package that combined them into one unit. With this diode bridge, we can light just one LED since all the electricity will flow in one direction. Or, if you want, you can add an LED in parallel to light more than one.

For a good description of how a diode bridge is setup, see this page on Wikipedia.

Step 5: Add Resistor

We also used a resistor (R1) in series with the LED (D1). In this case, we used a 300 ohm resistor. This limits the flow of electricity through the diode.

Step 6: Add Capactior

What we need now is a storage device to smooth out the current and provide a steady flow of electricity instead of the short bursts provided from our coil. A capacitor (C1) functions exactly this way. Without the capacitor, the LED would blink on and off like a strobe light.

Some human-powered flashlights use rechargeable batteries to store more power. We just used a 4700uF 16V capacitor, to keep things simple and cheap.

Step 7: Test It Out!

With the circuit now complete, we put some finishing touches on our flashlight. We used some fancy mechanical packaging (not really fancy) to enhance this device. We added thin DC2 magnets on either end of the tube, repelling the magnet inside. These magnets act as springs on either end of the tube to keep from wasting energy, slamming into the ends of the tube.

We've also included a graph of the power generated by our circuit. Yours could vary depending on the size of resistor or capacitor.

Step 8: Nerd Stuff: How Does This Work?

As usual, we always like to include a short blurb about how the things we make work. In this case, the answer is Faraday's Law. Faraday was an English scientist who studied electromagnetism. He discovered that moving magnets near a coil of wire yields electricity.

Here is a more specific definition of Faraday's Law: Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil. No matter how they change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.

In this case, we're going to move a magnet back and forth through a coil of wire. Each time the magnet moves from one end of the tube to the other, the magnetic field inside the coil will reverse direction (twice). The voltage generated is proportional to the quick change in the magnetic field direction, multiplied by the number of turns of wire. Voltage generated = (number of wire turns) x (change in magnetic field strength per second).



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16 Discussions

is there a way you could have two or three sets of pipe with wire wrapping on them for more power?

1 reply

I think that having multiple pipes side by side would effect the magnetic field, however, I am trying to see if having two coils on one pipe (with each their own supercapasitors) would give you twice the bang for your buck.

great instructable. I tried to make one, but I'm stuck as the output generated is not that much and the led dies out too quickly. I've coiled the wire 800 times and I've been using neodymium magnets(they are small as compared to yours). Also my tube is about 13cm. Can you suggest me some improvements?

3 replies

To add to what is said, it seems like you used a thicker, uninsolated wire. With Electro Magnetic Generators (the coil of wire), how effective your wire is depends on tightness, resistance (thickness) and activity.
Tightness: the tighter you can wind the wire, the more voltage you can generate. If your wire is too loose, you can't build enough of a charge in a single area to create a current (amps) out of your voltage(power).
Resistance: in electricity, especially on small scales like this, bigger is rarely better. Think of plumbing:sure you can get more water in a bigger pipe, but you compensate pressure to do so. These kinds of generators require electric pressure to gain enough voltage to transfer it into current. However, too small of a wire won't allow enough voltage to be created either. For this project however, the small 8 guage wire that's recomended is a great guide to what size of wire makes a good ballence of capacity and pressure. Also note that the reason that the wire used has been isolated with plastic is because if the bare wire was touching the rest of the wires in the coil, you would no longer have a coil, but a ring, which defies the point of the coil needed.
Activity: taking a quick look at your image, I can see that there's about enough space to fit 3 of your magnet set ups between the coil the end of your pipe. This means that the magnet has further to go before reactivating the coil. Yes, you want your magnet to fully leave the coil, but you don't need much space between the coil and your magnet to do so. By shortnening yiur pipe thos way, you'll create more activity in the coil part as you shake it.

magnet field from one magnet of big size are much stronger than combine of small ones.

Totally Different.

There could be many factors that could effect the outcome. 800 windings might be overkill...double the windings should theoretically double the voltage, however it is a case of diminishing returns. The farther away the wire is, the less effected it is by the magnet. Also, make sure the windings are nice and tight. You may also want to try to use one big magnet instead of four stacked together. The size of the magnet will also effect the voltage output. Consider placing a capacitor into your circuit to help keep a steady light (if you haven't done so already).

why does my capacitor wont light up my LED although its already shown that its already charge by 2V?

1 reply

Look at the forward voltage rating of the LED. If it is 2.8V you probably messed it up.

I had one of these that my brother gave me, it was a commercially made one. I had it in my carry on bag going through Boston airport. The TSA inspector was very interested in it after X-raying my stuff, pulling me aside to examine it.After showing it was not dangerous, he let me take it, but with the coil and magnet and capacitor wiring it sure looked suspicious on the examiner's screen.

3 replies

I understand why they would want to look at it, but it's very irritating to me that they pretty much thing everything is a bomb these days. My aunt was delayed because of her phone battery.

Yes I could see how they would want to take a closer look at it...especially one that looks very homemade like ours!


2 years ago

Nice project, thanks for sharing.

This is really neat and simple. Would there be any advantage to using an N52 over an N42? Would a magnet length greater than 1" give better results? Is there a formula of magnet size , tube length and coil turns to determine current output?

1 reply

A N52 magnet would have a bit of a higher magnetic field, which could produce a higher voltage output, but it probably wouldn't be significant. I'm not sure if a greater length magnet would make a huge difference in the output, but I would assume it would take less work to produce light, not as much vigorous shaking as a smaller magnet. As far as a formula...How deep into electrical engineering do you want to dive? There is ton's of stuff to go into this. Check out this link for a common formula for a solenoid

You can also play around with our units calculator and see what you come up with!