Project 29—Simple Induction Shocker

Project 29—Simple Induction Shocker

In 1831, Michael Faraday found that the electromotive force (EMF) produced around a closed path is proportional to the rate of change of the magnetic flux through any surface bounded by that path. Of course, that description of induction is a bit “nerdy” for my liking, so let me put it to you in a context that much better suits this book. If you throw a 9-volt battery across the windings of a transformer, you will get a shock if your fingers are touching the wires when the power is released. This induction effect is a bit strange, since the high voltage is only delivered as the power is removed from the windings, but this is due to the way electromagnets work, and great for creating fast shock pulses that feel a lot stronger than the one produced by the piezoelectric igniter presented in the previous project. For this project, you will need a small appliance transformer and a 9-volt battery as shown in Figure 7-5.

The exact size and number of wires protruding from the transformer are not really important; as long as you rip one of these from a small appliance, it’s guaranteed to do the job. A great source of these small transformers is old boom boxes (also known as “ghetto blasters”), AC wall adapters, video appliances, coffee makers with timers, and so on. The transformer will look similar to the one

shown in Figure 7-5 and will have two sets of wires coming from each side of the body. On one side of the transformer (the primary winding), there will be only two wires, which would normally be

connected to the 120-volt AC supply. The other side (secondary winding) might have between two and six wires, depending on what voltages the small appliances needed, although three wires on the secondary winding is typical. An AC transformer will change voltage between the primary and secondary windings depending on the ratio of windings from the primary to the secondary.

In small appliances, the primary winding of a transformer is connected to the 120-volt AC line and will contain many more turns than the secondary winding, which is why there is a much smaller voltage produced on the secondary winding. Typically, small appliance transformers will reduce 120 volts to less than 20 volts to power the electronics. All you have to do is identify the primary winding for this project, since it will be used to create a high-voltage induction when connected to the battery. As stated before, the primary winding will be the two wires sticking out of one side of the transformer, and often they are the same color. The schematic diagram for this device is extremely simple as shown in Figure 7-6.

In the schematic, one wire of the primary winding is connected to a battery and then to an output, and

the other wire of the primary goes to another output. You might think that this odd circuit may seem like it does nothing, since no current is flowing in the open circuit, and you would be correct. If you take each output terminal (one in each hand) and connect them together to close the circuit, the primary winding will be energized, but still nothing happens at this exact point. It’s when you disconnect the two terminals that things become interesting—a nice snapping sound and a good shock will flow through your body. When you open the circuit, the energy stored in the electromagnet collapses back through the now open circuit and sends a high-voltage induction into your fingers. So simple, yet so effective! Figure 7-7 shows the simple wiring needed to connect the battery to the primary coil as indicated in the schematic diagram.

The unused transformer wires should be taped off, but feel free to play around with the other wires to see how the shock effect is different. You will likely find that the primary windings will offer the greatest shock, whereas the secondary

windings will make a louder spark, but with much less shock factor. Now, once again you are faced with some creative thinking tasks in order to disguise your device in order to deliver it to your rightly suspicious friends effectively. This project lends itself to hundreds of cool designs, since the

Project 29—Simple Induction Shocker

Secondary Primary 9 V

Output

+

B

goal will always be to touch the two wires or terminals together. You could wrap the guts into a pair of tinfoil balls and tell you victim that it is almost impossible to touch them together, or put the unit into some type of fake strength-testing device that closes the circuit during use. I came up with the balance testing machine as shown in Figure 7-8, and it is very effective at getting the operator’s attention away from the inevitable shock that will soon come.

The balance tester is a great shock-delivery system, since the user is so preoccupied with standing on one foot that they always get caught off guard. “Hey dude, check this impossible balance test out, you have to jump up and down on one foot then try to touch the bolts together while

holding out your arms.” Of course, when they finally get those bolts together, the joke is on them! This device will run for a very long time on a single battery since the circuit is only closed for a few seconds at most. However, make sure that when the device is not in use that the bolts or wires are not touching each other, or your battery will be drained in a few minutes. Another fun game to play with shocking devices is what I call the “gladiator circle.” Have several people joint hands and then the person at the end of each chain has one bolt or terminal each. Complete the circuit to deliver the electric shock, then see who lets go first, so they can be eliminated one at a time until only the last two gladiators are in the circuit. To make the shock more intense, wet your fingers, or move on to the next project.