**Important:**

Do not do this if you have a wireless or electronic doorbell. This will only work on the old-fashioned doorbells that are simply switches. You could fry electronic doorbells very easily doing this!

**More Important:**

I am not liable for any damages incurred through the use of these instructions. Even though it is very hard to hurt people with this, it may freak them out and get you into a legal mess. Use at your own risk!

**Signing Up**

## Step 1: Theory

The purpose of a negative ion generator is to give extra electrons to air molecules, "ionizing" them. Negative ions are good for your health and make you feel better. In order to give molecules extra electrons, the generator must create a very high potential (voltage) between the generator and ground. In the case of this negative ion generator, it creates 15,000 volts.

Now, isn't that dangerous???

In short, no. High voltage doesn't kill people, high current does. A little math:

V*I=W

12v*0.1A = 1.2W

1.2W = 15,000v * 0.00008A

What this says is that

*if*the generator was 100% efficient, it could achieve a

*maximum*current of 0.08 milliamps. 5mA is the minimum current required for any lasting harm to be done, and this is well below that.

You only have to read below if you are very interested in high voltage and shocks.

Most static shocks occur due to capacitance with ground. Basically, every person is a walking capacitor. They are one plate, the ground is the other, and their shoes (or air) is the dielectric. You get charged up due to the triboelectric effect, and when you touch somebody else, you balance the charges in your capacitors. If you touch something metal connected to the ground, you discharge yourself.

This is one way to create a shock. The other way is to provide a direct path for the electricity to go, for example, touching two metal plates at different potentials at the same time. This is what causes most electrocutions. In this example, you are not a capacitor, but a conductor. These shocks are more effective because they are more controllable and more powerful, due to lower resistance.

I tried both methods when constructing this device. Method 1 (human capacitors) works fairly well when you are barefoot, but can barely be felt when you are wearing shoes. Method 2 (human conductor) works amazingly well no matter what.

Cool! The science behind pranks!

You can think of it like this: when you short circuit a battery, the voltage across it's terminals goes to zero (even if it is, say, 9-volts nominally.) Some finite amount of current (say, 4.5 amps) will flow through your short. This is known as the "short circuit current." Likewise, if you remove the short and measure the voltage of the battery, it will be sourcing no current, but will have 9 volts across it. Now imagine somewhere in between. If you load the battery with, say, a 2-ohm resistor across the terminals, you might measure a voltage of 4.5 volts and a current of 2.25 amps. If you repeat this experiment with several different resistor values and plot current versus voltage on a graph, you will find that you can (approximately) connect all the points with a straight line. It will intercept the voltage-axis at 9 volts and the current axis at 4.5 amps. If the battery were an ideal voltage source, this line would be completely vertical (no matter what the current is, the voltage will be 9 volts.) It turns out that you can approximate (model) a battery as an ideal voltage source and a resistor (not the load resistor, a new resistor, and not a physical one: one intrinsic to the battery.) In the above example, that resistor's value would be 2 ohms. This is often referred to as the "internal resistance" of the battery. Better batteries have lower internal resistance.

So how does this apply to the high voltage generator? The high voltage generator also has an internal resistance. If I were to short-circuit it, the voltage would also drop to zero, and the current would be finite, not infinite. This is how I determined that the machine was safe. I first determined that the machine would draw the most power when it was short-circuited. Then all I had to do was measure the short-circuit current. Since measuring the output side is hard, I used conservation of energy to simplify this measurement. I measured the power (energy per time) going into the input, and used the fact that the high voltage generator can not create power out of thin air. So, with the output shorted, the input drew 0.1 amps at 12 volts, or 1.2 watts. This means that the output will not be able to pump more than 1.2 watts into my body. At 15 kilovolts, this would only be 80 microamps.

There is a subtle misdirection here: if I am drawing 80 microamps from the output, there is no way it will still be at 15 kilovolts: the voltage will droop, just like the battery did. However, this can only lead to less current draw, not more, so my estimate is conservative. In fact it's not really an estimate so much as an upper bound to what the actual value is.

So I bet after all this you are still concerned with V=IR where V is 15 kilovolts and R is your body, so I must be larger than I claim. The fallacy here is that V is 15 kilovolts. The high voltage generator has an open-circuit voltage of 15 kilovolts, but as soon as you load it when, say, yourself, that voltage droops. And so using my measurements and conservation of energy, we can find what it droops to. Assuming we are putting 80 microamps into the body, with the body having a resistance of 20 kiloohms, we see that the actual voltage across your body is only 1.6 volts! The reason it feels different from touching a AA battery is due to capacitive and other transient / AC effects created by the high voltage.

So it turns out, compared to the resistance of your body, the internal resistance of the high voltage generator is huge (hundreds of megaohms.) It's a really crappy battery. So you can think of it like touching a 15 kilovolt source through a huge resistor. Another way to think about it is that the high-voltage generator is a better current source than voltage source.

If you'd like high voltage with lower internal resistance, consider grabbing onto some high-voltage power lines. Then you can experience 750 milliamps of current through your body (but not for very long!)