Post #18 Electricity and magic smoke part 2
Last post we started out discussion on electricity. If you didn’t read it, you’ll find it here.
Like any other form of power, there are a number of ways to measure electricity. The unit familiar to most people is voltage. If we take a look at our water tank, voltage would be the amount of water in the tank. In other words, voltage is the potential electricity has to do work. A 10,000 gallon water tank can supply a lot more water than a 10 gallon tank. A 10 volt power supply supplies a lot less power than 480 volt transformer for a factory. Most homes in North America are wired with an electrical system that is rated between 110 and 120 volts. Anyone who has worked with electricity and been “bitten” by this voltage knows its power. Depending on the person, this voltage can be lethal. But voltage is only part of the story. How fast the electricity flows through the wires is measured in amperes, amps for short. A 10,000 gallon tank hooked to a half inch pipe can’t produce much water flow. Placing your hand in front of the pipe wouldn’t be painful. The water equivalent would be GPM, gallons per minute. Hook a fire truck to the same tank with a three inch hose pushing out 100 gpm and you have some real force. Even 120 volts will only produce a little tingle if it’s going through something that restricts the flow of electrical current. In an electrical circuit this is known as a resistor. On the other hand, a small amount of voltage with high current can be just as dangerous. Most automotive batteries have a potential of 12 volts but are capable of delivering hundreds of amps of current. While unlikely to be fatal, a car battery can deliver a painful shock.
The third measure of electrical power is watts which is calculated as amps X volts. This is particularly useful when we write out the equation as WATTS = AMPS X VOLTS. Let’s say you have a 100 watt lightbulb and your home electrical system is 110 volts. If we fill in what we know, we have 100 WATTS = AMPS? X 110 VOLTS. If we rewrite the equation, we get 100 WATTS / 110 VOLTS = AMPS?. 100/110 = .91 AMPS. Having a single bulb on a circuit won’t be a problem, but if we have 20 bulbs on the same circuit our current jumps to 18.2 amps. If our circuit breaker (the switches in your electrical panel) is only rated for 15 amps, we run the risk of popping the breaker if all the lights are on at once. Circuit breakers are used to prevent over-powered circuits from causing a fire. If more current flows through a wire than it’s rated for, it can glow red hot and ignite any flammable material near it. This is how electric stoves produce heat, with a coil that glows when current flows through it. And why turning on a curling iron often trips the breaker. Appliances that produce heat with electricity pull a lot of amps.
When designing electrical circuits, pay attention to all the parts. The power supply (usually a plug in transformer) should have a label that lists how much voltage and the maximum current it will produce. If you use wire that is too small, it will restrict the current flow and possibly damage it. Same goes for switches, LEDs, sound devices and anything else that is attached to the circuit. This is where I have to let you in on a little secret: Electrical circuits actually run on magic smoke. If you let the smoke out, the circuit fails and you have to start over. And electronic projects are especially touchy about this fact. The smoke has a nasty habit of waiting until you are doing a demo of your new creation before making a break for it. I’d like to tell you there’s a way to put the smoke back in but there isn’t. Like water, smoke is a one way trip. In another post we’ll get into more detail on designing electronic circuits.
There are a ton of resources online about circuit design, components and all things electrical and electronic. YouTube is also full of some great videos on these subjects. Electricity can be a little intimidating at first, but it’s actually easy to work with once you understand the basics of both design and safety. And how to keep the magic smoke where it belongs.