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  • Writer's pictureDavid Peterson

Back to Basics - How AC Electricity Works

To be honest, I've always had a hard time understanding Alternating Current (AC) voltage.

Direct current (DC) is usually driven by a chemical reaction that pushes electrons through a wire. When these electrons pass through a load, the load activates as long as there is enough driving force. Pretty simple to understand.

AC voltage is entirely different.

It's usually explained as a push and pull of the force, alternating directions 50 to 60 times every second.

It took me a while to understand AC because the more I thought about it, the more it seemed impossible, or highly unlikely, for the electrons ever to arrive at the load if an equal time is spent 'pushing' and 'pulling' them through the wire. The electronics aren't really getting anywhere...

But then I realized something.

My assumption was true.

The electrons driven by the source will probably never arrive at the load.

How Electrons Move

If you live in a region where power is supplied by spinning wind turbines for example, those turbines push electricity to the wires. However, those electrons will probably never arrive at your house.

The good news is that the electrons do not need to travel from the source to load.

Electrical current relies on metallic materials called 'conductors' which have a certain number of electrons held fairly loosely at the outer edge of each atom.

If an electron in an atom is supplied with energy, such as from the generator of the wind turbine, that energy will force the electron to jump to an adjacent atom in a certain direction.

As soon as that energized electron arrives at the second atom, an electron is ejected, pushing into a third atom, and so on.

This process is called 'propagation', like a chain reaction where each movement causes another movement downstream.

If there is enough energy supplied, this chain reaction continues all the way from the wind turbine to your house and forces the electrons in a light bulb to move, and the light turns on!

There are a couple interesting things about electrical current:

  1. That very first electron is still sitting near the wind turbine generator. It might be progressing and hopping slowly through the wire, but I'll bet money that electron will never make it to your house.

  2. Electrical energy propagation moves very, very quickly (not quite the speed of light, but it's fast - like over 150,000 miles per second!).

  3. Electrons themselves move very, very slowly (like less than 1 inch per hour).

When the electrons are constantly pushed and pulled many times per second, the only way a lone electron can travel down the wire is if it happens to be pushed onto an atom, then a different electron is pulled, then that first electron is pushed again. It might move, but it's really just random chance...

Voltage Loss

I've used a phrase a couple of times - 'If it has enough energy'.

When a generator creates voltage (usually with a rotating magnet/wire coil), that's the driving push/pull for the AC electricity.

If only a small voltage is developed, the first electron will have some force, then the next one will have a little less, then a little less, until finally, we run out of voltage. This is bound to happen in really long wires.

Two things will help reduce voltage loss:

  1. We can use fewer electrons per second, or in other words, less 'current'. The faster they go, the more energy it will use up. We can accomplish this by increasing the voltage - power results from current x voltage. If you want current to go down, just make voltage go up.

  2. Use a bigger wire. Bigger diameter means the electrons don't have to move as fast, so they won't use up as much energy. It has the same result as point #1, but a different strategy.

Electrical engineers know all about these facts, so when they designed the electrical grid to use AC power, they faced a choice. Either jack the voltage WAY up to reduce loss, or use GIANT wire to reduce loss.

- Giant voltage is really dangerous.

- Giant wire is really expensive.

They opted for dangerous high voltage and placed the wires way up on power poles and safely inside fenced-in substations.

Grid voltage can be in the 10s or 100s of thousands of volts. When things go wrong, it's exciting.

Voltage in Your house

AC is the system of choice simply because there are transformers that can easily raise and lower the voltages without losing too much energy. It's much harder to do that with DC.

In your house, the AC electricity is brought down to 120 volts, which isn't a whole lot - but still nothing to play around with.

If you need to supply electricity a long distance from your service panel, you must use bigger wire or there will be too much voltage loss.

Also, if you need to supply a lot of current, you again need to use bigger wire.

Electricity is a fascinating subject, and it's a lot of fun!

We don't encourage playing with electrical systems unless you know what you're doing - but we'll always encourage learning! Get a safe training panel or electronics kit and dive into this awesome world of subatomic particles that are used in every part of your life.

Now go build something cool!

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