I have a very limited knowledge of electrical engineering that almost entirely revolves around music equipment. From everything that I’ve seen, music equipment ends up converting the AC power to DC power right at the power entry point (or at least soon after). It appears they’re converting AC power to a higher voltage and current DC power. Is the only real advantage of AC power to pump more power over a line to where devices will then manipulate it to what they need in DC? Are there any common household items that actually fully operate off of AC power or does everything convert to DC at some point?
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AC electricity has several important advantages.
The voltage used to transfer power is extremely important for energy efficiency and cost. The higher the voltage, the more energy efficient it is, and the thinner and cheaper the wires you need. For example, if you tried to heat a house with 12 V power, you would need cables as thick as your arm, and which would cost $100 per foot.
AC can have its voltage converted easily with low tech equipment using transformers. Transformers work because a changing electrical current causes a changing magnetic field, and a changing magnetic field can cause a changing electrical current. This allows a high voltage wire to transfer energy through a magnetic field into a low voltage wire. Note that the changing is important. If there is no change, there is no power transfer. Because AC constantly changes polarity, transformers provide a constant power transfer.
The use of transformers means that voltage can be increased to 500,000 volts for transfer between cities, then down to 50,000 volts for transfer in a city, then down to 10,000 for transfer between neighborhoods, then down to 100-400 volts for use by homes and businesses. Then electrical equipment can change the voltage down again to whatever they need.
The second advantage is that motors and generators are simpler and more reliable when built for AC power. In an AC motor, because the electrical voltage fluctuates constantly, it produces a constantly changing magnetic field. With some simple tricks, that fluctuating magnetic field can be made to look like it is rotating. If you have a rotating magnetic field, then it will drag a magnet around with it, and you have a motor. This means that an AC motor only has a rotating magnet and shaft as its moving parts. There is no need for electronics or complicated mechanisms.
A DC motor is different, because the magnetic field doesn’t fluctuate itself, it can’t make anything rotate on its own. So a DC motor uses a switch mechanism (called a commutator) attached to the shaft to convert the DC electricity into AC, which can then produce a rotating magnetic field. The switch mechanism contains moving and rubbing parts, so it wears out and requires regular maintenance. However, you can get motors with electronic commutators which use wireless sensors and electronic switches, these don’t wear out, they are electronic and quite high tech.
A similar issue occurs with generators. If you just spin a magnet next to some wire, you get AC power. If you want DC power, you have to convert it in some way.
When electricity for homes and businesses was being developed and rolled out, the obvious winner was AC. The generators were simpler (just rotating magnets), the transmission was simpler (transformers made long distance power lines cheap and practical), and motors for machines were simpler, cheaper and needed less maintenance. Lights and heaters worked just fine on AC and DC, so it made no difference for these.
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