eli5 ac vs dc current and why appliances run on specific ones
In: 5
You know how when you blow into a straw, you create positive pressure, but when you suck, you create negative pressure? Voltage is a bit like the pressure, and it can also be positive or negative. The higher the pressure, the higher the voltage.
If it’s constantly positive (or negative), that voltage is just pushing electrical current in one direction. It’s a Direct Current (DC). But if it’s oscillating back and forth between positive and negative pressure, eg, alternating between sucking and blowing, then it becomes an Alternating Current (AC). The conductor (the wire) is kind of like the straw.
DC voltage becomes weaker over long distances, but AC can affect the voltage over very long distances. So, high voltage AC is used to move electrical power from your electricity provider to your home, where it is stepped down to 120 volts or 240 volts AC. This is also known as your “Mains Power.” It is the plug in your wall.
Many older appliances run directly on 120 volts AC. However, this can be dangerous. That 120 volt shock can hurt or burn you, or even kill you if it passes through your heart. Nowadays, many appliances (edit: Not necessarily for reasons I had previously stated. See /u/Nacomment’s comments below.) use a power supply to convert the electricity from Mains AC (120 or 240 volts) down to a much safer and easier to work with DC voltage, typically under 24 volts. This power supply might be a brick that plugs in to the wall, like your phone, tabler or laptop might have, or it might be inside of the device itself, like your TV probably has.
A very common voltage nowadays for devices that do not require a lot of power is 5 volts DC. This is what USB devices run on, and what many internal power supplies convert to. 12 volts is common, too, and is what your car battery and “cigarette lighter” power outlet use. Desktop PCs use a mix of 5 volts and 12 volts.
One more thing… your basic power generator creates AC electricity. This includes the generators at your power company’s power plants. So it starts off as AC, which is convenient for long distance, and eventually gets converted down to DC as it makes its way into parts of your appliances. Though some heavier duty stuff (industrial tools, washers and dryers, etc) I think still mostly operate directly on AC, for that extra bit of “oomf.”
I hope this makes sense or helps.
Edit: The short answer of why some appliances want more voltage than others is, if a device needs more power, it’s easier to push more electrical power into it at higher voltages.
Edit again: I thank and defer to /u/NameUnavail to correct my inaccuracies here.
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