RV Electricity – Just Ask Mike (J.A.M.): What are AC and DC power?

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By Mike Sokol

Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM.


Dear Mike,

You’re always talking about AC and DC. So what exactly is the difference? —Angus Young

Dear Angus,

Well, I think someone named after the guitarist for AC/DC should know, and for everyone else here’s how it works. But first let’s be careful not to get Thunderstruck.

(Click any image to enlarge.)

DC power is the easiest type of power to explain, so let’s start there. It stands for Direct Current, which is the flow of electrons in a conductor (like a metal wire) which keeps going in the same direction. Just like the flow of water in a stream keeps going in the same direction all the time, the flow of electrons in a DC circuit always flow from the negative to the positive side of the circuit.

The simplest (and most common) form of DC power comes from a battery. Doesn’t matter if it’s the 12-volt battery in your car, or the 1.5-volt batteries in your flashlight, they all make Direct Current with different amounts of voltage (electrical pressure) and current (amperage). When you connect a DC power source (a battery) to a load (a light bulb) all the electrons keep flowing in the same direction.

AC power is a bit more complicated since it stands for Alternating Current. And as the name implies, it alternates (flips) the direction of current flow many times a second. In the USA it reverses itself back and forth 60 times a second. We call that rapid reversal Hertz (or Hz), after the German scientist Heinrich Hertz who discovered electromagnetic waves.

The most common form of Alternating Current comes from an AC generator, which is basically a bunch of wires and magnets spinning fast enough to reverse its polarity 60 times a second (Hertz or Hz). These generators can be small like the one in your portable generator, or HUGE like the ones at Niagara Falls (or any other power plant).

Going from AC to DC is pretty simple since you only need a few electronic components like a diode or two, and a storage tank like a battery or capacitor. However, going from DC to AC is much more involved since you need a fancy circuit that can reverse the flow of electrons 60 times a second and make a smooth current reversal if you want a pure sine wave of current.

The gadget in your RV that converts the 120-volt AC from the shore power cord to 12-volts DC for your battery is commonly called a converter. The most complicated thing it does is monitor your house battery voltage to prevent overcharging it. Oh, yes, it supplies power to all your 12-volt gadgets such as your RV’s interior lighting and perhaps your television set. Basically anything not plugged into the 120-volt AC circuit of your RV uses the 12-volt DC circuit, which is your house battery.

But the other gadget in your RV that converts the 12-volts DC from your battery to 120-volts AC for your bigger appliances (such as your microwave) is much more complicated and expensive. Called an “inverter,” it makes 120-volts, 60 Hz AC power when you’re not connected to a campground electrical outlet or your own generator.

Besides making power, its primary job is to protect itself from current overloads when you turn on too many appliances, as well as controlling its own output voltage (120 volts, please) and frequency (60 Hz, please). And there are different levels of filter action on the 60 Hz output, with the most expensive inverters making what’s called Pure Sine Waves. Read more about that HERE.

So how’s that? A painless lesson in AC and DC current with only one AC/DC music reference.

OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.

Let’s play safe out there….

 

Mike Sokol is an electrical and professional sound expert with 40+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.

##RVDT 1116; ##RVT 901

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Kenna Hoyser

Mike, followed you down to “diode” and “pure sine wave”. This article is really good for those of us that know nothing (super basic info on AC/DC) but since you’re assuming that level of knowledge in your readership you need to dumb down the rest of the terms. I totally appreciate the article since it started out at my level but I got frustrated with the more advanced terms.