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Tech Talker Shocks You with Electricity!

This week, I'm going to dive into some basic electrical terms that were brought up as questions after last week's episode on Tesla's Powerwall.

By
Eric Escobar,
May 28, 2015
Episode #174

There was a lot of talk last week about certain terms that I brought up when talking about the Powerwall. Namely, kilowatt hours and AC and DC currents. Hopefully I can demystify these terms and a few more to make electricity a little bit easier to understand.>

First, let's talk about voltage, current, and resistance. Picture a garden hose: when you squeeze the nozzle, a jet of water comes out. The water coming out of the hose can be compared to the electrons flowing through a wire. If you put your hand in front of the nozzle, the water will push against it, depending on how much pressure is in the hose. This water pressure is the same concept as voltage.

Voltage is the pressure pushing the electrons through the wire. Current, which is measured in amperes, is the rate at which electrons flow through the wire. This is similar to the amount of water coming out of your hose. So, how do all of these relate? Let's take a look at your garden hose. If you take the nozzle off, you can get a lot more water out of it, but it will have next to no pressure. In terms of electricity, this would be low voltage (pressure) and high current.

So, we've covered current and voltage. The next term I want to discuss is resistance. Resistance is probably the easiest to picture: it's simply the resistance to the flow of electricity through the wire. When you add items such as a motor, light bulb, or other piece of electronic, resistance is added into the circuit.

Electricity is most dangerous when you have a high current. However, voltage is also a factor. There must be enough voltage or pressure to overcome the resistance of the human body. Just picture standing in front of your garden hose—it would probably be uncomfortable, but as you start increasing the pressure and flow of the water, it will become much more uncomfortable to stay in place!

With these three terms you've got something called ohm's law, which I won't really go into today, but basically current x resistance = voltage. It's electrical engineering 101 and you can learn more by checking out the video I've posted in the show notes.

Now that we've covered those important terms, let's talk about DC and AC.

DC stands for direct current, and AC stands for alternating current. Going back to our trusty hose example, DC matches up perfectly because the water comes out of the hose in one direction.

AC current works differently in that the flow changes direction. It would be like you sucking water through a straw and then blowing it back out.

DC is used in almost all small electronics and control systems like your car, phone, laptop and batteries. AC is used in power transmission because it transmits electricity more efficiently over long distances. Now there are also some specialty systems that do transmit power with DC, but for general purposes AC transmission is used for homes and businesses.

When you plug your phone or laptop into the wall, there's typically a big or small box attached to your power cord or that is plugged directly into the wall. This box takes AC power and converts it to usable DC power for your electronics.

Now, let's delve into how power companies charge you for electricity. If you were to look at your energy bill, you would see that you are charged for the amount of kilowatt hours used (kWh). A watt is simply voltage times current. For example your phone charger runs off of 5v, 2amps (5 times 2 is 10, so ten watts).

Remember I mentioned the measurement, "kilowatt"? Kilo simply means a thousand, or a thousand watts. Charging a hundred phones at 10 watts would take a full kilowatt of electricity. If you charged 100 phones for one hour, that would be a kilowatt-hour!

Depending where you live in the country, electricity can cost 10 to 40 cents for every kilowatt hour you use. That means if you charged 100 phones for an hour, that would be about 40 cents at most.

Tech TalkerLet me list some appliances and their power consumption to give you a better idea. Your drier uses the most at around 2-4 kilowatts, followed by your hair dryer at around 2 kilowatts. Your TV is about 100 watts, and your fridge is about 200 watts! If you multiply the amount of watts times how long the device is on, times the cost per kilowatt-hour, you can find exactly how much each appliance costs you.

If you’re really curious to see how much power each appliance uses, I’ve mentioned the device before called the kill-a-watt. You plug it into a normal outlet and then plug in whatever appliance you want, and it will measure the amount of watts used.

Well, that’s it for today! Be sure to check out all my earlier episodes at techtalker.quickanddirtytips.com. And if you have further questions about this podcast or want to make a suggestion for a future episode, post them on Facebook.com/QDTtechtalker.

Until next time, I’m the Tech Talker, keeping technology simple! 

Electrical current image courtesy of Shutterstock.

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