I hope everybody enjoyed Ohm's Law. I enjoy Ohm's Law a whole lot more than I enjoy some of our current laws, but that is a different post, on another day, at a different time.
Today what I am going to talk about will be coming out of The No-Nonsense,Technician Class License Study Guide. Most posts in the near future will also be coming out of this study guide. Last time we talked about Ohm's Law. Well, Ohm's Law is presented on page 6 of the study guide. I am going to go back and cover page 5. On page 5 is electrical principals. Here in the guide this fellow starts off with voltage, amperage and current. What I didn't talk about last time was direct current (DC) and alternating current (AC).
DC current is what you get from a battery. It doesn't make any difference - little battery, big battery - they're all direct current. Your car makes it's own direct current. That is why you go in somebody's house or their shack, and you see a lot of cool radios, most of them operate off of 12 volts DC, or to be more precise, 13.8 volts DC. But, remember, last time - your car has
a 12 volt battery. While you are driving down the road it produces 13.8 volts which keeps your battery charged while you're using all the cool stuff like head lights, radios, electric windows - all the stuff in your car that uses electricity. So that's why, CB radios, ham radios and items of this nature operate off of 13.8 volts.
Okay, getting back to the real subject. Alternating current or AC is the kind of electricity that your house operates off of. Most houses in this country operate somewhere between 110-120 volts AC. It's a voltage that goes up and down and up and down like waves on an ocean. Half of the voltage is on the top side of zero and half of the voltage in on the bottom side of zero. This is AC.
Also in this section an amp meter and a volt meter were brought up. In the modern world today, the meter used is called a multimeter. It measures voltage, amperage, resistance or, get ready, ohms. Some of the really fancy ones measure other stuff, you know, like temperature. But I find the probes taste really nasty when I am measuring my temperature. A little humor there. Please remember that any time you are measuring electricity, remember, that it can do you bodily harm. This is not a joke. You need to pay attention to what you are doing. Don't be standing in a bathtub full of water. House current or voltage CAN KILL YOU. Take it very seriously.
Okay. So how do you use a multimeter? I'm afraid I can't show you how to use a multimeter on a blog. But I can direct you to a couple of YouTube videos and another handy little chart with a video - How to Use a Multimeter. One of the presenters only recommends a digital multimeter, which frankly, that's me speaking, is probably a little bit easier to use. But I am from the old school and I was trained how to use a multimeter before they had digital and that is what I still use today. But that's part of the system of choice.
There is good advice in the videos - start with the higher setting. An example, the wall socket in your house is around 115 volts AC. If you have your meter set to DC or resistance, which is ohms, and you stick the two probes in your wall outlet, then it will be time to go down to the store and buy another meter. If you have your meter set on AC, and you have it on, let's say, 25 volts and you stick it into a known source of 115 volts AC, then you will be making that trip again. Since you know your house voltage is around 115 VAC and you set your meter for 500 VAC, then your meter will only move slightly. If your next setting is 250 VAC then your meter will move about half way. I hope you follow my drift here. The same thing applies to volts DC. Start with a higher meter reading and work your way down. Measuring resistance is an entirely different ballgame. The power needed to measure resistance, or ohms, is from an internal battery in the meter. Most people use an ohm meter to just check for continuity. Continuity means that you have a complete line and there are no breaks in the circuit.
Okay. Watch the videos. Most of you will probably purchase a digital multimeter. Put the black probe in the common port or hole, stick the red probe in the voltage port or hole, set your meter for at least 250 volts AC. Now there is no positive or negative with AC. Go over to an outlet in your kitchen so you won't have to bend over. Stick one probe in the little slot and one probe in the big slot. You should have a reading on your meter.
Now this advice is only if you feel comfortable doing what you are doing. Reread the above paragraph again, watch the videos. But if you don't feel comfortable, don't do it. If you have a friend or neighbor or cousin Billy Bob, and any of them know how to use a multimeter, ask them to show you. Just remember that you need to have your meter in the correct mode.
There is AC, DC, resistance or ohms - give it a try. Or you can take a flashlight battery out of your flashlight. The bottom is negative, the top is positive. Set your meter for DC voltage. By the way, all DC batteries that are not rechargeable AA, AAA, C and D are all 1.5 volts. In the
rechargeable version is 1.2 volts. Let's say it's a regular non-rechargeable battery. You have the black probe on the bottom which is negative and the red probe on top which is positive and your battery is healthy, you should get a 1.5 reading. Now just for fun, lay this battery down on it's side, it will still measure 1.5 volts. Put another battery on top of the first battery. Now put the black probe on the bottom of the first battery and the red probe on the top of the second battery, make sure they are connecting in the middle and you should have a reading of 3.0 volts DC. Wa-la! You have just made a series circuit. When you put batteries in series, that's negative to positive to negative to positive, then the voltage increases with each additional battery. But the current or amperage stays the same. We'll talk much more about a series circuit and a parallel circuit in a future post.
Okay. Last time, we talked about some formulas - P = E x I; E = I x R. Now you can measure E = voltage, R = resistance, and now you can see these things in front of you. Knowing how to use a multimeter is critical if you're going to set up your own radio systems or, for that matter, change a light switch in your house. A word of caution. NEVER measure resistance on a live circuit. Live means it has power applied to it. Hopefully these little things help. Again, watch the videos and the other presentation. Your first multimeter should not cost over about $10.00. In my lifetime,
I have had two multimeters. Both Radio Shack, both analog, both inexpensive. The first one I used for probably 30 years and it finally just died. I bought another one just like it. I've had people give me digital multimeters as gifts and I wish they would stop.
Next time we're going to talk about the metric system. No big deal. Four or five things to learn here. Enjoy life. Get you a multimeter. Pay attention to the settings and try not to fry it. And if you really want to impress your friends when they come over, get the old type with the dial across the front, because the young guys won't know how to read it. Now where did I put my dial-up telephone??
Be safe. Time to go feed.
We'll talk more later. 73, Frank