# Basic Electronics – Power Source

Power source! Power source is what makes all electrical system, equipment and devices come to life. As a hobbyist it is
very important to have a strong foundation on such concepts because
there is no such electric circuit or system that will run without it. To learn
more in detail what electrical power is, in this video we are going to talk about
the following. 1. What is electrical energy; 2. Why power source has two
terminals; 3. Components of power; 4. Types of power; 5. Examples of power
source; 6. Choosing the right power source for your application. [Music] Energy is the capacity to do work. Wait! I said I will make this easier right? So let’s
consider you as an example. Say you pick a bucket full of water and you walk
about 10 steps. It means you just created work, literally. Energy is the ability to
do work, if you have lots of it you have the ability to carry the bucket at very
long distances. This means also that, power in this example has two components the amount of strength you asserted and the height of the bucket is lifted. In an electrical system the power is you,
the electrical circuit is the bucket full of water and the total distance you
walk carrying the bucket multiplied by the power you exerted is what we call
energy. Power which has a unit of watts, is the
product of two components voltage and the current. Given by this formula P is
equal to V I, voltage as a unit of volts while current has a unit of amperes. Energy on the other hand is the product of power and time having watts-hour as
its unit. In other words energy is the measure of power delivered in a span of
time. To make it clear, suppose you have a washing machine rated 1500 watts and you operated it continuously for one hour. That means 1500 multiplied by 1, is equal
to 1500 watts-hour. If you’re going to convert it into kilo, a standard binary
prefix it’s going to be equal to 1.5 kilowatt-hour. To convert it into actual electric
consumption, suppose your electricity rate is 10 pesos per kilowatt hour, then
the cost of your electricity to run your washing machine in an hour is, 1.5 times
10 pesos that is equals to 15 pesos. So now you have already grasped what is
energy and power in electricity. In a nutshell, an electrical energy is the
amount of electrical power used in a specific span of time. Our electric
utility records our electricity consumption on a monthly basis and they do this by means of our electric meters. Since we already talked about energy and
power, let us learn how it is being connected into our electrical system,
device or equipment. Since we are just starting out let us
leave the three-phase system on a future discussion. Every power source has two terminals line 1 and line 2, and every appliance, machine,
equipment and devices, which we now refer to as “load” has two input terminal
as well. To know where to connect each wires of
the source and load, we will first consider the two types of power. The DC
or the direct current, and the AC or the alternating current.First off, the DC is the type of source where the voltage and current is steady
on a specific level all throughout a given time, it will not change. On the
other hand AC current is opposite to that of DC, as it is varying. Looking back at the graph you can see
that the DC shows a straight line, while the AC is a form of a wave which is
called a sinusoidal wave. It varies as time progresses, in an AC there is what
we call one “full cycle”, which is divided into a “positive half cycle” and “negative
half cycle”. The number of full cycles that occurs in one second is known as
frequency, which has a unit of Hertz. The most popular frequency is the 50 and
60 Hertz. Since DC flows steady, we can safely
assume that it flows in one direction. This is why DC source has its “polarity”. You cannot reverse the connection otherwise your load will not run or
operate, or in worst cases get burned. Meanwhile, in AC, since the flow of
current is varying. We can say that the flow of current changes direction in
every half cycle. This means that an AC system, you can interchange the
connection of the two terminals. So now let’s consider some examples of
the two types of power source. For the DC we have the battery, DC motor used as
generator, PV or solar panels and others. For the AC, the 100 or 240 volts wall
outlet, transformers and AC generators. Now let’s talk about how to choose the
right power source. In most electronic boards the supply is usually DC, whereas
for large applications such as motors, electric distribution network and
industries, AC is commonly used. Most equipment and devices specify the type
of source it needs and it cannot be changed if it’s AC, then use AC, if
it’s DC, use DC. However there is one aspect we can
manipulate assuming that it is the required type of power source. That is
power rating, voltage rating, and current rating To generalize the most common question regarding power source, let us consider
these three example questions. 1. Can i supply 100 watts to my device which is
rated 20 watts? 2. Can I use 220 volts supply with my device rated 110 volts? 3.
Can I use 10A supply to my device which is rated 50A? Let’s summarize our answer into these
three factors: 1. The supply voltage should be equal to the required voltage
of any load. 2. The load rated power should be 70% to
80% of the power supply rating. 3. Ampere rating of the load should not be larger
than that of the power source. So to answer those three questions. Can i supply 100 watt to my device which
is rated 20 watts? The answer is yes. Since power is the ability to do work,
by common sense the power source must have greater capacity than that of the
load. Second question, can I use 220 volt
supply with the device rated 110 volts? Absolutely not! The most crucial
specification in electronics is the voltage level. 3. Can I use a 10A supply to my device rated 50A?
Yes! but the device might not work at 100%. This is the concept behind slow
chargers and fast chargers, the higher the ampere rating and the faster you can