Electric Current AC & DC (Explained For Beginners)

The electric charge was further defined as Electrons. There are two types of currents. i.e. Direct Current and alternating current. Both types of currents abbreviation are DC and AC respectively. However they are mostly said as AC current and DC current.

Definition of Alternating Current

An alternating current is the type of current in which the electric charge (Electrons) reverses its direction  and magnitude periodically. We further explain it as the current starts from zero and goes to a maximum limit.

When it reaches maximum it starts decreasing towards zero. After reaching zero,it continues in the negative direction and continues to increase until it reaches a maximum point in the opposite direction.

After the maximum point, it follows the same procedure and returns to its original value, once it reaches its original position again it repeats the cycle and continue to repeat it for unlimited times.

In simple words AC current is that current which is not fixed in both direction and magnitude.  It revers it direction 50 or 60 time per each single second.

AC current
AC current

Why is alternating current called AC?

AC stands for “Alternating Current”. AC is called Alternating Current because it changes its direction periodically. Change of direction means it reverses its direction.

Technically, the electric current, that reverses its polarity after a constant interval of time, is called AC current. That is why it is called “alternating” current. Because it alternates its direction/ polarity after the fixed interval of time.

The interval of alternating the current may vary to fulfill the needs of the load. In different countries, there are rules that state what will be the interval of current to alternate its direction for supplying the power to houses and offices.

The AC is a wave (generally a sine wave) and the interval of alternating is called the frequency of the wave. AC is used in houses and offices to power the fans, lights, air conditioners, and all the heavy equipment. Frequency is increased for heavy loads.

Although the new technology has developed these DC fans, motors, and lights nut the main power supply is always AC. Because the alternating current alternates between positive and negative and has less effect of resistance of wires over long distances. AC current cannot be stored. But they can be converted to DC and then stored.

The reason is that the AC alternates between positive and negative according to its frequency and the poles of a battery are fixed. Let us say that we have connected the battery directly to the AC supply. Assume that we have a method to know that the first half cycle will be positive in the live wire so we connect it to the battery.

During the positive half cycle of the AC wave, there will be no problem, but when the negative cycle of the AC wave arrives at the positive terminal of the battery, it will not be good for people standing close to the battery.

Because the AC current alternated its polarity and now became the negative current. While the battery is to be charged, needs a current that does not change its polarity.

Different Parameters of AC

The alternating current has different parameters we will discuss each in detail.

  1. Period of alternation current

The time interval between two consecutive crust or trough is called the period of alternating current. Another definition of the time period of alternating current is the value of time requires to attain the two successive levels.

  1. Frequency of Alternating current

The number of periods or cycles in one second is called frequency. Also, it is the number of back and forth oscillations of an AC voltage or current in one second. Different ranges of frequencies are used for different purposes and applications. Some of them are listed below.

  • The alternating current frequency of 50 to 60 hertz are low frequencies and used for domestic as well as commercial and industrial purposes.
  • Frequency range up to 100 Megahertz is used in television.
  • Frequency range above 100Megahertz is used microwave like radar etc.
  • Cellular mobiles use frequencies above 1 Gigahertz.

Advantages of Alternating current

  • The alternating current generation is easier than the Direct current.
  • For higher voltages, alternating current has less transmission losses.
  • We can convert alternating current to direct current using rectifiers if required.

Disadvantages of Alternating Current

  • Alternating current or voltage cannot be used in electric traction,electroplating, or charging batteries. There is no way to store AC current.
  • Working on a higher alternating current is more dangerous than direct current.

AC current generation

To generate Alternating current we need AC generator. The generation may be 1 phase or 3 phases generator. Single phase ac current is mostly suitable for domestic loads where no much power needed and all motor are single phase induction motors. But when it come to industrial and loads where large three phase induction motors and 3 phase loads are used, then a 3 phase AC generator is used.

For more information read my article about AC generators.

Alternating current formula

As mentioned above AC power generation is divided in two. 1 and 3 phases system.

Current formula for single phase loads.

I = P / (V * I * cos Φ)

Current formula for 3 phases loads

 I = P / (√3 * V * I * cos Φ)


How to measure AC current using multimeter?

Multimeter is the instrument which is used in electric voltage, resistance, current and some more measurements. To use it for alternating current calculation simply select alternating current and connect the device in series with the load.

A better way to measure current is to use current clamp-meter which need no series connection. just put the device core around the cable and take the reading.

multimeter
connecting the multimeter in series

Free android app to calculate AC current

Android apps for electricians are very useful. You can use any of electrical calculator apps. For me as an electrical engineer I use FAST ELECTRICAL CALCULATOR free app, I built it my self to help you make faster electrical calculations.

The app has also paid version so you can use the free one and then if you need ads free version install the paid one.

What is Direct Current?

Direct current is the type of current in which the flow of electrons is in one direction. In DC system, electrons move from the negative charge area toward the positive charge area. During this process, the direction of the flow of electrons remains the same.

A battery works on the same principles. In a battery electric energy is produced during the process of a chemical reaction. When we connect the terminal of a battery to the load circuit. Unidirectional current flows from the negative side toward the positive side. DC is opposite to the alternating current because AC current flows in both directions.

DC current
DC current

Properties of DC Current

  • The current flows in one direction, therefore it is also called unidirectional current.
  • As the direct of the current does not change, therefore the frequency of DC is always zero.
  • The movement of electrons is only in the forward direction, which means that from negative to positive.
  • The magnitude of the current is always constant. However, in some cases, it varies i.e. in the form of pulsating DC.
  • The power factor of Direct current is always One.
  • It could be charged and stored in batteries and then be use again.

DC current application and uses

The need for direct current is increasing day by day. Direct current is obtained from solar cells and batteries. The modern world is moving over DC systems. We will discuss different applications of DC.

  • The main uses of DC are in low voltage applications like mobile battery charging. Besides this, it is also used in security camera operation and emergency lighting in domestic as well as commercial buildings.
  • DC supply e.g. batteries are used in starting vehicle engines, Lights & ignition.
  • Networking devices also use direct current.
  • Due to less corona and skin effect, it is also used in high voltage power transmission. And direct current has an advantage over AC current due to fewer power losses.
  • DC can be stored and used for later purposes.
  • Used in the traction system of locomotive engines. Also used in new electricity cars.
Batteries are DC current source
Batteries are DC current source

Hereunder some devices use DC power

Most electronic circuits use the DC power supply. Electronic circuits have components that need unidirectional, and steady current. The laptops and computers are also DC-operated machines. Laptop and computers are connected to AC mains but there is a box on the wire of the charger of a laptop usually called an adapter.

The adapter changes the AC to DC. So, this DC then goes into the laptop. We are also aware of a component of a computer called a power supply. The function of power is also similar to the adapter. The power supply of a personal computer converts AC to DC which is then used to run the system.

DC motors are very popular these days. DC motors also use DC current to run. These motors are very efficient and less power-consuming motors. DC generators are very easy to construct. In power generating places (power stations), most generators generate DC electricity. But due to heavy losses over large distances of DC current during transmission, the DC is converted to AC and then fed to transmission lines.

Telecommunication devices also use DC power. If you see the connector of the modem that powers up the modem, it will be a bulky one. Because it has a rectifier circuit in it. That converts ac to dc for the modem to operate. Vehicles have electrical systems in them.

All the electrical devices in the vehicles use DC supply. The cameras, sensors, power windows, lights, indicators, and multimedia use DC current to work. We use DC power in our households too. The Best way to get DC power the house is by using solar panels. Solar panels provide DC power.

These days DC fans, lights, and air conditioners (inverters) are very popular. So, DC is used to power these devices in the houses too. Also, it can be stored very easily. Earlier when solar panels were not very popular. DC power was stored in batteries using a driver circuit.

Remote controls are also powered by DC current. A constant magnetic field can also be generated using a DC supply. Normally, it is known as an Electromagnet. That’s not everything, there are many other uses of DC current.

DC voltage sources examples

The main DC voltage sources are:

  • DC generators
  • Batteries
  • Solar energy.

While we know that using an inverter, we can generate a dc supply from an ac supply. Actually, we say it is rectification. So, by this we can get power from any source that generates the ac power and then run it through a rectifier, we can get dc power.

Say, an ac generator that is generating single-phase power is available and we need a dc supply. A 2-diode rectifier will be used to convert ac to dc. (Obviously, there will be other components too). For a three-phase Ac generator, a 6-diode rectifier will be used to convert ac to dc.

We also know that batteries provide dc power supply. Now if we need a dc supply, we can use a cell or a battery. Both provide a dc supply. We can charge a battery using ac supply. So, we should keep in mind that dc can be generated only by a DC generator, can be converted from different Ac sources to dc, and can be accessed from a battery.

DC Current Formula

Using Ohm’s law we can calculate current by dividing power in watt by voltage in volt

I = P / V

For example if we have a DC motor of 240 watt, running on 24v battery then the current drawn by the DC motor is I = 240 / 24 = 10 A

How long will DC motor run on a battery?

Say we have a battery of 24 V and 100 ampere-hour (AH), This battery has the ability to feed a 240 watt DC motor with its 10 A current for a time of 10 hours. This is because the motor draws 10 A each single hour. while the battery has 100 AH capacity i.e 100 A each single hour.

Why is residential power is not DC?

Current in our houses is the AC current. AC current is used in the houses because houses are far away from the power generating sites such as dams and powerhouses. If the DC current is used in transmission lines, there are too many losses. While using DC power, the heat and power losses are so much that it is impossible for electricity to reach our homes from the grid stations.

Also, the AC is safer than the DC. To transmit power over a large distance we need to transmit high voltages. Like a typical overhead transmission line have 11kV AC passing through itself. But if the same voltage is transmitted using the DC supply the power lines will be too much dangerous.

Also, over large distances, the DC power fades away. The first DC electric grid was unable to power a single house due to the power losses during transmission. About 50% of the load around the world is motors. Most of these motors work on the AC supply. That is why AC is preferred over DC.

The stepping up or stepping down the high DC power supply is a big issue. As the AC current produces the magnetic field and the transformers use this phenomenon to step up or step down the power. But in the case of a DC power supply, it will be very difficult to step up or down the power at the user end.

For more information about AC & DC power read my detailed article, here.

Which current is stored in batteries AC or DC?

Battery stores DC power. AC power cannot be stored in the batteries. The alternating current changes its polarity 50 times per second. In some countries, the polarity changes or the frequency is 60 Hertz. The terminals of the battery are fixed.

The terminals of the battery cannot change at the rate of 60 times per second. That is why it is not possible to store the AC in the battery. Even if, ignoring all the technical facts and logical explanations, someone tries to connect the live wire to the positive terminal and the neutral wire to the negative terminal of the battery.

The result should not be anything other than fatal injuries and an explosion. This is because the battery has to get a power supply that does not change its direction. The change in magnitude, to some extent, is bearable but the reversal of polarity leads to complete destruction.

Let’s take a hypothetical situation where the battery does not explode. Now when the positive cycle of the AC supply arrives, the battery will charge. But in the negative cycle, the power supply polarity will reverse.

The voltage and the current will reverse. So now the charge will flow out of the battery and again the battery will be at the same level as it was before the positive cycle. So, in either of the cases that the battery explodes or not, the battery will not charge. But it may cause fatal damage to the user.

Can I run my device on DC instead of AC?

Yep, but not all the devices. All the AC devices cannot be run using DC power directly. In many cases we can use an inverter to convert DC to AC power. Let’s discuss why AC device shouldn’t run directly on DC power.

Some engineers think that by using a rectifier circuit it will be okay to use the AC-powered device with a DC supply. It is not that simple. We know that some AC devices use transformers in them to get the desired power rating. We also know that the transformers do not work on DC supplies.

Keeping these facts that the device needs to either step up or down the voltage for which AC supply is needed and then providing DC, the device will not work. The AC current produces the magnetic effect that generates the voltage on the secondary side of the voltage. But DC current lags in this characteristic.

It does not change polarity periodically and thus is unable to generate the magnetic effect. It may hurt the transformer as the DC supply makes a lot of heat in the wires. But if we connect the DC supply at such a point that there is no transformer in its path to the circuit, it may work.

Some engineers use RC circuits to stepup or stepdown the voltages in AC circuits due to some reasons. We know that capacitors cannot pass DC power through them because they do not have any physical connection to pass current through themselves.

So, DC current will not be able to power those devices in which RC circuits are used to stepup or stepdown the voltage. Also, those devices that use voltage-doublers, will not work using the DC supply. Voltage doublers have diodes and capacitors.

There is no problem with the diodes but capacitors will not allow the circuit to complete. The circuit stays open (not working) for the DC current and your device will either not power ON or may get damaged.

So, washing machines, dishwashers, fans, and AC motors will not work on DC supply. An inverter air conditioner may run on an AC supply. Because modern technology has produced some UPS (uninterruptible power supply) powered air conditioners too. However, if you have an inverter with power suitable to the device you can use it to run the AC device on the DC power source.

Do computers run on AC or DC power supply?

The motherboard and all the internal components of the computer run on the DC supply. The transistors work on the DC power. We connect the computer to the AC supply in our houses but the same power is not transmitted in the circuit of the computer. It goes through a rectifying circuit that changes the AC power/voltage to the DC power/ voltage.

We know that modern computers have billions of transistors in them. Transistors need a one-directional current to open and close the gates. If we powerup the transistors using the AC supply, they will burn down. Registers in the memory part of the computer need the power in either 0 or 1.

A voltage reference is mapped as 0 and another voltage level is called 1. This is only possible in DC supply. Because DC supply either exists or is zero. You can say if there is a certain level of DC supply say 5V, it is a 1. Less than 5V is zero. Or for the 0V level, the bit is zero. And any number more than 0 refers to 1. Both these scenarios can be attained by the DC power supply.

Now, say, we have powered up a register with AC supply. Now AC voltage reverses its polarity after a while. During this reversal, the value of AC voltage also becomes zero and then further goes negative.

There are two problems now. Neither the bit value is preserved nor the register is safe anymore. The reverse voltage applied to the hardware of the register will burn it.

What type of current charges laptop?

There is no straightforward answer to this question. Because we plug our laptop charger in AC power but our laptop works on DC supply. The power we get from the AC power passes through the adapter that actually is a rectifier.

This rectifier converts the AC supply into a DC supply. The battery in the laptop gets charged with this DC power. The laptop too is run with DC power. So, to charge the laptop, we need DC power. But this DC power is attained from a rectifier that is fed by the AC mains. It is not compulsory to feed the rectifier that changes the Ac to Dc and charges the battery.

You can use a bigger battery to charge the battery of your laptop. But this process will require a new cable that will connect your bigger battery with the battery of your laptop. In this process, you have to make sure that the voltage and current rating keeps as same as the AC rectifier was supplying.

For example, the 45 Watts AC to DC adapter has a voltage rating of 19.5V and a current rating of 2.31A. So, the battery that you will use to charge your laptop battery must be providing you with a 2.31 A current and 19.5V. So, what charges your laptop is DC current.

Which current is used in my car wiring? Is it AC or DC?

The car uses DC current to run its components. Car headlights also use the DC current. The alternator generates an AC voltage. That is rectified to DC and then fed to the components of the car.

The battery is also charged using this DC voltage. The headlights of cars are also DC operated. Backlights and indicators, The multi-media in the car uses the DC voltage, The speakers, sensors, power windows, and lights inside the car, and the radio in the car also gets the DC current to run.

Android TV in cars is quite popular these days. Android TVs are also battery operated which means they too, run on DC current. But all the devices in the car do not use the same current level. So, voltage regulators are used to stepping up and down the voltage. Fuses are also used. The function of these fuses in the DC circuit is to provide safety to the devices.

What type of current does car alternator produce?

Car alternators produce AC current. As obvious from its name, “alternator”, it produces an Alternating current. This AC current is fed to the rectifier circuit that changes it to DC current.

As the alternator generates a 3-phase AC supply, 6 diodes are used for its rectification. DC current is a useful current for the components and devices of the car. Because all the devices run on DC current. In all cars, alternators come with rectifiers, so there is no need to worry about that part.

Can I measure the DC current with a clamp meter?

If your clamp meter has the function that allows you to measure the dc current, then you can measure the DC current using the clamp meter. It is a very good device to measure the current, as you do not have to break the circuit to connect the meter (as we do with the multi-meter). Let us see how it is done:

  • Turn the knob towards DC current measurement.
  • You will see some non-zero value on the display of your clamp. Don’t worry your clamp is working alright. It has a hall effect sensor that measures the effect of the magnetic field and displays the answer. It is showing the results due to the magnetic field of the core of the earth. Just press the button labeled as “zero” and it will be zero.
  • Open the jaws of the clamp and close it when only one cable is inside the jaws. Say, while measuring the current through the positive and negative wires of a battery you are using the clamp meter. Make sure that only one of these wires passes through the hole of the clamp meter when the jaws are closed.

Also, make sure that the negative wire is not too close to the clamp. Make sure that there are no magnets in the vicinity, magnets can affect the value of your DC current.

Can a DC current flow through the capacitor?

No, dc current cannot pass through the capacitor. There is no physical path for the current to flow from one side of the capacitor to the other side of the capacitor. As there is no flow of holes from the positive side to the negative side and no flow of the electrons from the negative side to the positive side, there is no flow of current.

DC is a unidirectional current it does not change polarity and magnitude during an interval. AC charges and discharges the capacitors due to the reversal of polarity periodically. And energy is transferred from one end to the other in the form of electrons making it possible to flow current through it.

As DC does not oscillate and thus is unable to charge and discharge the capacitor. It cannot pass through the capacitor.

Can DC current flow through an inductor?

The inductor acts as a resistance to the DC current. Because there is no phase change in DC current, there is no induced emf in the inductor. Let us assume a simple DC circuit that has an inductor connected in series with it. Initially, when potential is applied at the ends of the inductor a potential difference is attained at the two ends of the inductor.

The positive side has higher potential and the negative side will have a lower potential. A magnetic field from negative to positive will be generated to stop the current flow. An induced emf will be generated in the opposite direction of this magnetic field. With the passage of time, this emf will increase and it will let the current flow through the inductor.

The current flow keeps on increasing until the inductor starts behaving like a short wire. So, the DC battery terminals will be shorted.

Why dc current is not used in the transformer?

DC current is not used in the transformer because the DC current cannot generate mutual induction. DC current faces the phenomenon of DC isolation. The biggest reason for not using dc in the transformer is that there is no physical connection between the primary and secondary windings of the transformer.

So, for the dc current, the circuit is open (not functioning). AC supply works because of its phenomenon of mutual induction. The primary windings induce a voltage in the secondary windingdue to its magnetic effect, when supplied with the AC supply.

The magnetic effect is generated in the AC supply when the current reverses its polarity in the conductor. But in the case of DC, current does not change its phase (reversal of polarity). So, the phenomenon of induction is not present in the DC current carrying conductor.

So, primary windings will have no effect on secondary windings and voltage will be generated in the transformer. As the physical connection is absent current cannot flow from the primary to the secondary side. So, if we use DC current, energy transfer is impossible using a transformer. That’s why DC current cannot be used in a transformer.

Can you get an electric shock from a battery?

It depends. You may get a shock from a battery but mostly we do not get an electric shock even from a fully charged battery. Let us discuss why we don’t get an electric shock from the battery. Because the resistance of our skin is 10,000 ohms when it is dry.

If you hold a 9V car battery from both terminals with your hands. You do not feel anything because the human body poses too much resistance. The current won’t flow through it.

The main reason for the current not hurting you is the level of voltage. Actually, the value of current is enough to even kill you. But the pressure that pushes the current is too low to push current through your body.

But you can still get a shock from a battery. Because at a certain voltage value, the voltage will be enough to push that current right through your body that may fail your heart. Like in electric vehicles or hybrid-electric vehicles, the batteries are of much higher voltage.

You are advised not to even touch a single terminal of those batteries. Usually, DC batteries do not pose any danger up to 50V. But you are advised not to touch the battery when your body is wet. Dampness and humidity reduce your body resistance.

Also, if your skin is peeled off due to some injury, make sure it does not come in contact with the terminals of the battery because it can be dangerous.

Does DC power source has a power factor?

Power factor is unity in DC circuits. Power factor is the property of loads. If the load in a dc operated device is inductive or capacitive, it should affect the circuit in terms of power factor.

Like it should change the value of the power factor but it does not. Because in dc, nothing lags, neither the current nor the voltage. As there is no phase shift there will be no lagging. As we know that the angle is 0. So, the formula of power factor, in this case, will be;

Angle=0;

Cos (Angle) =1.

Some engineers prefer it to be “doesn’t matter”. This is because the question of the power factor of a circuit arises when either current or voltage lags. As told above, nothing lags in DC, everything is in the phase with each other.

For more information about Power Factor, read my article here.

Can we convert DC current to AC current?

Yep, DC can be converted to AC. It is a very common practice. The nationals of countries with power load shedding problems are much aware of this process by the device UPS (Uninterruptible power supply).

UPS has an inverter in it. The inverter converts the DC power stored in the battery of the UPS to AC power that is used to powerup the systems. In our countries, we are aware of this process with the help of solar power plants. There are different techniques to convert DC to AC.

Using an inverter is a well-known and efficient technique to do so. The inverter consists of an inverter bridge, a control logic, and a filter circuit. So, if we need, by passing through the inverter, DC can become 220V 50 Hz AC. We can also attain a different frequency and voltage level.

Another method to convert DC to AC is using transistors. We need a center-tapped transformer,2 2N2222 transistors, 2 IRD 630 MOSFETs, 2 2.2 micro-farad capacitors, 2 680-ohm resistors, and 2 12k ohm resistors.

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