What is the Difference Between AC and DC Currents

In today’s world electricity is most important next to the oxygen in the human. When the electricity was invented many changes have taken place over the years. The dark planet turned into a planet of lights. In fact, it made life so simple in all circumstances. All the devices, industries, offices, houses, technology, computers run on electricity. Here energy will be in two forms, i.e. alternating current (AC) and direct current (DC). Regarding these currents and the difference between AC and DC will be discussed in detail, its basic function and uses of it. Its properties are also discussed in a tabular column.

Difference between AC and DC

The flow of electricity can be done in two ways like AC (alternating current) and DC (direct current). Electricity can be defined as the flow of electrons throughout a conductor such as a wire. The main disparity among AC & DC mainly lies within the direction where the electrons supplies. In direct current, the flow of electrons will be in a single direction & in the alternating current; the flow of electrons will change their directions like going forward & then going backward.  The difference between AC and DC  mainly includes the following

Alternating Current (AC)

Alternating current is defined as the flow of charge that changes direction periodically. The result obtained will be, the voltage level also reverses along with the current. Basically, AC is used to deliver power to industries, houses, office buildings, etc.

Generation of AC

AC is produced by using called an alternator. It is designed to produce alternating current. Inside of a magnetic field, a loop of wire is spun, from which induced current will flow along the wire. Here the rotation of the wire may come from any no of means i.e. from, a steam turbine, flowing water, a wind turbine, and so on. This is because the wire spins and enters into different magnetic polarity periodically, the current and voltage alternate in the wire.

From this, the generated current can be of many waveforms like sine, square, and triangle. But in most cases, the sine wave is preferred because it is easy to generate and calculations can be done with ease. However, the rest of the wave requires an additional device to convert them into respective waveforms or the shape of the equipment has to be changed and the calculations will be too difficult. The description of the Sine waveform is discussed below.

Describing a Sine Wave

Generally, the AC waveform can be understood easily with the help of mathematical terms. For this sine wave, the three things which are required are amplitude, phase, and frequency.

By looking at just voltage, a sine wave can be described like the below mathematical function:

V(t) = V_P Sin (2πft + Ø)

V(t): It is a function of time a voltage. This means that as time changes our voltage also changes. In the above equation, the term which is right of the equal sign describes how the voltage changes over time.

VP: It is the amplitude. This states how maximum the voltage the sine wave could reach in either direction, i.e. -VP volts, +VP volts, or somewhere in between.

The function of sin( ) states that the voltage will be in the form of a periodic sine wave and will act as a smooth oscillation at 0V.

Here 2π is constant. It converts the frequency from cycles in hertz to angular frequency in radians per second.

Here f describes the sine wave frequency. This will be in the form of units per second or hertz. The frequency tells how many times a particular waveform occurs within one second.

Here t is a dependent variable. It is measured in seconds. When the time varies the waveform also varies.

The φ describes the phase of the sine wave. The phase is defined as how the waveform is shifted with respect to time. It is measured in degrees. The periodic nature of the sine wave shifts by 360° it becomes the same waveform when shifted by 0°.

For the above formula, the real-time application values are added by taking the United States as a reference

Root mean square (RMS) is another small concept which helps in calculating the electrical power.

V(t) = 170 Sin ( 2π60t )

Applications of AC

• Home and office outlets are used AC.
• Generating and transmission AC power for long distances is easy.
• Less energy is lost in electrical power transmission for high voltages (> 110kV).
• Higher voltages imply lower currents, and for lower currents, less heat is generated in the power line which is obviously due to low resistance.
• AC can be easily converted from high voltage to low voltage and vice versa with the help of transformers.
• AC power the electric motors.
• It is also useful for many large appliances like refrigerators, dishwashers, etc.
• Direct Current

Direct current (DC) is the movement of electric charge carriers, i.e. electrons in a unidirectional flow. In DC the intensity of the current will vary along with time, but the direction of movement stays the same all time. Here DC is referred to as a voltage whose polarity never reverses.

DC Source

In a DC circuit, electrons emerge from the minus or negative pole and move towards the plus or positive pole. Some of the physicists define DC as it travels from plus to minus.

Generally, the basic source of direct current is produced by batteries, electrochemical, and photovoltaic cells. But AC is most preferred across the world. In this scenario, AC can be converted to DC. This will happen in multiple steps. Initially, the power supply consists of a transformer, which later converted into DC with the help of a rectifier. It prevents the flow of current from reversing and a filter is used to eliminate current pulsations in the output of the rectifier. The is the phenomenon of how AC is converted into DC

Example of a Recharging Battery

However, for all electronic and computer hardware to function they need DC. Most of the solid-state equipment requires a voltage range between 1.5 and 13.5 volts. Current demands vary accordingly with the devices which are used. For example the range from practically zero for an electronic wristwatch, to more than 100 amperes for a radio communications power amplifier. Equipment using, a high-power radio or broadcast transmitter or television or a CRT (cathode-ray tube) display or vacuum tubes requires from about 150 volts to several thousand volts DC.

The main difference between AC and DC is discussing in the following comparison chart

S No	Parameters	Alternating Current	Direct Current
1	The amount of energy that can be carried	It is safe to transfer over longer city distances and will provide more power.	Practically the voltage of DC cannot travel very far until it begins to lose energy.
2	The cause of the direction of flow of electrons	It is denoted rotating magnet along the wire.	It is denoted steady magnetism along the wire
3	Frequency	The frequency of alternating current will be either 50Hz or 60Hz depending upon the country.	The frequency of direct current will be zero.
4	Direction	It reverses its direction while flowing in a circuit.	It only flows in one direction in the circuit.
5	Current	It is the current of magnitude which is varying with time	It is the current of constant magnitude.
6	Flow of Electrons	Here electrons will keep switching directions – forward and backward.	Electrons move steadily in one direction or ‘forward’.
7	Obtained from	The source of availability is A.C Generator and mains.	The source of availability is either Cell or Battery.
8	Passive Parameters	It is Impedance.	Only Resistance
9	Power Factor	It basically Lies between 0 & 1.	It will be always 1.
10	Types	It will of different types like Sinusoidal, Square Trapezoidal, and Triangular.	It will be of Pure and pulsating.

Key Differences of Alternating Current (AC) Vs Direct Current (DC)

The key differences between AC & DC include the following.

• The direction of current flow will change at normal time interval then this kind of current is known AC or alternating current whereas the DC is unidirectional, because it flows in a single direction only.
• The flow of charge carriers in an AC will flow by revolving a coil within the magnetic field otherwise revolving a magnetic field within an immobile coil. In DC, the charge carriers will flow by maintaining the magnetism stable along with the wire.
• The frequency of the AC ranges from 50 hertz to 60 hertz based on the country standard, while the DC frequency always remains zero.
• The PF (power factor) of the AC lies among 0 to 1, while the DC power factor always remains one.
• The generation of AC can be done using an alternator whereas the DC can be generated through the battery, cells & generator.
• The AC load is resistive; inductive otherwise capacitive whereas the DC load is resistive always in nature.
• The graphical representation of an AC can be done throughout different uneven waveforms like periodic, triangular, sine, square, saw-tooth, etc whereas the DC is represented through the straight line.
• The transmission of alternating current can be done over a long distance through some losses, while the DC transmits with slight losses over extremely long distances.
• The conversion of AC to DC can be done using a rectifier whereas the inverter is used to convert from DC to AC.
• The generation & transmission of AC can be done using a few substations whereas DC uses more substations.
• The applications of AC include factories, households, industries, etc whereas the DC is used in flash lighting, electronic equipment, electroplating, electrolysis, hybrid vehicles, and switching the field winding in the rotor.
• DC is very hazardous as compared with AC. In AC, the flow of the current’s magnitude is high & low at normal time interval whereas, in DC, the magnitude will also be the same. Once the human body gets shocked, then the AC will enter as well as exit from the human body at a normal time interval while DC will continuously trouble the human body.

What are the Advantages of AC over DC?

The main benefits of AC as compared with DC include the following.

• Alternating current is not expensive & generates the current easily as compared with direct current.
• The space enclosed through alternating current is more than DC.
•  In AC, the loss of power is less while transmission as compared with DC.

Why AC Voltage is Chosen Over DC Voltage?

The main reasons to select AC voltage over DC voltage mainly include the following.
The loss of energy while transmitting the AC voltage is low as compared with the DC voltage. Whenever the transformer is at some distance then the installation is very simple. The benefit of AC voltage is stepping up & stepping down the voltage according to the necessity.

AC & DC Origins

A magnetic field close to a wire can cause the flow of electrons in a single way through the wire, as they are repelled from the negative part of a magnet & attracted in the direction of the positive part. In this way, the power from a battery was established; this was recognized through Thomas Edison’s work. AC generators slowly changed the DC battery system of Edison as AC is very secured to transmit power over long distances to generate more power.

The scientist namely Nikola Tesla has used a rotary magnet in place of applying the magnetism through the wire gradually. Once the magnet was leaned in a single direction, then electrons will flow in the direction of the positive, however whenever the direction of the magnet was turned, then the electrons will also be turned.

Applications of AC & DC

AC is used in distributing power and it includes many advantages. This can be converted easily to other voltages with the help of a transformer because transformers don’t use DC.

At a high voltage, whenever the power is transmitted then there will be less loss. For instance, a 250V supply carries 1 Ω resistance & 4 amps power. Because power, watts is equal to volts x amps, so the power being carried can be 1000 watts whereas the loss of power is I2 x R = 16 watts.

AC is used by the transmission of HV power.

If a voltage line carries 4 amps power however it has a 250 kV then it carries 4 amps power, but the power loss is the same, however the entire transmission system carries 1 MW & 16 watts is an approximately insignificant loss.

Direct current is used in batteries, some electronic and electrical devices, and solar panels.
Formulas for AC Current, Voltage, Resistance, and Power

The formulas for ac current, voltage, resistance, and power are discussed below.

AC Current

The formula for 1-phase AC circuits is

I = P / (V * Cosθ) => I = (V/Z)

The formula for 3-phase AC circuits is

I = P / √3 * V * Cosθ

AC Voltage

For 1-phase AC circuits, the AC voltage is

V = P/(I x Cosθ) = I / Z

For 3-phase AC circuits, the AC voltage is

For star connection, VL= √3 EPH otherwise VL = √3 VPH

For delta connection, VL= VPH

AC Resistance

In case of inductive load, Z = √(R2+ XL2)

In case of capacitive load, Z = √(R2+ XC2)

In both the cases like capacitive & inductive Z = √(R2+ (XL– XC)2

AC Power

For 1-phase AC circuits, P = V *I * Cosθ

Active power for 3-phase AC circuits

P = √3 * VL * IL * Cosθ

P = 3 * VPh * IPh * Cosθ

P = √(S2 – Q2) = √ (VA2 – VAR2)

Reactive Power

Q = V I * Sinθ

VAR = √(VA2 – P2) & kVAR = √ (kVA2 – kW2)

Apparent Power

S = √ (P + Q2)

kVA = √kW2 + kVAR2

Complex Power

S = V I

For inductive load, S = P + jQ

For capacitive load, S = P – jQ

Formulas for DC Current, Voltage, Resistance and Power

The formulas for dc current, voltage, resistance and power are discussed below.

DC Current

The DC current equation is I = V/R = P/V = √P/R

DC Voltage

The DC voltage equation is

V = I * R = P / I = √ (P x R)

DC Resistance

The dc resistance equation is R = V/I = P/I2 = V2/P

DC Power

The dc power equation is P = IV = I2R = V2/R

From the above AC & DC equations, where

From the above equations, where

‘I’ is Current measures in A (Amperes)

‘V’ is Voltage measures in V (Volts)

‘P’ is Power measures in Watts (W)

‘R’ is Resistance measures in Ohm (Ω)

R/Z = Cosθ = PF (Power Factor)

‘Z’ is impedance

‘IPh’ is phase current

‘IL’ is line current

‘VPh’ is the phase voltage

‘VL’ is line voltage

‘XL’= 2πfL, is an Inductive reactance, where ‘L’ is an Inductance within Henry.

‘XC’=1/2πfC, is the capacitive reactance, where ‘C’ is capacitance within Farads.

Why do we use the AC in Our Homes?

The current supply used in our homes is AC because as we can alter alternate current very simply using the transformer. High voltage experiences extremely low energy loss in the line or channels of long transmission & the voltage is decreased to utilize securely at home with the help of the step-down transformer.

The loss of power within the wire can be given as L = I2R

Where

‘L’ is the loss of power

‘I’ is the current

‘R’ is the resistance.

The transmission of power can be given through the relation like P = V*I

Where

‘P’ is the power

‘V’ is the voltage

Once the voltage increases then the current will be less. Like this, we can transmit equal power by decreasing the loss of power because high voltage provides the most excellent performance. So because of this reason, AC is used in homes in place of DC.

The transmission of high voltage can also be done through DC, however, it is not easy to decrease the voltage for securely utilize at homes. At present, advanced DC converters are utilized to decrease the DC voltage.

In this article What Is the Difference between AC and DC currents is explained in detail. I hope that every point is understood clearly about the alternating current, direct current, waveforms, the equation, differences of AC and DC in tabular columns along with their properties. Still unable to understand any of the topics in the articles or to implement the latest electrical projects, feel free to raise a question in the comment box below. Here is a question for you, what is the power factor of an alternating current?

Photo Credits:

• Sine Waveform songsofthecosmos
• RMS Sine Waveform doctronic
• Example of a Recharging Battery washington