Analytical Instrumentation

# What is the Difference Between AC and DC Capacitor? ## What is a Capacitor?

A Capacitor is a type of electronic device that consists of two electrically conducting plates that are spaced apart by an insulator. Based on the capacitor’s capacity to store and discharge current, it is utilised in electrical applications and circuits that use both direct current (DC) and alternating current (AC) to produce certain effects.

### Types of Capacitor:

There are generally just two fundamental types of capacitors as far as electricity is concerned:

• Polarised Capacitor or DC Capacitor and
• Non-Polarized Capacitor or AC Capacitor.

Capacitors are classified in a variety of ways as it relates to building design and materials used in production.

• Electrolytic capacitors, also referred to as polarised capacitors (DC Capacitors), are strictly polarity- and voltage-conforming devices.
• For non-polarized capacitors (AC Capacitors), there is no polarity and merely a limited voltage rating.

### AC Capacitor:

In AC circuits, the alternating current alternately charges the capacitor in one direction and the other at regular intervals. The capacitor output current switches in phase with the AC voltage when the plates discharge during the direction change. Capacitors are said to “pass” AC in this method.

The capacitor will concurrently charge and discharge if alternating voltage is applied, at a frequency rate dependent on the frequency of the supplied AC voltage. Thus, the frequency of the input signal, which is continuously charged (or discharged), determines the capacitance of the capacitor in AC circuits.

The supply voltage changes more quickly in a positive direction at 0° (the angle between the current and the voltage), which can lead to the maximum charging current. The supply voltage has no increase (or reduction) when the applied voltage reaches its peak value at 90°. There would therefore be no current flowing across the circuit. The voltage slope turns negative when the applied voltage approaches zero at an angle of 180 degrees, causing the capacitor to discharge fully in the opposite direction. Greatest current flows at the 180° point along the line, where the voltage change rate reaches its maximum value. The cycle then continues from that point on. As a result, with AC-capacitors, the minimum current occurs when the applied voltage is at its highest, and vice versa. As a result, the current leads the voltage by 90 degrees (or 1/4 cycle). Capacitor thus 90° delays current.

Where, it refers to the capacitor’s capacitance rating. Microfarad (MF), Nano Farad (nF), and Farad (F) values are available for ac capacitors.

### Application of AC Capacitor:

• Examples of AC capacitors or non-polarized capacitors include:
1. Motor capacitors,
2. Ceiling fan capacitors,
3. Capacitor banks, and
4. Inverter output filtration capacitors.
• In order to improve power factor, AC capacitors are utilised. Multiple capacitors are combined to form capacitor banks, which use reactive power. Inductive loads cause a power system’s power factor to drop or lag when they are connected. The capacitor bank is consequently connected to the system in parallel. Since the capacitor bank generates the leading power factor, the system’s overall power factor is balanced.
• Ceiling fans or single-phase induction motors both use an AC capacitor. The single-phase induction motor is not self-starting, as we are aware. The motor capacitor is utilised to give the motor starting torque.
• In rectifier input circuits, AC capacitors or non-polarized capacitors are employed as an electromagnetic interference filter to lessen or completely eliminate electromagnetic interference.
• For the filtration of the inverter’s output power supply, AC capacitors are utilised in the inverter output.
• By means of its reactance property, an AC capacitor can also be utilised to reduce the voltage or voltage drop. You can see that AC capacitors are employed for voltage step-down in low-cost led driver circuits and transformer less power supply circuits.

### DC Capacitor:

Energy is stored as capacitance between the electrically isolated two plates of a capacitor. The capacitor will charge to the level of the applied voltage when DC current is applied to a circuit that just contains resistance and capacitance. Once the capacitor is fully charged, there is no further current flow because DC only flows in one direction. Capacitors are able to “block” DC current flow according to its property.

The following points will helps understand how a capacitor behaves in a DC circuit:

• A capacitor is rapidly (but instantly) charged to the applied voltage when a DC voltage is put across an empty capacitor. Providing the charging current are,
• When the capacitor is completely charged, the voltage across it stabilises and equals the supplied voltage. As a result, the charging current and (dV/dt = 0) are equal.
• In terms of DC voltage, an uncharged capacitor has a voltage of zero, which is equivalent to a short circuit.
• There is no current flowing in the circuit when the capacitor is fully charged. Consequently, a completely charged capacitor looks to dc as an open circuit.

### Application of DC Capacitor:

• Avoiding the AC (Alternative Current) from the power source, the capacitors function as a local store for the DC (Direct Current) power supply. As a result, when a stiffening capacitor encounters the resistance of the car engine batteries, the capacitors are also employed in automotive audio equipment.
• Between stages of amplifiers, signals are coupled using a DC capacitor.
• The use of DC capacitors in electrical filters and tuned circuits.
• Power supply systems that use DC capacitors to smooth rectified current.

### Difference Between the AC and DC capacitor:

FEATURES AC CAPACITORDC CAPACITOR
CHARGING
In the case of AC, the capacitor experiences continual current flow. This is because the capacitor charges and discharges at the same rate as the current’s frequency. Thus, if the current is AC, a capacitor enables continuous flow.When a capacitor is connected to a battery, once it is charged, it prevents any current from flowing between the battery’s poles. It so prevents DC current.
CURRENT FLOW
Current only flows when the power source is turned on and connected when an AC source is introduced to a capacitor.When a capacitor is connected to a DC source, the current increases initially, but as soon as the applied voltage is reached at the capacitor’s terminals, the current flow stops.
DIRECTION
In AC circuits, the alternating current alternately charges the capacitor in one direction and the other at regular intervals.DC only flows in one direction, and it stops once the capacitor is fully charged.
POLARITY
Polarity does not exist in an AC capacitor. Consequently, they are known as non-polarized capacitors.The polarity of a DC capacitor is fixed. Therefore, they are known as polarised capacitors.
FUNCTIONAccording to the withstand voltage level and the type of circuit requirements, an AC capacitor must be determined.Only DC circuits may use the ones designated with positive and negative poles.