# Capacitor Power Dissipation

• rebeka
In summary, a capacitor in an AC circuit charges and discharges according to the frequency of the signal voltage, with its impedance being proportional to this frequency and its capacitance. In a power supply, the current is regulated through the discharge cycle. However, when there is no place to discharge to, such as in a capacitive load, the capacitor does not dissipate power but rather absorbs and releases it. This means that, aside from any inefficiencies, there will be no current in the primary of the transformer beyond the initial charging of the capacitor. When considering capacitive loading of a transformer, the initial spike and inefficiency resistances of the capacitor and transformer should be taken into account. The current through the secondary may also limit the capac

#### rebeka

I'm having a really hard time wrapping my head around this. A capacitor in an AC circuit will charge and discharge with respect to the frequency of the signal voltage. Impedance in the circuit is proportional to this frequency and its capacitance. In a power supply the current is regulated through the discharge cycle. What happens to the energy when there is no place to discharge to? Just a capacitive load...

"This means that a capacitor does not dissipate power as it reacts against changes in voltage; it merely absorbs and releases power, alternately. " Does this statement mean that all ESR and leakage inefficiencies aside there will be no current in the primary of the transformer beyond the initial charging of the capacitor?? If this is the case what are the considerations for capacitive loading of a transformer just the initial spike and the inefficiency resistances of the capacitor and transformer? Does the current through the secondary still limit the capacitive load capabilities??

Last edited:
rebeka said:
I'm having a really hard time wrapping my head around this. A capacitor in an AC circuit will charge and discharge with respect to the frequency of the signal voltage. Impedance in the circuit is proportional to this frequency and its capacitance. In a power supply the current is regulated through the discharge cycle. What happens to the energy when there is no place to discharge to? Just a capacitive load...

"This means that a capacitor does not dissipate power as it reacts against changes in voltage; it merely absorbs and releases power, alternately. " Does this statement mean that all ESR and leakage inefficiencies aside there will be no current in the primary of the transformer beyond the initial charging of the capacitor?? If this is the case what are the considerations for capacitive loading of a transformer just the initial spike and the inefficiency resistances of the capacitor and transformer? Does the current through the secondary still limit the capacitive load capabilities??

I'm having a hard time parsing your post, but I believe that, if you were to charge up an (ideal) capacitor, and then disconnect it from the circuit, it'd just sit there waiting to zap the next unwitting victim (yes, we did this with small electrolytics and voltages in undergrad labs--even though the charge is dissipating, there was enough charge to give a small jolt). Many digital cameras use supercapacitors as a make shift battery to keep your settings / pictures while you change your main batteries.

See also: Leyden Jar:
http://en.wikipedia.org/wiki/Leyden_jar

I can provide some clarification on the concept of capacitor power dissipation. First, it is important to understand that a capacitor stores energy in the form of an electric field between its plates. When an AC voltage is applied to a capacitor in a circuit, it charges and discharges in response to the frequency of the signal. This means that the capacitor is constantly absorbing and releasing energy as it reacts to changes in voltage.

The impedance of a capacitor is inversely proportional to its frequency and capacitance. This means that as the frequency increases, the impedance decreases and more current can flow through the capacitor. In a power supply, the capacitor is often used to regulate the current through the circuit. However, in a purely capacitive load, there is no place for the capacitor to discharge its energy. This means that the capacitor will continue to absorb and release energy, but there will be no current flowing in the primary of the transformer beyond the initial charging of the capacitor.

Regarding the statement about power dissipation, it is important to note that there will still be some losses in the circuit due to inefficiencies such as ESR and leakage. However, these losses are relatively small compared to the energy stored in the capacitor and can be ignored for the purposes of understanding the overall behavior of the circuit.

In terms of considerations for capacitive loading of a transformer, the initial spike of current and the inefficiencies of the capacitor and transformer are indeed important factors. The current through the secondary of the transformer will also limit the capacitive load capabilities, as the transformer is designed to handle a certain amount of current. Exceeding this limit can result in damage to the transformer and other components in the circuit. Therefore, it is important to carefully consider the capacitance and frequency of the signal when designing a circuit with capacitive loads.

## 1. What is capacitor power dissipation?

Capacitor power dissipation refers to the amount of power that is lost or converted into heat when an electric current passes through a capacitor. It is usually measured in watts (W) or milliwatts (mW).

## 2. How is capacitor power dissipation calculated?

The power dissipation of a capacitor can be calculated by multiplying the voltage across the capacitor by the current passing through it. This can be represented by the formula P = VI, where P is power, V is voltage, and I is current.

## 3. What factors affect capacitor power dissipation?

The major factors that affect capacitor power dissipation include the capacitance of the capacitor, the voltage rating, the frequency of the applied voltage, and the equivalent series resistance (ESR) of the capacitor. Higher capacitance and voltage ratings, as well as higher frequencies and ESR, can result in higher power dissipation.

## 4. Why is capacitor power dissipation important?

Capacitor power dissipation is important because it can lead to heat generation, which can have negative effects on the performance and lifespan of electronic devices. It is also a factor to consider in terms of energy efficiency and cost, as higher power dissipation can result in higher electricity bills.

## 5. How can capacitor power dissipation be reduced?

To reduce capacitor power dissipation, one can use capacitors with higher capacitance and voltage ratings, as well as lower ESR. Using multiple capacitors in parallel can also distribute the power dissipation among them, reducing the load on each individual capacitor. Additionally, using capacitors with better thermal management, such as those with larger surface areas or heat sinks, can help dissipate heat more effectively.