Key points of this article
- What is an AC Capacitor
- How AC Capacitors Work in AC Circuits
- Practical Applications of AC Capacitors
In the novice period, have you ever seen a capacitor explosion? Once driven by curiosity, I connected a capacitor in the alternating current, the results of the “pop” a loud bang, a wisp of mushroom-like smoke, the remains of the capacitor splashed around. This is because then connected to the polarized electrolytic capacitors, rather than AC capacitors. So the question is, what is an AC capacitor?
1. The Concept of AC Capacitance
Every electronics designer is no stranger to capacitors. A capacitor consists of two conductive plates separated by a layer of dielectric. The structure of a capacitor allows it to store charge when voltage is applied to the terminals.
AC capacitance defines how a capacitor stores charge
The ratio of the amount of charge stored by a capacitor to the voltage applied is called capacitance. Capacitance is measured in farads (F) and is calculated by the formula:
C = Q/V
The greater the value of C, the more charge the capacitor can store when a voltage is applied. Capacitance values are of interest to electronic designers in both DC and AC circuits. However, capacitors behave differently in these two circuits.
2. Capacitor Behavior in AC Circuits
When a non-polarized capacitor is connected to an AC supply, the capacitor acts like a closed circuit but changes the phase of the voltage. When the AC supply is turned on, a positive cycle will charge the capacitor from one terminal until the charge equals the voltage.
Once the AC voltage peaks and drops, the capacitor will begin to discharge to keep the voltage constant. During this phase, current flows from the capacitor in different directions.
When the AC voltage turns negative, it will in turn charge the capacitor. This process continues until the negative voltage fully charges the capacitor. Once the voltage reaches its negative peak, the voltage value rises. The discharge cycle of the AC capacitor thus begins.
The discharge cycle continues as long as AC power is applied. When plotting the voltage and current values, you will see that the current is ahead of the voltage by 90° in phase. This is shown in the figure below:
Capacitance is not the only variable to be concerned with when designing AC circuits with capacitors. In addition to AC capacitance, it is also necessary to understand capacitive reactance.
An ideal capacitor will not leak when storing charge. However, actual capacitors do have some leakage due to the presence of some resistance. The resistance in a capacitor is called capacitive reactance and is calculated as:
XC = 1/2πfC
Capacitive reactance is inversely proportional to the AC voltage frequency and capacitance value. The larger the values of the latter two parameters, the lower the reactance and the more leakage there will be.
3. Application of Capacitors in AC Circuits
AC capacitors are very common in electronic design and can be used in split-phase induction motors to increase efficiency and improve phase shift in the secondary winding. For example, AC capacitors are commonly used in water pumps and air conditioners.
AC capacitors are also found in power supply design. Capacitors help suppress noise and regulate voltage. The ability of AC capacitors to store and release charge improves the efficiency of power transmission. Therefore, systems with inductive loads can also benefit from AC capacitors. AC capacitors also help correct power factor and compensate for current lag caused by inductive loads.
When designing systems with AC capacitors, the behavior of AC capacitors needs to be simulated and analyzed using reliable software that can make the design effort twice as effective.
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Post time: Nov-24-2023