## Electronics and Electrical Engineering Design Forum

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Sunday, January 21, 2018 by Hrithu O A

# When using capacitors as energy storage devices how is the phase difference between voltage and current from capacitor eliminated?

When using capacitors as energy storage devices how is the phase difference between voltage and current from capacitor eliminated?      I constantly read that capacitors provide reactive power. So how are they used instead of a battery? I mean in a battery the voltage and current are in the same phase. How is the phase change between the voltage and current in a capacitor eliminated without using an inductor, to use capacitor as a power source?

• Go back to fundamental electrical equations and look at the phase of an R-C circuit as it approaches DC.  Calculate the phase and that will answer your question.
• The short answer (as Mark implied) is that the concept of reactive power ONLY apples for AC not DC.

Conceptually, a capacitor is similar to a battery in that charge is stored and then released for use. The difference is that in a battery, the charge is stored chemically and in the capacitor it is electronic.

• by  Hrithu O A (edited)
Thank you guys. Will go back to my fundamentals again
• The reactive-power phase shift between current and voltage in a capacitor, is an example of the energy-storage function of the capacitor. Consider one half-cycle of the AC voltage sinewave, from zero volts to zero volts: As the voltage across the capacitor increases away from zero, energy is stored in the capacitor. As the voltage decreases back towards zero, the capacitor returns energy to the voltage source. This repeats every half-cycle. If you look at the product of voltage and current over successive quarter-cycles, you will see the products alternating positive (energy flowing into the capacitor) and negative (energy flowing out of the capacitor).