Can a capacitor be charged with direct current
Capacitor in the DC circuit
Each capacitor consists of two metallic surfaces. In between there is an insulating material, the dielectric. The capacitor can store an electrical charge between the metallic surfaces.
Charge: the capacitor is charging
When the device is switched on, the current jumps from zero to its maximum value. From this moment on the current becomes smaller and smaller according to an exponential function. The voltage source attracts the electrons on the upper capacitor surface and presses them onto the lower capacitor surface. During this process, the capacitor is charged. The shifting of the electrons creates a current flow. This is the charging current, which is very high.
The longer the charging process, the less current flows. The electrons on the upper surface become fewer. As the current decreases towards zero, the voltage increases from zero to the maximum value. The greater the voltage, the greater the resistance of the capacitor. A capacitor can only be charged up to a certain maximum voltage. A higher voltage destroys the capacitor.
If the capacitor voltage UC. the charging voltage Utotal reached, no more current flows and the capacitor resistance is infinitely large. The capacitor acts like a blocker for the direct current.
If you observe the ammeter during the charging process, there was a brief deflection during which the pointer slowly went back to zero. The charge is retained even if the charging voltage Utotal Will get removed. However, the capacitor discharges anyway.
Discharge: Discharge of the capacitor
The capacitor acts like a voltage source with a low internal resistance. From the time of discharge, the voltage drops from the maximum value to zero. The current changes its direction of flow (polarity) and drops from the maximum value to zero. So it flows in the opposite direction to the charging current.
The voltage UC. behaves like the current. It drops from the maximum value to zero. The polarity is retained. At the point where no more current flows, the capacitor is discharged (5 time constants).
Avoid discharging a capacitor too quickly. For example through a short circuit. Above all, capacitors with a high capacity can be destroyed by the briefly very high current. Capacitors should always be discharged and charged via a resistor.
If you observe the ammeter during the discharge process, you can see a brief deflection of the pointer, which, however, acts in the opposite direction of the current and quickly goes back to zero. Be careful with the wrong polarity of analog pointer measuring instruments.
Calculate the charging and discharging times of the capacitor
In order to add a temporal component to a circuit, capacitors are charged and discharged via resistors. To calculate the charging or discharging time of the capacitor, the value of the resistor that charges the capacitor and the value of the capacitor are required. The applied voltage has no influence on the charging time!
The lower the capacitance of the capacitor C and the smaller the resistance R, the faster the charging takes place.
The charging time only depends on the size of the capacitor C and the resistor R. Therefore, the product of capacitor C and resistor R is defined as the time constant τ (tau).
Within each time constant τ (tau) a capacitor charges or discharges itself by 63% of the applied or charged voltage.
After only 0.69 τ a capacitor has reached 50% of its final or original voltage.
After 5 time constants a capacitor is almost charged or almost discharged.
The charging or discharging time is 5 τ (tau) or 5 times resistance times capacity.
If you want to know the level of the voltage of the capacitor at a certain charging or discharging time, then you can calculate from the charging voltage Utotal the percentage of the time constant.
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