Download Current in AC Capacitor

Current in AC Capacitor
When a capacitor and a resistor are connected to AC lines, a constant current can be
maintained through the resistor, so long as the Rectance of the capacitor is greater than
the resistance of the resistor. The current flow depends on the value of the capacitor
assuming that the input voltage is greater than the output voltage.
The current through the resistor R is
I RMS = V1 x X C
Where X C is the Rectance of the capacitor
C
V1
230V AC
50Hz
R
V2
Suppose the line voltage V1 is 230 Volt at 50Hz. Then
I RMS = 230(2 Pi.50.C) = 72220 C or IRMS = 72mA / uF
Let us see the current from a 225 K (2.2uF) capacitor. First calculate the Rectance X of
the capacitor.
225 K Metal Film X rated capacitor
X = 1 / 2 Pi.f.C = 1 / 2Pi x50 x 10-6
Where 50 is the mains frequency, C capacitor value in uF (1 uF is equal to 1 / 106 Farad).
Therefore 2.2 uF is 2.2 x 1 / 106 = 2.2 x 10-6 Farads.
Final equation comes like this
X = 1 / 2Pi.f.C = 1 / 2 x 3.14 x 50 x C x 10-6
X = 1 / 2 x 3.14 x 50 x 2.2 x 10-6 = 1447.60 Ohms or 1.44 K Ohms.
Current through the capacitor is
IRMS = Volt / Rectance in K Ohms. That is 230 / 1.44 = 159.7 mA.
Thus a 225 K capacitor can give around 160 milli ampere current when the line voltage is
230 volt 50Hz.
As a rule of thumb, 70 - 75 milli amperes current will be available per uF from an
AC capacitor