RC Time Calculator

Capacitor Voltage With Respect To Time

Vc = V * (1- e^(-t / R*C))

Vc is the capacitor voltage, V is the supply voltage,
R is the resistance, C is the Capacitance, t is the time,
and e = 2.71828

RC Time Calculator

In the drawing at the left, the time required for the capacitor to charge to 63.2% of the battery voltage after the switch is closed is the product of the resistance and capacitance T=(R*C). For example, a 100 uF capacitor and 100K resistor would require 10 seconds to charge to 7.6 volts using a 12 volt battery. The Java calculator below can be used to determine the capacitor voltage at other times after the switch is closed. Any of the five variables can be determined by supplying the other four. For example, in the graph below, a 1 Farad capacitor charging through a 1 ohm resistor and 1 volt battery will reach 777 millivolts in 1.5 seconds. From left to right, the entries would be 1, .001, 1000000, 1500 with the "Instantaneous Voltage" field left blank, or zero. The result would be 0.777. Only one field should be blank or 0 before each calculation.

Supply Voltage (Volts)
Resistance (K_Ohms)
Capacity (Microfarads)
Time (Milliseconds)
Instantaneous Voltage


GW1NGL NA7KR Kevin Roberts Ham Radio

Page last updated on 09/10/2012 by Kevin Roberts NA7KR a colection of Ham Radio and Electronic Information