Capacitor Charge Time Calculator
A capacitor fills and empties through a resistor along a curve, not a straight line. This shows how long that takes, from the resistance and capacitance you enter.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
The time constant is the resistance times the capacitance, in seconds. After one time constant a capacitor has reached about 63 percent of its full charge.
The time to reach any other share is the time constant times the natural log of one divided by the share still left to fill. Reaching 99 percent takes about 4.6 time constants. Emptying from full down to the same leftover share takes the same time.
Worked example
A 10,000 ohm resistor with a 0.0001 farad capacitor has a time constant of 1 s. Reaching 99% of full charge takes 5 s.
Questions
What is a time constant?
It is the time a capacitor takes to reach about 63 percent of its full charge. It equals resistance times capacitance.
Why use a percentage level?
A charge never quite finishes. Picking a level such as 99 percent gives a clear point to measure to.
Does this fit every circuit?
It assumes one resistor and one capacitor in series, charged from a steady source. Other circuits behave differently.
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