Transformers and Power Supplies
Smoothing Capacitor Calculator
Smoothing Capacitor provides a checkable estimate of required capacitance. It is intended for scenario comparison, not as automatic approval of a component or installation.
Enter values for Required capacitance
Keep every entry on the units shown below.
Measurements and entries
Use voltage and current values from the same side of the transformer or converter. Nameplate and meter values are not interchangeable unless they describe the same condition.
Values used below a division bar must stay positive. A prefix error can move the result by several orders of magnitude. For the companion required capacitance calculation, open Motor Capacitor Calculator.
- Load current
- Default example: 2 A. Enter load current in A.
- Allowed ripple
- Default example: 1 V. Enter allowed ripple in V.
- Ripple frequency
- Default example: 100 Hz. Enter ripple frequency in Hz.
Before accepting the number
Mixing nominal and measured data is a common source of error.
Recheck decimal placement and unit conversion when the answer looks unusual.
From inputs to result
Here, Required capacitance is obtained from C = I ÷ (ΔV × ripple frequency). The formula draws on Load current, Allowed ripple, and Ripple frequency.
For the example shown, required capacitance equals 20,000 µF. Treat that value as a demonstration, not a recommendation.
Estimate smoothing capacitance from load current, ripple limit, and ripple frequency. The next worksheet may be Power Supply Ripple Calculator if ripple voltage is needed.
How to use the result
Interpret Required capacitance on the same basis used for the source values. Compare it with voltage stress, current stress, ripple, loss, regulation, and temperature.
Save the raw entries before testing another scenario. The broader analysis may also use Power Factor Correction Calculator.
Compare two operating cases
Change Load current from 2 A to 2.4 A while preserving the other measurements. The output changes from 20,000 µF to 24,000 µF.
Do not average the two cases if either could define an operating limit.
Checks before using the answer
Select a standard capacitor with adequate voltage, ripple-current, lifetime, and temperature ratings.
Additional checks may be needed for leakage inductance, parasitic capacitance, saturation, switching transients, and cooling. Resolve material omissions before selecting a standard size or rating.
Identify RMS, average, peak, and rectified quantities explicitly. If you also need capacitive reactance, continue with Capacitive Reactance Calculator.
Questions from practical use
How should I prepare the Smoothing Capacitor inputs?
Choose entries that describe the same case. Use voltage and current values from the same side of the transformer or converter.
What assumptions affect Required capacitance?
The result follows the displayed variables. Check leakage inductance, parasitic capacitance, saturation, switching transients, and cooling separately.
Why does the field result disagree with this page?
Differences can come from leakage inductance, parasitic capacitance, saturation, switching transients, and cooling, measurement uncertainty, or values taken under different conditions.
Can I change several inputs at once?
Keep unaffected entries fixed so the cause of the difference remains visible. Use voltage and current values from the same side of the transformer or converter.