Calculator Input
Formula Used
Apparent power: S = Vrms × Irms
Real dissipated power: P = Vrms × Irms × PF
Power factor from phase: PF = |cos φ|
Reactive power: Q = Vrms × Irms × sin φ
Resistive heat: P = I² × R
Impedance: Z = √(R² + X²)
Impedance power: P = V² × R / Z²
Energy: kWh = Average W × Hours / 1000
How to Use This Calculator
- Enter RMS voltage and RMS current for the AC circuit.
- Add phase angle, or leave it blank and enter power factor.
- Enter resistance and reactance for impedance comparison.
- Use duty cycle for pulsed, cycling, or intermittent loads.
- Add operating time and energy rate to estimate energy use.
- Press the calculate button. Results appear above the form.
- Use CSV for spreadsheet records and PDF for reports.
Example Data Table
| Case | Voltage | Current | Phase | Resistance | Reactance | Expected Use |
|---|---|---|---|---|---|---|
| Small heater | 120 V | 8 A | 0° | 15 Ω | 0 Ω | Mostly resistive heat load |
| Motor branch | 230 V | 5 A | 30° | 32 Ω | 18 Ω | Inductive power comparison |
| Capacitive test | 24 V | 1.5 A | -45° | 8 Ω | -8 Ω | Leading current example |
| Panel load | 400 V | 12 A | 25° | 24 Ω | 11 Ω | Higher power planning |
Electrical AC Power Review
Why RMS Power Matters
AC power work starts with RMS values. RMS voltage and RMS current describe the heating effect of an alternating waveform. When both are known, apparent power is simple. It is voltage multiplied by current. Real dissipated power depends on the phase angle. A purely resistive load has a phase angle near zero. It turns nearly all electrical input into heat, light, or useful work.
Phase and Reactive Behavior
Inductive and capacitive loads behave differently. They store energy for part of each cycle. Then they return energy to the supply. This produces reactive power. Reactive power does not create net heat in an ideal component. It still increases current, wire losses, transformer loading, and breaker demand.
Design Value
Dissipated power is important in panels, motors, heaters, supplies, lamps, cables, and test benches. It helps size resistors, heat sinks, enclosures, fuses, relays, and conductors. A small error can create unwanted temperature rise. A large error can shorten insulation life or damage nearby parts.
Comparing Methods
This calculator compares three views. The first uses RMS voltage, RMS current, and power factor. The second uses current squared times resistance. The third estimates impedance behavior from resistance and reactance. Comparing them is useful. If values disagree, check the measurement point, waveform quality, connection type, and instrument range.
Practical Use
Use duty cycle when the load pulses. Use time to estimate energy. Add thermal resistance to approximate temperature rise. The result is not a safety certification. It is a design estimate. Always confirm with rated components, standards, and real measurements.
Measurement Notes
Good input discipline matters. Use true RMS instruments for non-sine loads. Measure voltage at the load terminals, not only at the source. Measure current in the same branch used by the resistance value. For three-phase systems, apply the correct line and phase relationships before using a single-phase estimate.
Thermal Review
Power dissipation changes with temperature. Copper resistance rises as conductors heat. Semiconductor losses shift with switching frequency and junction temperature. Coils may have separate copper and core losses. For that reason, keep margin. Review nameplate ratings, ventilation, ambient temperature, and enclosure spacing.
Reports and Records
The chart helps compare apparent power, active power, reactive power, and resistive heat. The CSV file supports records. The PDF file supports reports.
FAQs
1. What is dissipated power in an AC circuit?
It is the real power converted into heat, light, motion, or useful work. In many practical loads, it equals RMS voltage multiplied by RMS current and power factor.
2. Why is apparent power different from dissipated power?
Apparent power includes total voltage and current demand. Dissipated power only includes the real part that performs work or becomes heat.
3. Should I use phase angle or power factor?
Use phase angle when you know it from measurement or design. Use power factor when it is listed on equipment or test instruments.
4. What does I squared R power show?
It estimates heat in the resistive part of the circuit. It is useful for wires, resistors, windings, and conductive losses.
5. Why enter reactance?
Reactance helps estimate impedance, impedance current, and impedance-based power. It is helpful for inductive and capacitive AC circuits.
6. What does duty cycle do?
Duty cycle converts steady power into average power. A 50% duty cycle means the load is active half of the selected time.
7. Can this replace field testing?
No. It is a planning calculator. Confirm important designs with proper instruments, rated parts, thermal checks, and applicable electrical standards.
8. Why do active power and I²R power differ?
They can differ when resistance, current, phase, or measurement points are inconsistent. Non-sine waveforms and changing temperature can also affect results.