How does a power generator work?
An electrical power generator (commonly known as a generator) is a device that converts the chemical energy of a fuel such as gasoline or diesel into electrical power. In detail, the conversion goes from chemical energy to thermal energy, thermal energy to mechanical work, and mechanical work to electrical power.
Generators are required to support electrical power requirements in many scenarios, including:
- Home or office use in the event of a power cut;
- Power for temporary equipment not connected to a local power grid;
- Difficult terrains where electric power supply is not available, e.g., camping and leisure activities; and
- Events, shows, and portable living spaces.
Generators are especially crucial for places where the potential lack of electricity may become dangerous for human life, e.g., hospitals.
The generator power calculator
The generator power calculator takes the total current requirement of the devices in amperes (A) and the supply voltage rating in volts (V) to calculate the apparent power in kilovolt-amperes (kVA), which is then used to calculate the actual power based on the power factor. You can also calculate the motor horsepower available using the efficiency of the motor and the calculated power.
What is the power factor?
The terms used in a generator power calculator might look scary at first — here is a simple explanation for each:
- Current (I) — the flow rate of charge through a conductor's cross-section. Sum the individual current rating of all devices connected to the network.
- Voltage (V) — the difference in charge between the two terminals of the power source. It drives the current through the circuit. The voltage rating of all devices should be the same; otherwise a converter is needed.
- Apparent Power (S) — a simple product of current and voltage, measured in volt-amperes (VA). It is not calculated for direct current (DC) circuits.
- Power factor (PF) — the ratio of working power (kW) to apparent power (kVA). It is usually taken as 0.8, meaning a generator is expected to work at up to 80% of its maximum load capacity. The power factor is mentioned on the specifications plate of the generator.
- Power (P) — the rate at which electrical energy flows through a circuit, measured in watts (W). The generator output power rating should be higher than the calculated power.
- Efficiency (η) — the ratio of output power to input power of the motor. It is used to calculate the output horsepower of the motor from the power rating.
Formulas used for the generator power calculator
| Power supply type | Apparent power (kVA) | Power (kW) | Motor output horsepower (HP) |
|---|---|---|---|
| Single-phase | V · I / 1000 | V · I · PF / 1000 | V · I · PF · η / 746 |
| Three-phase | 1.732 · V · I / 1000 | 1.732 · V · I · PF / 1000 | 1.732 · V · I · PF · η / 746 |
| Direct current | — | V · I / 1000 | V · I · η / 746 |
Single-phase alternating current changes its direction of flow periodically and has a single live wire and a neutral wire to complete the circuit. So two wires are enough for an appliance to work — it is usually used for domestic power supply. Three-phase power uses the factor √3 ≈ 1.732 and is common in industrial and heavy-duty applications, while direct current (DC) flows in a single direction and has no power factor or apparent power.
Metric and American unit systems
This calculator presents the result in both metric and American unit systems:
Metric units
- Kilovolt-amperes (kVA) — apparent power (AC only)
- Watts (W), Kilowatts (kW) and Megawatts (MW) — real power
American units
- Horsepower (HP) — 1 HP = 745.7 W; motor output HP uses the 746 W electrical horsepower
- BTU per hour (BTU/hr) — 1 W = 3.41214 BTU/hr
Estimated running cost
The calculator can also estimate how much it costs to run the generator. Enter the daily running hours and the energy/fuel price per kWh to see the daily, monthly (30 days), and yearly (365 days) cost. Supported currencies include USD ($), RUB (₽), EUR (€), GBP (£), JPY (¥), CNY (¥), INR (₹), and BRL (R$).
FAQs
How does a generator power a house?
Sum the current rating of all the devices you want to run, enter the supply voltage and select the supply type. The calculator returns the apparent power (kVA) and the real power (kW). Choose a generator whose output rating is higher than the calculated power to keep a safety margin.
What size generator do I need?
A good rule of thumb is to pick a generator rated about 20–25% above your calculated power requirement, so it never runs at full load. This calculator suggests a recommended kVA rating with that headroom included.
Why is the power factor usually 0.8?
Most generators are rated at a power factor of 0.8, meaning the real power (kW) is 80% of the apparent power (kVA). The exact value is printed on the generator's specification plate.
Why is apparent power not shown for DC?
Apparent power is the product of RMS current and voltage in an AC circuit and accounts for the phase difference between them. In a DC circuit there is no phase difference, so power is simply V × I and there is no separate apparent power.