Generator
Calculators
Fuel, running cost, cable size, kVA conversions, motor starting, noise and more. Quick answers, worked out the way our engineers do it.
Running a generator
What can my generator run?
Check whether a generator you have (or are looking at) can run your load, including the moment a fridge or pump starts.
Fuel use and run time
How much diesel a generator uses at your load, and how long a tank lasts.
Estimate from typical diesel fuel curves. The last 10% of a tank is not usable.
Storm fuel planner
How long your fuel lasts in an outage, and how much extra to store before a cyclone.
Store diesel in approved containers, away from the house and flood-prone areas.
Running cost
What it costs to run, per hour, per day, and per kWh compared with grid power.
Hire or buy?
How many days of hire it takes before buying works out cheaper.
Battery or generator for small loads?
How big a battery would cover a small essential load, like a fridge and lights overnight.
Allows 80% usable battery capacity and 90% inverter efficiency. For days-long outages a generator (or a generator charging the battery) is usually cheaper.
Carbon emissions
CO2 from the diesel burned, for business reporting.
About 2.7 kg CO2-e per litre (National Greenhouse Accounts factor, approximate).
Electrical
kVA, kW, amps and horsepower
Convert between the units on generators and equipment.
Convert
Supply
Generator size for a motor
What size generator starts and runs an electric motor, by start method.
Motor
Start method
For a motor sharing the generator with other loads, use the full sizing tool.
Cable size for distance
Smallest copper cable that keeps the voltage drop within the 5% limit.
Supply
Voltage drop only. An electrician must also check the cable current rating and installation method (AS/NZS 3008).
Extension lead check
Is your extension lead too long or too thin for the load?
Lead size
Changeover switch size
The changeover or ATS rating for a generator and site.
Supply
A licensed electrician must install the changeover so the generator can never feed the grid.
Heat and altitude derating
How much output a generator loses in hot or high places.
Typical spec-sheet derating above 40 °C and 1,000 m, plus tropical humidity. Each model differs.
Noise at a distance
How loud a generator will be at the neighbour’s fence.
Open ground. A wall behind the generator adds about 3 dB; a solid fence can take off 5 to 15 dB.
Fuel tank size
Capacity of a rectangular tank from its inside measurements.
Estimates only. Talk to Great Energy before buying or sizing equipment.