How to choose a generator
A generator that is too small trips out under load; one that is too big wastes fuel and money. Here is how to choose the right one for a shop, site, home or workshop.
1. Start with what you need to power
List every appliance or tool you want to run at the same time and find its running watts — usually printed on the label or in the manual. Add them up.
Anything with a motor (a water pump, compressor, refrigerator, air conditioner or power tool) needs a burst of extra power for a second or two when it starts, often two to three times its running figure. Add the surge of the single biggest motor to your total, because motors rarely all start at once.
- Total running watts of everything used together
- + the extra starting surge of the largest motor
- + about 20% spare capacity so the generator is not run flat out
2. Inverter or conventional?
An inverter generator produces steady, clean power, which is safer for electronics such as computers, billing machines, routers and LED lighting. It is also quieter and uses less fuel at partial load. A conventional (open-frame) generator usually costs less for the same output and suits power tools, pumps and general site work.
3. Petrol or diesel?
Small portable generators are usually petrol: they are lighter and easier to start. Diesel sets are generally preferred for long running hours and larger, heavier-duty loads because diesel engines are built for continuous work.
4. Features worth checking
- Fuel tank size and rated run time — how long it runs before refuelling
- Noise level, especially if the generator will sit near people
- The type and number of sockets you need
- Electric start if you will start it often, and wheels or handles if you will move it
- Automatic voltage regulation (AVR) on conventional sets, to keep the output steady
5. Run it safely
- Use a generator outdoors only, well away from windows and doors — exhaust contains carbon monoxide
- Keep it dry and on level ground
- Never feed power into building wiring without a proper changeover switch installed by a qualified electrician