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Portable generators Updated: 04 May 2007

Did you know?

We have George Westinghouse (picture, right) to thank for our alternating current distribution system.

If his great rival, Thomas Edison (inventor of the light bulb) had his way, we would have a direct current electricity system.

Alternating current has an overwhelming advantage over direct current for a distribution system: transformers can change its voltage. This allows high-voltage transmission lines to efficiently transport electricity over long distances. In its various guises, alternating current is used throughout the world.

So what's the difference?

In New Zealand's alternating current, for example, the supply voltage varies like a wave in a regular fashion 50 times every second. This is called the frequency.

The varying voltage means that, at any particular instant in time, the voltage could be anything from zero to about 325 volts (at its peaks). The 230 volts our system is rated at is a mathematical calculation, similar to an average, based on that 325-volt peak voltage.

The mains 230 volt supply varies very little. But non-inverter portable generators have a tough job keeping those factors constant: when the electrical load changes, the frequency and voltage can get temporarily out of shape. Inverter models (see Key decisions) are much better at keeping them stable.