Hello Clive,
Small generators tend to change speed when electrical appliances are switched on and off. This is due to the fuel supply to the engine not responding instantly, so when a large electrical load is connected the engine speed dips until the speed and fuel governor can compensate. Conversely, when a large electrical load is turned off, the engine races momentarily again until the governor can compensate. This is most noticeable where the applied electrical load represents a large proportion of the generators available capacity.
If the same electrical loads were applied to a larger generator the effects would be less noticeable.
The output voltage is dependant on the engine speed, so if the engine slows, the output volts drops. This condition does not usually damage electrical appliances, but if the engine races, then the output voltage spikes, and this can damage some sensitive equipment. e.g. tvs and computers, may be a microwave). It may only take a second or two for the governor to stabilise the engine speed but may be more than long enough to damage some electrical appliances.
The cheaper generators tend to suffer these issues, because the 230Vac output is taken directly from the mechanical alternator, but some of the more expensive units overcome this problem by using some electronics to stabilise the output voltage using an inverter.
An inverter type output uses electronics to sense and adjust the output voltage. Because it is using fast acting switch mode technologies it can respond quick enough to prevent excessive voltages, and it can compensate to some extent for under voltages as well.
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