SECONDHAND GENERATORS

Noise or the lack of it

One of the most important considerations is how much noise the generator will make in use. Most people would prefer their generator to make no noise at all, however this can be very expensive as well as bulky and heavy. If you are going to use the generator for small period of time on a building site which is very noisy, then you can accept quite a lot of noise. However the less ambient noise is around the lowder a generator will appear to sound. In the middle of the night when all goes quiet the sound of a quiet generator humming away could drive your neighbors mad.

The decibel which is normally abbreviated dBA is the unit used to measure the intensity of a sound. The human ear is incredibly sensitive, a person's ears can distinguish between wide ranging sounds such brushing their fingers on a notepad to the loudest explosion or Jet aircraft.

Generators are measured and compared within the industry @ 7 metres. To comply with EEC regulations all generators have to be marked in LWA this is a different measurement of sound which is taken from a different distance. For an example a quiet Honda EU20i is rated at its lowest at 52 dBA @ 7 metres on the LWA scale this would equate to approx 88 decibels. Please beware of this as all products have LWA marked on them, many do not have the industry rated @ 7 metres level.

The solution to problem is to have an acoustic enclosure which reduces the noise. The best ones reduce the noise to almost whisper quiet. It would be nice just to place an enclosure over a noisy generator however the generator would soon overheat.

The other way of reducing the noise from a generator is to place it some distance from the listeners ears. The sound level reduces as the sound disperses into the environment. There are a lot of factors such as the frequency of the sound and the environmental conditions at the time. Sound can be reflected and or absorbed by placing something heavy between the generator and the ear. Soft surfaces can absorb noise whereas hard surfaces as brick walls can reflect noise towards or away from a given point.

Diesel or Petrol

Smaller generators tend use petrol as it provides more power for the size of generator. Where size / weight is not as important diesel is more reliable and cheaper on fuel.

Petrol 2 stroke or 4 stroke

2 stroke engines provide more power to weight than a 4 stroke and can be cheaper to buy, however this come at the expense of fuel efficiency and reliability. In most cases they also need oil adding to the fuel making them more complicated to run.

The quality of electricity

There is always a balance between the cost of the generator, the amount of power it will provide and the quality of the electricity it will provide.

A generator built to power workman's tools may provide ample power, however the quality of the electricity may be low. Problems such as the generator speeding up or slowing down would affect the frequency of the electricity produced and give spikes and troughs in power. This could affect anything with complex electronics plugged into it. For example I would be very reluctant to use such a generator to power a computer. The solution is to build an inverter into the generator which produces clean electricity however this increase the cost of the generator.

Much larger generators have much better control over the speed of the engine and have better quality alternators, so produce quality electricity without the need for an inverter. However it is very important not to overload the generator or have big fluctuations of the amount of power required as this will almost certainly produce fluctuation in power quality.

If large fluctuations in the power demand are expected for example at a festival when the stage lights are going to be turned on and off in time to the music, then a much larger generator should be used, which can cope with the fluctuations in power required.

It is not recommended to use a generator at above 75% of it's rated power for any length of time as this can overheat the windings of the alternator which could burn out prematurely.