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Electricity Generators

Selecting an Electricity Generator For Emergency and Backup Power

Do you have power blackouts? Do you live in a place where the electrical supply is not dependable? It can be very annoying, can stop you working and even be life threatening. You may consider buying an electricity generator (a genset) but there are many to choose from and many other considerations such as how large should it be, will it be noisy or give vibration problems, petrol or diesel, automatic start and many other questions. Here we look at how to select a generator?

A reliable electricity supply is a luxury

In so called "developed" countries we usually take our electricity supply for granted. It is always there and is stable with a fixed voltage and constant frequency of 50 or 60 cycles per second. For those who live in poorer countries the power supply can be unrelaible at best and even non existant for extended periods.

The reasons why supply can be unstable are many: shortage of coal or oil for the generators, inadequate or overloaded equipment, poor maintenance, poorly trained staff, the list goes on and on.

So, if the power keeps cutting out, what can we do?

Uninterrupted Power Supply or UPS

If it is only the computer you are worrying about you can get yourself a UPS (an uninterrupted power supply) which will give you a warning sound when the power cuts off and some precious minutes you need to save your work. A UPS can only supply a small amount of power.

A good friend has recently opened a spa but he has one major worry that gives him sleepless nights. The elctrical supply is unreliable and, if he loses power he will lose customers and contracts and his business will collapse.

He must have a reliable power supply so he has decided to install a generator. the power will cost more but he will have a reliable soyrce of power under his control and the power will be very stable.

Selecting an Electric Generator or Genset

Generators come in a wide range of sizes and specifications so where do we start?

How Much Power Do You Need

First we have to determine how much power we need and, of course, the smaller the generator the lower the cost both to buy and to run. You need to think carefully whether you can switch some equipment off should the power fail thereby reducing the amount of power you need to generate.

Peak Load

You also need to consider “peak” load. Peak load is the maximum you may use at any one time and for most households and businesses with many items switching themselves on and off this is random so that probability (or is it sod’s law?) says that every now and again many things will switch on at around the same time and you have a sudden dramatic increase in power demand giving you a “peak” that your supply somehow has to be able to satisfy.

By careful management you can keep the peak load down. You can make sure that someone doesn’t start using a microwave while the toaster is switched on. By putting a timer on the electric water heater you can heat your water at times when other things such as air conditioners are not running. There are many things you can do.

Generator Size

Generators are sized in KVA (Kilo Volt Amps) but be careful, because of a little known and even lesser understood phenomenon known as power factor (the efficiency of the generator) the rating in KVA is not the same as the power output in Kilowatts. A 35 KVA generator will generally deliver around 25 kilowatts of power.

One of my clients has an establishment which has a 3 phase power supply of 22,000 watts. His demand is for air conditioners, pumps and heaters leaving little opportunity to reduce the power he needs to keep his business going if the mains supply cuts out.

Single Phase or 3 phase

Generators come in either single phase or 3 phase and this should match your own supply so that the generator can simply cut in and supply the same circuits.

Noise and Silent Type

Generators also come as open or silent type. Silent type means the generator is mounted in a sealed steel box which considerably reduces the noise it makes. Generators can be very noisy things. Remember the noise at a fairground or a circus? All caused by diesel generators to drive the roundabouts and lights.


Vibration is another important consideration. A silent generator will still vibrate and the vibrations going through building foundations will be felt right through the building. I suppose our friend could persuade his Japanese guests that the vibration is part of the treatment but insulated vibration absorbing pads may be a better idea to keep his business going normally. Brain surgeons, for instance, do not like operating next door to large generators – it has a tendency to create madness.

Petrol Diesel or Gas?

Next consider what sort of engine you require. You can get petrol, diesel, gas powered engines, water powered and these days wind generators. A water cooled engine will be a lot quieter than an air cooled generator.

Some people prefer a generator that will go forever with minimum maintenance and the old solid Perkins, Lister and Cummings engines fit this bill but can be expensive. Japanese engines such as Mitsubishi and Yanmar are good engines, they are usually lighter and cheaper but not as durable.

If you only want small amounts of power you might consider photo voltaic cells or a wind generator. You will need batteries to store the power to cover the times when the sun is not shining or the wind dies but can be very useful in the right circumstances.

Automatic Start

If you decide to install and electric generator you will also probably need an automatic starter which detects when the mains supply is cut and automatically starts the generator. If you want to go off and find your shoes and crawl into the back garden on a dark rainy night to start your generator that’s alright you won’t need an automatic starter circuit.

Voltage Stabiliser

You will also probably need a voltage stabiliser for your mains supply because when the voltage drops (as it does frequently with an unstable supply) it can confuse and even possibly damage the generator's automatic starter.

How does a generator compare with your electricity supply company for the cost of power? There are many factors to consider to come to any meaningful figure and in addition to the fuel cost you must cover the purchase cost of the generator and equipment, servicing and maintenance costs for the generator and the time taken to check it and test it on a regular basis. The answer put simply is “considerably more than the supply company” I am afraid and a generator can be very inefficient. Remember that if you have a large generator running that is capable of driving your swimming pool pumps or a water heater that large machine still has to run when you only need one light on.

Copyright © Phil Wilson March 2008
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