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How to choose the right size generator is the most common question people ask, follow these steps and you will get it right.

Step 1 – Decide what you want to power

Simply determine all of the appliances you would like to use at the same time.

Step 2 – Determine the maximum total power requirement for all of your appliances

This involves adding up all of the power consumption figures for your appliances. This information can be found on a data plate, or in a manual. This information is usually in watts, and if it is in amps it is best to convert it to watts for ease of choosing the right generator.

It is crucial to get the starting and running power requirement for each appliance!

Most appliances with electric motors or compressors require more power to start than to run. For some appliances this can be 3 or 4 times the running watts. Your generator needs to be able to start your appliances as well as run them. Make sure you find out the starting watts. This information is sometimes found on data plates and manuals, but often requires contacting the manufacturer/supplier or using a watt meter. Another option is giving the size of the motor to a generator specialist.

Step 3 – Convert generator kVA to Watts and choose the appropriate size

Generator sizes are given in kVA (kilo-voltamps), and this must be converted into watts so you know which appliances you can power.

Multiply kVA by 0.8 (this is known as the power factor) to obtain the watts produced by the generator.

e.g. 10kVA x 0.8 = 8kW (kilowatts), or 8000 watts

This is the rated power output for the generator.

Generators will be able to provide more power than this for a short period of time (this is known as the maximum output). How much depends on the engine and the alternator, a good rule of thumb is to treat the kVA given in the size as the maximum kW, so a 10kVA unit is likely to be able to produce 10,000 watts for a short time. It is not recommended to run a generator at this level for more than a few seconds, just long enough to start appliances. If it needs to run at its maximum level for longer than this, then you need a bigger unit. You will risk damaging the engine and voiding warranty if you overload your generator.

Hint: You may find that you don’t need to start all of your appliances at the same time, or that you can turn some off while starting others, allowing you to use a smaller size of generator. For example, you may leave other appliances off while starting an air conditioner or compressor.

Stationary generators are rated for prime power or standby power. Prime power is the amount of output the unit can handle continuously, for extended periods, it is also known as the continuous rating. Standby power is for shorter intervals, typically when used for backup. The prime power capability of a given unit will be lower than the standby power. It is recommended that prime power units have high quality, durable engines designed to handle heavy loads. To determine the best unit for your application it is best to speak to a large generator specialist.