Step 1

Make a Checklist of Electrical Devices & Apliances you will need to run

The first thing you need to do is to decide what you need to power when the power is out. This will rank depending on personal preference and situation but usually ranks like this.


Remember cooking and heating equipment takes ALLOT more energy than anything else in your home. If you must power those appliances (if the power is of for an extended amount of time) you can perhaps power only those appliances or get a generator able to power all of your equipment at the same time.

Step 2

Learn how much power each device draws and add it all up.

Once you have identified the appliances you need the next phase comes into play.

When you are sure on what you need to power the next goal is to identify how much power each appliance draws. In the article below there is a comprehensive list that shows the average power requirement of common household appliances. Write down each appliance usage (this is a number indicated by watts) and add it all up to final figure. 

If a certain appliance that you need to power is not listed (uncommon device) either do a internet search for the manufacturer or use a electronic clamp meter to measure the current while the appliance is switched on. Measure the current (Amps @ AC current). This can then be used to find the wattage value via this equation: watt = amp × volt. Voltage in South-Africa is AC 220V (50 hertz)

Example: A device that measures 2.2 amps at 220V = 484 watts.

Alternatively as a more advanced user you can measure your power draw directly on your Power Distribution Board. However this is dangerous to the uninformed and best suited to a qualified electrician (but will yield a very accurate result)

Once you have a sum of total power requirement for your home/business you have the information needed to make the decision on a backup power generator.

Fossil fuel power backup generators have been and probably will be for some time the most effective backup power sources in relation to cost and ease of use. Now that you have a size to go on the next step is to fit that to a machine.

The Best practice is the make sure your backup source is capable of providing 15 percent more power than your average use.

For example you have noted your household requires 4500 watts of power. This is 4.5 kW of power on average. The ideal power source must provide at least 5500 watts (5.5 Kw) of power.

The reason for overshooting is that certain appliances such as fridges require a higher amount of power when switched on for a few seconds. In other words when you switch everything back on your household will draw approximately 15 percent more power for a brief few seconds.

The generator is manufactured to handle a brief surge of power but only for a few seconds. Keep to the manufacturers specifications and you will never overload the generator.

Step 3

When you know how much power you require take a look at our range of generators

Once you know how much power or size you need head over to our power generator range page and make a selection. We have similar models in Diesel and Petrol. Either fuel does not make a difference in the working of the machine however for Silent type a diesel machine is more beneficial. Choose a machine that you can easily obtain fuel for based on your location.

Generator Prices and Specs Link: https://www.adendorff.co.za/Products/Generators

Thank You for Reading

8 thoughts on “How to choose the right size of generator

  1. Lance Heydenrych says:

    I am looking for a 1kw to 2 kw silent diesel generator to run our fridge and deep freeze for use in a power shedding application. We cook on gas.
    And where is the nearest Ardendorff Branch to Balfour or Heidelberg?

    • Francois Landsberg says:

      Hi, the nearest would be our Vereeniging Store. We stock a 2kw model and larger options too please visit our store locator link at the top to contact the store in Vereeniging.

    • Francois Landsberg says:

      Hi, there please visit our generator range. The link is below the infographic under generators. We have detailed info on each generator along with pricing.

  2. Lj says:

    I bought a 12kva generator feom adendorff and it battles to start up my cooling unit of my cold room its 4.8kw please advice

    • Francois Landsberg says:

      Hi there. This is 3-phase I’m sure. Is the machine three phase too or hooked up to one specific phase?

  3. VJ says:

    Hi what size generator do I need to run a 12000 BTU a/c with my Led TV and Fridge and a few Lights for about 6 to 8 hours?

    • Francois Landsberg says:

      Just a quick estimate but a 5kw machine should do it. We are not familiar with the power draw on the compressor on the aircon though. I would recommend taking a look at the electrical panel on the radiator perhaps they have a wattage listed there?

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