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.

Lights>Refrigeration>Cooking>Entertainment>Heat>Cleaning.

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

46 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.

    • R says:

      Hi LJ
      Any motor requires 5-6x it’s rated current to start. Your cooling unit would therefore require 25-30kW generator. Please also remember to derate at altitude by 1% per 100m.

      • Francois Landsberg says:

        Thank goodness we have some smarter people than us on here to answer these questions. I was a little unsure about starting current. Thank you R

      • D says:

        Hi LJ

        I am sure that you have resolved the issue with the your cooling unit. User R above is correct in what he is saying, however, this only applies to 220V machines at that rate. Three phase motors and units rarely have more than a 10% spike in amperage on start-up due to the windings being different. You will however experience an issue if the machine was only connected to one of the three phases, as opposed to being connected onto all three phases.

    • 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?

  2. Kwena says:

    Please advise 2 fridges, lights for 4 bedrooms, alarm elec fence, cameras, garage door, gate motor stove, how many kwts Generator should I buy.

  3. YUSUF says:

    Hi Francois

    I need a generator to power a few lights, a fridge and a freezer, TV & PC (alternativley). will the 2.8kva currently advertised for R3700 be sufficient?

    Kind regards

  4. Mike says:

    Francois,
    If I am looking to put in a silent generator for my entire house with automatic switch-over, and my house has a 63A breaker, would the house require approx. a 17KVA single phase generator ?
    Calc assumption 63A x 240V at 1.15 for start-up. I am assuming 63A because at that rating my board does not trip, having a 250L geyser. Went with the upper limit of 220-240V and added 15% for extra capacity on start-up load.
    Am I over-sizing or under-sizing?

    • Francois Landsberg says:

      Yes and no. For that size, we have only been able to source 380V machines since you can’t offer that kind of current on the circuitry of a 220V machine. 380V machines can be connected up to supply you but you will have to speak to a qualified electrician and have him take a look at your board. Take a look under our generators here and see our 20 kva machine with an ATS (autostart): https://www.adendorff.co.za/product/mac-afric-20-kva-16-kw-standby-silent-diesel-generator-ats-380v/

      remember on a 380V you need to use all phases equally so you can’t just hook it up with 1 220V output. Otherwise, the alternator is not balanced and you will gradually shake the machine apart.

  5. Karin says:

    Please advise 2 fridges, 1 freezer, lights for 3 bedrooms, alarm, cameras, stove, electric kettle, cell phone chargers, how many kwts Generator should I buy. What hind of generator is best, petrol or diesel. And is is it more adviseable to buy an invertable generator?

    • Francois Landsberg says:

      Inverter machines are more silent and efficient but come at a much higher price. At this stage, we do not find them good value and for a home that size you will have to make a massive investment. For 2 fridges and the rest, a 7kw is recommended, you can make a 5kw work but might have to switch on the fridges 1 by 1 to prevent current spiking. Diesel vs petrol is more about preference but we have seen diesel is more efficient longterm and the engines can last longer over the years, however our petrol machines last a very long time too. Diesel open frame machines are also noisier though. Diesel machines are a better option if you live on a farm or outlying are and have better access to diesel (for example you have farm implements on site and use a tank)

  6. Katryn Snyman says:

    Kan jy vir my asb ‘n prys gee op 2.5kva kragopwekker en waar in Pretoria kan ek gaan kyk. Dankie Kan jy asb dit vir my email.

  7. Jenny Martens says:

    Hi

    What size petrol generator would I require to run 4 fridges, ignite a gas geyzer (I have converted over to gas), 3 T.V’s. WiFi, 2 computers, cellphone charging, inside lights for a medium house, 2 garage doors, electronic gates and maybe a microwave at times. I have gas cookers so dont need the stove.

    • Francois Landsberg says:

      A 7kw should be able to just about manage that, but a 10 kw would be recommended. This is just an estimate so we recommend to do an actual load test on your DB board to get the maximum current draw.

  8. Jonathan holl says:

    Good Day
    I am looking to run our office which is held by a 3 kva true on-line UPS.
    What size generator do i need to run this?

  9. Le Roux Jordaan says:

    Francois, n persoon het drie fase toevoer, voorsien drie fase na huis, kantore,werkswinkel en n kleiner huis. Net die boorgate is drie fase pompe wat se aanvraag oor die drie fases gebalanseer is. Wat is die persentasie verskil tussen fases indien een of twee fases se aanvraag meer is as die ander fase,bv, indien een fase 16 Ampere trek en die ander fase 10 Ampere ens. Enkelfase toerusting in die huis, kantoor en werkswinkel kan die fases se aanvraag laat verskil. Kan die generator bv. op een fase 16 Ampere hanteer, op n ander fase 10 Ampere en bv. op die ander fase 6 Ampere op een gegewe tydstip, of wat is die maksimum verskil in persentasie tussen die fases op een gegewe tyd? Ek hoop my vraag is duidelik.

    • Francois Landsberg says:

      Ja sien soos vorige vraag. Ons kennis is kerp op wat die masjien gee. Alhoewel hierdie is n gesprek wat jy met n kwalifiseerde elecktrisian moet he. Daar is manier om hom te balanseer en dit hang af hoe hy dit konekteer.

  10. Le Roux Jordaan says:

    Dag Francois, 12kw drie fase gen wat enkelfase toerusting in n huis, kantoor, werkswinkel en kleiner huis bedien. Wat is die persentasie verskil maksimum tussen fases wat gebruik kan word, m.a.w. indien een fase 16 Ampere trek, die ander fase 9 Ampere en die derde fase bv. 10 Ampere. Wat is die meeste wat die fases mag verskil in Ampere? Ek vertrou dat my vraag duidelik is.

    • Francois Landsberg says:

      Ek sal nie meer as 10% nie. Dit is moelik om dit op te stel sodat dit gebalanseer is. 15% op die meeste. Jammer vir laat reply ons comments hier was offline tot nou toe.

    • Francois Landsberg says:

      We generally don’t recommend using elements and recommend gas. However, the stove by itself will probably be too much just by itself. You will need at least 10kw for both on our estimates.

  11. Felix Maringe says:

    What size generator do I need for a three bed lighting, two lounges lighting, TV , two fridges, garage door, alarm. Gas stove???

  12. Marius says:

    Good day

    We have a 4 bedroom house (all rooms on LED lighting), 1 x 150L normal geyser and a 50L geyser, 1 fridge, 1 deep fridge (210L), 3 Tv’s, normal 4 plate stove. Wi-Fi and 3 x OVHD units what will be the ideal size Generator to buy?

  13. Albert Ruthenberg says:

    You mention in this article “In the article below there is a comprehensive list that shows the average power requirement of common household appliances.”
    Where do I find that article as see no link or similar.

  14. Craig Kisten says:

    Hi,

    What size generator i will need to run the following:
    QLED TV,
    DSTV DECORDER
    FIBRE ROUTER
    24000 BTU AIRCON
    FRIDGE/FREEZER COMBO
    GEYSER
    ALARM SYSTEM
    THREE ROOM LIGHTS

    • Francois Landsberg says:

      Hi, we aren’t sure exactly how much wattage the aircon would take you can measure it with a tester or find out from the manufacturer. The geyser should be between 2 – 3 kw so a 7kw 8.7 kva machine should be ablt to handle it. But it’s recommended getting an accurate measurement from an electrician. This should be fine for a 7 – 10 kw machine depending on if you are willing to witch the geyser of while you have load shedding. We recommend this.

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