Have you realized how dependent we are on electricity? And without electricity, our day to day life will stop. At the time of a power cut or hurricane, you can rely on a portable generator.
The portable generator makes your life a whole lot easier, and above all, it is very easy to store and operate. However, all people have the same question when they buy their first portable generator, and that is, “What size of portable generator do I need?”
Unfortunately, there is no single answer to this question, but instead, there are many variables that come into play when deciding the size of your generator. But first, let’s understand the steps, and then I will explain different terminologies.
Choosing the Generator Size 101
When choosing the generator, you need to consider its fuel-type, its power-producing capacity in surge watts & running watts, its size, and its application. After taking into consideration these factors, follow the below steps for choosing the generator size.
- The first step is to decide where you will be using your generator. You can use it for recreational use, including camping & RV, powering the whole house, or you need it for industrial usage and emergencies.
- The next step is to make a list of what appliances you will be running on your generator.
- The third step is to calculate the running watts and peak watts of all the appliances you made a list from step two. (We have explained this below)
- Finally, by adding the total running watts and maximum starting watts, you will get the minimum power output that your selected generator needs to produce. (Also add extra 25% watts in case your power demand increases in the future)
Generators for different application
As I said earlier, the size of the generator dramatically depends on what type of application it is used for. For example, do you need it for emergency power? Or do you need it for recreation such as camping & RV? Here we have illustrated three such applications and their estimated wattage. If you don’t like calculating starting watts and running watts of your appliances, then you can use this wattage estimation guide.
1. What size generator do I need for a power outage?
If you experience occasional power outages and you want to run minimal appliances such as window A/C and refrigerator, then you don’t need a high wattage generator. Any generator between 2000 to 3000 watts will be enough for you. Now, if you have some extra appliances in addition to refrigerator and AC, then add some extra wattage, and you will be good to go. Below we have listed the estimated wattage of all the possible appliances that you will be going to use in your home.
2. What size generator do I need for home backup power?
During a hurricane, there is no telling when the power will come back. It can take several days, and without electricity, you cannot do anything. At a time like this, you need a high wattage generator ranging from 10,000 watts to 18,000 watts power output. There are some portable generators available on the market that come with 10,000 to 12,000 watts power output, but if you still need more power output, than I suggest you choose the stand by generator. The standby generator can easily power high BTU AC, furnace, space heater, and many other appliances simultaneously without overloading the generator.
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3. What size generator do I need for recreational use?
If you like traveling a lot, then you know how important a camping generator is. For camping, you can choose an inverter generator, solar generator, or dual-fuel generator as long as it is small and compact enough to be carried easily. You don’t have that many electronic devices on outdoor trips, so you can choose any generator between 2000 to 3000 watts that can easily run an electric grill, coffee maker, and charge phones.
Now, if you like to go on trips in your RV comfortably, then you may want to consider a bigger generator because there may have many onboard appliances in your RV. For example, to run a mini-refrigerator, mini AC, microwave, and TV, you need to have at least a 3000 to 5000 watts generator.
4. What size generator do I need for Jobsite/office/farm?
Many contractors that work on Jobsite require a portable generator to run their power tools when working on a remote location or where electricity is not available. The size of the generator largely depends on which power tools you are going to use. Even if you do not have that many power tools, but if you are going to run all of them simultaneously, then you may have to consider a big generator.
For small power tools, any generator between 2000 to 3000 watts will be sufficient. For a larger crew that uses all kinds of power tools, including sander, air compressor, table saw, and drill, and that too at the same time, then choose a generator between 5000 to 6000 watts power output.
That being said, we have added the chart of wattage estimation of the generator for different applications such as office use, Jobsite, and farm application.
What is running watts and surge watts?
Generator or any appliances are rated for two watts known as starting/peak/surge watts and running watts. First of all, let us understand this phenomenon with respect to electric machines.
- Starting watts: It is the power required by an inductive load to start at first (it lasts 2-3 seconds), and this power is very high compared to its running watts.
- Running watts: it is the power needed for any appliance to run continuously without any interruption.
In the case of generator starting watts is the maximum amount of power the generator can produce for only 2-3 seconds to jump-start any inductive load, and the running watts is the maximum amount of power it can continuously provide continuously. The selection of generator depends on its starting watts and running watts producing capability.
What are the types of load?
You may not know that not all the electric devices need starting watts; instead, only inductive loads require additional power (which is more than running watts) for a successful startup of the machine. Let’s understand the types of loads.
1. Resistive loads
I will not go into more detail because it will be hard for you to understand this concept, so I will try to make it as simple as possible. Resistive loads do not involve a magnetic field; hence, there is no reactive load. Thus it does not require any starting power, and for resistive loads, the surge watts are zero.
Example of resistive loads;
- Light bulb/Incandescent bulbs
- Electric Heater
- Toaster & coffee maker
2. Inductive loads
Almost all the appliances today contain inductive load, be it electric motors, fans, vacuum cleaners, dishwashers, washing machines, and the compressors in refrigerators and air conditioners. Inductive loads deal with reactive power, so they require additional power to start, but once the device is running, it does not require additional power; instead, it only requires its rated running watts. Typically the starting power is three times the running power.
Examples of Inductive loads;
- Electric motor
- AC/Refrigerator
- Power tools
- Air compressor
3. Capacitive Load:
There are not so many capacitive loads you will see in daily life. One such example of the capacitive load is the capacitor itself, which is widely used in fans, and another example is the capacitor bank, which is used power factor correction. Also, the synchronous motor is also used for power correction.
Examples of Capacitive loads;
- Capacitor banks,
- Buried cables
- Capacitors used in various circuits such as motor starters and fans etc.
Generator energy conservation
As you know, the wattage information of the device is printed on it, but sometimes there might be only one number printed such as it can be amps or only running watts.
Watts = Amps x Volts
Amps = Watts / Volts
Volts = Watts / Amps
To find the starting watts, you can use the above formulas. By multiplying the running watts with three, you will get the starting watts.
Similarly, if only the ampere rating of the device is given, then you can find the wattage consumption of that device easily. Usually, the voltage is 120-volts in the US, and some devices may use 240-volts, so look out for that.
Calculation of required wattage
Now, after finding the running watts and starting watts of each appliance, now it’s time to calculate the actual wattage usage.
First, see which appliance on your list has the highest starting watts and write it down. Then add running watts of all the appliances you made a list earlier and then add that running watt with the highest starting watts. The final answer is the required wattage your generator needs to produce, and to be on the safe side, add an extra 15-20% in it to suffice the future needs.
