How Many Watts do I Need on a Power Inverter?

Hello folks and welcome to Today we are going to do another article on the topic of power inverters. These inverters are a great tool to have installed on your vehicle or power back up system. There are many uses for inverters such as going on a long road trip with the family and wanting a television plugged in for the drive,  camping off grid and wanting to have a warm cup of coffee in the morning, or you are without power and want to run some electronics while you wait for the power to come back on.

Whatever your reason is for using a power inverter there are a lot of questions that surround these tools. How exactly do they work? What size of inverter should you buy? In this article we are going to provide you with a basic overview of how these inverters work and then look deeper into exactly what sized power inverter that you need. Let’s dive in.

How Many Watts do I Need?

Let us first understand the basic principle of a power inverter. They work by connecting directly to your vehicle’s battery. Once connected you are then able to plug-in appliances or electronics using the outlets on the inverter. The battery in your vehicle has stored direct current, or DC, energy. DC energy is what is used to start your vehicle, power the interior lights, your radio, and many other things. Appliances or electronics that you wish to run through your inverter use alternating current, or AC, energy. All of our homes and offices use AC energy for power. What the power inverter does is draw the DC energy from your battery and converts it over to usable AC energy. Once converted you are then able to use the AC energy to power your appliances.

Now that we understand the basics of these inverters let us know take a look at exactly how many watts you need in order to power your appliances or electronics. Watts are a measurement of how much power is required to run something. The higher the watts the more power it is going to take. Power inverters come in a variety of sizes ranging from a few hundred watts all the way up to four or five-thousand watts. Sizing your inverter is important as it is not always best to go big or go home and buy the largest inverter out there. If you undersize your inverter though then you will be unable to provide adequate power.

The first thing you need to do here is determine the total wattage of the appliances or electronics that you wish to power with your power inverter. This is actually a pretty easy exercise. All you need to do is review the label on the item you are wishing to power. In some cases they will have total wattage used right on the label. In other instances you will not be able to find the watts but instead only see the amperage draw. This is just as good. If you find the total amps used you can determine the total wattage. All you have to do is take the amp number and multiply it by the volts. The volts number is just a measurement of the type of plug-in the appliance uses. In our case we are going to be using the standard one-hundred and twenty volt plug-in that is found in all of our homes. So, the math becomes amps times volts equals watts. For an example let’s say we have a five amp coffee machine with a one-hundred and twenty volts. The math becomes 5 times 120 equals 600 watts.

One thing to look out for when determining total watts is what is known as starting watts and running watts. The more complex appliances will require an additional boost of power in order for it to power on. This initial boost typically only lasts a few seconds but it is needed to start the appliances. Once started the power demands settle back down to a lower constant number. This initial boost is known as ‘Starting Watts.’ When it settles back down to a lower constant wattage that is known as ‘Running Watts.’

It is vital that if your appliance has starting watts that you factor that into your total wattage calculation. If you do not then you may not be able to turn the appliance on. Some examples of a machine with starting watts are refrigerators and freezers. Each of these require a compressor to start the refrigeration cycle. This compressor requires a large boost of energy to start. Be sure to factor this in when totaling up your wattage.

Once you have determined the total watts you now need to look at the various sized power inverters. A rule of thumb here is to add an additional twenty or thirty percent to your total wattage needs. What this does is give you some wiggle room so that if you did miscalculate by mistake OR if you have another appliance that you wish to power then you have the wattage reserve to do so. With our six-hundred watt coffee machine example above I would suggest purchasing a nine-hundred or one-thousand watt inverter. This gives you plenty of room to power a phone, laptop, or other small device along with the coffee machine.

If you do end up needing a power inverter greater then one-thousand watts then it is recommended to purchase a high output alternator. The alternator is what provides your vehicle with power and is also how your battery gets recharged. If your inverter is pulling too many watts and your alternator cannot keep up then you could end up with a dead battery even while driving down the road. This is not a good situation to be in. A high output alternator will produce more watts and be able to keep up with the high demands of a larger power inverter.

The last thing to mention here is if you plan to run your power inverter while your vehicle’s engine is off then you will most likely need a secondary deep cycle battery installed. Your standard automotive battery is not meant for long term use. It is a cranking battery that provides short bursts of power to start your vehicle’s engine. If you use a power inverter off of this standard battery with the engine off then you could drain your battery after only thirty to sixty minutes. This is why it is recommended you either run the inverter while your engine is on so that the battery is constantly recharged OR you look at installing a secondary deep cycle battery. Deep cycle batteries can last for hours and sometimes even days off of one charge.

Installing a secondary battery can be a bit tricky. If you are an experienced tinkerer with vehicles the you should be able to handle it by following this guide that I found. However, if you are no as comfortable working on vehicles then I recommend taking your vehicle into the dealership or a local mechanic and tell them that you want a secondary deep cycle battery installed. If you also already have the power inverter purchased you can ask them to install it as well. Otherwise, you can install it after the fact.


As you can see from the content above there is a lot to consider when it comes to finding the right wattage for your power inverter. In short though just remember to add up the total wattage of whatever you wish to power and make sure that number is LOWER then the wattage of your power inverter. If you do that then you should be good.

Thanks for reading folks,

Alec Johnson


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