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Power Inverter Buyer’s Guide

Power inverters are a great tool to have in your car, truck, RV, boat, or any other mobile vehicle. They can provide you with that much needed power to run a coffee maker, charge your laptop, or even run your television. Whatever your need is the power inverter can help you out.

The question though is that when you are looking to purchase a power inverter what exactly should you be looking for? There are a lot of questions on power inverters and what exactly they do, how they work, and what you can expect when purchasing. This article aims to tackle all of these questions and also provide you with a full buying guide. Let us dive in and take a look!

How They Work

I will not bore you with all of the technical details here but instead give you a short abridged version on how power inverters can work for your vehicle. First we need to understand that there are two main types of electricity in today’s world. There is the alternating current, or AC, and there is the direct current, or DC. Now AC electricity is found in your home, office, or other environment. If you plug something into the wall at your home you are using AC electricity. DC electricity is found in any mobile application such as a car, truck, boat, motorhome, or any other kind of vehicle.

AC gets its power source from the power grid and nearby power plant. DC energy get its source from your vehicle’s engine and alternator. While the engine is on the alternator runs and produces electrical energy. A power inverter takes this DC energy produced by your alternator and converts it over to AC energy. Typically a power inverter will have a connection point on one end to your vehicle’s battery and then one or two one-hundred and twenty volt outlets for you to plug-in appliances.

When installed you are now able to plug-in your laptop, television, or whatever else you wish to power. It is that simple.

Wattage Requirements

Before purchasing a power inverter there are a few main things you need to look out for. The first is the overall wattage of the power inverter. This example inverter is a very basic model that comes in at only three-hundred watts. This three-hundred watt unit is one of the smallest units out there. Some of the most common inverter sizes are one-thousand watts, two-thousand watts, and three-thousand watts. You can find some four-thousand watt models, but they are rare.

It is not always best to go big or go home when it comes to purchasing an inverter though. You should first ask exactly what am I trying to power with it? This will give you a guide as to what size you need. Once you know what you want to power you then need to determine the wattage requirements of that appliance or electronic.

Now many appliances do not show actual wattage but instead show you amps or amperage usage. Not to worry though as you can still find the watts rather easily. The only thing you need to do is take that amperage number and multiply it by the volts. Remember, that volts are the type of outlet that it plugs into. So, let’s say for example you wish to charge your laptop computer. Charging a laptop will typically use around 0.5 amps. You will plug that computer into a one-hundred and twenty volt outlet. The math becomes 0.5 amps multiplied by 120 volts which results in 60 watts used.

The three-hundred watt inverter we linked above will be more then enough to power your laptop. That is because powering a laptop is a very low power function. If you were to power something that has movement to it, produces heat, or produces cold then you are going to require a lot more power. This is seen as the ‘Golden Rule’ with power inverters. If there is movement, it produces heat, or it produces cold then you can expect a lot more power requirements. An example of this is a coffee machine. While a coffee machine may seem simple you have to remember that it has to heat the water before creating the coffee. This heating action requires a lot of amps.

Again, lets look at an example. A standard coffee machine can use anywhere between six to eight amps. If we perform the same math as before we end up with 6 amps times 120 volts equaling out to 720 total watts required. The three-hundred watt inverter we recommended above would NOT be enough to power your coffee maker. This is why it is so important to accurately determine the wattage you will need before purchasing. If you do not then you could purchase too small and end up wasting your money.

It is also recommended to go at least twenty or thirty percent higher then what your wattage requirements are. This gives you some leeway in case your calculations were slightly off OR if you wish to add more appliances down the road. In the example of the coffee machine I would suggest going with a one-thousand watt power inverter. An example model from Amazon can be found by clicking here.

Batteries & Alternators

The first question I have to ask in this section is how do you plan to run your power inverter? Is it intended to be on and running while you are driving and your vehicle’s engine is on? If so, then you most likely will not have to add an alternative battery to your vehicle. When the engine if your vehicle is on the alternator generates electricity which powers the electronics in your car, charges your battery, and will power your power inverter.

The thing to look out for here is that you are not asking for too much power from your alternator. If you have a ton of high wattage appliances plugged into your inverter then you could end up exceeding your alternator’s capacity. When this happens the alternator will begin to drain your vehicle’s battery as well in order to compensate for the large power demand. If this happens then your battery could end up completely drained and the engine could end up shutting off. You are then left with a dead battery and your vehicle not running. This is NOT a good position to be in.

If you do expect to use excessive wattage while driving, say over one-thousand watts, then I would suggest purchasing an aftermarket high capacity alternator. These replacement alternators are able to create more electricity to handle your vehicle’s demand. A standard alternator produces anywhere between forty to one-hundred and twenty amps. A high output alternator can produce up to two-hundred and fifty amps. Be sure to find the right high output alternator for your vehicle before purchasing!

Now if you plan to run your power inverter while your vehicle’s engine is powered off then that is a whole different story. You see when the vehicle is turned off you are relying on the vehicle’s battery to power your inverter. This is the same battery that allows you to listen to the radio or have the lights on while the engine is off. These standard twelve volt batteries are very limited. Their intended purpose is to start the vehicle and they are NOT supposed to fall under ninety percent capacity. If they do then you could end up damaging the battery or shortening its lifespan.

This is why it is highly suggested to install an alternative battery on your vehicle. These alternative batteries can be installed easily enough by adding a mounting plate, securing the battery, and then hooking up the wiring properly. I will not get into all the details here, but for a guide on how to setup alternative automotive batteries I recommend this article found by clicking here. If you decide to go the alternative battery route then I highly suggest that you purchase what is known as a deep cycle battery for your alternate.

Deep cycle batteries are intended to run for a long time without power. While the standard twelve volt battery is not meant to fall under ninety percent capacity a deep cycle can fall as low as fifty percent, or more, without damaging it. You typically see deep cycle batteries installed on RVs or motorhomes already as alternative batteries. The deep cycles allow you to power the RV while the engine is not running. NOTE that if you do plan to install an alternative battery you will also need to install a battery isolator as well. This isolator acts as a switch between the batteries and allows both batteries to be used.

Now if it was me and I wanted to be one-hundred percent safe here then I would install both a high capacity alternator AND a deep cycle alternative battery. This will give you all of the power you need without risk of draining your battery.


Now one of the last questions here on power inverters is how to hook them up to your vehicle. This really depends on size. If you are purchasing a smaller three-hundred watt model then in most cases all you need to do is plug it in to the cigarette lighter or other power connection found right in your dash.

However, if you are purchasing a larger inverter model then you will need to hook it up directly to your battery under the hood of your vehicle. You will then need to route the wiring through your vehicle’s firewall and into your cab. This is not the easiest of tasks and if you are not already a do-it-yourselfer then you may ask for a mechanics help. For a guide on this I recommend this YouTube video. It walks you through the steps and also answers most questions. Click here for the YouTube link.

True Sine or Modified Sine?

This topic gest a bit tricky as it dives into electricity knowledge and how it all works together. In short a power inverter can produce two types of waves for it’s electrical output. These are Modified Sine Waves and True Sine Waves. The Modified Sine Wave models are the most popular when it comes to power inverters. They produce the consistent power that is needed to power most devices.

A True Sine Wave power inverter are going to be the most expensive out of the two. These are the luxury models. The main difference between them is that a True Sine Wave inverter will deliver the highest quality and consistent power source to your appliances. Some sensitive equipment like laptop computers, medical equipment, or very specialized tools require True Sine Waves to operate correctly. If powered by Modified Sine Waves the appliance could end up damaged.

In most cases you will be ok with Modified Sine Waves but if you have questions then it is recommended to review the product’s instruction manual for details on what type of waves are needed. If you are still unable to find the information then it is recommended to call the manufacturer to be one-hundred percent certain.


As you can see folks there is a lot that goes into installing a power inverter. But, it really depends on what you are planning to use it for and exactly how much power you plan to use. If you are just powering a laptop, phones, DVD players, or other small electronics then you can most likely get away with the simple three-hundred watt inverters. These are much easier as you typically do not have to route any wiring or even install alternative batteries. Just be aware that if you are running the inverter with your engine off you COULD drain your battery.

On the other hand if you plan to use a lot of power be sure to follow our guide above.

Lastly, note that working with car batteries can be dangerous due to the acid that they contain. Please take all necessary safety precautions when working with them. We here at ToughAssTools are not liable for any damage or injury caused from working with these products.

Thanks for reading,

Alec Johnson

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