Installing a Power Inverter in a Car or Truck

Inverters are handy gadgets that take a 12V DC input and provide a 110v, or 220v in many countries, AC output. In simpler terms, they take the electricity that's available from the cigarette lighter or accessory socket in a car or truck and turn it into the type of electricity that's available from the electrical outlets in a home.

This can be useful in a car, truck, or RV because it increases the types of electronics you can use on the road. Since nearly all household gadgets and electronics run off alternating current, adding a power inverter to your car effectively allows you to take a device that you would normally only be able to use at home and use it on the road.

The utility provided by a good power inverter is handy for salespeople, truckers, and other people who spend a lot of time in their vehicles. A car power inverter can be a lifesaver on a long road trip, camping excursion, and in a lot of other circumstances.

Inverters are useful but have limitations. The inverter design and the method you use to connect it to your vehicle's electrical system limit the amount of power an inverter provides. Some equipment and appliances, like refrigerators, use an enormous amount of electricity when they first turn on or intermittently during use, which can be a problem if the inverter isn't big enough to handle the surge.

How to Install a Car Power Inverter

If you're thinking about installing a car power inverter, there are three major considerations to think about before you begin:

  • Portable device power requirements: The inverter needs to supply enough power for all the devices you want to plug in at once.
  • Inverter installation locations: You can install inverters most anywhere, but you need to think about accessibility for plugging in devices, how you will connect it to power and ground, and whether it will dissipate the heat that it generates during use safely.
  • Power inverter wiring issues: You can plug small inverters into a cigarette lighter or accessory socket. Larger inverters must be wired to the battery with a large in-line fuse.

The first and most important consideration is how much power your device requires since that determines the size of the inverter, the installation method, and the installation location.

We'll get into this more in the following steps, but here are some rough power requirements to get you started:

  • Portable heater: 1,500 watts
  • Standard hair dryer: 1,500 watts
  • Mini fridge: 100 watts (500 watts on startup)
  • 17" laptop: 90 watts (less for smaller models)
  • Cast iron plate: 1,500 watts (1,100 for coiled burner models)

Power Requirements vs. Alternator Output

You'll need to figure out what your power requirements are to properly select an adequate inverter size. Consider portable devices and alternator output.

Portable Device Power Requirements

To estimate the right inverter size, a general rule of thumb is to multiply the amps of your device by the volts, which will provide the wattage requirement:

V x A = W

For example, suppose you upgraded your old PS3 to a PS4 or Xbox 360 to an Xbox One, and you're not sure what to do with your old console. These consoles may not be portable or the easiest way to add in-car gaming to your car, but you can easily jury rig one to act as the core of a DIY automotive multimedia system.

The rating on the Xbox 360 power supply shows that it draws 4A at 110V, so if you want to play an Xbox 360 in your car, take those numbers and plug them into the above-referenced formula:

110V x 4A = 440W

Here, you need an inverter that provides at least 440W. However, it's important to note that you'll need to find one that can provide 440W continuous instead of 440W peak. You'll also need a bigger inverter if you want to plug in anything at the same time you're using the Xbox.


Alternator Output and Power Inverters

The other side of the equation is exactly how much power the alternator can put out. You can sometimes find this number by looking at the alternator, but you may have to contact your local dealer to get a hard number. If you have trouble finding hard numbers, a car electrical shop (or any repair shop with the necessary equipment) can test your car's real-world power output and consumption.

Most alternators can put out more watts than the stock electronics consume, and they can typically handle additional electronics like amplifiers.. However, the exact output varies from one make and model to another. If you want to run a lot of power-intensive equipment off your inverter, you may need to install a high-performance alternator.

If you drive a truck with space for an additional battery, it's also a good idea to take advantage of that situation. This is especially true if you want to use your inverter when you shut off the engine since adding an additional battery will help ensure that you don't drain the main battery to the point where the vehicle won't start.

Car Inverter Locations

The first step in installing a car power inverter is to decide where to put it. Some locations to consider include:

  • In the trunk
  • Underneath a seat
  • Inside the glove compartment
  • Mounted to the floorboards
  • Placed under the dash

When considering potential installation locations, think about where the power input will come from and how easy it will be to plug in your devices. If you want to run electronics in the main cabin of your car, then a trunk installation may not be convenient. On the other hand, that may be a great location under other circumstances.

It’s also important to consider heat dissipation. Inverters typically come with built-in fans, and a lot of them are designed as big heat sinks. If your inverter has a fan, find an installation location that won't block the airflow.


Temporary Car Inverter Installation

The easiest way to install a car power inverter is to plug it into a 12V accessory outlet. These outlets have traditionally been used for cigarette lighters, but many new vehicles eschew the lighter entirely. Some vehicles also have multiple outlets, or remote outlets, besides the one that's in the center console.

Since the cigarette lighter, or 12V outlet, is tied into a circuit that typically includes other electronics, there is a limit to how much power you can draw from it. For that reason, many cigarette lighter inverters artificially limit the available wattage when using this type of connection.

That's a major downside if you want to use power-hungry devices, but it's a trade-off for how easy it is to plug an inverter into an accessory outlet and use it. These plug-in inverters are great for laptops and other small electronic devices. Some even include built-in USB receptacles for powering cellphones, GPS units, and anything else that uses a standard USB connection.

For more power-intensive equipment and permanent installations, you'll need to do some wiring.

Permanent Car Inverter Installation: In-Line Fuse

One way you can permanently wire a car inverter is to tap into the power wire or go straight to the battery. If you opt to go straight to the battery, you'll have to find where the wiring harness passes through the firewall and fish the power wire through.

After you tap into the battery, an in-line fuse will ensure that nothing melts down or catches on fire when you switch on the inverter.

If you tap into an existing power wire, you could easily end up with the same set of problems you deal with in plugging into a cigarette lighter socket. Therefore, you must have a good understanding of what's on a circuit before you tap into it.

Adding a significant power load to an existing power wire and circuit can spell trouble, which is why going straight to the fuse box is a good idea if you don't want to fish a wire through the firewall.

In-line fuse.

Andy Arthur / CC by 2.0 / Flickr

Permanent Car Inverter Installation: Fuse Box

Some fuse boxes are located under the hood, but many are conveniently found somewhere under the dash. That makes the fuse box a good place to wire up a car power inverter if you aren't interested in fishing wires through the firewall.

If the fuse box has any empty slots, that's usually a good place to tap into. You can either install a new fuse in the empty slot and tap into the back of the fuse box or use a spade connector to plug into the front of the fuse box.

Adding a new fuse looks cleaner, but plugging in a spade connector is a little easier. However, you'll need to add an in-line fuse if you choose to go that route. If you don't include a fuse somewhere in the circuit, you could end up with a fire inside your vehicle should anything go wrong.

When getting power from the fuse box, you should check whether the connection always has power or only power when the ignition is on. If you want to plug into your inverter at all times, you'll want a connection that is always hot, while using one that's only hot when the ignition is on will prevent your battery from accidentally going dead.

Once you've decided how to wire the inverter into the vehicle's electrical system, you may also want to consider whether you need a pure sine wave inverter. While most applications don't require the extra expense, some electronics can be damaged by a modified sine wave inverter.

A fuse box.