Installing a Power Inverter in a Car or Truck

install power inverter in car
The easiest way to install an inverter in your car is to plug it into the cigarette lighter socket, but that option has drawbacks. Alan Levine / Flickr (Creative Commons 2.0)

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 your car or truck and turn it into the type of electricity that's available from the electrical outlets in your home.

This can be tremendously useful in a car, truck, or RV, because it vastly increases the types of electronics that you can use on the road. Since nearly all of your 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 especially useful to salesmen, truckers, and other people who spend a lot of time in their vehicles, but car power inverter can also be a lifesaver on a long road trip, camping excursion and in a lot of other circumstances.

Important: Inverters are useful, but they have limitations. The amount of power that an inverter can provide is limited by the design of the inverter itself and the method that you use to connect it to your vehicle's electrical system. Some equipment and appliances, like refrigerators, use a huge 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

car inverter
A car power inverter is the only way to use a lot of gadgets when you're away from home, but there are a few things to consider before you buy and install one. Image courtesy of Andy Arthur, via Flickr (Creative Commons 2.0)

If you’re thinking about installing a car power inverter, there are a three main considerations that you’ll need to think about before pulling the trigger:

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

The first, and most important, consideration is how much power your device requires, since that will dictate the size of your 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

high performance alternator
If your wattage needs are high enough, you may need a high output alternator. Image courtesy of Jason Young, via Flickr (Creative Commons 2.0)

Portable Device Power Requirements

In order 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, let’s say that you've 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 terribly 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 indicates that it draws 4A at 110V, so if you wanted to play an Xbox 360 in your car, you'd take those numbers and plug them into the above referenced formula:

110V x 4A = 440W

In this case, you would 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 as opposed to 440W peak. You’ll also need a bigger inverter if you want to plug anything in 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 your alternator is capable of putting out. You can sometimes find this number by looking at your 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) will be able to test the real-world power output and consumption of your car.

Most alternators are capable of putting out more watts than the stock electronics consume, and they can typically handle additional electronics like amplifiers, but 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 that has 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 the engine is shut off, 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

Location is a vital consideration due to ease-of-use and wiring concerns. Image courtesy of Andy Arthur, via Flickr (Creative Commons 2.0)

The first step in installing a car power inverter is to decide where you’re going 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, it’s important to think about both where your power input is going to 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 actually designed as big heat sinks. If your inverter has a fan, you’ll have to find an installation location where the airflow won’t be blocked.

Temporary Car Inverter Installation

If you don't have huge wattage requirements, a temporary installation is a good choice. Image courtesy of Brett Levin, via Flickr (Creative Commons 2.0)

The easiest way to install a car power inverter is to simply plug it into a 12V accessory outlet. These outlets have traditionally been used for cigarette lighters, but a lot of new vehicles eschew the lighter entirely. Some vehicles also have multiple outlets, or remote outlets, in addition to the one that’s located 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, a lot of 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 just plug an inverter into an accessory outlet and use it. These plug-in inverters are great for laptops and other small electronic devices. Some of them 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

In in-line fuse is essential if you pull power straight from the battery. Image courtesy of Andy Arthur, via Flickr (Creative Commons 2.0)

One way to permanently wire a car inverter is to either tap into 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 your own 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. This is why it’s vital that you have a good understanding of what’s on any given 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.

 

Permanent Car Inverter Installation: Fuse Box

Using a blank slot in your fuse box is the cleanest way to wire a car inverter, but it isn't the easiest route. Image courtesy of Henrique Pinto, via Flickr (Creative Commons 2.0)

Some fuse boxes are located under the hood, but a lot of them 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 your 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 directly into the front of the fuse box.

Adding a new fuse looks cleaner, but plugging in a spade connector is a littler easier. However, you’ll need to add an in-line fuse if you do 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 also check to see whether the connection always has power, or if it only has power when the ignition is on. If you want to be able 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 you're going to wire your inverter into your vehicle's electrical system, you may also want to consider whether or not you need a pure sine wave inverter. While most applications don't require the extra expense, there are some electronics that can be damaged by a modified sine wave inverter.