12V Adapters for Your Car

When Going from DC to AC and Back Again Isn't the Best Idea

12v adapter
Check your power adapter to see what input voltage and amperage your device needs. Image courtesy of Sean Dreilinger, via Flickr (Creative Commons 2.0)

Although you can plug virtually any electronic device into an inverter, that isn't always the most elegant (or best) solution. Some devices won't run correctly on an inexpensive modified sine wave inverter, some delicate medical equipment can actually be damaged, and some electronics run much more efficiently if you cut the inverter out of the equation entirely. We're talking about electronics that run on DC power that's provided by a rectifier, which you may know as an "AC/DC adapter," "wall wart" or by other equally colorful names. These devices can be powered in your car by a 12v adapter plugged into a 12v socket (either a cigarette lighter or an accessory outlet), and there are a few reasons that you might want to consider going that way.

Ditching the Inverter

Although it's easy to just plug regular AC wall adapter for your laptop or cell phone into a car power inverter and call it good, it's actually somewhat wasteful. Since no inverter is 100 percent efficient, there is always some loss of energy when converting from 12v DC to 110v AC. When you plug a DC rectifier into your inverter, you're actually just reversing the work that the inverter just did, and losing even more energy in the process.

This might not seem like a big deal either way, but it all depends on how you use electronics in your car, truck, or RV. If you only plug in when the engine is running, then the only place you're going to feel the pain is at the pump (i.e. the additional power usage is going to result in some decrease in fuel efficiency.) However, a 50 percent loss in efficiency can make a huge difference when you're camping or otherwise using your electronics when your vehicle is parked. After all, if you're sucking twice the power out of your battery that you need to, you're going to run it dead twice as fast.

Finding the Right 12v Adapters

Although any device that uses a AC/DC rectifier can use a 12v DC adapter, it isn't always easy or intuitive to find the right one. If the manufacturer doesn't offer one, then there are three factors that you need to consider:plug size/style output voltage output amperage

12v Adapter Plugs

In terms of 12v adapter plugs, there are a few size characteristics that determine whether one is going to work with your device. The outer diameter of the barrel, inner diameter of the barrel, length of the barrel, and thickness of the pin all affect whether a plug will fit and make proper electrical contact.

Universal adapters typically come with an assortment of plug tips, and they often list which devices that they work with. If you're unable to find one that specifically mentions your device, then you may have to take some measurements and do a little research to find the right one.

12v Adapter Voltage and Amperage

If you look at the AC/DC adapter or wall wart that came with your device, you should be able to find its voltage and amperage outputs. In order to find a 12v adapter that will work with your device, you'll have to look for one that puts out the same voltage and amperage. In some cases, you may be working with a range instead of a hard number. Universal adapters, in particular, are typically capable of outputting a range of voltages and amperages in order to offer the widest coverage.

A Simpler Solution

Of course, both of these issues are moot if you're dealing with a device that uses the USB standard. Most modern cell phones and tablets use this standard, as do other devices like GPS navigation units. The general rule of thumb is that if it has a mini or micro USB port, then you can probably power it with just about any 12v USB adapter. However, in practice, things are a little more complex than that.