The 12V socket, also known variously as a car cigarette lighter or 12V auxiliary power outlet, is the primary method by which power is delivered to portable electronics in cars, trucks, recreational vehicles, boats, and in a handful of other contexts. While these sockets were originally designed to heat up cigarette lighters, they quickly gained popularity as a de facto automotive electrical outlet.
Today it's possible to power anything from a cutting-edge phone or tablet to a tire compressor with the same exact socket that was once used only as a car cigarette lighter.
Some vehicles come with multiple sockets for the express purpose of powering multiple accessory devices, although it is uncommon for more than one to be capable of accepting a cigarette lighter.
Accordingly, the specifications for these power sockets that are contained in ANSI/SAE J563 include two variants: one that works with cigarette lighters and one that doesn't. If you've ever tried putting a cigarette lighter into a cigarette lighter socket only for it to fall right back out, that's why.
The History of Automotive Accessory Power
When the first automobiles hit the road, the idea of an automotive electrical system didn't exist yet. In fact, the first cars didn't even include electrical systems of any kind. These cars had engines that relied on magnetos to provide a spark, just like your lawnmower probably does today, so no battery was necessary. When lighting was included at all, it was by way of gas or kerosene lamp, so no electrical system was required there either.
When automotive electrical systems finally did arrive, they used DC generators. These generators, unlike modern alternators, didn't require any voltage input to operate. They were belt-driven, just like modern alternators, and they provided the necessary DC power to run accessories like lights.
The next innovation was the addition of lead-acid batteries to store electricity and provide a source when the engine wasn't running. With this addition, it suddenly became possible to add other accessories that we take for granted today, like electric starter motors.
Although early electrical systems that included both a DC generator and a lead-acid battery technically made electrical accessories possible, the widely variable voltage produced by these generators created issues. Mechanical devices were used to regulate the voltage, but modern automotive electrical systems didn't really arrive until the introduction of alternators.
Unlike generators, the alternators found in modern cars and trucks produce alternating current, which is converted into direct current to charge the battery and provide accessory power. Although this type of electrical system still doesn't provide entirely uniform voltage, the voltage output does remain relatively steady regardless of how fast the alternator is spinning, which was a key factor in the rise of the car cigarette lighter as a de facto DC power outlet.
The Smoking Gun
Although people had been powering accessory devices with their automotive electrical systems ever since automotive electrical systems were first invented, accessories had to be wired in manually. The appearance of a 12V automotive electrical socket was almost accidental, as it was co-opted from a completely different initial purpose.Tom Blaha / Creative Commons / CC BY-SA 3.0
Cigarette lighters, along with lights and radios, were among the first accessories to take advantage of early automotive electrical systems, and they started to appear as OEM options by about 1925.
These early cigarette lighters used a “coil and reel” system, but it was the so-called “wireless” cigarette lighter that would eventually become the de facto automotive and marine power socket.
These “wireless” car cigarette lighters consist of two parts: a cylindrical receptacle that's typically located in the dash of a car and a removable plug. The receptacle is connected to power and ground, and the plug contains a coiled, bi-metallic strip.
When the plug is pushed into the receptacle, the coiled strip completes an electrical circuit and subsequently becomes red hot. When the plug is removed from the receptacle, the red-hot coil can be used to light a cigar or cigarette.
Introducing the 12V Socket
Although they weren't originally designed with the purpose of supplying power to accessories, car cigarette lighters provided an opportunity that was simply too good to pass up. Since the actual lighter portion was removable once the coil-and-reel version fell out of use, the receptacle itself provided easy access to power and ground.
That easy access to power and ground allowed for the development of a power plug that could be inserted and removed with no need to permanently wire an accessory into the electrical system of a car.
The ANSI/SAE J563 specification was developed to ensure compatibility between cigarette lighter receptacles and 12V power plugs made by different manufacturers. According to the specification, the cylinder portion of a 12V socket has to be connected to battery negative, which is ground in most automotive systems, while the center contact point is connected to battery positive.
With the ANSI/SAW standard in place, third parties were able to design and introduce a massive range of devices, from tire pumps to hairdryers, that were designed to draw power from cigarette lighter sockets.
Problems With Using an Automotive 12v Socket
Since car cigarette lighters weren't originally intended for use as accessory sockets, there are a few inherent issues with using them in that capacity. Accordingly, devices that are designed to use a 12V socket have to be capable of working around these shortcomings.
The biggest issue with using a car cigarette lighter receptacle as a 12V socket is the inner diameter and depth of the receptacle itself. Since there is some variation in the size of these receptacles, which are sometimes referred to as cans, 12V power plugs typically have spring-loaded contacts.
By using spring-loaded contacts instead of fixed contacts, 12V power plugs are able to maintain electrical contact within a fairly generous range of tolerances. However, it also means that this type of plug may lose electrical contact from time to time.Tom Blaha / Creative Commons / CC BY-SA 3.0
Another issue with using an automotive 12V socket is related to the way that automotive electrical systems work. Although modern alternators are capable of maintaining a relatively uniform voltage output, the normal operation does allow for a range of output voltages.
With that in mind, all automotive electrical accessories have to be capable of running on roughly 9-14V DC. In many cases, a built-in DC-to-DC converter is used to convert the variable input voltage to a steady output voltage on the fly.
Could the Car Cigarette Lighter Be Replaced?
Although smoking isn't as popular as it once was, car cigarette lighters are unlikely to go anywhere anytime soon. Some cars have shipped over the years without cigarette lighters, and others have included an accessory socket with a blank plug instead of a lighter, but the idea of ditching the car cigarette lighter altogether still hasn't caught on.
The issue is that even if people aren't using car cigarette lighters for the purpose that they were originally designed, far too many portable devices rely on the technology as a de facto power source to ditch it altogether.
USB may prove an acceptable replacement because so many portable devices use USB for data and power. It's feasible that USB ports could eventually overtake cigarette lighter and accessory sockets in cars, but it's so easy to simply plug a USB charger into a car cigarette lighter that automotive manufacturers may hesitate to fully embrace that type of change.