The cigarette lighter receptacle (also called a cigar lighter receptacle or cigar lighter socket) in an automobile was initially designed to power an electrically heated cigarette lighter, but became a de facto standard DC connector to supply electrical power for portable accessories used in or near an automobile. While the cigarette lighter receptacle is a common feature of automobiles and trucks, as a DC power connector it has the disadvantages of bulkiness, relatively low current rating, and poor contact reliability. Examples of devices that can be operated from a cigarette lighter receptacle include lights, fans, beverage heating devices, and small motorized tools such as air compressors for inflating tires. Many portable electronic devices such as music players or mobile telephones use a cigarette lighter receptacle to recharge their internal batteries or to directly operate from the vehicle electrical system. Adapters for electronic devices may change voltage to be compatible with the supplied device. Devices that require alternating-current mains electricity can be operated with a plug-in inverter. Automobiles may provide several 12 V receptacles that are intended only to operate electrical accessories, and which cannot be used with a cigarette lighter. Car manufacturers may offer a cigarette lighter only as an optional extra-cost accessory. Usually, only one 12 V receptacle near the driver will be able to accommodate an actual cigarette lighter, with other receptacles designated as "12 V auxiliary power outlets" which are not physically able to power a lighter.
The electrical cigar-lighter was invented and patented in the early 1880s by the German inventor Friedrich Wilhelm Schindler. In the 1890s, these tools were sold as electrical cigar lighters (Cigarrenanzünder), and later as Zigarrenanzünder in the major German warehouse catalogues. Probably in the 1920s they were renamed "cigarette lighters", as cigarettes overtook cigars in sales.
In 1921, the Morris U.S. Patent 1,376,154 was issued for a so-called "wireless" or "cordless" lighter with a removable element. The igniter was heated in the socket and then manually removed for use after an appropriate time interval.
In the United States, cigarette lighters started appearing as standard equipment in automobiles in 1925–1926.
In 1928, the Connecticut Automotive Specialty Company (Casco) in Bridgeport patented its version of an automotive cigarette lighter, which used a cord and reel. In the reel-type lighters, the igniter unit was connected with a source of current by a cable which was wound on a spring drum so that the igniter unit and cable could be withdrawn from the socket and be used for lighting a cigar or cigarette. As the removable plug was returned to the socket, the wires were reeled back into it. The circuit was closed either by pressing a button or removing the igniter from its socket.
The modern "automatic" removable automotive V-Coil lighter was developed by Casco in 1956, for which it received U.S. Patent 2,959,664, issued in 1960.
The lighter is a metal or plastic cylinder containing a thin flat coil of nichrome metal strip, through which high current (~10 amperes) passes when the device is activated, usually by pushing it into the socket as though it were a push-button. When pushed in, the lighter is held against the force of a spring by a clip attached to a bi-metallic strip. The heating element glows orange hot in seconds, causing the bi-metallic strip to bend and release the mechanism, and the handle pops out, eliminating the need for the user to time the heating operation. If the lighter is then promptly removed from its socket, it can light a cigarette, cigar, or tinder.
In newer cars, the socket is equipped with a plastic cover without the lighter heating element. However, the socket has been repurposed and continues to be used to power consumer electronics in vehicles. Often, a vehicle may come with several outlets for convenience, some in the rear passenger area of the vehicle or even the cargo area, for such purposes as powering portable GPS devices, recharging mobile phones, or powering a tire inflator, a vacuum cleaner or a thermoelectric cooler. These outlets usually have a plastic cap tethered to them, and are usually labeled as being only for DC power, because they are not intended to withstand the heat produced by an electrical cigarette lighter.
The use of cigarette lighter receptacles to supply 12 volt DC power is a classic example of backward compatibility to a de facto standard. The connector falls far short of ideal, being physically large and awkward to use, while being less reliable than alternatives such as the Anderson Powerpole connector (which is often used by amateur radio enthusiasts in mobile operations). Nevertheless, cigarette lighter receptacles are in widespread use, and all but the lowest-cost cars, trucks, RVs, and even boats can be expected to have at least one such receptacle. Portable cigarette lighter receptacles attached to cables and alligator clips for connection directly to car batteries are available for temporary use. In newer vehicles, one or more USB connectors may also be provided, as a source of modest amounts of 5 volt DC power, but even in these situations a cigarette lighter receptacle is provided for 12 volt DC power, and for applications that require higher current.
Standardized 12 volt DC automobile plugs are defined in the United States by UL Standard 2089 regarding vehicle battery adapters. This standard covers plugs and cord sets that insert into cigarette lighter receptacles. In Europe, 12 volt plugs and sockets are not specially regulated, and do not require approvals for the CE mark.
The male plug is sometimes used to feed power into a vehicle to recharge its battery. For instance, portable solar battery maintainers generally connect to a vehicle's battery in this manner. Trickle chargers also sometimes connect in this way, eliminating the need to leave a vehicle's hood open, as well as eliminating the possibility of reversed polarity. In some models, the cigarette lighter outlet is not powered when the ignition key is removed and charging is not possible.
The sockets and mating plugs are defined in the ANSI/SAE J563 specification. For the 12 volt systems, the "contact point", which is the center part of the plug when viewed end-on, carries the positive voltage, whereas the "can" part, which is the outer part of the connector, carries the negative voltage (which is the "ground" connection for most automobiles, which have a negative ground electrical system).
12 volt auto connectors are made to comply with a standard by Underwriters Laboratories for safety. UL2089 was developed to cover the requirements for portable adapters rated 24 V DC or less that are intended to be supplied from the battery powered electrical system of a vehicle. Products covered by the standard include cord assemblies of a plug that mates with the standard cigarette receptacle found in automobiles.
Plugs often include a pilot light LED indicator to indicate that electrical power is connected. Optionally, the plug may be equipped with an internal fuse for electrical safety, usually rated at 10 amps or less. In some designs, the tip of the plug may be unscrewed to reveal a cylindrical glass fuse; other variants may use a newer blade-type fuse inserted into the side or back of the plug.
Since the cigarette lighter socket was originally designed only to heat a cigarette lighter, repurposing these sockets as generic power connectors can lead to many problems. In addition to the issues with partially-compatible physical dimensions, the plugs can vibrate out of the socket under normal driving conditions, owing to poor retention. Also, there have been reports of melted plug tips due to poor contact and heat generation from ohmic resistance. Non-vehicular use in stationary settings may avoid vibration problems when used as an alternative to 120 volt AC outlets, but low-quality connectors may still develop high resistance or intermittent contact.
A second problem is that nominally "twelve-volt" power in cars fluctuates widely. The actual voltage will be approximately 12.5 volts when dormant (less in cold conditions), approximately 14.5 volts when the engine and the alternator/generator are operating (more when cold), and may briefly drop as low as 5–6 volts during engine start. When used, DC to DC converters will usually compensate for small fluctuations, but reliable power may not be available without an independent battery-powered uninterruptible power supply.
Rarely, more extreme cases of voltage fluctuation can occur when the car battery is disconnected while the engine is running, or when the car receives a jump start. When the battery is disconnected while the engine is running, a load dump transient can produce very high voltages as the built in voltage regulator has been controlling the alternator field current to charge the vehicle battery and although it will attempt to reduce the field current to keep the output voltage constant, the field winding is highly inductive and setting the current to its new value takes several hundred milliseconds, during which the alternator output voltage will exceed its intended value. The load dump transient may also ruin the diodes in the alternator by exceeding their breakdown voltage. A car receiving a jump start from a truck may be subject to a 24 V electrical system used in some vehicles. Also, a "double battery jump-start" is performed by some tow truck drivers in cold climates.
Equipment intended to be powered by the receptacle needs to account for intermittent contact, and voltages outside the nominal 12 V DC, such as maximum voltage 9–16 V continuously, or maximum voltage of 20 V lasting 1 hour, 24 V lasting 1 minute, and 40 V lasting 400 ms. An example of protection component ratings tolerance is +50 to −60 V DC. Robust equipment must tolerate temperatures varying between −40 and +85 °C (−40 and 185 °F), plus possible high humidity and condensation of water.