The cigarette lighter receptacle in an automobile was initially designed to power a coil heater or electrically-heated lighter for cigarettes. It was later used as a de-facto standard DC connector to supply electrical power for portable accessories used in or near an automobile.
Currently, automobiles may provide several 12V receptacles that are intended primarily to operate accessories and are not to be used with a cigarette lighter.
Parts:
The lighter assembly has two parts:
- the receptacle (socket)
- the lighter body
The Socket:
For the 12-volt socket, 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).
It has a bimetallic strip which engages and disengages the lighter.
A bimetallic strip is used to convert a temperature change into mechanical displacement. The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases brass instead of copper. The strips are joined together throughout their length by riveting, brazing or welding. The different expansions force the flat strip to bend one way if heated, and in the opposite direction if cooled below its initial temperature. The metal with the higher coefficient of thermal expansion is on the outer side of the curve when the strip is heated and on the inner side when cooled.
The sideways displacement of the strip is much larger than the small lengthways expansion in either of the two metals. This effect is used in a range of mechanical and electrical devices. In some applications the bimetal strip is used in the flat form. In others, it is wrapped into a coil for compactness. The greater length of the coiled version gives improved sensitivity.
Diagram of a bimetallic strip showing how the difference in thermal expansion in the two metals leads to a much larger sideways displacement of the strip:
A bimetallic coil from a thermometer reacts to the heat from a lighter, by uncoiling and then coiling back up when the lighter is removed:
The lighter body:
It can be either plastic or metallic which has a heating element which is attached to the spring loaded handle.
The heating element is made up of nichrome wire.
Nichrome is a trademark for a non-magnetic alloy of nickel, chromium, and often iron, usually used as a resistance wire, produced by the Driver-Harris Company. A common alloy is 80% nickel and 20% chromium, by mass, but there are many others to accommodate various applications. It is silvery-grey in colour, is corrosion-resistant, and has a high melting point of about 1400 °C (2552 °F). Due to its relatively high electrical resistivity and resistance to oxidation at high temperatures, it is widely used in electric heating elements. Typically, Nichrome is wound in coils to a certain electrical resistance, and current is passed through to produce heat.
How does it work?
Cigarette lighters work on a principle of mechanical thermostatic action (that's scientific notation for "popping out when it's hot").
The traditional lighter is a metal or plastic cylinder containing a thin coil of nichrome wire, through which high current (~10 amperes) passes when the device is activated, usually by pushing it into the socket as though it were a button. When pushed in, the lighter is held against the force of a spring by a hook attached to a bi-metallic strip.[4] The heating element becomes glowing orange hot in seconds, causing the bimetallic strip to bend and unhook the mechanism, and the handle pops out. If the lighter is then promptly removed from its socket, it is capable of setting cigarettes, cigars and tinder (among other things) on fire.
The circuit is usually protected by a 20 ampere fuse.
Waterproof sockets are available for offroading vehicles and bikes. They are basically the same sockets but have a lid on top which has a rubber lining which snaps shut causing a waterproof seal. This doesn't allow water to enter into the socket. However, the connections at the back must be sealed using a silicone glue. These are available on ebay.
Troubleshooting:
- Cigarette charger not working:
99% of the times, it's a blown fuse or one of the electrical connections at the back have come loose. Check the fuse first and if it's fine, check the electrical connections at the back. Disconnect the battery first.
- Fuse & connections are fine, still it doesn't work:
this could be due to corrosion. Disconnect the battery, spray some anti rust agent (eg. WD40) and let it evaporate. Connect the battery and check.
- Still not working
Check the complete electrical line from the battery to the lighter using a continuity tester. Check if the earthing contacts are not corroded. Try replacing it with a new socket otherwise.
- My charger is working, but the heating element doesn't get hot
This could be due to the coils inside getting clogged with rust/ash/dirt. Clean first with a wire brush carefully and then with either hot water or WD40 and wait till it dries and try again. You can also use a earbud dipped in isopropyl alcohol and clean the coils (again wait to dry before using). If it still doesn't work, maybe the nichrome wire has broken inside and the circuit is not complete. Replace the unit then.
- Heating element doesn't pop out (heats up though).
This could be either due to the spring in the handle going soft or the bimetallic wire going bad. In either case, replace it. An overheated wire may blow a fuse.
Cleaning the socket:
Disconnect the negative terminal of the battery and spray WD40. Wait to dry completely and then reattach the terminal.
As a rule, if there is too much rust, better replace the entire assembly rather than trying to clean. it's not very expensive and the risk of shorting the cars electricals is higher if you don't replace.
Sources:
http://en.wikipedia.org/wiki/Car_cigarette_lighter http://en.wikipedia.org/wiki/Nichrome http://en.wikipedia.org/wiki/Bi-metallic_strip http://uk.answers.yahoo.com/question...0014336AATe0xe http://www.onlineautorepair.net/1/po...-problems.html http://www.carscorals.com/carsfaqs/h...ter-38829.html