[Tejas@perioimpl]

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

[SAS]

Awesome article. This is like a whitepaper on the humble cigarette lighter socket. One question: can you put a list of typically what is the maximum load one should put on it?

Reason I ask is I have a belkin DC-AC inverter which provides 200W continuous AC current. That would mean around 18amps load on the DC current at a full 200W AC load with around 10% losses for converting between DC to AC.

[MileCruncher]

Originally Posted by Tejas@perioimpl

Currently, automobiles may provide several 12V receptacles that are intended primarily to operate accessories and are not to be used with a cigarette lighter.

Thats a very good article but may I ask why cigarette lighters shouldn't be used on them now?

Cheers

[SS-Traveller]

Originally Posted by MileCruncher

...why cigarette lighters shouldn't be used on them now?

Because some of the sockets do not have the bimetallic strip built into them to eject the lighter after adequately heating them up, and have 12V DC marked on them - the connection is a direct connection, and a cigarette lighter inserted into the socket would overheat and burn out the surrounding plastic. Usually found in sockets that are built into the boot / rear luggage space.

[Tejas@perioimpl]

Originally Posted by SAS

Awesome article. This is like a whitepaper on the humble cigarette lighter socket. One question: can you put a list of typically what is the maximum load one should put on it?

Reason I ask is I have a belkin DC-AC inverter which provides 200W continuous AC current. That would mean around 18amps load on the DC current at a full 200W AC load with around 10% losses for converting between DC to AC.

I'm not very sure frankly.

I guess you need to make sure your alternator is in good shape and your wiring from the battery to the socket is of a excellent quality.

Your battery life may shorten due to continuous use. However, this last part I'm speculating and am not 100% sure.

Will do a bit of research and put up a list.

See this superb article:

http://ponderingfools.blogspot.com/2...rt-2-of-4.html

[SS-Traveller]

Originally Posted by SAS

One question: can you put a list of typically what is the maximum load one should put on it?
Reason I ask is I have a belkin DC-AC inverter which provides 200W continuous AC current. That would mean around 18amps load on the DC current at a full 200W AC load...

Missed this query earlier.

The usual fuse rating protecting the cigarette lighter socket is a 15A or 20A fuse. The Belkin has a 20A fuse protecting it (my own Belkin's fuse has been replaced with a 10A fuse, while the car's wiring circuit has a 15A fuse as original - I'd rather the more accessible fuse on the Belkin blew, not the one in a little box hidden away below the steering under a plastic cover). Given the fuse ratings, the max load is obviously limited by this, i.e. 15A or 20A.

At full load on the Belkin (~20A), the wiring supplying the cigarette lighter socket is likely to heat up (remember, it's designed for short term use, perhaps 30 sec, before the lighter drawing about 10A pops out and breaks the circuit) - my recommendation therefore is to avoid connecting more than 100W AC into it. For other equiipment too, like car vacuum cleaners and tyre inflators, do not draw >10A on a continuous basis - give a break after 1-2 minutes.

[Sutripta]

^^^
Two points.
If there is no separate relay for Acc, that current is going through your ignition switch. If so, I'd be careful. Check your cars electrical diagram.

There are two sizes, the Jap and the US one, which I think differ by 1 mm. Causes a lot of problems with adapters popping out.

Regards
Sutripta

[SAS]

Originally Posted by SS-Traveller

Missed this query earlier.

The usual fuse rating protecting the cigarette lighter socket is a 15A or 20A fuse. The Belkin has a 20A fuse protecting it (my own Belkin's fuse has been replaced with a 10A fuse, while the car's wiring circuit has a 15A fuse as original - I'd rather the more accessible fuse on the Belkin blew, not the one in a little box hidden away below the steering under a plastic cover). Given the fuse ratings, the max load is obviously limited by this, i.e. 15A or 20A.

At full load on the Belkin (~20A), the wiring supplying the cigarette lighter socket is likely to heat up (remember, it's designed for short term use, perhaps 30 sec, before the lighter drawing about 10A pops out and breaks the circuit) - my recommendation therefore is to avoid connecting more than 100W AC into it. For other equiipment too, like car vacuum cleaners and tyre inflators, do not draw >10A on a continuous basis - give a break after 1-2 minutes.

True. Typically I use it only for powering my laptop which consumes around 65W or directly plug my orbital polisher which consumes around 60W. Then too it gets warm after a period. Reason I asked was whether anybody had experience of running higher loads..

[pganapathy]

Sorry to bump up an old thread.

I want to install a cigarette lighter in my Alto, principally for use as a DC unit for charging my phone, my iTrip etc. I am happy to pay more but I want a high quality one as am not willing to damage an iPhone, iPod, psp etc for saving a few bucks. Please let me know what brand charger and where I can get it in Bangalore. I don't mind traveling as long as I can be sure of a genuine high quality unit.

[carboy]

I have used the 12V socket in Swift few years back to power a walkman. But haven't used it after that. Today I tried plugging a charger on it and it didn't seem to power on. I don't think I will be able to check the fuse connectors myself - so what was wondering what kind of a shop do I take it to get it repaired? Do I have to take it to a Maruti ASS or can some local chap check this & fix this?

[P76]

@pganapathy, Xenos Cigarette lighters are the best quality available today. There used to be very good quality Stanley Japanese Cigarette lighters. Now only Taiwan/China made lighters are available here, and they are not worth, the sockets are not up to standards, and charging equipments tend to get disconnected due to vibrations. Xenos is pretty good.

[Eddy]

Originally Posted by carboy

I don't think I will be able to check the fuse connectors myself - so what was wondering what kind of a shop do I take it to get it repaired? Do I have to take it to a Maruti ASS or can some local chap check this & fix this?

Any roadside electrician worth his salt should be able to change the fuse.

However, make sure that its the charger that is at fault maybe by plugging it somewhere else or using a different charger in your car.

[carboy]

Originally Posted by Eddy

Any roadside electrician worth his salt should be able to change the fuse.

However, make sure that its the charger that is at fault maybe by plugging it somewhere else or using a different charger in your car.

I think you have misunderstood what I have said. I think the problem is *not* with the charger. I think the problem is with the 12 V Socket in the car. I was asking where to take the car to get the 12 V socket fixed?

[Eddy]

Originally Posted by carboy

I think you have misunderstood what I have said. I think the problem is *not* with the charger. I think the problem is with the 12 V Socket in the car. I was asking where to take the car to get the 12 V socket fixed?

I understood exactly. The roadside mechanic will replace the fuse for the cigarette lighter.

But before approaching him, and asking him to fiddle around, just ensure that its the lighter which is faulty, and not the charger - i.e. is the charger working on some other socket ?

[SS-Traveller]

Originally Posted by carboy

I think the problem is with the 12 V Socket in the car.

Commonest problem with the Swift 12V socket (and in whichever car it's mounted vertically - the Ford Fusion is another) is dust accumulation at the base, effectively insulating the +ve terminal (the central spot where the 'nose' of the charger contacts). Disconnect the battery and scrape & blow the bottom of the socket clean with a screwdriver or similar.

Reconnect the battery and your socket should work again if the fuse is intact. If not, any auto electrician will replace the fuse in 5 min. Taking it to MASS involves too much time for too minor a bit of work IMHO.