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car cigar lighter extention


CeeJay

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On the way back down from UK yesterday I stopped and bought an extension for the cigar lighter socket to enable us to use the car kettle in a more convenient place.

After about 3 minutes I could smell burning and saw smoke coming from the new extension!!!!

Quickly pulled it out and disposed of it but am wondering what the cause was. The packaging said it was for 12v or 24v and I am wondering if there was a switch or something for just 12v.

We normally use the kettle quite safely and indeed after this incident it was plugged into another socket with no problem.

Any ideas?
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I would be very surprised if the extension cable was rated for anything near the current that a car kettle would pull, someone will confirm what the fuse is on a mdern vehicle accessory socket but they have huge cables running to them those on an arc welder, I once nearly burnt my tent down when using an 12v compressor to pump up a matelas and the motor seized, the accessory fuse did not blow but the pump cable went up in smoke and melted through my groundsheet.

The 12v 24V thing is a red herring, its the current capacity of the lead which is in question, if the smoke was only coming from one end of the lead it could be a bad connection, my money is that the lead has undersized cables and should only be used with low wattage devices, I would not trust a car kettle even when plugged directly in to the socket, I would Watch it like a hawk, my advice is dont use any extension lead.

 

There is a good reason why the lead on your kettle is so short that you cannot use it in a convenient position [I]

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Whenever you are going to plug something in to a car socket you need to check the spec of the socket and the power requirement of the appliance. For things like kettles/car heaters and fans you would need a heavy duty extension socket which will have thicker wires and the appropriate fuse. The typical extension you buy in garages for a few euros is designed for phone chargers and sat navs and things like that.
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What is always forgotten, ignored or never learned, is Ohms Law.

A device on mains supply rated at say 2,000 Watts (e.g. twin bar electric fire) draws 2,000 ÷ by 230 Volts: = 8.696 Amperes (Amps) of current.

Now if the supply is just 12 volts, the amperage becomes 166.66 Amps! [:'(]

I have looked at the tech specs of some car kettles and the best seem to operate at 120 Watts. Now on 12 volts, that is 10 Amperes!

No way I would trust a fag lighter on a car's dash, for ten amps, since the connections are loose and sloppy and then this causes what is called High Contact Point Resistance, which again zooms up the amps. If you look at the wiring loom, the size of the wire feeding into the lighter is rather light.

The only safe way to use such a device, would be to wire in a dedicated - fused - extra feed circuit, with a very tight and top quality plug and socket, rated at minimum 15 Amps @ 12 volts DC.

The other consideration is car kettles take circa 15 to 20 minutes (or more) to raise the water from ambient to 100 deg C. Thus the feed will become hotter and hotter if the potential is too low.

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[quote user="Gluestick"]
No way I would trust a fag lighter on a car's dash, for ten amps, since the connections are loose and sloppy and then this causes what is called High Contact Point Resistance, which again zooms up the amps. If you look at the wiring loom, the size of the wire feeding into the lighter is rather light.

[/quote]

 

Actually the opposite is true, the additional resistance(s) will reduce the current flowing (ampères) but  will cause heat.

 

I think the wiring on modern cars to the accessory sockets is rated for 15 amps, the same being true for the Hella accessory sockets, the socket in the rear of my Ford Galaxy presumably for fridges etc was fed by the thickest wire in the whole wiring loom, but as you say the old design of the cig lighter socket gives a very dodgy contact, even worse if you use a Hella plug with the red adaptor which is fitted to most 12v kettles and fridges, it partially dislodges the first time the car goes over a bump, if the centre pin is ground back in length the contact is much more secure but may in turn give problems when used in a Hella socket.

 

Hopefully car makers in the future will dispense completely with the lighter and ashtrays and just fit proper Hella accessory sockets or create a new better standard.

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Just a small correction Gluestik.

"since the connections are loose and sloppy and then this causes what is

called High Contact Point Resistance, which again zooms up the amps."

The higher the resistance with a constant current + lower amperage, but the point of that high resistance is like yet another heating element and will get hot and burn if left long enough even although the current is lower.

But I agree that it should be a big no no to use a kettle on a cigar lighter socket unless the rating is higher than the kettle will take and the less sets of connections the better. Most cars these days have a 12v socket and if you check in the handbook it will/should give the ratiing

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On checking the rating for said kettle I found that it is 12/24v x 170watts.

On checking the small print in the car handbook I found that the maximum recommended for the 12v sockets was 120watts.

Start looking around for a lower rated kettle or.......just buy a decent vacuum flask!!
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Not totally convinced adding contact resistance would actually lower the current, Jonz and Chancer.

Since by adding in yet more - spurious - resistance would increase the current demand from the kettle. Since as the voltage would drop, significantly, the current trying to flow in te circuit would increase.

This was practically reinforced to me back in the early 1980s...

In those far off days, amongst other things, I owned a Data and Telle Comms company I founded.

I gained a contract to install an advanced Blik intercom system by desk telephones system in a City of London office.

The system was powered by a mains PSU, with a 13 amp standard plug. Standard current draw probably around 8 amps, maximum.

The system kept blowing 13 Amp fuses. My installations manager had sourced a  cheapo  nasty plug ( I always insisted upon MK or similar). Fool!

In the end, I travelled up to the client's offices to diagnose the problem. The damned mains plug! [:@]

Poorly machined prongs; high contact resistance: BANG! Ad infinitum.

Replaced with a brand new MK unit; no more problems.

Food for thought, perhaps?

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The maximum current draw in a circuit is determined by the voltage and the resistance of the load, it's simple Ohms law where I = V/R and high resistance contacts in the circuit can only ever reduce that never increase it.

The heat generated by your crap plug is probably what was taking the fuses out it certainly won't have been excess current.

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In my post I said "The higher the resistance with a constant current + lower amperage". That should of course have been voltage!

I agree whole heartdly with you Ernie. A higher resistance can not possibly cause a higher current with a fixed voltage. Ohns law is totally correct. I had it drilled into me when I joined the R.A.F. as a Boy Entrant airvraft electricition and further so when I did my 1 year Fitters course to become a Junior Techniction.

V over IR is set in stone [geek]

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Ah, now you are bringing the power facter into this and the inductive losses caused by a power facter of less than 1 can be corrected by a capacitive load. But that apart you don't get very much in the way of AC in a car init [blink]

And if you try it with 3ø then it can get complicated especially if the phases are not ballanced.

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[quote user="Jonzjob"]

V over IR is set in stone [geek]

[/quote]

With the exceptions of Maxwell's Equations and Kirchhoff's circuit laws. Which came later and modified, qualified and defined Ohm's work.

I am still pondering this question.

Consider:

If a resistance be added to a circuit, then this causes both current limitation (e.g. LED current limiting resister):

However, adding a resistance lowers voltage in the circuit: a given dynamic.

However, again, using Georgie Ohm's Law, if voltage is lowered, the since (in the case of the car kettle) it still demands to operate at 170 watts and is a resistive load:

Ergo, again Ohm's law, since the voltage is lower, then therefore the current must increase.

Puzzling...

[8-)]

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However, adding a resistance lowers voltage in the circuit: a given dynamic.

It doesn't.

 

There will be a voltage drop across the resistance, you could probe the voltage at the supply wire to the accessorie socket and it would be the nominal 12.7v after the contact it will be a few millivolts less, before the heating element a few millivolts less again (the resistance of the lead) after the 170 watt element it will be to all intents and purposes zero volts but it will probably be say 2 millivolts because there is still some resistance in the return path to the battery -ve terminal, maybe 1 millivolt the other side of the accessory connector and a true zero volts at the battery -ve terminal.

 

It can be difficult sometimes to visualise whats happening in an electric circuit, one cannot see électrons being agitated, the best way is to think of it as water in a plumbing system, the voltage (potential) being the height of water in the holding tank (potential energy) the diameter of a pipe being the wire section, the résistances being the length of pipe, the bends (connectors) flow restrictions like a radiator or small bore valves, the work being done, the load could be a paddle wheel being moved by a jet of water.

The current is the volume of water being passed per second.

Visualising in the above terms you will realise that by adding a resistance to the circuit, a poor connector or a small bore valve then the current or water flow will not increase.

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But Gluey, the voltage will not drop. The voltage will stay at 12v, or nearer 14v with the engine runnung, and when the resistance rises due to a bad connection then the current must drop, not the voltage. Just as if you put a low wattage light bulb into a light socket at home it will take less current than a high wattage job. The resistance across a low wat bulb is higher than a high wat bulb.

You have a circuit with a battery, incandescent bulb, switch, ammeter and reostat, OK. You turn the reostat to the minimum restance setting, switch the circuit on. The ammeter will read high and the bulb is bright. You now turn the reostat to the max resistance setting. The ammeter reading will drop and the bulb will dim. That's because the voltage across the bulb will drop due to there being a drop across the reostat.

You have not changed the bulb wattage, but what you have done is to share the volts drop across the reostat and the bulb.

Say that the battery is 12v, bulb 12v 12w, the reostat at min is 0 Ω. When you switch on the current will be 1 amp. Volts drop across the bulb is 12v.  You now increase the reostat to 1Ω, the same as the resistance of the bulb. The volts drop across the bulb will be 6v and the same across the reostat, the current will halve to 1/2 amp.

Now, if you were to put 2 12w bulbs in series you would get the same effect and halve the current, but if they were in parallel then you would halve the resistance and double the current to 2 amps.

BUT, that isn't taking into account the slight inductive load caused when you switch on an incandescent bulb and the current builds through the tight coils of the filament and Faradays Law kicks in for a moment.

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Can I just throw in the words, series and parallel, which can also bugger up an equation set in stone! Auto electrics, I gave up on doing my own years ago, a field now totally on it's own, and no fun at all!! Anyway according to my Merc' wiring diagram, the three "power sockets" are two in parrallel, and one in series, this series one having the lower rating...............

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I still have a good understanding and notion of D.C. electric circuits and can do most calculations in my head, I always struggled with the AC theory, I use ohms law but know that inductive circuits dont follow it especially regarding start up loads. I have no problem with series and parallel resistance theory, got those all still squared away in my head, I often have to make potential divider circuits.

 

I have an American Maytag commercial tumble drier, supposedly 6kw but I soon realised that it had been derated for the UK market to 2kw and as such was very slow to dry and the auto dry function did not work. i measured the resistance of the element, used ohms law and it confirmed my thoughts.

 

I bought a 6kw element on US EBay, a bit confusing as it was 5.6kw but on a US 2 times 110v split phase supply, I decided that it would give me 6kw at 230vac, when I got it I measured the resistance and it was very similar to my existing one, according to my calcs it would have drawn 2kw, I tried it anyway and to my great surprise on checking my compteur it was indeen now drawing 6kw, how could that be with the same resistance as the 2kw one?

 

I asked the question on a forum and the answer was that the resistance had a negative temperature coefficient (or maybe positive) as it heated up the resistance lowered and hence the current increased, so yet another complication for mental calculations.

 

My drier works just fine now, this is the guy who not long ago said that he would never have a tumble drier all the time that he drew breath!!!

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[quote user="f1steveuk"]Can I just throw in the words, series and parallel, which can also bugger up an equation set in stone! Auto electrics, I gave up on doing my own years ago, a field now totally on it's own, and no fun at all!! Anyway according to my Merc' wiring diagram, the three "power sockets" are two in parrallel, and one in series, this series one having the lower rating...............

[/quote]

Actually, Steve apart from such as ECUs etc, it is very much the same: if one considers the dynamics as main digital stuff, such as ECUs, and all the sub-systems and senders, etc which are still mainly analogue.

Most of the peripheral bits, even where some solid state devices have been used, can usually be repaired. Luckily, I have an excellent contact in Norfolk who is electronically whiz enough to repair ECUs etc.

The only problem thus far has been Air Mass Metering Devices: since to re-fettle these and set 'em up, needs an accurate air flow bench.

Resorting to first principles, recently, allowed my son (with a bit of help from his poor old Dad) to recently sort out a problem with his Porsche Boxter S. The car was suffering from a spurious battery discharge, for no good reason. There were certain strange phenomena, too; such as the so-called Audio-Visual module, which consists of Sat Nav; Computer; CD/Radio and onboard cell phone would crackle and his through the speakers when not in use...

Also, the Audio-Visual Module would either work or not, as it felt at the time.

The Phone sub-assembly was under the driver's seat; a pig to remove.

He doesn't need or want the phone, as he has a very good hands free iPhone system.

The phone module was at fault. The Audio-Visual Module uses Fibre Optics instead of plain ol' wire.

Solution: purchase a fibre optic loop, which removes the phone from the audio-visual module but still allows the rest to function correctly; and disconnect power from the phone.

His previous vehicle was a Mini-Cooper Turbo R56 or summat: always going wrong as detectors, senders and sub-systems gave many problems.

All far too complicated for a simple man such as myself. I adore simplicity!

K.I.S.S

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Getting back on thread. We picked up our Vauxhall Corsa on Friday afternoon from Bristol airport. Low and behold, the dammed 12 socket doesn't work!!! The cigarette lighter if you want to call t that. Not I'm trying to find out whhat fuse is responsibe for the supply?

I didn't discover the problem until we had left the hire car place and it would have been too difficult to return it! Has anyone any idea of which fuse it could be???

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