12V Cigar Lighter in 24V Automotive System

Yes. You may already have 12V available somewhere in the cab of the vehicle. Check your manuals and look for the fuse box inside the cab (check under the dash, ahead of the left of the driver side door or in the glovebox). If not you can simply bring a heavy gauge wire from each lead of one battery and connect these to the cigar lighter. Use red for the + terminal and Black or Green for the - terminal. I would put a fuse in series with the red wire just to keep things safe. Any decent autoparts store will have what you need. If you are not handy with electrical wiring, an auto shop or car stereo place should be able to fix you up. Good Luck!

Thanks.

[You may already have 12V available somewhere in the cab of the vehicle]

I didnt find any 12V available in the cab.

[If not you can simply bring a heavy gauge wire from each lead of one battery and connect these to the cigar lighter]

This is a cost reduction process. And so if I have to modify the harness,it will not serve my purpose.Kindly give some alternate ideas.

I would use a buck converter to obtain 12v from the 24v. That way your twelve volt load does not imbalance the charge in your batteries, which is not a concern, though, if the system happens to charge each battery separately rather than in series.

I would use a buck converter to obtain 12v from the 24v. That way your twelve volt load does not imbalance the charge in your batteries, which is not a concern, though, if the system happens to charge each battery separately rather than in series.

Good Answer! No need for anything to be added or changed. Just push in the lighter and get ready to catch it as it may pop out with a little more force. It will get hot a lot quicker than on a 12 V circuit.

This isn't a good answer! You don't use a cigar lighter to just light cigars anymore! Any 12v. device you plug into this will get fried!

Are you trying to get a 12V power point for things liek cell phone chargers or just a cigarette lighter?

Big difference. If its a power point you want then you have to use either an extra wire from the half way point between the two batteries. Be careful not to use the TOP half since that would place your outlet "ground" at 12V above the metal body of the vehicle and that could cause som ebig sparks.

You said this is a cost reudction exercise. Mweaning what? You want a cheap fix or you are designing a low cost accessory for a production item. How many units are you talking about. If its just for your own use, you eithe rput in the time to run an extra wire or you spend the money on a DC - DC converter. Take your pick. A real cheap and nasty solution is available but only of you have a constant load current needing 12V. Place a big honking resistor in series with the 24V and waste half the power. This is not a recommended procedure since the hot resistor is a fire hazard.

I design 24V systems and I prefer the DC-DC converter. These come in all sizes from 1A to 30 Amp.

from shankar, india

some decades back i bought a record player from an used equipment dealer for throwaway price. i was deflated later to find that the player was a 110 volts device whereas in india the supply voltage is 220 volts. i overcame this problem by including a 20 watt electric bulb in series in the player circuit. it worked with no harm.

try to include another cigarette lighter, if cost is no criterion or a light bulb which work on 12 volts in series in the circuit.

or preferably: quit smoking cigars. cigarette smoking is injurious to health

regards and good luck

Who said he is going to use it for cigarette!.

He is going to use it as Mr. Bean in "Mr. Bean on Holiday" to keep himself awake while driving.

Yes ! ! ! but you need a 3 rd wire from the centre connector between the two 12vdc

batteries. from that point to the opposite post of either battery is your 12 vdc supply to your cigar lighter. If a cigar lighter is all you will use it for, you will not likely be very concerned with imbalance of charging. On the other hand, if you are going to use this cigar lighter socket as a 12 vdc outlet for any other 12 vdc heater element, and/or 12vdc motors, you maybe well advised to install a switch that alternately selects both of the 2 opposite posts, so you can regularily connect your 12vdc load to the opposite battery.

If you don't mind getting risky, and you will only use the lighter socket for a cigarette lighter, Just hook it up to 24 V. The cigar lighter pops out and breaks the circuit when the temperature reaches the desired level. If you run the lighter at twice the design voltage, you will heat the element four times as fast. That should mean that the lighter will just pop out in one quarter of the time it would take at 12 V. Use big wire and connect close to the batteries with a big fuse.

Don

well as far as i know you can by just connect to one of the batteries to live earth but if you are going to run eny thing heavier you must use a voltage dropper other wise you will fry one of the batteries as i know this as it happend to us on our fishing boat we were useing 4 h d 6 volt batteries we took off to of them to get 12 volt but we were running a small fridge and radios it worked fine but after time that two batteries cracked but with the voltage dropper on every thing is very good ok by

Hi LanceV,

I must assume this is for an accesory outlet not to light cigarettes. Do NOT use a connection to the 12V centre point of your battery set the result will be that the lower battery (0~12V) will get discharged, not neccesarily seriously so, while the upper battery (12~24V) will still be full charged. When the batteries are on charge this will result in the upper battery being overcharged and failing early as noted by andrew wiseman.

Use a 24 to 12 converter with the 24V input connected via a fuse either to 24V direct or to the accesory connection on the ignition switch. All this can be done under the dash in the cab. A good unit for 10A should be about 100€ or $US which is a good bit cheaper than a large truck battery!

regards

Chas.

Dear all!

thank you so much for all the replies. I m working in a heavy vehicle manufacturing comp and we are trying to reduce the overall cost of each vehicle. We are already using a 24V cigar lighter. But since a 12V CL is much cheaper,so we are working on it. I am a new joinee and dnt hav much experience practically. From what i have understood that a 24V to 12V dc-dc converter will be the best idea if we forget the cost reduction. So i want to know how to connect it in a circuit.Does the amp rating of the converter depends on the component used?how to specify the current rating of the converter?Can a single converter be used in other 12V devices(in case i try to reduce the voltage rating of other devices like the head lamp bulbs) .

regards

It would be good of you to state what you require this 12v outlet for, this would help to reduce the many posts in answer to your question and give you an explicit answer.

I've been out of the circuits for a bit, but wouldn't 2 properly rated caps (12V and 12V) in series with a center tap provide the right voltage bias?

Would love to learn, especially if it means I get to deflate ego at the same time.

Happy Holidays.

If you are referring to capacitors, they block current flow when wired in series. They also can release a lot of current very quickly when a load is applied. This would not work. Some other circuitry would have to be employed to regulate the voltage, etc.

Actually for serious cost savings, quit goofing around with the lighter (which has to be knocked down to 12V or one of your customers is going to blow up his electronics) and take the entire vehicle down to 12V.

The military long used 28V, and the cost of specialized lamps for the dash, a component that should be nearly free, was staggering. All of the gauges and instruments have to be specially spec'd for 24V, exterior lights, engine sensors, all to keep mechanics from taking home a light bulb.

Do an analysis of the one time cost of converting over to 12V everything, against the cost you are paying for specialized components EVERYWHERE and you might be a hero to your firm. The best part of this conversion is most of your current wiring could probably be retained as it is probably oversized already. Some of the high current components like starters and wipers might need some wire upgrade. But the cost of 24V components is staggering.

Otherwise buy a transformer to knock the voltage down to 12V for the cigarette lighter and move on. A cigarette lighter shouldn't pull more than 10A @ 12V, so find a cheap tranformer with center tap to go from 24V to 12V and put a 15A fuse inline to the lighter.

Transformers will not work on DC. Are you referring to a DC to DC converter? Much more complicated and expensive device.

Doh!

Very early here when I typed that - thanks for straightening it back out.

Except for the (corrected) goof about the transformer, that was a good cost-saving suggestion. You may still want the 24 Volts for a few special functions, like engine starting, for the extra torque. You can get that by having two batteries, but charging them in parallel from a 12 Volt alternator of appropriate ampacity, and then configuring the batteries in series only during starting - and only for starting.

Nowadays, another possible alternative would be a higher power buck dc-dc converter (24 Vdc in, 12 Vdc out) to power your entire dash and all other functions not under the hood. That gives you conditioned (clean) power for the circuits that may need it, and allows for the use of relatively inexpensive commercial components, while still providing the extra power you need under the hood and maybe for auxiliary power for military items that are designed for 24 Vdc use.

Edigan, sorry to disagree but going to 24V is the cost saving way to go. Haven't you been paying attention. Even the automotive world is considering going to a higher voltage. The military did not go to 28V to keep the guys from taking a few bulbs home.

Doubling the system voltage means you only have 1/4 the losses in the wiring. Conversely with a higher voltage you reduce the load current for a given wattage. Remember watts = I X E current multiplied by voltage. In production this equates to huge savings in copper wire not to mention weight. And that was the primary reason for going 24V 400Hz in military aircraft as early as WW2.

Systems running on 24V AC @ 400 Hz required much less weight in transformers, smaller wire diameter for a given load current ( assuming you stipulate same percentage losses) and better immunity to hum compared to 60Hz.

In the marine world we have been shifting to 24V DC electrical systems. cost of equipment is not that much different and 24V equipment is becoming more and more common.

BTW you have it backwards. Going from 24V to 12V will require increasing all the wire diameters. Not exactly a cost saving measure. As for illumination. All you have to do is change the load resistor in an LED light and the same LED can be used in either 12V or 24V.

BTW SAE standards sets the current limit for cigarette lighter outlets at 8 Amp. Anything above that requires special wiring.

While the automotive world is looking at a 42 Vdc battery standard, it isn't there yet for production, and 12 Vdc parts are much less expensive than 28 Vdc parts at present.

Aircraft went to 115Vac, 400 cycles, in large part to save weight and space. Going to 24 Vac wouldn't have saved any wire weight. 24 Vac is derived from 115 vac for use in items like synchros and resolvers, but that technology is somewhat dated at this point.

Use a 12 volt zener diode in series with your cigarette lighter. Make sure it is rated at a high enough wattage for your fuse to blow first. You may want to heat sink the zener. Zeners are cheap enough but some power will be lost. I would recommend experimenting with this. If you use a resistor, the voltage to your load will vary depending on the resistance of the load. As we all know, cigarette lighters are not used exclusively to light cigarettes. If you use a DC to DC converter it will probably negate any cost savings. Tapping only one battery has it's drawbacks as previously mentioned in other posts. Your best solution in a 24 volt system is a 24 volt cigarette lighter. I hate it when companies compromise quality for cost reduction.

Most of the tips you have been given are downright dangerous or wrong or both.....

The best way is to use a voltmeter and go between ground and the positive of each battery, find out which battery shows only around 12 volts or so to ground (not the one that shows around 24 volts to ground!) and connect a suitable inline fuse and cable to this point. Run the wire carefully into the cab, connect the cigarette lighter between this cable and ground to have 12 volts (nominal) available for any units that you may want to use.....

This will work and involves the least problems.......do not forget to use a fuse and to dimension the cable carefully and to lead it carefully past sharp edges only when the cable is securely connected and not likely to get snagged or damaged in any way shape or form....

The unbalance usage of the battery will never be noticed unless you connect an inverter! If you want an inverter, buy one for 24 volts, they usually cost exactly the same as the 12 volt versions!!! They empty batteries quickly, so keep a wary eye on the voltage.....

This makes good sense (with the idea of the battery direct), but why would he want to use an inverter?

Are you trying to get AC from a battery?

As expected, another good answer.

I have a golf cart with 48 volts. The hard way. 6x 8 volts. To get a good 12 volt source for a two way radio, I had to put 2 small 12 volt lawn mower batteries is series, and connect them in parallel to 3 of the 8 volt batteries. Then tap into the 0-12 lawn mower battery for the radio. Two years old, and no problem yet.

I think you guys are forgetting that he does not want to rewire the harness. Am I right? That means he doesn't want the expense of extra cables and connectors just for a 12 volt source. He doesn't want the expense of redesigning the system to 12 volt. He doesn't want additional expense. The whole idea is to save money, not spend more. This is in a production vehicle so no jury rigging, right? Correct me if I'm wrong.

No I am not forgetting the original post. The point is he said he was new at the plant and was looking for a good idea to save money while offering what is likely a common request from end users. He was probably also looking to earning brownie points with his supervisor.

The fact remains a 12V DC outlet - commonly called a cigar lighter - is among the top request items in just about every vehicle, vessel and private aircraft I have seen. Our consumer oriented society has a plethora of devices intended to use these ubiqutous power points for all sorts of things. The fact remains that when you do not necessarily know what load is going to be plugged into it; you cannot use a simple drop resistor or a zener or a simple wire tap. A number of manufacturers provide DC - DC converters and even DC - AC inverters. The company I used to work for even makes a 75 watt cigarette plug to power laptops. It just plugs in and hardly takes up any space at all. They also made a variety of 18V outputs for HP and other computer makes.

Going the other way 24V DC to 12V DC would require a special order, but is not particularly difficult. You just have to commit to ordering a few thousand pieces. Even so, it is still the cleanest and most elegant solution. And it would not require modification to the original truck wire harness. I somehow doubt the OP intended this to be just for lighting up a cigar or cigarette.

Hi Andy, That is why i asked what the cigarette lighter socket was to be used for, the author of this post never stated what this was. So as far as I could see most of these posts were just rambling around the subject with little or no help at all.

Why do posters not follow up on requests for a bit more information which would help for a more precise answer??

Happy new year to you Garth

...and to you too Sir!!

Post 4 is good answer and will work properly.

Unfortunately almost all other answers are neglecting few things:

1. The cigarette lighter fits is a slot of its own size. How to fit any other gadget like DC DC converter or one more cigarette lighter or additional load bulb? Nothing can be fitted. Thus most of the answers are invalid

Zener diode can be fitted to the back of the cigarette lighter before inserting. Why don't you guys that have your little good answer club get your heads out of...

A zener won't work by itself. You need a dropping resistor in series with the shunt combination of zener and lighter. Since the potential is dropped 12 Volts, and the fuse is typically 15 Amps, you will need a series resistor power dissipation on the order of 2 kwatts. That device will not fit behind the cigarette lighter. The zener approach does not appear to be a practical solution.

Aha! My existence has been acknowledged. You can use only one zener as long as you fuse the circuit to take into account the power rating of the zener. If he wants 15 amps he better stick with his 24v. cigarette lighter as I previously indicated.

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This zener would be good up to 3.6 amps. Perhaps lower voltage ratings in series would allow more amperage but you get into the cost factor again. No, the best thing for him to do is keep his mouth shut on this one.

If you use a zener clamp without a dropping resistor the zener will try to clamp the battery potential to the zener potential. All that will do is pop the fuse or fry the zener, if the fuse isn't properly rated.

If the zener is wired as a shunt regulator, it will draw full design current continuously. And the limit resistor additionally consumes the same power. Wired in series, a zener will drop its rated avalanche voltage without regulating anything. The series zener will dissipate a large amount of power at max rated current; the same as a resistor sized to drop 12V with the same load. Series and shunt connections are both impractical here due to the heat generated. A zener shunt regulator is very wasteful with variable loads. Its efficency is vastly improved when regulating steady loads where the zener current can be minimized. Steve

Why not simply supply the lighter socket using a separate circuit connected to anode and cathode of one of the 12V batteries? This will match the 12V lighter socket to the voltage across it, no?

hii all!!

Sorry for not making this clear on the very outset but the 12V socket is meant for a cigar lighter used to light only cigars/cigarettes. From what I have gathered from the ideas,tips and discussions that I should drop this idea of replacing the 24V existing cigar lighter with a 12V. The reasons i have listed below. Pls correct me if I am wrong :

1) Splitting the battery: 24V vehicles are built from a pair of 12V batteries in series. We can tap off 1 battery to draw 12V. But this not a good idea as it means draw on the batteries is out of balance .One battery will continuously lose more charge than the other and then be at a lower voltage. Even the extra cables used will result in modification of the harness and hence add to the cost.

2) Using a voltage converter: We can use a 24V to 12V DC-DC voltage converter but again it means that the cost will increase.

3) Using resistors: If we get the current rating of the cigar lighter then we can put a resistor (resistance calculated) in series with the lighter so that we get 12V across it. But the resistor will dissipate energy mostly as heat, so if lot of current flows through it, we have to protect it from the wires and as such the method will not be cost effective.

4) By putting a forward diode circuit: A diode drops (wastes) about .7V, so we can put 20 of these in series for a low current method to use up 14V (most 24V systems can hit upwards of 28V).

thanks and regards,

roza

At last after a plethora of posts you have finally said what you want to use it for.

In this case 1[ Splitting the battery:would work fine , one cable one in line fuse thats not a big ask? battery out of balance ?? how many cigars do you expect the driver to smoke? Normal charging would make up this difference without causing any stress to your 24V end battery, it would not even be noticed in the scheme of things.

...however, it is now inescapably clear that your intent is to use a 12V-specified filament that you already have, instead of incurring the cost of purchasing a replacement 24V-specified filament (including the cost to find one of suitable fit).

Your question, it seems, involves the trade between the cost (price) of modifying the 24V lighter socket circuit and the price of a 24V replacement filament--one just hates to see a working, 12V lighter filament go to waste .

Such being the case (and taking the example of tapping 12V from one of the batteries), and given that a short length of wire and spade connectors (assuming you have crimp tools) is probably cheaper and easier to acquire than the 24V filament, then it will boil down to the difficulty (in your situation) of running the wire from battery to socket...and whether or not the existing, 24V lighter circuit wire could be scavenged and re-routed to serve as a 12V battery tap wire for the 12V lighter circuit.

I agree that being on the lookout for a suitable 24V filament replacement, and flicking your Bic in the meanwhile, is more likely than not your best answer; and will let you put your mind to more pressing problems. But...

Taking a fresh look at your contention about unbalancing the battery series...

It is hard so see how occasional use of the lighter would create an intolerable (or noticeable) imbalance as you have suggested. For one, it must be remembered that on most (practically all) occasions when the lighter circuit will momentarily (be used to) draw current, these will occur when the engine is running...at the same time during which no current other than that drawn by the lighter will be drawn from (either) a battery or from the battery series--all other engine and chassis systems will be supplied by alternator output. As to any minute charge (i.e., discharge) imbalance that might occur, would not the batteries, being series connected, immediately restore a condition of charge balance...such that balance of internal resistance of each battery is restored...again, because they are in series?

But let us take the case where, for any reason, the net charge detected on the battery series falls to a point at which voltage regulator routes charging current to the battery series...again the restoration of charge balance across the 24V battery series is automatically restored.

Therefore it would only be under conditions in which continuous drain by the (tapped) 12V load (and not drain caused by momentary, 12V, high-resistance draining caused by lighting of a cigar)...only under such conditions should tapping 12 volts from the battery series become worrisome.

Comments/rebuttals are invited and appreciated.

Guest I presume you are referring to the previous post not mine?? Your post has just confirmed what I stated in my post to state the obvious thank you.

Thanks...merely trying to elucidate the obvious and not so obvious; I figured you would be amenable...including having your own perceptive post further "punctuated" as to context.

Regards,

UG

Obviously