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#1 kirkd   Members   -  Reputation: 505

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Posted 24 August 2001 - 09:45 AM

OK, this is truly the wrong place to ask this, but I had to find some like minded folk to tell me I''m an idiot or I''m right. While listening one of those call in car shows on the radio, a lawyer asked the question, "Do daytime running lights cause my gas mileage to go down?" I agree completely - stupid question. Anyways, the answer from the hosts was that it could only cause such a negligible decrease that you would not even be able to compute it reliably. But, is this right? Would daytime running lights have ANY impact on MPG performance? My argument is that an increased expenditure of electricity does not translate into an increased load placed upon the alternator. Yes, the electricity produced by the alternator will be used to displace the drain on the battery by the running lights, but there is effectively zero increase in drag as induced by the alternator. I welcome all comments. Actually, I just want people to tell me I''m right. 8^) -Kirk

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#2 kdc6794   Members   -  Reputation: 122

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Posted 24 August 2001 - 04:19 PM

Well I am not that smart, but I can''t see that it would have a affect.

#3 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 24 August 2001 - 04:24 PM

When you need useless information, go to the right place:

http://www.straightdope.com/mailbag/mradiomileage.html



#4 kirkd   Members   -  Reputation: 505

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Posted 25 August 2001 - 04:50 AM

Thanks for the link!!

My mistake was to assume that an increase in demand for electricity increased the actual load on the alternator. I''m surprised to hear that it free-wheels in the absence of electrical demands.

-Kirk








#5 kdc6794   Members   -  Reputation: 122

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Posted 25 August 2001 - 04:39 PM

That is interesting. I guess I should study up on cars alittle more.

#6 flame_warrior   Members   -  Reputation: 122

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Posted 26 August 2001 - 05:07 AM

quote:
Original post by kirkd
OK, this is truly the wrong place to ask this, but I had to find some like minded folk to tell me I''m an idiot or I''m right.

While listening one of those call in car shows on the radio, a lawyer asked the question, "Do daytime running lights cause my gas mileage to go down?" I agree completely - stupid question.

Anyways, the answer from the hosts was that it could only cause such a negligible decrease that you would not even be able to compute it reliably.



If I am not wrong its a coil which takes care of the headlights and horn, not the petrol. If you start the car with the lights on, chances are you will burn the coil. It shouldn''t have any effect in gas usage. I doub''t anyone would design a vehicle to use gas to run the lights. IMHO that would be a very bad design.

Regarding work done - A flywheel stores energy which reduces the work done.

quote:
Original post by kirkd
But, is this right? Would daytime running lights have ANY impact on MPG performance? My argument is that an increased expenditure of electricity does not translate into an increased load placed upon the alternator. Yes, the electricity produced by the alternator will be used to displace the drain on the battery by the running lights, but there is effectively zero increase in drag as induced by the alternator.



Surely the battery has to recharged. From my understanding in my years of mechanical engineering the chances of battery of going down will increase if you start the engine without switching lights off.



Lot more is there to working of a car than whats there on that site :-).


#7 kirkd   Members   -  Reputation: 505

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Posted 27 August 2001 - 02:36 AM

I think the true essence of the question is, "Does electrical drain while the car is running translate into increased gas usage." Again, if an increased electical demand leads to an increased physical load on the alternator, the answer is yes. I didn''t think it mattered. I assumed (wrongly, apparently) that the alternator had a constant load applied and the regulator controled whether the generated electricity was applied to the battery or wasted.

-Kirk

#8 Vaporisator   Members   -  Reputation: 122

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Posted 27 August 2001 - 02:49 AM

Why should a regulator do that? Have you ever seen a huge cooler with a dummyload below your bonnet? This would only increase the danger of burning your car! Well, however, I can only guarantee that this isn''t the case in German cars, but however, American car technology is said to be inferior...

#9 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 27 August 2001 - 03:18 AM

quote:
Original post by kirkd
OK, this is truly the wrong place to ask this, but I had to find some like minded folk to tell me I''m an idiot or I''m right.

While listening one of those call in car shows on the radio, a lawyer asked the question, "Do daytime running lights cause my gas mileage to go down?" I agree completely - stupid question.

Anyways, the answer from the hosts was that it could only cause such a negligible decrease that you would not even be able to compute it reliably.

But, is this right? Would daytime running lights have ANY impact on MPG performance? My argument is that an increased expenditure of electricity does not translate into an increased load placed upon the alternator. Yes, the electricity produced by the alternator will be used to displace the drain on the battery by the running lights, but there is effectively zero increase in drag as induced by the alternator.

I welcome all comments. Actually, I just want people to tell me I''m right. 8^)

-Kirk


As long as the coil gets enough voltage to produce the spark need to burn the gas. I don''t see how daytime running light could effect gas miliage unless they draw an abnormal amount current.



#10 Anonymous Poster_Anonymous Poster_*   Guests   -  Reputation:

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Posted 27 August 2001 - 05:34 AM

As I understand it, most cars are actually maxing out the alternator during the first 20 to 30 minutes of driving just to recharge drain caused by /starting/ the car. One of several reasons people should walk if they''re only going to be driving 3-5 miles.

Anyways, a friend of mine has a digital miles-per-gallon display in his car that updates every second or so. Turning the headlights on and off didn''t produce any measurable change.

#11 TM   Members   -  Reputation: 122

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Posted 28 August 2001 - 04:10 AM

WTF does it matter man?

This topic is a waste of time, money, bandwidth, energy, power, disk space, ...
even this reply isn''t even worth it!


#12 Landsknecht   Members   -  Reputation: 234

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Posted 28 August 2001 - 04:30 AM

Actually, if your alternator is in good condition, it only takes 3-5 minutes to recharge a cold cranked battery. I drive nearly EVERYWHERE because where I live it is 110 degrees(F) a huge chunk of the year.

Technically, using your lights DOES lower milage due to the extra load from the engine turning the alternator. But it is so miniscule that it really does not matter. Using your Air Conditioning dwarfs headlight power consumption - shut off your AC first...

My bits,
Landsknecht

PS - Inferior auto technology??? Come on - we burn dinosaurs just as good as you...

#13 Vaporisator   Members   -  Reputation: 122

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Posted 29 August 2001 - 12:08 AM

Yupp, but you need twice as much dinosaurs to run your cars...

Beside it I definitively agree to what you were saying Landsknecht!

BTW, ''Landsknecht doesn''t sound very english...

#14 TANSTAAFL   Moderators   -  Reputation: 1152

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Posted 29 August 2001 - 06:39 AM

An alternator is a generator. It takes rotational mechanical energy produced by the engine, and turns a set of magnets that induce an electrical current in a coil of wires. The electrical current is potential energy, which can be used for a number of things. The primary reason for an alternator is to recharge the battery (which stores this electrical energy in the form of a chemical reaction). Now, if the battery is fully charged, then this potential energy goes to waste as heat. If the lights are on, then it will go to the lights, and some of the potential energy will be sent through a high-ohm resistor that heats up and emits light, draining some of this potential energy. If the amount of potential energy consumed by the lights is less than the amount of potential energy being produced by the alternator, then there is no increased load, and therefore no extra fuel consumed because of conservation of energy. If instead the air conditioner is on, which consumes more potential energy than is usually supplied by the alternator, then you have an increased load, and more fuel is consumed.

#15 Drizzt DoUrden   Members   -  Reputation: 100

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Posted 29 August 2001 - 06:58 AM

My input on this is:


Screw that, drive a bike. I dont know how you guys like to debate on car energy, but I have enough trouble debating my 12 times tables. So I will just get the heck outta here.

"I''''ve sparred with creatures from the nine hells themselves... I barely plan on breaking a sweat here, today."~Drizzt Do''''Urden

#16 kirkd   Members   -  Reputation: 505

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Posted 29 August 2001 - 07:25 AM

TANSTAAFL,

So we''re back to the original question. Does increased electrical demand lead to increased load on the alternator? That is the fundamental quesion. Obviously the air conditioner has other issues including running the compressor unit which imposes a significant load and decreases fuel efficiency. But, something as simple as the radio, the lights, etc - is there any increased load?

TM: Not interested? Don''t read.


-Kirk

#17 Vaporisator   Members   -  Reputation: 122

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Posted 29 August 2001 - 11:01 AM

TANSTAAFL, this is true for the old DC alternators, but nowadays, maybe not in the USA , cars have a three-phase current alternator that uses several static coils and one rotating anchor to produce electricity. This way you don''t need any permanent magnets and the control can regulate the power output from zero to max power. This way you don''t need any resistor burning your energy overproduction, cause there is none.
BTW such a resistor would emit very little to no light, but mostly heat (yea you could call this also light...).
And yes, switching on the lights will drain more power from your cars power net -> regulator increases alternators power-production -> alternator needs more mechanical energy -> motor needs more gas in order to keep its RPM/speed.
Hope this was understandable

Yesterday we still stood at the verge of the abyss,
today we''re a step onward!

#18 flame_warrior   Members   -  Reputation: 122

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Posted 30 August 2001 - 06:40 AM

quote:
Original post by kirkd
TANSTAAFL,

So we're back to the original question. Does increased electrical demand lead to increased load on the alternator? That is the fundamental quesion. Obviously the air conditioner has other issues including running the compressor unit which imposes a significant load and decreases fuel efficiency. But, something as simple as the radio, the lights, etc - is there any increased load?

TM: Not interested? Don't read.


-Kirk


Well being able to switch on the headlight without running the engine answer this question ??

This is tough to explain - In my car I can put in the key and give a turn. That puts a light on - then i can switch on any lights. When I turn the key a little more the actual ignition take place. So headlights and gas don't come into the contact at all. Its always the battery and headlight. So there is no load from the headlight on the motor I suppose thats how its to be said so there should be literally no effect on mileage due to headlights.





Edited by - flame_warrior on August 30, 2001 4:30:12 PM

#19 Vaporisator   Members   -  Reputation: 122

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Posted 31 August 2001 - 12:03 AM

And where is the power from the battery from? Yes right from the alternator which is attached to the motor!
And what difference does it make when the lights are directly attached to the battery? The alternator is attached to the battery too, so it DOES affect the load on the alternator and by this also the milage!


Yesterday we still stood at the verge of the abyss,
today we''re a step onward!




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