The question is asked: How much more gas would be used if all cars in the US were to use daytime running lights?
Turns out it is a lot, as indicated by the answer.
Something doesn’t seem right about the answer though. I can’t understand how having the headlights on can possibly use added fuel. My thinkig goes this way:
Gas is burned in the car,and produces mechanical motion. That motion powers the car, and at the same time, runs generators and whatnot already in place. So if the lights are off, the generator still spins and produces electricity, and that electricity must have to go somewhere. If it is not used, it must either be lost as heat or stored in the car’s battery. Then, the headlights are turned on again, and the energy goes to the lights, INSTEAD of being stored or lost as waste heat. Am I correct here?
So how do headlights cause the car to burn more gas, if the mechanics that produce electricity are already in use right from the beginning? All I can see happening is that the electricity produced is used in a different way.
Am I out to lunch here? Is there some simple answer I have overlooked? Someone shine some light on this for me. There must be some stupid little thing I have missed, either in the article or that I haven’t thought about…
You’ve made a faulty assumptions: You’ve assumed you’ll use the lights the same amount when using DRL, and when not using DRL.
You won’t. Obviously, you’ll use more power in the lights when using DRL, especially as most people drive mainly during the daylight hours and in the US, we only turn our headlights on at night, or when it’s raining or heavily clouded over.
Now, some of that energy that’s not used goes to charge the battery, and some will, granted, be lost as heat, but I’m certain it’s not as much as would be used by DRL. However, I’ve a feeling it’s also significantly less than what the article claims it is.
Una is going to know this in way more detail, but in short: The more electrical power your car consumes, the harder it gets to turn the generator. More work, higher fuel consumption.
S. Norman - fully expecting to be proven completely wrong…
Ok, but the question still remains: If the mechanism that produces the electricity still is in use, regardless of lights on or not, how is is causing the engine to use more fuel? It either uses the energy it produces for lights, or it doesn’t. The energy is still being produced regardless, so the amount of fuel used is the same.
The energy produced is NOT the same. As Spiny Norman correctly pointed out, it takes more work for the engine to spin the generator if you’ve got a larger electrical load. Say you were cranking the generator by hand. With no electrical load, it would be pretty easy to spin. In fact, the resistance you’d have to overcome is the friction in the generator. If you attach a large electrical load (lots of lights, etc.), the generator would get harder to turn- you’d have to apply more force to keep the thing turning. That’s what a generator does- convert mechanical energy to electrical energy. If you demand more electrical energy, you must supply more mechanical.
Back to the car- as you apply more electrical loads to the generator (i.e. turn on your running lights), it gets harder for the engine to keep spinning the generator. This is exactly like the engine working harder to keep the tirings spinning if you’re going uphill.
As an aside, just because the generator is spinning doesn’t mean that electrical power is produced. If there is no load connected, then there is still voltage at the output of the generator, but no power is being consumed. The electricity doesn’t go anywhere- it’s just like a battery, sitting there powering nothing. As soon as a load is applied, current starts to flow, and power is consumed. The generator then gets harder to turn
A generator gets harder to turn the more power it is supplying. If you were spinning the generator by hand but it wasn’t connected to anything you’d have no problem - the generator would give you almost no resistance. But hook it up to a lamp or something and suddenly it gets much harder to turn it.
Same thing for your engine. Put the lights on, crank up the A/C, make yourself a coffee with one of those widgets that plugs into the lighter socket and the generator becomes harder to turn. So the engine uses more gas to turn it.
What varies is the resistance to turning the alternator as the electrical load increases. This resistance results in an additional power drain, which requires more power form the IC engine and thus more fuel consumption.
You can test this if your car has a loose alternator belt. Turn on the car, and let it idle. Now turn on all accessories in the car - fans, light, windshield wipers, etc. You should hear one of two things, depending on your engine management controls - either the engine speed will drop noticably, or if your belt is loose you will hear it squeak from slipping, as it no longer has the “grip” required on the alternator pully to turn it against the electrical load.
Of course, in a Fuel Injected car with a really smart computer, the idle might be raised automatically. But you should still hear a momentary drop in speed.
That’s what I forgot all about! The resistance from the generator! Wow, what a load off my mind.
Man oh man, I though I was going nutty there.
Thanks everyone! It all makes sense again.
Some sailboats have big-ass alternators to charge big battery banks to supply power when the motor is not running. Some will even have two alternators fitted. That can easily mean 5HP taken from the engine. Diesels should be warmed up for a few minutes before loading them and 5HP on an engine which is not huge is a substantial load (not to mention when you are cranking it to start it!). Some regulators will allow you to switch off the field so the alternator will not load the motor. After a few minutes the alternator starts charging.
