Headlights & fuel consumption

[chinabiker]

Chinabiker, I'm a little confused by your statement. Is the amount of power consumed by the generator from the engine constant? As in it makes no difference what electrical devices are turned on?

Top Gear did an experiment a few years ago where they drove an SUV around a test track with the AC on, and another with it off to compare fuel savings. I think the experiment didn't work however because of some problems having to do with using the track.

Here is a "How Stuff Works" article claiming that fuel/money can be saved by not using DRLs but I'm not certain about the math or science being used.

The amount of mechanical power used by the generator depends on the amount of electrical power the generator has to provide to light bulbs, grip heaters, fuel pumps, ... The output voltage is (roughly) constant at usually 12 Volts, thanks to the regulator. Output power depends on the load. If you take 60W electrically out of the generator (bulb, grip heater, ..), someone must put the 60W into the generator - what else if not the engine. An extra 60W load on the engine results in higher fuel consumption. If your engine would be rated at 6000W (approx. 8.5hp) the 60W bulb would consume 1% of it's power and therefore it would consume fuel. The more electrical power taken out of the gen, the more mechanical power - and fuel - it will consume.
I repeat - this amount can be neglected for one individual.

P.S. As every machine, the generator has losses (bearing friction, electrical losses). A generator like the ones in cars and bikes are not really efficient - around 15-20% losses. This means that the 60W electrical power taken out, would actually require around 70W to be put in.

[Lao Jia Hou]

Thanks Chinabiker - your explanations help.

Perhaps my misunderstanding was that I assumed electrical power was constantly being produced by the generator.

For example, when you start the vehicle, the generator is producing (let's say, for example) 100 Watts at idle RPM (e.g., 1,000 rpm). This electrical power is routed to whatever devices need it (e.g,. primary ignition, fuel pump, electronic gauges, sensors, etc.). Often, however, there is insufficient electrical generation, at idle, to also top up the battery, so there is often little battery charging happening. Everything that is being produced at idle speed is being consumed by the basic (mandatory) electrical devices.

As you increase RPM, the generator spins faster, and this increases electrical power generation. As an example, perhaps at 3,000 RPM, the generator is now producing its maximum capability (e.g., 300 Watts). But perhaps you do not have any optional, electrical accessories turned on (e.g., lights, heated grips, etc), so the extra power generation is routed to battery charging. If your battery is fully charged, the system dumps the excess electricity to ground.

If your generator is producing its maximum output (e.g., 300 Watts) at 3,000 RPM, and you start turning on accessories (lights, heated grips, etc), the generator will "fund" the requirements up to the maximum of 300 Watts. If you turn on enough accessories (e.g., 400 Watts) to go over the generator's capacity, the extra requirements of 100 Watts is "funded" from the battery. Eventually, you run down the battery.

Chinabiker, you explain that power production is not done until there is a load - for example, you turn on the lights, effectively closing a circuit thereby creating a drag on the generator due to an increase in the magnetic field through which the windings travel, albeit the "drag" would be infinitesimally small. That would be possible, and makes sense.

I thought, however, that modern electrical systems (i.e., post 1960s) were designed so that the generators were always producing the maximum output, dependent upon RPM, and dumping excess production (i.e., sending it to ground). Maybe I'm wrong. Again.

It would be interesting to have someone test this in the real world.

I recall Mythbusters tested the A/C versus open windows, and found that they were about equal. The extra drag created by open windows reduced mileage by about the same amount as running the A/C with the windows closed.

One myth that I was "corrected" about was the lugging of an engine ...

I had a driver in China who drove a standard transmission vehicle. I cringed each time he shifted to a higher gear at (what I considered) to be way too low an RPM. We'd be in 5th gear before 30 km/h. After finally getting the nerve to say something, the driver responded with "it saves gas" and "its easier on the engine & transmission". That made no sense to me.

A couple of years later, I had the chance to meet the fellow who had designed & developed two of the world's most revolutionary engines. I related the story of my Chinese driver and, MUCH to my surprise, this genuine expert confirmed what the Chinese driver was doing - yes, lugging an engine is more fuel efficient ... and yes, it is easier on the components, if done correctly.

I've since kept my mouth shut.

[TexasAggie]

This is what I don't understand. In any electrical generation found on vehicles (generator, stator, alternator), there is no physical/mechanical contact between the windings and the magnets/poles. Because there is no physical contact, how can drag/load be created? The only possible way (in physics) would be for a magnetized force to increase, thereby effectively pulling on the spinning windings (or, in bikes, generator's spinning basket) - but it doesn't - magnetization (if present) is a fixed amount.

What I understand is that the output varies, based on RPM, to a ceiling amount (regulated).

Where the "problems" can occur are when the electrical load exceeds either the generator's output, or the regulator's output, or both. For example, if your bike generates 300 watts, but your load is 400 watts, you have a negative drain. Eventually, your battery goes dead because it's storage has been topping up the system requirements.

In the old days, with oil-filled coils (pre CDI), when the electrical power production was insufficient, the spark would be weakened. There was a linear relationship, and this would be why cars would sometimes drop the idle speed, and/or lose torque, when you turned on the lights (an indication of a poor alternator, regulator, coil, wires, ect). It is my understanding that one of the advantages of CDI was that it helped compensate for these oddities.

But I still can't see how there can possibly be an increase in fuel consumption due to lights. There is no mechanical connection, anywhere, and the generators cannot be "dragged" due to an increased draw. The direction of electrical power production is unidirectional - from the generator outwards.

If it were true (headlights/mileage), presumably, the boom-box cars must get poor mileage with their 1,000 watt amplifiers.

Essentially, the generator's output is fixed, regardless of the demands being required down the line.

You have been here long enough to know you need to stop using logic in a logic free zone before your hurt yourself.

[chinabiker]

Thanks Chinabiker - your explanations help.

Perhaps my misunderstanding was that I assumed electrical power was constantly being produced by the generator.

For example, when you start the vehicle, the generator is producing (let's say, for example) 100 Watts at idle RPM (e.g., 1,000 rpm). This electrical power is routed to whatever devices need it (e.g,. primary ignition, fuel pump, electronic gauges, sensors, etc.). Often, however, there is insufficient electrical generation, at idle, to also top up the battery, so there is often little battery charging happening. Everything that is being produced at idle speed is being consumed by the basic (mandatory) electrical devices.

As you increase RPM, the generator spins faster, and this increases electrical power generation. As an example, perhaps at 3,000 RPM, the generator is now producing its maximum capability (e.g., 300 Watts). But perhaps you do not have any optional, electrical accessories turned on (e.g., lights, heated grips, etc), so the extra power generation is routed to battery charging. If your battery is fully charged, the system dumps the excess electricity to ground.

If your generator is producing its maximum output (e.g., 300 Watts) at 3,000 RPM, and you start turning on accessories (lights, heated grips, etc), the generator will "fund" the requirements up to the maximum of 300 Watts. If you turn on enough accessories (e.g., 400 Watts) to go over the generator's capacity, the extra requirements of 100 Watts is "funded" from the battery. Eventually, you run down the battery.

Chinabiker, you explain that power production is not done until there is a load - for example, you turn on the lights, effectively closing a circuit thereby creating a drag on the generator due to an increase in the magnetic field through which the windings travel, albeit the "drag" would be infinitesimally small. That would be possible, and makes sense.

I thought, however, that modern electrical systems (i.e., post 1960s) were designed so that the generators were always producing the maximum output, dependent upon RPM, and dumping excess production (i.e., sending it to ground). Maybe I'm wrong. Again.

I think you're mixing up power and voltage.
Voltage, measured in Volt [V], is available at the output terminals of the generator. This voltage is proportional to speed times magnetic field.
As soon as you connect a load (resistance, measured in ohm [Ohm]), current (measured in amps), which is equal to voltage divided by resistance begins to flow. The electrical power, determined by the voltage applied and the current flowing through the load, equals voltage times current and is measured in watts [W]. So far the very basics.

One would prefer a constant voltage of course, but as we see above the voltage is depending on speed, which in a vehicle has a real wide range from 1000rpm at idle and not seldom to way above 10000rpm at maximum. The voltage we want to have in most vehicles is 12 Volt and we want to have this constant (or in a small band) from idle to maximum, so we need a regulator. Speed cannot be controlled by the regulator, but as said above there is another component voltage is depending on, the magnetic field and this is what the regulator controls - nothing will be dumped here btw.
So far the principle of electric power generation in a combustion engine powered vehicle.

Needless to say that an output of electrical power from the generator requires mechanical power to be put into the generator, which comes from the engine. More engine power means more fuel.
Anyway, the extra amount of fuel for a headlight bulb can be neglected.

Sorry to add mor to your cofusion

[MJH]

Regardless to whether the light are on or not the kilowatts are being generated to power them its a constant.
For example turning your light off at the home will not reduce the generation at the power plant. There is always wasted energy, it is not a smart system. However if everyone turns their light off then the need for power decreases and the system ramps down generation, but it always is generated regardless to whether it is used or not.


If the lights are on they have to be powered and the settings reflect that existing load mostly at idle. If you see the light dimming you can see them brighten when you increase the rpm. The generation is constant and a function of the ratings of the generating source that is going to be reached at a certain rpm and then constantly offered after that, if you use it or not. If you do not it simply is wasted, just like the power plant it is not smart.

[Lao Jia Hou]

Regardless to whether the light are on or not the kilowatts are being generated to power them its a constant.
For example turning your light off at the home will not reduce the generation at the power plant. There is always wasted energy, it is not a smart system. However if everyone turns their light off then the need for power decreases and the system ramps down generation, but it always is generated regardless to whether it is used or not.


If the lights are on they have to be powered and the settings reflect that existing load mostly at idle. If you see the light dimming you can see them brighten when you increase the rpm. The generation is constant and a function of the ratings of the generating source that is going to be reached at a certain rpm and then constantly offered after that, if you use it or not. If you do not it simply is wasted, just like the power plant it is not smart.

Thanks - that is also how I understand it.

For example, if your "generator" is rated at 300 Watts @ 3,000 RPM, the generator is going to produce it (production), regardless of whether you use it (consumption). The electricity is there.

Imagine the following:

1) a bike's most basic, mandatory, consumption requirement is 80 Watts, for example, to power the primary ignition system (spark), a fuel pump, gauges and sensors;

2) you are zipping along at 3,000 RPM;

3) the "generation system" (production) makes 300 Watts available, but you are only using 80 Watts;

4) You turn on your headlights, which require an additional 50 Watts. So you are now consuming 130 Watts (80 + 50), but the production is still 300.

5) The difference between what is available (300 Watts) and what is consumed (80, without headlights; or 130, with headlights) is directed towards battery charging. In this example, that difference would be 220 Watts, or 170 Watts, respectively.

6) If your battery is fully charged (storage), those 220 or 170 Watts are either sent to ground (dumped, wasted, etc.), or just not drawn out of the production system. This would depend on the engineered design of the electrical system.

Yes, this is like a power plant's production. A power plant produces, for example, a constant 1 million Kilowatts (yes, I know power plants can increase or decrease production, but they usually remain relatively constant). The power is sent out into the Grid, which includes storage facilities. During times of low consumption (e.g., middle of night), the power goes into the grid and tops up the storage facilities. Once the storage is full, the power that is still being produced is sent to ground (or, better, sold to other Grids). During times of high consumption (e.g., dinner time on a hot day, when stoves and A/C are being used), perhaps all of production is being used and a little bit of storage.

Back to the initial question of headlights/fuel consumption. The needed electrical power to illuminate the headlights is already being produced. Consumption within the system's electrical limits, should have no effect on any mechanical drag. Even if consumption exceeds the limits (e.g., > 300 Watts), that amount will come from storage (the battery).

Following this all through, one would assume, therefore, that riding with a discharged battery increases fuel consumption. I am pretty sure that isn't true.

@ZMC888 - "cold drinks are bad for your health" explains warm beer in China. I love this one, because while the server is handing over a warm beer (with the explanation), the server is also offering you a cigarette!

@ TexasAggie - I am still a newbie in terms of learning logic "with Chinese characteristics", but trying hard to "fit in." For example, when I am walking across a road, I no longer make eye contact with the bus driver. This miraculously makes me immune from disaster. It is even better if I purposefully turn my head and look in the other direction.

@ Lobotomous - In Canada, DRLs are the law, yet the fuel consumption figures are the same as the USA (where there is no DRL law). In the USA, the NHTSA has conducted studies that demonstrate DRLs are safer ... but people feel it impinges on freedoms (like helmet laws).

[MJH]

The stator creates a constant source of alternating current, that is converted and buffered by the regulator -rectifier to a constant Vdc current of 14.4, that is the constant applied to the battery at all times. That is what also powers the lights etc. What comes off the generator is variable as it designed based on the rpm it is rotating at, it has to generate more then enough AC to be converted to 14.4 Vdc constantly at all rpms.


So the source is a constant and the regulator rectifier meters the current, it maintains it at a constant 14.4vdc.


Some older small bikes had a 6 volt system, these mostly have a 12 volt system. The amount of AC current coming off the stator would fry the battery and burn all the light out if it was not buffered. The electrical systems are 12 to 15 Vdc.


The variance is discharged same as based load energy if not used it gets discharged, in the power plants they have beyond base load that comes on in peak demand usually NG powered, to the best of my knowledge I do not believe that any power grid stores electricity, the required banks of batteries would not be economical or cost effective. There are batteries on the grid but they are not part of the grid they are consumers on the grid, in the event the grid goes down as in battery back ups. They protect critical systems and are typically configured with secondary generators and are not part of supply grid they are private or secondary on the grid.


Most people have trouble with that concept, that the substation are discharging excess generation, its normal operation.

[chinabiker]

Regardless to whether the light are on or not the kilowatts are being generated to power them its a constant.
For example turning your light off at the home will not reduce the generation at the power plant. There is always wasted energy, it is not a smart system. However if everyone turns their light off then the need for power decreases and the system ramps down generation, but it always is generated regardless to whether it is used or not.


If the lights are on they have to be powered and the settings reflect that existing load mostly at idle. If you see the light dimming you can see them brighten when you increase the rpm. The generation is constant and a function of the ratings of the generating source that is going to be reached at a certain rpm and then constantly offered after that, if you use it or not. If you do not it simply is wasted, just like the power plant it is not smart.

The stator creates a constant source of alternating current, that is converted and buffered by the regulator -rectifier to a constant Vdc current of 14.4, that is the constant applied to the battery at all times. That is what also powers the lights etc. What comes off the generator is variable as it designed based on the rpm it is rotating at, it has to generate more then enough AC to be converted to 14.4 Vdc constantly at all rpms.


So the source is a constant and the regulator rectifier meters the current, it maintains it at a constant 14.4vdc.


Some older small bikes had a 6 volt system, these mostly have a 12 volt system. The amount of AC current coming off the stator would fry the battery and burn all the light out if it was not buffered. The electrical systems are 12 to 15 Vdc.


The variance is discharged same as based load energy if not used it gets discharged, in the power plants they have beyond base load that comes on in peak demand usually NG powered, to the best of my knowledge I do not believe that any power grid stores electricity, the required banks of batteries would not be economical or cost effective. There are batteries on the grid but they are not part of the grid they are consumers on the grid, in the event the grid goes down as in battery back ups. They protect critical systems and are typically configured with secondary generators and are not part of supply grid they are private or secondary on the grid.


Most people have trouble with that concept, that the substation are discharging excess generation, its normal operation.

Wow. I never read that much nonsense

[Lao Jia Hou]

Wow. I never read that much nonsense

Hahaha - aren't forums wonderful?

[chinabiker]

Wow. I never read that much nonsense

Hahaha - aren't forums wonderful?

Indeed forums are wonderful but shouldn't they be helpful too