Safe Speed Forums

Oh but we do have a say. Look guys, I've explained this before and it's really quite straightforward.

1. We tell our government to get stuffed, we're not having this crap.

2. Our government passes that message on to the EU, in whatever diplomatic language they elect to use, but the message is exactly the same. Let's have no confusion please. The message is still "Get stuffed, we're not having it."

3. We, the buying public, tell the car manufacturers to cut out this crap or we delay buying a new car for a further three years beyond the planned introduction of this nonsense. Let's see how they survive that.

General rant: Governments, and big business, and a fair proportion of the 'clever' people in the technology sphere are becoming a pain in the arse to the normal private citizen and it's time some wings were clipped. While some of their activities are welcome, an increasing proportion of what they're doing is becoming too intrusive, and costly to us, and it needs stopping without further ado.

Best wishes all,
Dave.

that rather depends what else i was using the engine for.

Not sure about this one. The vast majority of HGVs I see on the roads now have some form of DRLs (daytime running lights) already.



This is the "meat" of the argument - the way that Brussels roll out the CO2-reduction argument when it suits them, and tuck it away in a draw when it doesn't. Government hypocrisy always makes for a good story.



And this is the counter-argument. LEDs use only a small amount of energy. If DRLs become the standard in Europe, car manufacturers will respond by making all DRLs on EU market cars LED-based, quashing the energy/environmental concerns.

An open-and-shut case, as far as I can see.

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“For every complex problem, there is a solution that is simple, neat, and wrong.” - H. L. Mencken

Perhaps weepej has a point though (can't believe I've just written that, mind!) - what if we separated the action of propelling the vehicle from the actions of driving all the auxiliary loads, and had one larger engine pushing all of its output into doing the former, with a much smaller one powering the latter? Would the savings realised by unloading the main engine be sufficient to cover the costs of running the auxiliary engine (and in lugging around its additional mass)?

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Chris

Generally large (and particularly low reving) engines tend to have better specific fuel performance than small ones.
Running two small engines instead of one large one in a *normal* road vehicle with one to provide the electrics would lilky use more fuel rather than less.

However, there are exceptions. (I did say normal )

Vehicles which have a high electrical demand when stationary and spend a lot of time stationary with those loads running may benefit from having self contained auxilliary generators. (as opposed to ideling the main engine)

A good example of this is a main battle tank. Large trucks may also possibly benefit under some circumstances (Dont freezer trucks do this??)

But in a standard car or light van there would be unlily to be any advantage in having an APU. Especially when one considers that it would also represent yet another layer of complexity to go wrong!

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"The road to a police state is paved with public safety legislation"

I don't have a point; absolutely if a small portion of the power of a less efficient engine is diverted to power a specific device then that engine (and hence that device) will use more petrol than a smaller engine given there is a system between the petrol and the output of the device and that system use more petrol to keep it going in larger engines.

If you get what I mean.

Not of the scale that the ridiculous Daily Mail story is insinuating though.

The efficiency of engines isn't normally know.
A mpg rating is based on the engine pulling its self and the vehicle it is bolted to along against the road, against gravity and friction.

Larger engines tend to be in larger, or heavier, vehicles so would have more weight to pull along. The energy going to the electrical systems remains the same regardless of weight.

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Andrew.

Yes but you are persisting in this myth that small engines are more "Efficent" than large ones.

This is NOT generally the case.

Sure large engines in large vehicles use more fuel than small engines in small vehicles, and indeed, you could (not entirly unreasonably) argue that large vehicles are not a particularly effecient way of moving a single person arround.

But..

This does NOT mean that from a technical POV that the machine/engine is in itself less effecient. ISTR seeeing a documentory some years ago that suggesed that Concorde at cruising speed has the most efficent engines ever built beating the thermal effeciency of even large marine diesels. The point being that Concorde didnt use loads of fuel because it ws "Inefficent" but because it takes a great deal of power to fly through the air at twice the speed of sound!

As far as the lighting issue is concerned it is the "Technical" effeiency that is important not the "PeeCee" efficency.

Small vehicles are likly to suffer greater relative deterioration in fuel consuption (%age drop in MPG) and greater increace in absolute fuel consumption (Gm/Hr for a given similar electrical load) than larger ones.

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"The road to a police state is paved with public safety legislation"

Slighty, but I fully understand I can make a big powerful engine that is more efficient than a small one percentage wise, although if you measure efficiency by the amount of petrol it takes you to travel , say a mile, then the smaller one will normally win out.

I'm not disputing that, but does the amount of petrol used to ultimately deliver that power differ?

Well the amount of extra fuel used to power the extra load would go up by a factor relative to the efficiency of the engine alone, not of the vehicle.

The extra load would be there whether the vehicle is travelling up hill, down hill, quickly, slowly or not at all.

If the larger engine is more efficient then smaller cars might use more fuel to run the extra lights.

The difference between lights on and lights off is only 5*4=20 Watts, plus cable/conversion losses. These losses have nothing to do with the mechanical side of the vehicle. Fuel > engine > alternator > circuitry > cables > lights.
The energy user or lost as heat in the circuitry, cables and lights would be the same on all vehicles. (although probably less losses if using 24v?)

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Andrew.

I absolutely understand that, but in this case we're interested in the conversion of energy from source (petrol) to destination (light), whereas I think most others here were only thinking about the amount of energy the light itself consumes.

Yep, and that would be based on the efficiency of the engine on its own. If only we knew some real figures for different engines then this whole debate would be so much easier.

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Andrew.

But wasn't the original question whether or not big cars would use more fuel than small cars to power their lights?

Talk about arguing over how many angels you can stand on the head of a pin!

The amount of power consumed by the daytime running lights will be very small and it will be the same for a big car and a small car - the only real difference being whether or not one of them has LEDs rather than incandescent bulbs.

The wiring and connector losses will be about the same on a big car and a small car - a vanishingly trivial amount of power in each case.

The alternator efficiency will be about the same on a big car and a small car - 50% or thereabouts.

All that's now left is the engine efficiency. The specific fuel consumption (in kg per kWh) of all petrol engines of the same age will be very similar. Same with all diesel engines. I agree there will be small differences and I don't know any absolute values.

So what we're talking about is a very small percentage of the engine's output (for a small car) versus an extremely small percentage of the engine's output (for a big car) AND THEN only the fraction of that very small percentage that is actually wasted!!!!

At the end of the day do we really give a toss over how much if any power is used to power the lights?

The real question is: what are the safety implications of having cars and motorcyles driving during daylight hours ?

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Prepare to be Judged

If we were foolish enough to adopt this idea, there would obviously be a small extra cost in fuel used, but in percentage terms I doubt if it will be worth bothering about. There is likely to be a much larger difference between people that are good economy drivers, and those that don't bother about their mpg. There is also an added cost in having extra bulbs to fail and need replacement, or shortening the life of headlight bulbs; and bear in mind that a 'simple' bulb change on some modern cars can be an expensive and tiresome affair.

In safety terms I think it would be a bad move, particularly with regard to the advantage currently gained by motorcyclists, and in any case it just seems so unnecessary to me.

What would be much more to the point would be a driver education campaign that included the sensible use of lights generally, not an insistence on daytimne running lights or the use of dipped headlights, regardless of the conditions.

One day last summer I saw a car in Scarborough with headlights and front foglights on - and it was about mid-day on a beautiful sunny day. The guy looked like a complete tit!

Best wishes all,
Dave.