about alternator amp outage and fuel consumption

[lengarden]

g'day team,

hey i'm a rank novice with a maybe silly question?

not knowing anything about altenator amperage output and the fuel consumption of a vehicle i need to ask a question?

if one where to take an extra 2amps above what is used in the normal opperation of a car, how much extra fuel would say a 1300cc 4 cyl' motor use driving the altenator to supply that extra power?

me assuming here that the larger a motor gets the less the impact of supplying that extra 2 amps?

i have tried googles seeking some answer with no luck, the question comes out of statement made on another forum about a massive use of extra fuel to provide that 2 amps of power.

many thanks in advance for any help.

len

 

[lengarden]

oh could the answer be kept simple please?

len

 

[Compositepro]

Two amps at 12v is 24 watts. One horsepower is 750 watts. You should be able to do the math from there.

 

[lengarden]

thanks compositepro,

i can see that 24 watts is around 1/3 of a horsepower is that right?

but not going to be able to go further as i have no idea how much fuel that much horsepower might use in the everyday application of a motor cars use?

len

 

[thruthefence]

actually it's 1/31 of a horsepower.

750/24 = 31.25

 

[GregLocock]

Typicall when cruising a car uses 10 or 15 hp. So roughly you'd expect an increase in fuel consumption of about 0.3%, if the alternator were 100% efficient.

Alternators aren't 100% efficient, but oddly enough the engine will be following the Mills line and the alternator would do the same and so is going to be very efficient at generating extra power.

So as a number, much less than 1% difference, but probably a bit more than 0.3%.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[lengarden]

sorry looks like i boobooed and in the wrong area? so thanks for the answers guess i'm outa here.

ta

len

 

[brutus1955]

two amps will be unmeasurable in terms of increased fuel consumption, outside of anywhere but the most accurate test cells on the planet

in the real world you will never notice the difference

bob g

http://www.microcogen.info

 

[lengarden]

g'day bob,

thanks for that yes looks like from all teh answers i got that the issues of 2amps would be all but unnoticable.

len

 

[mattsooty]

Modern Audis that use active alternator control/recuperation get a small but significant improvement in CO2 emissions by using this system over the relevant drive cycle (FTP75/MVEG-B).

MS

 

[waross]

Headlights take more current than this. Has anyone complained or even noticed an increase in fuel consumption while driving at night?
Smaller motorcycles and some older large motorcycles used a somewhat wasteful control scheme but any automobiles that I know about use an efficient active control scheme for the alternator.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DRWeig]

Say Bill,

I actually spent some time in South Korea last year, and noticed that a high precentage of the cars had automatic headlight dimming -- they'd only go to full brightness on a road with no street lighting at all. In the city where the street lighting was brighter, or on their main highways, the headlights would all dim down to a level that made me think they had alternator problems... Still enough to improve one's ability to notice the car, though.

I also spent an entire two weeks without seeing a single incandescent light bulb in a building...

You're right, I've thought often about how much gasoline we could all save by improving headlight efficiency, I bet it's huge when the number of cars is considered.

Good on ya,

Goober Dave

 

[waross]

I agree with you Dave, the potential saving may be huge but for each individual car the saving would be very small.
But the headlights dimming reminded my of Canada. New cars must have daytime running lights. Some use dedicated lamps, some use the headlights at reduced brightness. Many new cars have automatic headlight control. With the right intensity of street lights it is possible that Canadian cars would do the same. But we either have a higher cut-in point on the headlight control or our street light are not as bright. You do see that effect in Canada when cars enter a tunnel or snow shed and the reduced light kicks the headlights from "Daytime" to full night-time brilliance.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[TurboXS]

Here is something from Audi;

http://www.carwinism.com/content/us...rbon-dioxide-emissions-90000-tonnes-year-swed

 

[joff]

Alternator efficiency is fairly bad at 50% due to AC->DC rectification/regulation and the fact that the rotor does not use permanent magnets and requires an external field current to excite the electromagnet.

24 watts of electrical energy take 50 watts of kinetic energy away from the motor.

 

[drwebb]

LEDs offer an alternative solution:

 

[waross]

A smaller alternator may imply smaller cross section, higher resistance windings that waste some of the gain in 1[sup]2[/sup]R losses.
That's the way accounting driven engineering works.

Bill
--------------------
"Why not the best?"
Jimmy Carter