Just curious what you foks think. I was listening to Car Talk on NPR yesterday and a lady called in and said thier boyfriend would never use his running lights or headlights unless it was after dark because he believed that fuel consumption was increased if the Alternator was under a load. Tom and Ray agreed but said it might account for a 1/10 of a MPG loss but that was it.

I can understand your AC compressor dropping the MPG because of the physical load that it applies when switched on but does the Alternator actually increase the physical load on the main shaft via the fanbelt as DC power consumption demands increase? I always thought that the Alternator puts out max power, like 125 amps at all times and you only tap the power load when you need it.

I'm not going to loose any sleep over it but wonder what others think. Does anyone have a degree in physics?

 

i have a degree in physics, but am no help.

if you have questions about galactic formation, or the universe in general, PM me.

 

I don't have a degree in physics, but if the lights are creating that much of a draw on the alternator then somethings wrong. I may as well turn off the radio too... I think the amp draws more power than lights. But I'm not gonna lose sleep over it either. I didn't buy my Disco for fuel economy.

Eric

 

I have a degree in chemical engineering, so I don't understand anything about ekeltricity. But, the only thing I've ever been sure of affecting any Land Rover's fuel economy is driving style. And maybe bad O2's.

Probably if you are being all fuel-savings conscious enough to remember to only turn certain lights on then you are driving in a manner that will improve fuel economy anyway.

 

I was under the impression that the alternator is always kicking out the same amount of juice.

 

Not an engineer, but this is how I would describe it....

The alternator does not put out max amps all the time, this would lead to your battery having a very short life.

The alternator "senses" the draw, or amperage, the battery has loaded to it and adjusts the output accordingly. I believe the alternator has a capacitor that does this, I could be wrong. I do know the alternator has a diode pack internally that changes the output of the alternator (A/C voltage) to D/C voltage - which is what cars use.

So if the load on the battery changes the alternator output, then having HIGH draw items on CAN cause load to the crankshaft pulley via the belt. And, yes, the alternator can cause a lot of load on the engine. This is why when the base idle and timing are set on cars, the headlights, A/C, blower motor, etc need to be off.

The large draws in a car are usually the blower motor on high speeds, headlights on high beams, and believe it or not the rear defrost can use a lot of amperage.

Stock stereo's and low beam headlights do not ususally cause much load on the electrical system and since DOT has proven time and time again the headlights being on can severely drop the chance of someone not seeing or hitting you I usually choose to turn the headlights on.

 

I have a mitsubishi eclipse that the previous owner removed parts of the idle control from. When I run accessories such as driving lights and the blower motor it idles noticeably lower due to the load on the engine and not being able to compensate with increased engine speed. I'm not sure how it works but it definitely puts a load on the engine, which should affect mpg.

 

Tom and Ray were right. I don't know if it is really 1/10, but the drag is going to be so small it would probably be unmeasurable. The chick's B/F is an idiot.

 

I used to have a 91 VW jetta and every time i put all the power windows down the headlights would dim and the idle would come down until i released the switches.

 

ALL electrical loads that are switched on will put a "load" on the alternator, thus onto the engine, so YES it would affect fuel consumption, but its how much that would be difficult to measure. Over a long period of time it would def add up to a more measurable amount.