Quote:
Originally Posted by ShadeTreeMech
I have to disagree with many people here about this.
The common philosophy is to go alternatorless will save buckets of energy. My question is, if an alternator is drawing no power, how much gas does it consume? The answer is very little in comparison to the gas usage of the vehicle needing to move down the road. If a 100 amp alternator is drawing full power, how much gas does it consume?
@100 amps output, we could assume 50% efficiency, which make 200 amps effective draw from the crank.
750 watts=55.6 amps @13.5 volts
13.5 volts (roughly the voltage of a running alternator) times 200 amps = 2700 watts
2700 watts divided by 750 watts (or 746 for those who are particular) = 3.6 hp.
At cruise the Scanguage calculates I am creating 50 hp from the gas I burn. So 7.2 percent of gas burned at cruise goes to the alternator ASSUMING the battery is dead and requires a recharge, which would require all the alternator has to give. However, generally speaking, with a topped off battery and a healthy alternator, it would be a fraction of that draw. Lets say half that, I'm sure it's less, but half makes easy math.
7.2 hp required divided in half = 3.6% required from my 50 hp output at cruise. At cruise I can easily exceed 30 mpg, so we'll stick with 30 mpg. So if I delete the alternator and ignore any possible side effects from a lower voltage requiring more amperage to components (higher amps = more heat) I'll save 3.6% of 30 mpg which equals 1.08 mpg and a nearly dead battery after a healthy drive.
Where's the benefit when I can allow the alternator to efficiently create electricity on the fly and hardly if ever open the hood to recharge a nearly flat battery?
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Hi ShadeTree,
I like what you said above, but I do question the 50 hp at cruise. Of course this does depend on what speed you are going.
Cycle magazine used to use a third wheel to measure various factors such as acceleration, braking, hp at 60 and so on.
Back then the motorcycles of the day used to use something like 6 hp to go 60 mph. Of course a motorcycle has less frontal area and less weight, but a much higher Cd.
Based on this, your car should use something around 20 hp to go sixty. That 50 number sounds too high if you are really going 60 mph at the time.
EDIT: If your driving the van, well, then maybe the 50 hp might be accurate.
Quote:
Originally Posted by ShadeTreeMech
Where's the benefit when I can allow the alternator to efficiently create electricity on the fly and hardly if ever open the hood to recharge a nearly flat battery?
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As fuel becomes more scarce, I believe the 3% increase in fuel mileage will become more important to all of us. And I still like your analysis.
Jim.