[urq] NAC : Electrical draw on an average car...

[Louis-Alain Richard]

HI everyone,

 

I want to write a text about the pros and cons of the Start&Stop and
regenerative braking systems that will be popular very soon on non-hybrid
cars. 

 

Now, I need to evaluate the average and peak amperage draw of an average
car. Peak is at 75 amps, average is 20 amps in my calculations.

Second, from what I know, an alternator is only efficient at 50-60%. Is this
true ?

Third, a gasoline engine efficiency is around 30%, right ? 

 

So, from that, at peak draw (winter driving, all lights, rear defrost, seat
heaters, blower, etc) :

- 75A at 14V = 1050 W

 

- Engine draw is double. 2100W. 

 

- At 30% efficiency, those 2100W needs 7000W of fuel energy. That is 7kW/h
for an hour of driving.

 

- Fuel energy is 10 kW/h/liter
(http://en.wikipedia.org/wiki/Gasoline#Energy_content)

 

Thus, those 75A during 1 hour are worth 70% of a liter of gas : in Qubec
today, that is 65¢. 

 

During summer, amperage would be 1/3, so 22¢ an hour.

 

Are my calculations OK ? Can I print this ? :-) 

 

Louis-Alain

1983 Quattro 

(whose 150mA draw is still an unsolved mystery.)