Question on Electric Cars?

[Crewman47]

I have serched on this and have found various answers so I just wanted to find out what answers I could get from here.

Basically I'm just wondering why alternators, similar to those in your usual liquid fueled car, can't be used in electric cars to keep the battery charged?

I do understand a little about alternators and although they don't fully power a car, only run the electrical parts and that fuel is required to actually start the car. But for electric cars then, to start the car you'd have the charge in the battery required (if I understand the concept properly) and the alternator would then keep the battery charged for the length of time your driving.

If I've got any of this wrong then i'm just trying to learn as I was just thinking earlier today why, even at this point in our technological development, we aren't all driving in electric cars.

 

[Robert Maxwell]

The simple answer is "efficiency." Having an alternator in an electric car would not keep the batteries charged because the alternator loses some energy in the process of generating it. I suspect an alternator would cause the batteries to drain even more quickly, as the alternator itself would consume more energy than it could produce.

Electric cars use techniques like regenerative braking to reclaim energy.

What you're suggesting would amount to a perpetual motion machine, which thermodynamics tells us is impossible.

 

[Jadzia]

There would be no obvious benefit. The drive system in an electric car is a motor. To power an alternator (which offers some resistance) and keep it's speed up, the motor would have to burn more electricity. The electricity the alternator produces would be less than that burned by the motor. So an alternator would cause a net energy loss.

There may be some special circumstances where it could play a positive role, perhaps if the motors work more efficiently at high power, and if there's a saving to be made from running them at a higher power then you could reclaim what power you don't use through an alternator.