generator-powered electric car

[Joe1234]

Would an electric car with no batteries whose electricity was derived from an efficient generator at a constant rpm be more efficient than that same car with it's standard gas engine or... would the conversion from gas to electric to mechanical energy waste more energy than if you had just left it alone and kept the normal gas engine? I'm speaking in general terms. Weight and horsepower of the two different systems being the same.

[Saskwatchian]

It works for heavy-duity high-torque applications (think locomotives and some mining equipment) but I don't think you could easily downsize it for a car, especially if you want to get any kind of acceleration out of it.

[Ryland]

The only way you are going to make it work is if you have a battery buffer so that the generator is always running at peek efficacy and use the battery buffer to absorb that energy while the generator is producing to much and use the buffer when you need to climb a hill or to start moving from a dead stop.
but even at that it's still only going to be most efficient with city driving, direct mechanical connection to the wheels has losses that are under 10% if I remember right (someone had a chart a while back) while an gas to electric to mechanical drive train has losses well over 10% between the engine and wheels, that is why vehicles like the Prius and Volt have a planetary gear power splitter, a more efficient prototype drive train that Chevy apparently tested for the Volt involved the engine running at a constant speed and the motor/generator was used to vary the speed of the car but they wanted that feel and sound of the engine varying in speed that people are used to, then at highway speed, when you are most likely to need the gas engine anyway, the engine is running at the ideal speed to power the car and is tuned for the best mileage at that speed and your gas mileage would go way up.
Reasons why having the engine run at a set speed would increase your mileage so greatly is that if it's tuned for only a single speed the exhaust, intake, timing and everything can be optimized for that speed, you no longer need a throttle plate even and you save weight and space, it's like designing a trumpet that only plays a single note, you get rid of all the other valves and junk.

[mort]

Originally Posted by Joe1234

Would an electric car with no batteries whose electricity was derived from an efficient generator at a constant rpm be more efficient than that same car with it's standard gas engine or... would the conversion from gas to electric to mechanical energy waste more energy than if you had just left it alone and kept the normal gas engine? I'm speaking in general terms. Weight and horsepower of the two different systems being the same.

Hi Joe,
What you are describing is an electric transmission. As things stand now, in general terms, the best electric transmissions are 90% efficient, good mechanical CVTs are 95% and gear meshes are 98% - for cruising automotive conditions.
And a gas engine could be as good as 34% efficient, compared to the 25% that conventional cars average.
So .34 x .90 = .30 vs .25 x .98 = .245
However, electric transmissions weigh more and cost more than mechanical.
But for a large vehicle, like a Ford F150 the weight difference might not matter. You could go from 18 MPG (EPA combined) to about 22 MPG. To break even in 100000 miles the electric option needs to add less than about $4000 to the cost of the truck.
If gas continues to cost more and electrics get just a little cheaper...
-mort

[Joe1234]

A better way to ask this question would be to say, If I had two, identical civic VX's, took one and swapped out the gas motor for an electric equivalent, left the stock transmission in, added a few batteries for a buffer, and kept the batteries charged via an averagely efficient electric generator, would the "electric version" cost me less to operate than the gas version assuming they were both driven in exactly the same way OR, has the electric version lost so much in the conversion of energy process that it would actually cost more to operate?

[Frank Lee]

Mort pretty much just laid it all out... right?

[Joe1234]

nope. It seems like the scenarios he's talking about make use of a different transmission than the stock one. He also seems to only address a purely electric vs a purely gas drive-train whereas my scenario is different.

[Ryland]

Nope, Mort was even more clear then I was and with what looks to be more accurate and exact figures for three drive train options even, he didn't talk at all about a plug in electric.

[Frank Lee]

Originally Posted by Joe1234

nope. It seems like the scenarios he's talking about make use of a different transmission than the stock one. He also seems to only address a purely electric vs a purely gas drive-train whereas my scenario is different.

He didn't say anything about the transmission; when the engine/generator has to be running in order for the vehicle to move, the electric drive motor is merely functioning as an electric transmission whether there's a mechanical transmission between it and the wheels or not.

Anyway, by the time you get through buying all that stuff and likely increasing the weight and complexity of the vehicle, I don't see much money or even fuel saving potential.