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Why do EVs need batteries?

by Chris
(Richardson, Texas, USA)

Are Batteries Really Necessary?

Are Batteries Really Necessary?

Why use batteries? Batteries are heavy, and maintenance hogs. Why not integrate a diesel powered generator, and use an AC motor to power the car? That way, there is no need for an inverter, and DC controller.

Hi, Chris -
I see what you're saying.
Electric motors are better, more efficient, than internal combustion; however, they sort of lose it on the FUEL side with those heavy, high-maintenance batteries. Why can't we have the best of both worlds, then - skip the batteries, and power the electric motor with a diesel generator?


Here's the problem:
The power demands of a moving vehicle are HIGH. Sometimes you go up hills, sometimes you step on the accelerator to join the freeway crowd, sometimes you've got three oversized teenagers in the back. If you've got a generator pumping out electrons, and there's no storage device (such as a battery pack), that generator's got to produce electrons at exactly the same rate as you're demanding them. I don't know of a generator capable of that.

Second - as I am fond of saying - generators are no friend of the environment. Regular cars benefit from years of pollution-control technology...generators don't have that, because they're not required to.

Anybody else want to comment?

Regards,
Lynne

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Must have batteries...
by: Anonymous

The problem with using a generator as the power source for an electric motor is this: Take a typical EV motor, rated 20hp. At startup when the motor draws the most power, the motor may be putting out approx 100 hp before tapering down to the 20hp at cruising speed. What this means is the idea that a generator for an EV with a 20hp motor would have to be sized to put out at least 100hp, to handle the initial demand of the motor upon startup. With efficiency losses, you're looking at a generator that may have to be around 125-150hp. Thats the size of a typical 4 cyl engine in any of the cars typically used for EV conversions. You'd be cutting your own throat by adding such a heavy engine (and generator head) to the car instead of the batteries. For all intent and purpose, you wouldnt have any room in the car for this kind of apparatus. If you need a 150hp generator, you may as well stick with the original powertrain the car came with. While locomotives are diesel/electric, they have to have gigantic diesel generators to supply the power for the electric motors. The only reason they use this setup is because the electric motors deliver max torque at startup (needed to pull those mile long trains at 10mph across the street you take going to work). Diesel and gasoline engines cant meet this demand, without being even larger. Better setup (as normally used in hybrids) is having a generator sized only slightly larger than the electric motor so once the car is at crusing speed, the surplus power from the generator (which is now able to drive the motor once the car's moving) can be used to recharge the batteries for the next stop and go cycle.

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third fuel option
by: Stan Bertram

I have been thinking along these lines for some time now. I think that gas and diesel will be gone within the next century. Hydrogen generation requires the electric fracture of another finite resource, water.
The model T ford was run on alcohol which we all know can be made in great quantity and burns cleanly. In a pinch it can made at home, with the permission of the ATF of course.
Wind management by design as in the Aptera. With front wheels powered by an electric motor on an existing drive train and a generator in the rear a balance is reached via weight ratio. Then a redesign of the body covering the new power train slipping through the air like a jet.
The concept of the electric motor and the diesel generator has been in use by the railroad and some large sea going ships for many years. In short, It works.
This concept could also work for the trucking industry as well if only they would do it.
But what do I know. I'm just another trucker.

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Diesel electric drive
by: Dan Bentler

In order of maintenance hours per operating hour
highest batteries
medium gasoline engine
small diesel engine

There is nothing new about diesel electric propulsion. Railroads have been doing it since mid 40's. Marine has been doing it for long time also most common example Washington State ferries. Both I believe are using AC drives.

Diesel electric is more efficient than direct drive in that the engine is generally run at constant RPM. HOWEVER this efficiency gain may be lost by losses in alternator say 3% and more losses in motor say another 3%. Add on a couple more percent in the VFD (motor has to be variable speed thus Variable Frequency Drive)

The whole idea behind electric only is to get away from fuel for whatever reason owner chooses to justify. Myself I like divorce from the fuel companies, better efficiency, lower maintenance, cheaper operation cost, no NOISE.

Dan Bentler

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