Re: SRT-10 Got Beat By Battery-Powered
Three phase electric motors rotate at the speed (in hertz) of the applied AC. (Depending on the number of poles the motor has)
The beauty about this is, that the speed can be very efficiently controlled by varying the frequency applied to the motor, from 0 rpm to max rpm of maybe 20,000 rpm or so. The speed of the motor is infinitely variable, providing a smooth, stepless acceleration. You already know the big difference between granny shifting, and staying on the gas as you bang the gears, well thats the difference with a vehicle that doesn't shift at all. It spends more time accelerating, since it doesn't pause to shift.
These type of motor drives are called VVVF, for Variable Voltage, Variable Frequency. They take the DC from the storage battery, and produce an "artificial" AC by using two power transistors back to back, one PNP, and one NPN. These two power transistors comprise one "phase board", usually on a big heat sink with cooling fins. The GM Impact, or EV1, had a water cooling system for them, to dissipate the heat. Each transistor takes its turn at gating the DC either in a positive curve, or a negative curve, thereby making the "artificial" AC, in a single phase. Add two more phase boards, and you have 3 phase power. The transistors on the phase boards are gated, or switched on and off, by cicuits that produce the desired profile of acceleration.
And since maximum torque is available throughout that RPM range, an electric car can start out from 0 MPH with maximum torque, accelerate to its maximum speed, without the need to change gears. With a max RPM on the order of 20,000 RPM, and a flat torque "curve" throughout its RPM range, gear changes are not neccessary. Yes, they do have some gear reduction to multiply the torque, but they don't change the ratio on-the-fly, like a gas engined car does, as the driver is obligated to go through several gears to get the most acceleration from the torque and HP characteristics of the engine. No "transmission" in an electric car means less wasted energy.
Most all-electric cars have some form of dynamic braking, coupling the motor to the wheels, forcing the motor to rotate turns the motor into a generator, that harnesses some of the kinetic energy of the moving vehicle back into electricity to charge the batteries. The braking action usually is combination of friction material and regeneration, since not all the kinetic energy can be converted and applied to the batteries. (They just don't accept such a rapid influx of electrons!) On a side note, there are municipal busses in Europe that recover almost ALL the kinetic energy by turning a big flywheel, that aids in take-off. Compare this efficiency to the common brake, that just wears out pads, dusts rims, and makes crazy heat, making no good use at all of the kinetic energy of the vehicle. Sort of like a modern day tail skid, just dragging the load to a stop. Not too bright. Add to that the fact that internal combustion engines make massive amounts of wasted heat, take horsepower just to rotate the mass, wear themselves out internally, require frequent oil changes, etc, and the total picture of energy usage looks pretty dimwitted. I forgot the numbers, but I think something like 25% of the energy of a gallon of gas is actually converted to moving the vehicle, and the rest is wasted in heat, and combustion byproducts. That is still practical, since there is so much energy in the gasoline. Even with such a dismal conversion efficiency, the gasoline internal combustion engine still performs very well. And every year, manufacturers learn how to harness more of the power available in the gasoline. Todays' small block V8s are producing as much as some of yesterdays' big blocks. But there is still a long way to go before automotive technology catches up to the best available technology of mankind.
In an electric car, the energy from the batteries is converted more directly to forward motion, compared to internal combustion engines. But the biggest drawback of all this is the weakest link, the storage battery. Until this technology improves, the all-electric car remains impractical because of its relatively short range, and long recharging time, regardless of battery type.
Hydrogen fuel cells sound great as a source of electric, but no one mentions that hydrogen takes a lot of energy to make, energy that comes from oil or nuclear sources.
Hybrids make use of the flexibility of electric power, and the range and shear explosive energy of gasoline. But no Prius for me just yet!
Someday, if they make an electic car that does 3.5 seconds 0-60, and tops out at 200 MPH, maybe I'll buy one!
