high performance electric cars

[Sisyphus]

I was looking at the Tesla Roadster. It seems too good to be true. Is it?

[insane_alien]

its real. high performance electric motors have existed for decades. its only now that we've managed to produce batteries and supercapacitors that are capable of supplying the power for long enough and in a small enough package to be used in a car.

 

A 248hp electric motor is nothing special, or that big come to think of it. it's smaller than an equivalent powered piston engine. lighter too.

[Rocket Man]

lithium ion is one of the most potent battery types, one of the lightest too,

 

electric motors are normally the most efficient, and lightest...

do i see a trend?

an IC engine needs a housing made from fairly sturdy stuff, that adds weight.

 

an induction engine just needs something to hold the bearings and coils in place that cuts way back on the materials needed, also, you dont need such grunty cooling mechanisims which are also heavy.

a 3phase induction motor, by principle, can aplply an even torque from zero to the frequency the coils are operated at. so you don't need much of a transmission.

if you take into account everything that becomes redundant in a switch from IC to electric, the electric is not just lighter but ridiculously so.

 

the only advantage of an IC engine is the energy density of the fuel which has been accounted for only recently

[Sisyphus]

One advantage of an internal combustion engine that occurs to me is the easy transfer of the fuel. I don't know how long it takes to charge the batteries, but I'm guessing it's quite a bit longer than filling a tank of gas. So it wouldn't be all that practical for long road trips, for example. Also, how long would that battery last before it needed to be replaced?

 

(I'm really reaching for cons, here. The pros are obviously huge.)

[insane_alien]

yeah, batteries at the moment take a while to recharge. Fuel cells can deliver the power and be refilled as quickly (or even quicker) than a petrol tank but we've got to tweak it a bit for viable safe storage of the hydrogen(or methanol depending on the fuelcell). Supercapacitors can be charged very quickly if you use a special high voltage socket but they lack the energy density to be practical at the moment.

[Gypsy Cake]

This sounds impressive. So do electric motors have the potential to go faster than regular engines due to the reduction in weight?

[insane_alien]

well, they have a much higher power to weight ratio so they can accelerate a car of the same mass faster. they also have a relatively flat torque to RPM line so they offer nearly the same torque from stationary to the top speed.

 

to go faster than the tesla does they will still need a gearbox as the engines still have a rotational speed limit although it is much much higher than an IC

[Rocket Man]

most high speed trains are electric, infact, most trains anywhere are electric.

on a decent sized loco, you can have a more efficient means of burning fuel becuase you can take advantage of the power to weight ratio of a turbine, the only reason they don't put them in cars is because the're notoriously difficult to maintain and are hard to scale down. most cargo trains run a diesel turbine and a generator.

[insane_alien]

not only that but the turbines produce very very hot exhaust. i watched a documentary about a gas turbine motorbike and they had stopped at lights and the car behind started melting where it was plastic and rubber. the guy in the car kept edging forward for a better look.

 

you also have to consider that a turbine takes a lot of fuel to get it started. this is fine for trains travelling a few hundred kilometers and up but for a car running down to the shops and back its not going to be very efficient. it would probably waste more fuel.

[Rocket Man]

iirc, a turbine has it's highest fuel intake at it's highest loading, i guess it's all down to how it's started.

as for hot exhaust, BMW is prototyping a steam engine to run off the exhaust heat of a standard IC to give it that little extra torque.

i still wouldn't want to have to tweak a turbine on the side of the road.