On 7 Oct 2015 at 14:40, Knapp wrote:

> "The car motors are rated to a peak power of x watts. They don't need
> to run at peak output otherwise you couldn't get the rated range
> figures."
>
> Is this because of air and road friction or does the motor loose
> efficiency at peak output.

Neither. at least if you are asking what I think you are asking.

The motor may have a peak power usage of X kW. That'd be hit climbing
a hill, or accelerating hard.

But running on flat, relevel ground, it will likely be using a small
fraction of that.

Another factor is that most electric vehicles have regenerative
braking. When you hit the brakes, the motors become *generators*
pumping power back into the batteries.

This procees is *very* efficient. I'd guess at least 70% maybe as
high as 90%.

So, for example, going down a hiill would get you back 75-90% of the
energy it took you to climb it.

Likewise slowing from 60 to 20 would get back a big chunk of the
power it took to accelerate from 20 to 60.

That's one of the *big* advantages of an electric over internal &
external combustion engines.

Oh yeah, not only will batteries get better with TL, motors will too.
Lighter, more powerful, etc.

But currently, batteries are the big limit. For electric cars to be
used widely, you need *two* battery advances.

First, higher energy denisty (joules per kg).

Second, you need the batteries to be made from something *common*
enough that you can *make* that many batteries at an affordable
price.

Clear back in the 60s there were some demonstrator electric cars that
had decent range and speed. But they used things like silver-zinc
batteries. and there was no way you'd get enough silver to make
batteries to replace the gass guzzlers on the road.

The situation with silver is a bit better now that film photography
is mostly dead. But not *that* much.

Another problem is that as batteries sapproach (or pass) the energy
density of gasoline, they get dangerous. A battery fire with
batteries that powerful is a *really* bad thing. So are shorts and
the like.

Look at the problems with defective laptop batteries. Now expand that
to a battery that weighs a under times more and has more like *200 to
300* times the energy in it (larger batteries tend to be more
efficient at storing power)

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com