"The Natural Philosopher" wrote in message
...
If you want to think about 'three 3 kw electric fires' instead think about
a 300bhp car that runs at 25% efficiency - so 900bhp of HEAT is being
dumped by that cars radiators. Around 675 kW. It's no big deal to dump
9kw. And extra fans could be built into the charge points

The difference is that engines are built to withstand high temperatures.
Batteries (electrolyte and plates) are not - and if the battery includes
lithium, you definitely don't want any possibility of *that* catching fire.
I presume the rate of chemical change in the battery is the rate-limiting
step for charging rate.

I'd not actually done the sums: 300 bhp at 25 % efficiency is a lot of power
to be lost as heat. OK, so that's peak instantaneous power, only during
acceleration or at non-legal road speed, and the normal average power will
be a lot less. The figure I quoted for a very fictitious 99% charging
efficiency (which I'm sure is pie-in-the-sky) is a continuous power of 10 kW
for as long as it takes to charge the battery.


A bigger problem is the cable that plugs in. And safety. To get currents
down to less than - say 100A - you need 10KV or better. having that sort
of power handled by your typical Europhile ArtStudent„¢ is a frightening
prospect.

Yes. Assuming you want a charging cable that is easy to coil up into the car
when not in use and which isn't so stiff and heavy that you need to be built
like Arnold Schwarzeneger to wrestle with it, you need to keep the conductor
cross section (and therefore the current) to a reasonable level. And as you
say, if you want a certain power and the current must be low, the voltage
must be frighteningly high. I'm not sure I want to be close to a cable
carrying 10 kV, no matter how good the safety interlocks are to prevent
power being applied until the cable is proved to be safely connected, and so
it will cut out as soon as the cable is removed.




I think we will need to resign ourselves to an *enormous* step backwards in
convenience: having to stop more frequently is not the end of the world, but
if every one of those stops is for half an hour or several hours (depending
on how much power EVs really *can* use for charging) then it completely
****s up a long journey that is greater than the car's range. Whenever we go
on a cruise, we have a journey from Yorkshire to Southampton (or back) and
we tend to do that in one go: I've driven all the way before now, and at
worst it's a stop to go for a pee and to change drivers - a lot less than
the recharging time for an EV. I suppose we will have to be able to
guarantee that we will always be able to fully charge an EV overnight before
the journey, and won't be starting in a half-charged state. There is also
the social etiquette for your friends and family compensating you for your
electricity they use to recharge their car while they are visiting: there
will have to be a little financial transaction on the quiet. I'm assuming
that using your own electricity supply will always be cheaper than using a
roadside charger, so no-one will ever use the latter if the former is
available.

I don't see charging times being reduced by the order of magnitude that is
needed to match refuelling time for petrol/diesel cars, so let's hope
technology gradually evolves to increase the range so there is never the
need to recharge half-way through a journey. As my mum's friend's husband
(former professor of fuel technology) used to say "never underestimate the
energy in a gallon of petrol - that's what we have to match with alternative
fuel".