On 19/05/2021 13:25, NY wrote:
"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.

So what? batteries can do 60C engines can do 100C. Not a lot of
difference at the end of the day



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.

which we have already established is less than 5 minutes.

Remmember if you want your 300bhp car to be hurtling down the autobahn
at 160 mph then it IS continuous power.

Also, the reason that lithium cells *can* be charged quicker is that
their internal resistance is so much less with new technology. The price
you pay is weight...

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.


charging cables would of course not be part of the car any more than the
petrol pump hoses are.

It would be a suspended cable from the filling station - probably servo
assisted to get it into the right place to make contact with the cars
socket.

10KV is no big deal really, unless you touch it...need some serious
earth leakage trips

I would imagine a smart plug/socket arrangement with a barcode on the
cars socket linked to a debit card, and a charging regime, that would
allow no current to flow until a valid car was in fact plugged in, and
some safety barriers erected, and the seat sensors indicated the car was
empty...or whatever was deemed to be suitably 'safe'




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".

I think that several things will in fact happen.

1. Fuel cars may be banned from residential town areas, but they will
not disappear.
2. Urban car ownership will decline, with fully charged driverless taxis
being the urban norm
3. Charge times will reduce a lot
4. Range will increase a little.
5. 'Renewable' energy will vanish
6. Nuclear power will run everything. People will tell you that 'the sun
is renewable and it's a nuclear reactor innit' in a massive exercise in
doublethink
7. As fossil fuel costs increase, synthetic hydrocarbons rather than
hydrogen will replace them. Since these will use CO2 and water to make
them they will be considered 'renewable'
8. But mostly, we will be (nuclear) electric where ever possible for
everything



--
"What do you think about Gay Marriage?"
"I don't."
"Don't what?"
"Think about Gay Marriage."