On 19/05/2021 23:04, bilou wrote:
Le 19/05/2021 Ã* 10:53, NY a écritÂ*:
If (and this is a big assumption) an electric car needs about the same
amount of energy to travel the same distance, then that's 60*38 = 2280
MJ (2.28 GJ). And that energy needs to be supplied in the stated 5
minutes (300 seconds).

OK, so the power needed is 2280/300 = 7.6 MW.
+1
And if you take into account the power loss in the charging cable and
the internal resistance of the battery you get to the conclusion that
the topic is stupid.

No,. if you were an engineer and no an ArtStudent you would do the
research and the calculations and see that it was challenging, but not
impossible at all, and the stupid person was in fact you.

May be with a 100 KV battery but good luck to build a 100 KV motor :-)

Oh dear. semiconductors that function up to certainly 25kV as used on
overhead electric trains that develop up to 50MW...are patently myth!


The sweet spot is probably around 5KV for charge CABLES. The battery can
be whatever you want. Semiconductor inverters and regulators will feed
the appropriate 4.2v to each and every cell.

As far as motors go, again the choice is almost limitless. lots of turns
of thin wire or a few turns of thick wire - the motor doesn't care. A
few turns of thick wire are good but that means you need very big
control transistors. In reality Id guess at something between 100V and a KV.

In short the constraints are about optimising the following issues

1. Charge cables. Too low a voltage means a massively heavy cable. Too
high a voltage makes safety a concern and also the ability to down
convert using readily available cheap semiconductor inverters. If you
limit current to 100A, then you need a KV for each MW of charge power.
2KV is within reach of plenty of semiconductors. That's a 2MW charge
lead. 2MW will charge a 100kWh battery in 3 minutes. All other things
being equal

2. Motor voltage. You probably again want to go high here, but without
getting into super dangerous territory, mainly so that connecting wires
and switching transistors have to handle less current. For a single
motor/conventional transmission a 300bhp motor (225Kw) running at say
500V and 450A is ok and in fact things get easier with 4 wheel motors.
Again you might want to push up towards the 2kv limit of cheap
semiconductors to get peak currents down, but, realistically you need to
look at the overall usage on the motor. It wont do 300bhp forever one
suspects, or need to.

3. Battery voltage - well you make that the same as the motor voltage
for simplicity. 250 cells in series nets you about a kV. It is really no
big issue.

What it boils down to is this. Can you make a cable and a connector that
will deliver a MW that is no worse to handle than a petrol pump hose
and nozzle?

If we go to 5KV, we need 200A. IEEE tables suggests that needs around 70
sq mm of cable to not overheat, which means that two such, and an earth,
would certainly fit inside something no bigger than a petrol hose.
lets say the overall cross sections end up around 200 sq mm and the
'hose' is two meters long - that's 0.4 cu dm of copper weighing about
4.5kg.

Not something you would want to lift unaided, but probably not much
worse than a fuel nozzle on a big truck diesel pump

And in fact aluminium has a better current to weight ratio, so would
probably be used instead.

Make the thing out of hundreds of small strands, and its flexible,
cover it in silicone rubber for primary insulation, and a wire spiral
and rubber overcoat - earthed for extra protection - and you have a MW
charge lead.

The plug and socket would be an interesting challenge - able to be
connected in less than a second by a complete numpty with no possibility
of wrong insertion, inherently lockable and capable of doing 200A.,..and
insulated to 5Kv.


I think id put some simple robotics in the charger side that rotated
things to alignment, wiped all the contacts carefully before clamping
them hard and then monitored the temperature in the whole shebang, and
couldn't be pulled loose without shutting off power first

I don't see any serious problems in any of this. Its not radical
technology, its just coming up with a standard
plug/socket/voltage/current that is *good enough*.

And then having the cars own electronics down convert that to suit the
battery in use.



--
There is nothing a fleet of dispatchable nuclear power plants cannot do
that cannot be done worse and more expensively and with higher carbon
emissions and more adverse environmental impact by adding intermittent
renewable energy.