Nick Maclaren wrote:

In article , The Natural Philosopher wrote:

Dave Plowman wrote:


If you're going to build underground car parks for all city cars that
haven't their own off road parking, wouldn't it make much more sense to
spend the money on extending the tube network and making it cheap/free?
An electric car is only suitable for city use and will do nothing for
congestion.

That is simply not so.

With 300 mile range and potentially one hour fast charge from flat, it
would be ideal for rural use and commuting.


Yes,indeed, it would. It is, I agree, a more realistic target than
breeding flying pigs.

2) The petrol used in 300 miles by a typical modern car contains
about 1 GJoule. If we assume a factor of two higher efficiency, then
charging in an hour needs 140 KW. A standard domestic power circuit
is rated at 7 KW. You have a factor of 20 to make up.


I never said you would use the domestic circuit to fast charge. The
scenario was a 'fats charge' station like a petrol station where you
could plug in, have a pee, have a coffee, and come back with a more or
less charged car in under an hour. Typically you would NOT run the thing
totally flat - more like do 200 miles and then wait 40 minutes to charge it.

I am not going to repeat the figures, but I and someone else came up
independently with 9/10 hours at 20A to do the charge. That would mean
essentially 200A or 50Kw to do the one hour charge. I am not sure where
we differ between 50Kw and 140kW. My figures derived from taking the
shaft bhp used on a normal run, and electrifying those: The figures were
borne out by an actual test car that is running.

Ah. You have assumed a factor of two efficincy. I think that you should
be looking at 3 or more for a start. Petrol engines are not markedly
effuicient at part throttle. Transmission and ancillary sttuff
(alternator and other takeoffs - colling fans etc - sap more). They are
0% efficient sitting at traffic lights whereas electric motors can be
stopped altogether.



Dammit, a CYCLIST will expend some 20 MJ in 300 miles. Recharging
that in an hour needs 6 KW! There is NO WAY that you will design a car
to be as efficient as a cyclist, despite the motor lobby propaganda.


Well I dunno about cyclists. My figures were for about 50kWh (180MJ) for
the 300 miles. And those figures are borne out by other test sites I
found - no I haven't got them to hand because it arose in another
discussion elsewhere. Might be able to dig them up if you are
interested. ireckon a cyclist ambling along at 15mph might need about a
horsepower.. 750W - and would take 20 hours. That's 15KWh or 55MJ? yeah.
within the same range as you. For a back-of-the-envelope calculation.

If we take say 60mph as the average speed, its a 5 hour trip averaged at
10Kw, or about 15bhp. That seems eminently reasonsable for something
like a Fiat Punto - 50bhp - run at on average 1/3rd throttle. I am
assuming better than 90% conversion efficviency, because that is what a
decent electric motor, cells and controller can do. These are not fairy
land figures.



2) Despite claims, such devices would NOT help with congestion to
a detectable degree.


No one said they would. what we are aiming for is almost zero pollution
at teh point-of-transport, and utilkisation of an existing electricity
infrastructure, especailly use of off peak electricity, which allows for
better efficiency of generation anyway.

Congestion can only be reduced by either dramatically raising speed
limits, or taking cars actually off the road.




You CAN fully charge a lithium car in about an hour, but you need
specailsed charging facilities to do it safely.


You need specialised facilities to charge the damn things at all, at
any rate. The necessity for fancy protection mechanisms is one of the
reasons that they are expensive.


Nothing too fancy is needed. A simple voltage and temperature monitor is
all that is required.

Currently the ones being developed for model use are about 30% of cell
cost - a few dollars only. How this would scale with larger cells is
unknown. Its the last area to investigate.





Please could you take this stuff to a newsgroup (a) where people are
knowledgable about this sort of thing and (b) where it is on group?


Well you seem to think YOU are, and so does IMM. AND I think its is
interesting enough to stay here until it dies of boredom.

Its no more YOUR group than it is mine. Its marginally nearer on topic
than 'britney spears nude'




Regards,
Nick Maclaren.