Followups set somewhere more relevant.

In article ,
The Natural Philosopher writes:
|
| 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.

Well, excluding the minor detail that taking an hour to 'fill up'
where it currently takes 5 minutes is not something that I should
want to do, using a 200 A circuit safely or even practically isn't
like using a 13 A one. Even in industry, the maximum plug that is
used just like a domestic 13 A one is rated at 32 A.

Inter alia, contact corrosion, condensation and so on are BAD NEWS
at 200 A.

| 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.

I was estimating on the basis of distance driving. 50 KW is too low,
except for the smallest runabout, which would not meet most people's
requirements. 100 KW is more plausible, even given your factor of 3.

In article ,
"Nick Smith" writes:
|
| 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.
|
| What ??? I can't imagine a human being able to develop a horsepower
| for very long at all - more like 100 or 200 watts and even that would not be
| sustainable for long. So how does the average "regular" cyclist ride a bike for
| an hour or so at 15 mph covering 15 miles ?

At 200 W.


Regards,
Nick Maclaren.