On Mon, 25 May 2009, Roland Perry wrote:

In message , at 21:51:54 on Mon, 25 May 2009,
David A Stocks remarked:

And in London the problem is distributing the electricity from the
grid to the end users. Even if there was a plentiful source of
electricity, you'd have to do quite a lot of work to get it where
it's needed.

Just dig up the relevant bit of road/pavement and tap into the
existing domestic supply cables that are under every street. This
must have been the approach for the existing charging points, and
it's hardly rocket science.

You'll soon overload it if it's more than a few charging points per
street.

A trickle-charge point is equivalent to a 13A socket inside a house.

You want a bit more than a trickle charge - we were talking earlier about the
use of three-phase and up to 100amps.

But if you'd read either the Reg article or Mizter T's second post, you'd
know that Boris *is* talking about trickle charge - 2000 of the points are
to be 13A. Another 150 are to be 32A x 240V three-phase, which in power
terms are scarcely a problem (equivalent to about three sockets rather
than one), but will obviously access to a three-phase supply. The 200A x
500V charge points aren't given a target number, as they're still being
investigated.

Typical cars I've seen take about 3 hours at 12kw (that's 48amps) to
charge up.

That would put the amount of energy delivered at ~130 MJ.

The Reg reports that the 13A points will "charge a car over several
hours", and that the 32A ones will "deliver a decent charge to an EV in
roughly 30 minutes". The former would put the power delivered at somewhere
between 44 and 79 MJ, depending on where 'several' falls in the range 4-7
[1], the latter at 13 MJ.

That's obviously quite a disparity - or rather, two disparities, between
your number and the Reg's, and the Reg's two numbers! I don't know if
someone's missed some zeroes, or if you've just seen some real
electron-guzzlers.

tom

[1] If it was less than four, it would be a few, not several, hours, and
if it was more than seven, it would be many!

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