Re: Switch Your Engine Off When In A Queue

Adrian wrote:

Chris Whelan <cawhelan@xxxxxxxxxxxxxxxxxxxxx> gurgled happily, sounding
much like they were saying:

If Citroen manage to have the (far heavier load) hydraulic suspension
pump (which, mechanically driven, used to be guesstimated at requiring
about 7bhp) running electrically on C5s & C6s, reliably, and kicking in
as soon as the car's unlocked, then I'm sure it's not that big an
issue.

Yes, but that would only run briefly before the engine is started.
Electrically driven A/C would need to run for much longer periods.

Aircon compressors are much more efficient than they used to be.

But still take a significant amount of power.

A quick google shows them to be a couple of kW. But, of course, they
don't run continuously or at full power other than to initially cool a
car that's been sat in full sun for a while.

What mechanism on a *standard* A/C setup lets it reduce the amount of power
needed?

I use my A/C extensively, not to reduce heat, but to "condition" (ie dry)
the air. Later versions of my car, and many others on the market,
automatically turn the A/C on as soon as demist is selected for this very
reason.

Many cars with climate control, although capable of reducing output, and
hence power needs, still run the compressor virtually all the time.

I could supply a link to a large PDF entitled "Impact of Vehicle
Air-Conditioning on Fuel Economy, Tailpipe Emissions,
and Electric Vehicle Range", that amongst other things says:

"The power necessary to operate a vehicle air-conditioning compressor is
significant - it can be greater than the engine power required to move a
mid-sized vehicle at a constant speed of 56 km/h (35 mph)."

It's a large file to DL however.

IIRC Audi use solar panels
to run the aircon whilst the car is parked to keep the interior ready-
chilled for when the driver returns.

Electric
power steering pumps - again, always used to be a big mechanical load -
are common on plenty of cars now.

AIUI, electric power steering is not just an electric motor running a
hydraulic pump continuously, instead of the engine driving the pump.
What would be the point of that?

What's the point of power steering on a 1.0 mini-hatch anyway...?

Precisely because of the type of person likely to drive such a vehicle.

Oh, and the extra weight of equipment such as A/C makes it desirable of
course!

Small electric motors are incorporated into the steering column, and
only operate when extra effort is needed. The electrical demand would be
minimal, and again would only be needed when the engine was running.

Not all. Many are electro-hydraulic.

Oh, and ITYF the Pious and other hybrids already have electrical aircon
compressors.

ITYF that such vehicles actually need to have quite a large store of
electrical energy by their very nature...

They don't use the traction batteries, though, but the "normal" 12v
system batteries. They have both.

Nope. Totally incorrect. See here:

http://tinyurl.com/2eth8r

Toyota have resorted to a 3-phase inverter/motor combination driven off the
traction batteries. Yea Gods! How much complexity can one vehicle have!

Ford continue to use the petrol engine to drive the A/C, but at times of
high cooling need, keep it running!

Honda have a dual compressor. One part of it is petrol driven, the other
part is electrically driven, again from a 3-phase motor/inverter. As Ford,
at times of high cooling need the petrol engine keeps running.

I'm sorry Adrian, but there is no way that a 12vdc motor would realistically
be able to power a vehicle A/C.

Chris

--
Remove prejudice to reply.
.

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