The idea is that the drain on the engine is relatively constant. The
electric compressor pulls a lot of current but only for a short period. The
battery acts like a buffer and the alternator drains less HP at any one
time. In other words, with a small engine the belt driven compressor turning
on can momentarily make the car dangerously underpowered where an electric
compressor would just drain the battery which would be recharged by the
alternator over a longer period of time. Electric units can be very
efficient. I assume that you get your "twice the drain of a mechanical unit"
from the loss of energy in producing electricity at the alternator which is
always spinning anyway though not with a load. Hondas are usually considered
to be very efficient cars. If you ever purchased a car with electric ac you
would see the benefit of driveability with a small hp engine, the better gas
mileage compared to a belt driven ac unit and unfortunately the higher cost
of the system which is why you don't see it on cheap low hp "American" cars.
I quote American because all of the small low hp American company econoboxes
that come to mind are made by foreign companies. Electric compressors have a
more stable power source that does not vary depending on driving
conditions. This allows a more efficient design in the electric unit than
the belt driven so I would argue your claim of twice the power needed.
Chris
----------
From: DANMAS
To: CREICHLE; mgs
Subject: Re: Electric A/C system?
Date: Tuesday, August 26, 1997 11:00AM
In a message dated 97-08-26 09:29:12 EDT, CREICHLE@nsc.msmail.miami.edu
writes:
> On an engine with little power they claim
> the electric ac does not hurt driveability
That's hard to believe, since an electrically driven A/C unit with the same
capacity will place a horespower drain on the engine of about twice the
drain
of a mechanical unit. Plus, you would need a humongous alternator!
There may be many advantages to using an electrically driven A/C, but
reduced
load on the engine is not one of them.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://www.sky.net/~boballen/mg/Masters/
'74 MGBGT---3000mile/year driver, original condition
'68 MGBGT---organ donor for the '74
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