I don't know what people are thinking in reference to electric fans, but
I think of the auxiliary fans that are installed in some rear-wheel-drive
cars, and the fans in front-wheel-drive cars. All of these are
controlled by temperature-activated switches. Consequently, they're only
running when the engine gets hotter, i.e. when the car's moving slowly.
As a result, the fan uses less energy than an engine-driven one, but only
because it isn't always on. When it IS running, it uses more power than
an equivalent engine-driven fan, because of the energy consumed by the
alternator and the wires. Since it isn't running when the car's moving
fast, it doesn't take any of the engine's power to run it. If there are
any electric fans that always run, they're definitely a waste of energy,
and the owner would be wise to install a switch to cut the fan out when
the engine cools off.
Sorry to belabor the obvious, but it seemed worth pointing out.
'72 TR6 CC79338U(being restored)
On Tue, 12 Aug 1997 DANMAS@aol.com wrote:
> In a message dated 97-08-12 18:49:53 EDT, firstname.lastname@example.org (David
> Massey) writes:
> > You are forgetting that the engine driven fan is waaaay oversized at any
> > speed except at idle when it is needed the most. An electric fan runs at
> > the same speed all the time and consumes the same amount of power whether
> > the car is idling or at redline. And if you use a thermostatic switch the
> > fan is off most of the time anyway.
> In my original post, I said "for the same cooling." That applies to whatever
> RPM the engine is operating at. If it takes 21.6 HP to operate the mechanical
> fan at 4800 RPM, it will take at least 26 HP to operate an electric fan with
> the same air flow.
> I also said, in my second post on this subject, that there are many reasons
> to use an electric fan. The arguments you make in your post clarify this, and
> I agree with them totally (although I believe your numbers are high - the
> mechanical fan would provide about the same air flow at 2400 rpm as the
> electrical fan, and would consume about 0.1 HP at that speed. I don't know,
> so I won't argue the point).
> My original point, however, is still valid. Many people are of the opinion
> that it does not take engine power to operate electrical accessories. People
> have responded to this thread with just that concept. I remember quite well
> in the energy crisis of the '70s, that people were asked to turn on their
> lights to remind others to conserve energy. The idea being that electrical
> power was free in a car. Not so! The whole point of my original post was to
> point this out.
> For anyone contemplating a swap to an electric fan, it would be a good idea
> to have all the facts. Anyone making the swap to gain 18 HP, especially at
> normal driving speeds, will be disappointed. Likewise, at normal driving
> speeds there won't be a dramatic increase in economy. Due to the sporting
> nature of our cars, they are most often driven around windy, twisty, roads,
> at a relatively slow speed. An electric fan would be on quite a bit under
> these conditions.
> Dan Masters,
> Alcoa, TN
> '71 TR6---------3000mile/year driver, fully restored
> '71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
> '74 MGBGT---3000mile/year driver, original condition
> '68 MGBGT---organ donor for the '74