Hot Damn!! Here comes the thread that should start discussing frequency
(hertz), peak voltage and rms, field coils and how a voltage regulator
works. I am also surprised that no one has mentioned that on most older
american v8 cars the belt driven fan has a viscous clutch that reduces
the amount of power required to drive it when the car is being driven.
(Hot Damn - another thread!!!) :)
> -----Original Message-----
> From: Roger Helman [SMTP:rogerh@digimation.com]
> Sent: Tuesday, August 12, 1997 3:04 PM
> To: David Massey; triumph listserv
> Subject: Re: Electric Cooling Fans
>
> David Massey wrote:
>
> > >In a message dated 97-08-10 16:54:47 EDT, Jody007@aol.com writes:
> >
> > >> It's said that you'll gain about 18
> > >> horse power by removing the fan.
> >
> > >That's very interesting. That implies that the alternator is more
> > than
> > 100%
> > >efficient. In other words, it produces more energy that it takes to
> > run
> > it.
> > >Assuming, of course, that you are getting the same cooling with the
> > electric
> > >fan that you got with the mechanical unit.
> >
> > >Dan Masters,
> > >Alcoa, TN
> >
> > Dan,
> >
> > 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
> > hether
> > the car is idling or at redline. And if you use a thermostatic
> switch
> > the
> > fan is off most of the time anyway.
> >
> > Not so for the fan on the crankshaft. It turns at engine speed. It
> > is
> > sized to give adequate air flow at idle and the rest of the time it
> > pulls
> > much more air than is needed.
> >
> > Consider this: I have a fan (from a VW Rabbit) that draws 10 Amps
> at
> > 12
> > volts. That is 120 watts. at 645 watts per horsepower and 50 %
> > efficency
> > thats about 0.1 HP. If an engine driven fan is sized for the same
> air
> > flow
> > at idle then the load on the engine at idle is 0.1 Hp. The power
> > required
> > to drive a fan is porportional to the Cubed of the speed. which
> means
> > the
> > fan that requires 0.1 Hp at at 800 RPM will require:
> > 0.1 x 6^^3 HP at 4800 RPM or 0.1 x 216 or 21.6HP!
> > At Red line. At normal driving speed (eg: 2400 RPM) it is more like
> > 2.7
> > HP!
> >
> > The electric fan draws 10 amps from the alternator. Assuming a 50%
> > efficiency the engine load is 2 x 120 watts / 645 = .37 HP! Even if
> > the
> > fan runs all the time there is a significant net savings!
> >
> > Dave Massey
> > St. Louis, MO
>
>
> Perhaps I'm showing my ignorance, but doesn't the alternator
> produce
> the same number of amps per rev. So the more revs the more amps with a
> max 35 amps for the stock unit? So no matter what the amps being draw,
> the hp to drive the alternator remains the same? Or does the force
> (BHP)
> needed to spin the alternator increase with the amps being drawn? If
> the
> first case is true and there are enough amps to drive the Fan, then
> the
> running with a fan would NOT cause a decrease in available BHP from
> the
> engine.
>
> --
> Roger Helman 71 TR6 CC67866L
> Digimation Inc.
> http://deepthought.digimation.com/rogerh/
> New Orleans La.
> www.digimation.com
> Voice. 504.468.7898
> Fax. 504.468.5494
>
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