Water pump....questions

[treed2@u.washington.edu (T. Reed)]

Actually, this isn't correct. The more electrical stuff you connect to an
alternator, the harder you have to work to turn the pulley. In a -greatly-
simplified manner, think about the alternator coils as being an
electromagnet whose strength is proportional to the electrical load
connected to it. Then think of the shaft/pulley as being another magnet
of opposite polarity that is pushing away from the first magnet as it
spins around. It takes more force to spin the shaft and "overcome" that
repulsion when you have less resistance in the electrical circuit
connected to the electromagnet.

If you've ever played with an electric motor and a battery, you would know
that if you connect the power and get the motor up to speed then remove
power, the motor takes a second or two to spin down. If you want it to
stop immediately, all you have to do is short the two terminals of the
motor. This creates "infinite" current between the terminals, exerting a
strong opposing force to the permanent magnet in the electric motor.

Of course, an alternator isn't 100% effecient, so there is always some
resistance to turning even when there is an open circuit between the two
terminals. Not to mention bearing friction, rotating mass, etc.

Okay, so maybe this isn't the clearest explanation possible but its the
best I could muster after being brainwashed by college physics textbooks
to speak in terms of mathematical.. stuff. I'm sorry.. my brain is
literally mush.

Perhaps the best way to explain this would be simply conservation of
energy. If you're making energy, it has to go somewhere, right?
Disconnecting the electrical load means it has no where to go. The heat
explanation doesn't fly either because there is no current flowing through
an open circuit. But even if it did, a 90A alternator making 14v (lets
simplify this model by pretending there is no regulator) spinning full
bore would produce 1260 watts of power. If you've ever touched a 100 watt
light bulb when it was on you would know how hot 100 watts is, and thats
not even 100 watts because heat is only produced from the "waste" power
of an inefficient light bulb. You can't tell me for a minute that 1.26
kilowatts are being dissipated as heat.. the alternator case would be red
hot.

-Toby

On Fri, 28 Feb 2003, Rhett Farnum wrote:

> If your alt was still spinning wouldn't that still cause friction and pull
> from your HP anyways? I mean if you turn the alternator off all you are
> doing is opening the external circuit, you wouldn't really be lessening the
> friction from the alt because it would still be turning and makeing energy,
> it just wouldn't be pushing it into the entire electrical system.
>
> Disclaimer: this is an amature electrical student talking, I am not really
> knowledgable on the pulley end of things but electrical is a diff. story so
> this is how *I* see it.
>
>
>
> Peace Out,
> Rhett
> Rocco_crossing
> '83 Rocco (autocross ready, 20 days till season opener)
> '92 Olds Cutlass Ciera (DD)
>
>
>
>
>
> >From: frank <fish26133@yahoo.com>
> >To: ATS - Patrick Bureau <txrocco@sbcglobal.net>
> >CC: Scirocco Mailing List <scirocco-l@scirocco.org>
> >Subject: Re: Water pump....questions
> >Date: Fri, 28 Feb 2003 10:34:50 -0800 (PST)
> >
> >Patrick, On a street driven car you would probley want
> >to use a underdrive pulley on the crank & mabey a
> >larger one on the water & powersteering pumps, A good
> >machine shop could turn these down out of
> >aluminum.(Ron should know more about that)
> >You could also install a switch that will cutout the
> >alternator while racing, just besure to switch it back
> >on for normal driving
> >Good Luck,FJ
> >--- ATS - Patrick Bureau <txrocco@sbcglobal.net>
> >wrote:
> > > Working on my 2L project and thinking...could it be
> > > possible to not install
> > > the pulley driven Water pump and install a type of
> > > electrical water pump
> > > instead and gain some HP?
> > > I have been obviously reading too many racing
> > > catalogues, I am getting
> > > ideas, but no real clue what type would electrical
> > > driven (yeah I can hear
> > > the gremlins already getting ready to attack this
> > > thing) water pump ?
> > >
> > > any one have any ideas on this?
> > >
> > > ATS - Patrick Bureau - txrocco@sbcglobal.net
> > >
> > >
> > > _______________________________________________
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> >
> >
> >=====
> >Later, F Jones
> >        87 16V Scirocco
> >
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