Bob,
Perfectly explained.
The battery is charged by the dynamo/alternator thus also sapping the
engine, allthough a bit spread out so peak HP will suffer a bit less.
Kees Oudesluijs
Bob Spidell schreef:
> This got me to thinking (always a dangerous proposition) ...
>
> Aren't we forgetting about the Law of Conservation of Energy?
> (http://en.wikipedia.org/wiki/Conservation_of_energy). If I read the
> law correctly (I'm not a lawyer) if it takes X HP to drive the
> water/air through/over the engine you'll use X HP from a) the engine,
> for a mechanical pump or fan or b) the alternator for an electric
> pump/fan. Assuming little or no slippage from the belt, the
> engine-driven pump/fan will be operating at near 100% efficiency
> (minus the fluid 'slippage' at the fan blade or pump
> impeller--essentially the same for both electrical or engine-driven
> units). I don't know the actual number, but alternators are probably
> around 80-90% efficient at converting mechanical energy to electrical
> (by rectifying the AC output to DC you're losing some of the
> electrical power, and some goes up as heat and there's always friction).
>
> IOW, if you convert X HP to watts, you'll increase the load on the
> alternator by (X HP->Y Watts), and the alternator will produce the
> additional watts by converting more engine HP to electricity.
>
> The advantage of electrically-driven accessories--it seems to me--is
> the ability to reduce or shut off the motor power when not needed.
> Yes, you can run them off the battery, but usually you'll be running
> off the alternator.
>
>
> Bob
>
>
>
> ----- Original Message -----
> From: "Eric (Rick) Wilkins" <e-wilkins@cox.net>
> To: "Oudesluys" <coudesluijs@chello.nl>
> Cc: "healeys" <healeys@autox.team.net>
> Sent: Wednesday, February 4, 2009 9:48:55 AM GMT -08:00 US/Canada Pacific
> Subject: Re: [Healeys] electrc fan vs. belt drive
>
> Not that simple math.
>
> There is the efficiency of each item to be considered. You can run
> the water pump from a battery for maximum HP, but an alternator may/
> may not use more mechanical energy than your belt driven pump. Also,
> once the pump is removed you are reducing the engine from driving an
> alternator AND a pump, to just a an alternator.
>
> Wilko
>
> On Feb 3, 2009, at 2:20 AM, Oudesluys wrote:
>
> > A water pump and a mechanical fan need a fair amount of power to be
> > driven. They are not perpetu|m mobilae, so that power needs to come
> > from somewhere: ultimately the engine, and it does not make any
> > difference if that is through the alternator/dynamo and battery. So
> > the power needed for the alternator that will feed the battery and
> > powers the water pump will not be available to drive the wheels.
> > Simple mathematics.
> > Kees Oudesluijs
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