[Healeys] electrc fan vs. belt drive

[Eric (Rick) Wilkins]

Like I was saying... It's not simple mathematics at all.

Wilko

On Feb 4, 2009, at 12:43 PM, Bob Spidell wrote:

> 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