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Re: [Healeys] electrc fan vs. belt drive

To: Bob Johnson <bjsbj8@gmail.com>
Subject: Re: [Healeys] electrc fan vs. belt drive
From: Bob Spidell <bspidell@comcast.net>
Date: Thu, 5 Feb 2009 17:41:50 +0000 (UTC)
<part 2> 




An analogy is an air conditioning compressor. With A/C off, at idle, the 
compressor is not pushing refrigerant through the system. Turn the A/C on, and 
the compressor has to push the refrigerant through the system, the load on the 
engine increases and the idle speed will drop (modern cars compensate with the 
idle control valve/solenoid, so usually you don't get the drop). Similarly, 
when the load on an alter/generator increases, the unit is required to push 
more electrons through the resistance of the load. If you were turning the 
alternator by hand, you would feel more and more resistance--more effort 
required, i.e. more HP--to turn the alternator, at the same speed, as the load 
increases. Since the power output of an engine is more-or-less fixed, there 
will be less HP at the driven wheels when you have more electrical accessories 
running. 

Actually, electrically-driven accessories are LESS efficient than engine-driven 
accessories. Let's say the alternator is 90% efficient (it probably isn't), and 
a typical electric motor is 90% efficient (again, probably optimistic). Since 
the two are in series--and belt friction/slippage and the inefficiencies of the 
fan or impeller are a wash with mechanically-driven accessories, basically--the 
efficiency of the two is .9 times .9, or roughly 80%. Hence, the 
electrically-driven accessories would be roughly 20% less efficient, all else 
being equal. 

Again, the value of the electrics is the ability to cut or reduce the power to 
the motors when not needed. Also, you can crank up the fan motor at idle--when 
the engine is turning slowly and cars are more inclined to overheat--to keep 
the engine temps down. 


Bob 





----- Original Message ----- 
From: "Bob Johnson" <bjsbj8@gmail.com> 
To: "Oudesluys" <coudesluijs@chello.nl> 
Cc: "Bob Spidell" <bspidell@comcast.net>, "healeys" <healeys@autox.team.net> 
Sent: Thursday, February 5, 2009 8:24:29 AM GMT -08:00 US/Canada Pacific 
Subject: Re: [Healeys] electrc fan vs. belt drive 


There is an implication here, I believe, that the greater the power 
requirement, the harder it is to spin the generator/ alternator. Isn't the 
relationship between the engine and the gen/alt a fixed relationship between 
the pulleys? And following that, the the regulator controls the amount of 
electrical output as required to run whatever you are trying to run on your 
vehicle? I don't know, but it just seems logical to me that the motor turns, 
the gen/alt turns and the horsepower to do this work would be essentially 
constant regardless of electrical power requirements. If you take the 
mechanical water pump out of the system you would save hp requirement for the 
engine, IOW the engine would spin more easily. Then the electrical water pump, 
while requiring hp to run the pump motor would be "free" because more 
electricity would be released by the regulating system. It was always being 
produced, just not being used. Is this true or false? 

Bob Johnson 
BJ8 
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