<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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