Thread: Engine Braking
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Old 10-07-2012, 08:36 PM   #30 (permalink)
Mustang Dave
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Join Date: May 2009
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Trigger - '07 Ford Mustang V6 Premium Coupe
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90 day: 32.76 mpg (US)

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Quote:
Originally Posted by wobombat View Post
My understanding of Alternators is that they constantly draw power from the engine and constantly produce a certain amount of amps. If you go over that amp amount, then you'll slowly lose power and your battery will die, but otherwise, electricity is free because whether you use 1 amp or 50 amps you aren't changing the load the alternator draws from the engine. Yet some threads here seem to think that your electricity use effects your fuel economy. I am pretty sure that's wrong and I've seen tests done running the engine without any electrical things going, then running it with everything full blast, and there wasnt any noticable difference between the two in fuel use. So to me there's no reason to not have my lights on all the time because electricity in cars is essentially free.
Your "understanding" violates the laws of physics. The alternator generates enough power to maintain system voltage around 13.8 V with the ECU, radio, and whatever other electrical accessories operating. The power to drive the alternator is proportional to the electrical load placed on it. ANY additional electrical load places a mechanical load on the engine.
I actually DO have a degree in electrical engineering.
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