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Re: I'm Kinda Dense: Alternators Again
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Posted by Bob M on March 09, 2005 at 13:26:12 from (151.190.254.108):
In Reply to: Re: I'm Kinda Dense: Alternators Again posted by Allan in NE on March 09, 2005 at 12:28:08:
>But, on an internally regulated alternator (I’m talking GM), the exciter circuit does not provide field current in any way whatsoever and the battery does not provide any field current to the alternator in any form.< Not quite! The exciter circuit uses battery current to provide the initial “flash” current to the field at startup. It draws this current until the alternator develops an output voltage higher than the battery voltage. >If this were the case, the darned alternator would stop charging if you removed the battery. It doesn't, take the battery out of the picture and the alternator just keeps right on a doin' it's job of maintaining system voltage and providing field current as needed.< Not recommended! The battery serves as a stabilizing ballast and helps the regulator system voltage under control. With the battery removed the system is liable to go unstable and either exhibit wild voltage swings (25 – 30 volts or more), or the alternator may simply self-destruct. Don’t ask how I might know this! >The exciter current only turns on the regulator gate and takes the alternator out of isolation. Yes, by hot-wiring the exciter, the regulator stays on all the time, but so what? There is always power at the light switch too. Since the regulator uses the alternator's own induced voltage as a field voltage source, without rotor rotation, there is absolutely no draw thru the field circuitry anyway.< Again, not quite. If the rotor stops, the regulator draws a couple hundred milliamps from the #1 terminal as it attempts to reflash the field. It will continue to draw this current until the alternator resumes generating current. If you run the alternator daily it won’t be a problem. But if left idle for several days the constant small drain will kill the battery. Thus you must have a switch to cut off voltage to the #1 terminal when shut down. Hope this makes sense! Bob M
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