Thread: Idle rpms
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Old 10-02-2001, 01:03 PM
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mburman mburman is offline
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Join Date: Jul 2001
Location: Tampa, FL
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How an alternator works...

I hate to correct people but as a generator mechanic I can't resist this one...

Yes, an alternator is an A/C generator. The voltage does NOT change with rpm, the frequency of the alternation (positive or negative) does. The voltage is maintained by the (usually internal) voltage regulator. The voltage regulator varies the amount of voltage in the exciter (another part of the alternator) which increases or decreases the output voltage. 14.7 volts IS excellent output! In fact, any voltage above the battery's voltage will charge it. To measure battery voltage, with the engine off, connect the meter across the + and - terminals at the battery. If you then start the engine, this measurement becomes alternator output voltage. The current produced by the alternator is a function of demand. Its rating is based upon the wirings ability to handle the heat produced by a given quantity of current. An alternator will maintain its voltage (unless mechanically impaired) down to a very low rotational speed.

Hope this clears up any misconceptions.
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