Actually, the regulator does not ever remove the alternator from the
circuit. That happens only with DC generators. For an alternator (AC
generator), reverse current is prevented by the diodes. The regulator
only adjusts the output voltage. The set point actually varies a fair
amount with temperature (higher when cold), it's not fixed at 14.00 V.
When the alternator is charging (or supplying power to loads), there is
a small, but measurable voltage drop between it's terminals and the
battery, due to current flowing through the (tiny) resistance of the
wires. It should only be a few 1/10ths of a volt, and can normally be
ignored. However, bad connections, corroded wires, etc. can cause it to
be large enough to interfere with charging, so it's worth checking if
you are having troubles. Also check for voltage drop between the
alternator case and the battery negative terminal.
Randall
"James A. Ruffner" wrote:
>
> It should measure the same, since the voltage at the battery terminals, when
> the altenator is active, is the altenator voltage. The altenator runs at
> 13.5-14.5 V, depending on the level of charge on the battery. If the
>altenator
> is not in the circuit (engine speed is low enough that the altenator's output
> voltage is generally below about 13 V,) the regulator removes the altenator
> from the circuit, and the voltmeter will drop to about 11 V. The difference
> between the battery's natural voltage (12.64 V) and the altenator's 14V is
> enough such that the the altenator charges the battery (14V - 12.64V = 1.36V)
> is enough the keep the battery charged. The voltmeter thus will only see the
> altenator's voltage when the regulator allows the altenator to be in the
> circuit.
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