Re: GeneratorYouSay?

[jlandry@domain.elided (John A. Landry)]

In a brilliant stroke of genius, alice@domain.elided blurted out:

>Now for the real mystery.  Why is the second +12v wire 
>required on the DR alternator (either #1 or #2).  It appears to go to 
>the same node (nominal +12v), yet a separate wire is run!?!

Mark,

The number 1 terminal on the Delco alternator is the low voltage source for
the pre-excitation circuit.  In the IH Scout, this terminal is fed by the
resistance wire which is switched on and off by the ignition key.  When the
ignition is turned on, the alternator's rotor field is charged so when it
(the rotor) starts spinning, the stator can begin producing current.

The number 2 terminal provides the internal regulator with a battery
reference voltage.  This allows the regulator to continuously monitor the
battery voltage and control the rotor's field strength, which in turn
controls the alternator's output.

Of course the "BATT" terminal is the alternator's output to charge the
battery, which gets routed through the ammeter.

I haven't tried it, but in theory if the number 1 terminal were
disconnected *before* the alternator is started, it would fail to produce
current when spun.  It couldn't get started.

If the number 2 terminal is disconnected, then the internal regulator has
no way of knowing the true battery state of charge.  Since it sees no
voltage from the battery, it assumes it's dead and adjusts the alternator's
output accordingly.  The result should be *full* alternator output at all
times... which of course would boil the battery dry in short order.

You can imagine the importance of keeping a good clean circuit for both the
number 1 and 2 terminals of the alternator, if it's expected to put out
proper voltage at all times.  Higher than normal resistance in the number 1
terminal supply wire (from corrosion or bad connections) would mean lower
voltage to start the alternator's rotor field.  In that case, I would
expect alternator "cut-in" would be delayed (higher rpm).  High resistance
in the number 2 terminal would cause the regulator to think the battery is
undercharged.

Hope this helps,

John L.
-------------------------------------------------------------------------- 
jlandry AT halcyon DOT com      |
Conservative Libertarian        |  Scout(R) the America others pass by
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Commercial Helicopter - Inst.   | 1976 Scout II Traveler "Patriot" model
http://www.halcyon.com/jlandry/ |     1977 Scout II Traveler (Parts)