Re: [alfa] Alternator explanation needed.

["Dean W. Cains" <dwc@xxxxxx>]

Hi Brian:

I've seen it mentioned elsewhere that disconnecting the battery is a way to 
test an alternator, but also that it's a good way to damage the diodes 
within the alternator.  Don't know which is right, or maybe neither 
is.  Anyway, connect the B+ terminal from the alternator to B+ terminal on 
the starter solenoid, and connect the D+ terminal on the alternator to the 
green lead from the alternator warning light.  To test the alternator, use 
a voltmeter and look for better than 13.7V across the battery with the 
engine running above idle speed.  I've got a Milano alternator on my '74 
Spider, wired as described, and it's been working well for several 
years.  The reason your car keeps running with the key off but the green 
wire connected to 12V+ is that you're energizing the ignition circuit 
through the alternator warning bulb.  The bulb is wired to illuminate when 
it sees a difference in voltage across its filament, between the alternator 
and ignition circuits.  I could describe how an alternator works, but 
that's probably not necessary.

Regards,

Dean


At 01:22 AM 7/25/2004, you wrote:

> Date: Sun, 25 Jul 2004 01:21:25 -0400
> From: "Brian Shorey" <bshorey@domain.elided>
> Subject: [alfa] Alternator explanation needed..
>
> Hey folks,
>
> I'm trying to help a friend get a car running for the convention, and I need
> an explanation of how an alternator works..  We're wasting too much time
> staring at wiring, and not making fast enough progress.
>
> We finally got the car running today, but when trying to determine if the
> alternator is charging we came across some puzzling data.  First, an
> explanation of what we're working with, then the data we're observing.
>
> The car is a late 60's Giulia Super.  The dash and gauges are a hybrid of
> stock and aftermarket (stock gauges, aftermarket ignition switch).  The
> engine is a Spica injected 2 liter.  There is no wiring harness (we're
> making it up as we go), and the fuse box is some aftermarket thing.
>
> To confuse things even more, we didn't have an external voltage regulator,
> so we tossed the alternator that came with the 2 liter and bolted up a
> Milano alternator.
>
> The Milano alternator has one stud, to which we connect to the hot lead on
> the solenoid.  Then it has only one other lead, to which we run a green wire
> to ???
>
> It looks like the green wire should be connected to an alternator warning
> lamp.  Ok..
>
> If we don't connect the green wire to anything, the car starts and runs
> fine, and stops when we turn off the ignition switch.  However, to test the
> alternator, I tried disconnecting the battery with the car running and it
> stalled immediately.
>
> However, if I apply 12v to that green wire, the car will run with the
> battery disconnected.  BUT, if I turn off the ignition, it won't stop
> running until I disconnect the green wire.
>
> I'm not sure I understand how this should be working, what I need to connect
> it to, etc.  The best I can see is on a wiring diagram for a late 70's Spica
> Spider, which shows the green lead connected to the alternator warning lamp,
> and the other side of the lamp connected to a switched ignition lead?
>
> Thanks in advance for any insight anybody can provide.
>
> bs
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