Subject: Alternator is taking a while to kick in

[Ben Swann]

Thanks Jim for your clarification and better explanation.

The point is/was the D+ requires a path through the alternator light to establish field current.

Ben

On Tuesday, October 08, 2002 2:36 PM, Dupree, Jim [SMTP:dupree at alldata.com] wrote:
> Your close. With the key on engine off,  battery power is supplied from the
> ignition switch to the charging/alternator/battery light and the D+ circuit
> provides the ground for this light. The current flows through the light (the
> light illuminates)  and grounds through the windings in the alternator and
> initiates the magnetic field in the alternator. When the engine is started
> and the alternator starts charging the D+ becomes a 12 v circuit (via power
> generated by the alternator). The voltage on the D+ (alternator voltage)
> circuit should be the same as the voltage  (battery voltage) to the
> charging/alternator/battery light from the ignition switch and with the
> voltage on both sides of the light no current can flow and the light goes
> out.
> If there is a break in the D+ circuit then the alternator will take longer
> to start charging because there was no current to start the magnetic field.
> It will generate enough current on its own to start the magnetic field but
> it usually takes higher rpm than idle.
>
>
> Thanks
> Jim
>
>  -----Original Message-----
> From: 	Ben Swann [mailto:bswann at worldnet.att.net]
> Sent:	Tuesday, October 08, 2002 10:40 AM
> To:	'passat TS'
> Cc:	'quattro at audifans.com'; 'Comcast'
> Subject:	RE: Subject: Alternator is taking a while to kick in
>
> Carlos,
>
> Study the Bently diagram for your car carefully.
>
> We just went through a similar ordeal with Sean Shoemakers car.  There is
> much discussion recently regarding how the alt works and uses the field
> wire.  Basically, it need to pass a small voltage through the alternator
> light when you start the engine, which activates the field current.  The
> voltages then "equalize" and the alt light goes out, letting you know there
> is no problem and the alt is charging.
>
> This is an oversimplification, I know.  The Bently diagram for all this
> seems rather complex, as there are current track from D+ going all over the
> place, since D+ can also provide the bulb current for the other warning
> lights as well.  Essentially the D+ is the voltage feed for all of the
> warning indicator lights.
>
> Once a field current is established, it becomes self generating, and the D+
> field current is no longer needed (except to power the warning bulbs).  In
> some alternators, they do away with this altogether, but this is how it is
> used on the '80's generation of the AUDI charging circuits AFAIK.
>
> It does sound by your description below, that you have things wired
> incorrectly for the field current to be established. Be careful, as
> improper connection of the D+ wire either to ground or to a high amp source
> like battery + can blow the alternator diodes.  Also, running the alt
> without a load can also blow the diodes.
>
> Ben
>
>
> [On Tuesday, October 08, 2002 10:45 AM, passat TS
> [SMTP:passat_ts at hotmail.com] wrote:
> >
> Ben,
>
> I didn't think about current.
>
> This is a custom panel (used to be a digital crap) that I wired to the male
> connector of the digital dash (I desoldered from a
> broken one). Everything else works fine.
>
> This D+ is the only thing giving me trouble.
>
> 1. I use 12V small bulbs for all the idiot lights.
>
> 2. The Bentley says the D+ should show 12V.
>
> 3. What I understood by reading the arquives is that I should provide 12V
> to the bulb, when ignition is on, and wired the D+ to
> the other lead. So, when the ignition is on, but the car is not running it
> should come on, then when the car starts the D+ switches
> from ground to 12V, and the light turns off.
>
> 4. The behave of the light isn't like that. When I turn the ignition, it
> stays off, when I start the engine it blinks, then stays off.
>
> 5. The alternator seems not to be working for a period of time (voltimeter
> shows less than 12V) then it jumps to the normal
> 14V.
>
> 6. Once it starts to work (14V reading) it charges the battery, since the
> voltimeter shows 12V when the ignition is on but the
> engine is off after a little engine running.
>
> Does it help to give a better idea?
>
> Thanks for any help,
>
> Carlos.]