Re: Battery Light (+ good tech info) - techies MUST READ

[Cheapass Ron <rapieper@yahoo.com>]

Al you are truly a wonderful guy...you can explain this so's I can
unnerstan it.  Thanks.

List:  here's a lesson on how valuable a nuclear physicist can be (when
properly applied).  

Ron

--- Allyn <amalventano1@home.com> wrote:
> I'll go into 'the details' for marc (p.s. marc, you know all this
> stuff
> already).
> 
> An alternator has rotating winding (armature), as well as stationary
> windings (stator).
>     Current goes through the armature winding (via the rings/brushes
> many of
> you have seen), making it one big rotating magnet. This magnetic
> field is
> felt by the stator windings, causing them to produce an AC output.
> This AC
> is then rectified (converted to DC) and sent out to your battery. The
> regulator 'senses' the DC output voltage and varies the current to
> the
> armature, varying the intinsity of the field, thus varying the output
> voltage. You may be wondering 'what the heck does the regulator part
> have to
> do with the light staying on till i rev the engine*&#$^@', here's
> your
> answer:
>     Picture the car off, alternator is not spinning, nothing
> 'generated' by
> the stator, since the armature is not rotating. The reverse is true
> here: no
> generated voltage, regulator has no voltage to make the armature
> current
> from (dont go thinking it has battery voltage, the battery cannot
> supply
> current TO the alternator, since it would be going backwards through
> the
> rectifier (just go with me on this, it doesnt work that way)).
> Compared to a
> gas grille, the gas is off and there is no flame.
>     Now, you start your car. Belts start spinning the armature. Wait
> a sec,
> there is no armature current, and no stator voltage to make it. So
> now, "The
> gas is on, but there is no flame". What the heck%*&@)%. How does this
> thing
> ever get going you might wonder???
>     Answer: There is a small magnet built into the center of the
> armature
> winding. It supplies the initial field, just enough for the stator to
> generate some voltage (our "spark"), just enough for the regulator to
> send
> current to the armature and 'jack up' the output voltage to the 14VDC
> we're
> all happy to see from a working alternator. The whole process is
> called
> 'flashing the field', which is why i related it all to a gas grille.
>     Question #2: Why does my alternator do this flashing light thing
> now,
> when it didnt do it when the car was new?
>     Answer #2: Several possibilities:
>         1. Magnet is getting weak: rust, heat cycles (remember, from
> high
> school, heh), vibration.
>         2. Rectifier diode(s) are open: the stator on our alternators
> are '3
> phase AC generators' to rectify this type of AC down to single phase
> DC, you
> need a group of 6 diodes. 3 phase systems are high reliability (the
> entire
> power distribution system on my submarine was 3 phase), portions of
> them can
> totally not work, but there will still be at least some output. 1 or
> 2 of
> these diodes can be broken causing the DC output to be weakened.
> While this
> may be ok once the field has flashed, it will require a higher
> rotating
> speed to get it flashed to begin with.
>         3. Stator field winding open: one of the 2 windings could
> have an
> open wire. The effect is the same as open diode(s) associated with
> that
> field.
>     You can 'knock out' one of the 3 phases and still get nearly 50%
> power
> output. Thank VW for overengineering everything, since your scirocco
> can
> probably still run just fine on the 3 phases.
> Hope this info helps everyone.
> Al
> 
> Allyn Malventano, ETC(SS), USN
> 87 Rieger GTO Scirocco 16v (daily driver, 170k, rocco #6) running -
> for now
> 87 Jetta 8v Wolfsburg 2dr (daily driver, 260k, 0 rattles, original
> clutch,
> driveshafts, wheels :)
> 
> 
> ----- Original Message -----
> From: "Marc scirocco Québec" <marc_scirocco@yahoo.ca>
> To: <scirocco-l@scirocco.org>
> Sent: Monday, November 05, 2001 7:36 PM
> Subject: Re: Battery Light
> 
> 
> > This is normal on some alternators, depending on your
> > model.
> >
> > The alternator needs to get "excited" by some voltage
> > to start producing electricity. Without going into too
> > many details bla bla bla, it is normal for some of
> > them.
> >
> > Do not forget that even though it puts out DC Voltage,
> > it actually produce Alternative Current, which then
> > goes through the regulator who rectifies it (with
> > diodes), and regulates it so that it does not goes any
> > higher than 14V.
> >
> > Cheers.
> >
> > Marc
> > '83 Scirocco
> > '88 Scirocco Slegato
> >
> > --- Bill Collins <photo@intrex.net> a écrit : > This
> > comes up on the Vanagon list from time to time.
> > >  The consensus is that its just one of the things
> > > that makes VWs unique.
> > >
> > > I wouldn't worry about it as long as the light
> > > reliably goes out the first time you rev the engine.
> > >
> > > Bill
> > >
> > > > only going out after I've revved the engine past
> > > 3k.
> > > > Then it goes off and stays off.
> > >
> > >
> > > --
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> > >
> >
> >
> >
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> >
> 
> 
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