Sonerai Alternator Regulator/Rectifier

Andre,
Yes, this approach works. I have a '71 Norton Commando (British 750cc
twin)that has a similar alternator (see later comment on "similar").
Norton uses a two-wire alternator that produces about 18 or 20 VAC at
a couple thousand rpm. The AC is rectified and applied directly across
the battery. There is a high-current 13 (approx) Volt Zener diode
also across the rectifier/battery to provide some shunt regulation to
avoid overcharging the battery. The variation on this theme is to
eliminate the battery and allow the Zener to "regulate" and stabilize
the voltage. This is the scheme I am currently using with my Norton.
The Zener must be sized (power rating) to be able to handle (ie.,
waste (turn into heat))the maximum output of the alternator as would
be the case where you had no electrical load on the running engine (no
radios or lights, etc...)
You did not say, but I will assume your VW has a starter so you will
be using a battery.
So, all you need is a:
1) rectifier (full-wave recommended altho half wave is simpler and is
ok if your electrical load is light and you are primarily only
recharging the battery after a start).
2) shunt regulator (Zener diode) of sufficient power handling
capacity. Finding a high-power 13.5 (approx) Volt Zener diode may be a
problem. Years ago, thay were common but not so anymore. An
alternative equivalent is to make up a shunt regulator with a
low-power Zener and power transistors.... all cheap parts but requires
some "design" and experimenting.
Now, the comment on "similar". Your reported measurements indicate
that you have a center-tapped alternator winding with the center tap
connected to Ground. My Norton alternator winding is two-wire
floating so a simple full-wave bridge rectifier is appropriate. With
your grounded center-tap winding, you will use what is essentially a
half-bridge.

Also, many (most?) of these type alternator systems use a large
(several thousand microFared) electrolytic capacitor across the system
bus to reduce alternator noise. You may not need this... try without
first.

And finally, as an aside, Revmaster (California VW engine builder)
also uses a simple alternator system.

And really finally, I am not aware of any "off-the-shelf" automotive
solution.
Regards,

Sid Knox
Velocity N199RS
Starduster N666SK
KR2 N24TC
W7QJQ


I think it's the motorcycle crowd that you want to enquire from. some
bikes use simmilar crude alternator systems that use very simple
regulator systems.
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Cheers,
Jonathan Lowe
modelflyer at antispam dot net