[T3] Alternators for T-3's...
jadney at vwtype3.org
Sat Apr 28 08:25:11 PDT 2012
I'm always amazed by the amount of interest this topic brings up.
Having driven Type 3s with OE generators for over 40 years, I've
never had any need for something "better." Yes, VRs, brushes, and
bearings wear out and need occasional replacement. But alternators
also have VRs, brushes, and bearings. Early alternators, up thru
about 1974 used external mechanical VRs, but by the mid '70s everyone
had started building solid state ones into the alternators. Both
styles occasionally need to be replaced. I've replaced quite a few of
the later style, built-in, solid state regulators. For Bosch
alternators it's easy to do, and the VR assembly includes a new set
of brushes. I think it's a lot harder, or impossible, on some of the
Japanese alternators (meaning, you get to replace the whole
alternator, instead of just the VR.)
My impression is that the "problem" that ends up frustrating many
DIYers is a simple lack of understanding of how to troubleshoot
electrical problems in general and charging systems in particular.
Thus, the charging system seems like a black box that needs to be
replaced, rather than a collection of discrete components, each with
its own function, and each separately testable and repairable at much
I should note here that if you are minimally competent with a
voltmeter, I have a writeup that I'll gladly send to anyone who
requests it. It will walk you thru testing the OE generator system
and allow you to pin down and fix most of the common problems that
arise with it.
Also, if you're having trouble with your OE generator itself, that
you can't fix there, I can usually fix it here, cheaply. They are
heavy, but Priority Mail flat rate boxes make this reasonable. If I
can't fix it, I have lots of good ones here that I can sell.
In all cases, the voltage stability is controlled by the VR, down to
the lower rpm point where the alternator/generator can no longer keep
up. Both systems have these lower thresholds.
Both systems have their weak points. The generator system has a low
rpm threshold that is above the idle speed, simply because generators
have an upper rpm threshold that limits the pulley ratio. Alternators
have no upper rpm threshold, so their pulley ratio can be high enough
to put their lower threshold below idle, but they have 9 (sometimes
6) solid state diodes which can be zapped instantly by an accidental
short or overload that would not bother a generator.
I realize that the 30 Amp generator that comes with 12 V Type 3
systems may seem small to many people, but it's more than enough to
keep up any possible load you could put on the car while driving. If
you like to run all 4 headlight filiments, the windshield wipers, and
the 4-way flashers, all while idling and running enough sound system
power to entertain a block party, then, yes, you're going to run your
What most people don't understand is that you'll probably run your
battery down doing this with a 50 A alternator system, too. Because
your 50 A alternator can't come anywhere close to 50 A at idle.
You'll probably be lucky to get 10% of the full rating out at idle.
I've got a DC clamp-on ammeter that I'll try to remember to bring to
Co Springs. If there's someone there with an alternator upgrade. It
would be interesting to check it out.
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
More information about the type3-vwtype3.org