--- On Sat, 9/26/09, Stephen A. Lawrence <sa...@pobox.com> wrote:
> From: Stephen A. Lawrence <sa...@pobox.com>
> Subject: Re: [Vo]:Car Alternators Vs Old Style Generators
> To: vortex-l@eskimo.com
> Date: Saturday, September 26, 2009, 10:05 AM
>
>
> Chris Zell wrote:
> > The last car to use generators that I'm aware of was
> the VW Bug. I
> > suppose alternators were cheaper to build.
What a coincidence, I remember an incident where my (pre 70's?) Car Me Ghia? VW
had its alternator go out, and was in fact surprised to learn it was instead a
generator. Your post made me remember this. A freind has a porsche engine in
the older VW busses they made.
> That would make sense. Once cheap reliable high
> current diodes became
> available, the alternator design appears simpler.
>
> On the other hand, I've always heard that alternators are
> preferred
> because they perform better than generators at low RPM --
> in other
> words, their "power band" is wider, which is important for
> something
> which turns at a fixed rate relative to the engine (no
> transmission on
> the generator). I've never checked that claim out,
> however.
Because the (car) alternator has its field regulated, it is designed to
constantly produce 12 or 13 volts, probably even at the lowest rpm available to
it by idle of the automobile.
The PMG site however claims that high amperage extraction at low rpms must be
avoided as it will overheat the stator windings. The one I am purchasing will
be used for a small Brown's gas torch; driven by a 10 hp lawnmower engine. What
this means is that the generator that developes higher voltage at higher rpms
will have a load that "kicks in" only after a certain rpm developes. This is to
be negotiated by the number of cells in series that the unit employs. It would
seem then that my variable speed drive will come in very handy here. As noted
with 40 cells in series, the thermoneutral electrolysis point only being 1.4
volts/cell, this implies that the load should kick in at 56 volts from the
generator, which is probably just under mid range engine rpm for an automotive
application.
HDN
>
> Most of my experience with generators comes from the old
> flathead Willys
> Jeep engines we used in my father's boat, back in the
> day. (Two in
> succession; first replaced when the cylinder walls rusted
> through, due
> to use of an open cooling system in brackish water.
> It's a tradeoff --
> a closed system is more expensive, more complex, and takes
> more
> maintenance, but an open system requires replacing the
> engine block
> every ten years or so.)
>
>
> >
> >
>
>
