high-output alternators? - made really long

[DeWitt Harrison]

On Tue, 03 Oct 2006 21:51:13 -0400
        Huw Powell <audi at humanspeakers.com> wrote:

> > Huw- I don't know about Brett's car, but with a good OEM alternator,
> > I've never had any electrical issues related to the alternator in my
> > old car.
>
> > I've never had an issue with the alternator not being able to output
> > enough to run all of the electrical stuff in the car.
>
> I haven't either, even with silly stereos and lights.  (at least, not
> due to inadequate "good" parts) But the 200q20v has a lot of accessories
> that want to run on their own a lot, I guess.
>

It has definitely happened to my '88 5000CS tq. Had an alternator
failure once and was never again able to get another 90A alternator
to survive for long in spite of much troubleshooting and many current
measurements. Nothing was ever obviously amiss but even an
Audi supplied alternator would not last long. The dreaded splice
checked out fine. The solution was to convert to the 110A alternator.
I can't explain it except that I surmise the 90A Bosch unit was
marginal by design (the Audi Philosophy of Electrics) and that, as
the car aged, a bunch of minor degradations gradually added enough
additional load that the OEM alternator could not support it. (My car
has remained close to stock, electrically.) There must have been a reason
Audi made the change from 90A to 110A in the type 44s around 1989.
Btw, an alternator's nominal rating is a peak value. It's sustained output
capability is more on the order of 60% of that rating. That could
explain some things.

> > Is 2 gauge sufficient? I thought you'd need 0 gauge at least for
> > 130A.
>
> I make 2 ga good for 120 amps, very conservative rating.  And you'll
> never be sending that to the battery, anytime you're up in that range
> it's going to accessories.

My sources give 2 AWG wire a 180A rating for "chassis" wiring;
the assumption is that the wire is installed in free, room temperature
air and not as part of a big bundle of other wires, heat dissipation
being the issue. Worst case, bundled with several other heavily loaded
2 AWG wires, #2 is good for 94A. Clearly, the appropriate gauge
depends greatly on the given performance criteria and environment.
There is no 'one size fits all' answer. 120A seems conservative for
2 AWG in our situation, just like the man said, in terms of whether it
burns up or not. But the voltage drop through 2 AWG could also
be a factor to be considered.

> Hmm, maybe he should also add some heavier
> wires to the fusebox, rad fan, etc........