Re: Voltage and suspension questions

[Heather & Jeff <hjr@buffnet.net>]

> The ground looks okay also.  Am I correct in thinking
> > that there should be no change in the voltage (as measured by the center
> > console volt. meter) when the car is under a heavy electrical load.  I
> > notice it especially when the engine fan kicks on.  I'm worried that the
> > alternator may be dying.
> 
> My ur-quattro has the LED strip to indicate battery voltage - if I'm sitting 
> quietly in stationary traffic in summer with the windows open I can see the 
> display drop one or even two segments when the fan kicks in.
> 

A buncha stuff influences your system voltage question.  First of all,
if your alternator is "maxed out", ie it is putting out all that it can
at the particular engine rpm, and you have more electrical load running
than that alternator output, the system voltage will drop from the 14.0
nominal alternator set voltage to closer to the battery steady state
voltage of 12.6.  (or much lower, as in the case when using the starter)
Keep in mind that automotive alternators don't put out much power at
engine idle.

Second of all, when you have a high load, such as the engine fan,
voltage drops will occur due to the resistance in the supply wires from
alt to battery to fan.

Thirdly, all alternator regulators have a design limitation called "load
slump".  This means that with no load, the alternator will put out 14.0
volts.  Under full rated load, the voltage will typically drop from 14.0
to something less than that, typically 13.6 to 13.8.  ( I think the
Bosch spec is 0.2 drop, or to 13.8)  If you put on a cheapie aftermarket
reg, the voltage slump could be worse, say to 13.5 or worse.

By your symptoms, it doesn't sound like you have a problem.  However,
alternators are three phase AC machines that rectify to DC.  If you drop
one phase, thru a stator winding open or a diode blowing open, you lose
1/3 the output.  This is very difficult to diagnose on the car. 
Consequently, we find that up to 40% of alternators that are returned to
us for warranty are actually OK; people think they have a problem, but
cannot easily diagnose it.

We came up with an interesting solution to this problem that we offer on
our alternators that are sold for Class 8 heavy trucks (Semis),
ambulances and fire trucks.  (output range 130 to 270 amps) It's called
our Smartchek self-diagnostic regulator system.  It has circuitry that
analyzes the voltage signature of all three AC phases, plus the DC
level, and field drive current, and if everything is ok it lights a
bi-color LED mounted on the regulator to glow green.  If it senses a
fault, it changes the LED to glow red.  

Jeff Waterstreet
Director Sales & Marketing
Leece-Neville div Prestolite Electric (we be big-ass alternators, inc)

88 80q (obligatory Audi reference)