While I agree with most of what you say to the lil' CAF feller here, there
are a couple of points that I feel the need to open my big mouth about...

And when that happens, the voltage drops to the 12v level of the
battery so that it can kick in the few extra amperes that the
alternator can't for those brief moments in time...

That's wrong, way wrong. Voltage plays no role in which componant
supplies current. The battery and alternator always share the total load
of the cars electrical system. When current demands exceed that of the
alternators output capability, the battery (which has many times the
reserve of any alternator) shoulders a greater share of the load.
Voltage doesn't make any difference - the voltage doesn't even need to
drop for this to occur.

But it DOES drop with increasing current draw. The alternator doesn't all
of a sudden max out at a particular current. The current delivered is
limited by the output impedance of the alternator which, although highly
nonlinear due to the feedback nature of the alternator output, causes a v
drop with increasing current draw. This of course is the nature of the
system's v drop. And the CAFer is partly right in saying the voltage will
approach that of the battery as the battery is required to deliver more
current due to the decrease in v output from the alt. Unfortunately, he
decided to oversimplify things a bit.


Your light bulbs dim simply because light bulbs are brighter on 14.4v
than they are on 12v... that's not a sign of a charging problem.

Again, you ignore current. I'd like to see you light a household light
bulb with 10 AA batteries, and see how bright it gets. The dimming is
because of a lack of current. The dropoff in voltage is a symptom, not a
cause.

When you hook up those 10 AA batteries to the bulb, a current will flow.
This current will cause a v drop across the battery's effective output Z
such that the voltage at the terminal of the battery array will no longer be
15v. Ohm's law tells us that v and i are non-separable (except at the
asymptotes, I suppose).


The capacitor smooths the transition from alternator to battery,

There is no "transition".

Thank you. This needed to be pointed out. I don't know whether he's
oversimplifying here or if he truly believes the battery turns on and off
its current delivery.

quite
dramatically even.. the results can be seen in greatly reduced
headlight dimming, as there's a nice [relatively] slow transition down
to 12v now, rather than a temporary, sudden slam to even below 12v
every time there is a large transient peak.

This may come as a newsflash, but there are capacitors built into
amplifier power supplies, and generally they supply sufficient charge
for normal operation.

Yeah, but they're not good enough. Engineers don't know how to build their
own equipment, right?

Also, there is a lag time for caps too, and it is a function of the load
across the capacitors terminals. That is why manufacturers recommend you
locate the caps closest to the amps.

I have no idea why they recommend this. It can be demonstrated using ohm's
law that placing the caps as close to the headlights (or ECM, or whatever
device is exhibiting the symptom), and thereby lowering the ESL/ESR to the
symptomatic device, reduces the dimming/fluctuation.