On Sun, 21 Dec 2003 11:14:06 -0500, "Mark Zarella"
wrote:

WHAT?!?!?!?!....ok if ur headlights dim.... that means that its not
only the headlights that have the shortage issue its everything
sitting on this electric circuit...installing a cap near the
headlights will only take care of the headlights....not everything
else...the car will still be affected by this lov voltage

Well, as Mark said, installing the cap near the headlamps
gives the headlamps preference when it comes to using the capacitors
output, but the rest of the car's electrical system still sees the
benefits of the capacitor.
Mark and I cordially disagree on this point, though. I think
that if there's enough of a voltage drop between the battery and the
headlamps such that you need to put the cap near the headlamps, then
the headlamp wiring probably needs some attention.

It's not the headlight wiring causing the v drop. It's the entire
electrical system. So when capacitors provide high current to the devices,
the impedance of the wires (and the impedance of the cap itself) are the
only limiting factors, and therefore cannot be neglected.

This is based on
my installs, where the connection between the battery and the cap (if
a cap is even needed) is never less than a 4-gauge wire. This means
that there's essentially no voltage drop between the cap and the
battery, so if there's a voltage drop between my cap in the trunk and
the headlamps under the hood, it's a deficiency with the headlamp
wiring.

This is where you're mistaken. 12 ft of *perfect* 4 gauge wire is .003
ohms. The inductance is even more critical (much more critical in fact),
but the effect can be described with just the resistance. Anyway, the
resistance of 5 ft of 12 ga for the headlights is about .008 ohms. So if you
install the cap at the amplifier terminals, the impedance presented to it
from the amp is much smaller than .011 ohms and therefore all of the current
is essentially delivered to the amplifier. Installing it near the
headlights makes the impedance from cap to headlights much smaller than the
.011 ohms in the other direction. You can model this with a simple voltage
divider circuit putting the cap at different nodes. Maybe I'll put up a
website later with the simulations.


With the numbers you're using, 0.003 ohms resistance between the
battery and the headlamps, and 0.008 ohms between the cap and the
battery, I'd consider that "no voltage drop". In this case, your
headlamps would have to draw 300 amps of current before they saw a
1-volt drop between the battery and the headlamps, and they ain't ever
going to draw that much. Even putting the cap back in the trunk, and
using the combined .011 ohms, the headlamps would have to draw 90 amps
before the wiring caused a 1-volt drop. This still isn't going to
happen.

I still say that if putting the capacitor closer to the headlamps
versus back in the trunk with the amps makes a big difference in how
effectively it reduces flickering, then there's something wrong with
your headlamp wiring.

Scott Gardner