On Sat, 20 Dec 2003 10:17:10 -0500, "Mark Zarella"
wrote:

I heard that the car battery cannot supply current at a fast enough
rate
(because of chemical reaction neccesary)

You heard wrong. Current due to electron flow moves at the speed of
light.


You're right, Mark, but it is fair to say that a battery might not be
able to "supply current at a fast enough rate" in some instances. If
you have a large current draw that the alternator cannot keep up with,
and the battery has to make up the difference, you can get a
significant voltage drop due to the relatively high internal
resistance in the battery. (This is why even a "good" battery will
often drop down to as low as 9.6V while starting your car.)

That's correct. All power sources have an output Z. But that's quite
different from what he said. Especially in regard to his next comment.


for subwoofers and that a cap is
needed.

At what power ratings should one start to worry about this?

You should start to address whether or not a capacitor will help you if
your
headlights are dimming such that it's become an annoyance to you. When
that
happens, consider installing capacitors as close to the headlights as
possible. Oftentimes it won't be much more money to buy a high output
alternator or have yours modified by a shop. This is a much more
effective
tool to reduce dimming.

I would go even further and recommend upgrading the wiring to the
headlights before trying a capacitor.

I've demonstrated before (in a post to Eddie Runner about 6 months ago - the
math is there in a google search) that the headlight wiring makes no
difference.


True enough. I should have suggested checking the connections and
general condition of the wiring rather than using the vague term
"upgrading". Ten to fifteen amps of current shouldn't tax the factory
wiring, assuming all of the connections are clean.

I noticed you suggested placing the capacitors as close to the
headlamps as possible. If the headlight wiring makes no difference,
than the placement of the caps shouldn't be that critical. If the
headlamp wiring is of adequate size that there's not a voltage drop
between the battery and the headlamps, then there's no reason to worry
about the physical placement of the caps. You could put them in
parallel with the battery, at any location in the car, as long as the
wiring between the capacitors and headlamps doesn't produce a
significant voltage drop with the rated current. I maintain that if
placing the caps closer to the headlamps makes a difference, then the
existing headlamp wiring has problems.


Scott Gardner