I heard that the car battery cannot supply current at a fast enough rate
(because of chemical reaction neccesary) for subwoofers and that a cap is
needed.

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

Most of the people here will tell you that you never have to worry
about a cap, since it is useless - I do not completely agree with that
though. If you have a power problem, invest your money into a better
electrical system (battery/alternator).

My opinion is that if your light on the car dim a bit on deep bass
tone, a cap will fix this problem. I bought one to fix this and I see
no diming anymore; it also look cool.

The way you asked the question, it sounds like you do not know if you
need one. If you don't know if you need one, you probably don't.

Andre.

"Johan Wagener" wrote in message ...
I heard that the car battery cannot supply current at a fast enough rate
(because of chemical reaction neccesary) for subwoofers and that a cap is
needed.

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

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.

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.

On Fri, 19 Dec 2003 11:53:52 -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.)

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. And I agree, if you can get a
new alternator or get your current one rewound for reasonably little
money, that's probably the way to go.

Scott Gardner

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.

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

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.

Dimming isn't a matter of taxing the wiring though. It's the system voltage
fluctuation. That's why the resistance of the wire has no bearing on the
level of dimming. Just the average power of the headlight output.

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.

I wouldn't call it critical. If the cap is part of the aesthetics of the
installation, then install it wherever. But it's most effective near the
device that needs it, as it minimizes the impedance between the cap and the
symptomatic device (eg. headlights) while maximizing it elsewhere. Ideally,
you'd diode isolate the headlights, but then you have to deal with high
current diodes and a diode drop. Placing the cap near the headlights is the
second best solution, because the ratio of impedance between cap and
headlights and cap and rest of system is maximized in that case, and as a
result the currentfrom the cap "preferentially" flows through the
headlights.

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.

But there's always a v drop. The question is how significant it is. Well,
if the cap is delivering a large amount of transient current (which is
supposedly the point of using them), then the v drop can be substantial.
And in fact, it turns out the inductance of the wire may even be more
detrimental.

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.

Neglecting reactance, let's suppose the resistance of the wire from
headlight to battery is equal to the resistance of the wire from battery to
amp. Then by putting it in parallel with the battery, or even better, on a
separate lower impedance wire (right next to the headlights, for instance)
the resistance from cap to headlight will be halved (or better).

So why does this matter? It's not uncommon for the resistance of the wire
from battery to amp to be, say, .01 ohms (about 15ft of 8 gauge, not
including connections and imperfections). The resistance from the battery
to headlights is probably at least that amount (6ft of 12ga is about .01
ohms). Putting the cap at the amp doubles (at least) the resistance between
cap and headlights AND increases the current draw from the cap due to the
amp which contributes to the effective v drop due to a faster rate of
discharge since the amp draws more current than the headlights. In summary,
it's ideal to minimize the resistance between cap and headlights AND
maximize resistance between cap and the remainder of the system. Diode
isolating the headlights is the extreme of this concept, as the resistance
between the cap and the rest of the system approaches infinity. And as I
mentioned previously, the inductance of the wire also plays an important
role due to the transient nature of the cap discharge, and there's a linear
relationship between inductance and wire length - which can get rather long
with a typical amplifier power wire.

"Mark Zarella" wrote in message ...
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.

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.


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

On 21 Dec 2003 00:47:27 -0800, (Stevo)
wrote:

"Mark Zarella" wrote in message ...
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.

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.


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. 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. Other people's installs may have different results.
Also, Mark makes the point that just because you're seeing
flickering of your headlamps and/or dash lighting, the rest of your
car , including your stereo, may be perfectly happy. Lights will
noticeably flicker with as little as a 1-volt drop, but things like
ignition systems, computers, and most stereo components are regulated
to work just fine with anything from 11V or lower up to 16V. Even if
you have an unregulated power supply in your amplifier, the
short-duration voltage drop probably isn't going to be noticeable to
your ears, even if it causes your lights to flicker.

Scott Gardner

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.

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

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

Who cares about the rest of the car? What's the fluctuation going to hurt?
The only reason the driver even notices that there's a fluctuation is
because of dimming. If the fluctuation is so severe that it could
potentially cause damage, then more important issues must be addressed.

X-No-Archive: Yes

A capacitor is basically a reservior with a very small internal resistance.
It is very effective at supplying a very high instantaneous current.

It's best placed as close as possible to load requiring high instantaneous
current. When there's a demand for more power, electricity comes from a
source with smallest impedance. In this case, a low internal resistance
capacitor placed within a foot of amplifier rather than from rather high
internal resitance battery connected a few feet away.

By letting the capacitor supply peak demand, you can reduce the sagging on
upstream.

Johan Wagener wrote:

I heard that the car battery cannot supply current at a fast enough rate
(because of chemical reaction neccesary) for subwoofers and that a cap is
needed.

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

In article ,
"Johan Wagener" wrote:

I heard that the car battery cannot supply current at a fast enough rate
(because of chemical reaction neccesary) for subwoofers and that a cap is
needed.

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


When the current is high enough to worry, you're in need of more storage
than the usual 1 to 3 F cap. Car audio stiffening caps are mostly a
gimmick.

"Kevin McMurtrie" wrote in message
...
In article ,
"Johan Wagener" wrote:

I heard that the car battery cannot supply current at a fast enough rate
(because of chemical reaction neccesary) for subwoofers and that a cap
is
needed.

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


When the current is high enough to worry, you're in need of more storage
than the usual 1 to 3 F cap. Car audio stiffening caps are mostly a
gimmick.

explain who there a gimmick, if you need a big boost of volts for a bass
note you'll need the cap then the batt. will never get the power down the
line quickly enough.

explain who there a gimmick, if you need a big boost of volts for a bass
note you'll need the cap then the batt. will never get the power down the
line quickly enough.

What do you mean? It moves at the speed of light.

"Mark Zarella" wrote in message
...
explain who there a gimmick, if you need a big boost of volts for a bass
note you'll need the cap then the batt. will never get the power down
the
line quickly enough.

What do you mean? It moves at the speed of light.

electricy does not always move at the speed of light, it depends on the
medium

explain who there a gimmick, if you need a big boost of volts for a
bass
note you'll need the cap then the batt. will never get the power down
the
line quickly enough.

What do you mean? It moves at the speed of light.

electricy does not always move at the speed of light, it depends on the
medium

Right. In fact, it never moves at the speed of light. But relatively
speaking, it's close enough. So that still doesn't clarify your point.

"Johan Wagener" wrote in message
...
I heard that the car battery cannot supply current at a fast enough rate
(because of chemical reaction neccesary) for subwoofers and that a cap is
needed.

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


some people don't realize that if you have a fully regulated amp, you get
little to no benefits. if it's un-or-semi regulated you may/can see some
benefits

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


some people don't realize that if you have a fully regulated amp, you get
little to no benefits. if it's un-or-semi regulated you may/can see some
benefits

How do you figure? Headlight dimming would be more pronounced if anything
for a fully regulated amp.

Just to add alittle to the Headlight dimming and the cap issue. Take the
cars charging system. Simulations lack Time Lag for the Regulator to pick up
on a Voltage fluctuation. Not to mention that the Cars electrical system is
run buy the alt when running. WHen demads are high enough the Alt cannot
keep up and we have Voltage sag, which inturn drops the enitire voltage of
the charging system.

Seeing that almost all electrical components are in parallel with the Alt
and battery. That fluctuation will be felt throughout the electrical system.
So those that say if a 50A draw causes a 1V flucuation at the amp that sag
will be produced throughout the entire system.

Not to mention that most auto manufactures do not use the best techniques
for wiring Headlights. Their are reasons why wpoplw rewire Headlights with
Bigger Ga. Wire, Relay's and use the Head light switch wiring for Relay
activation.

--
1991 Tornado Red Corrado, CCA Member # 6645
Stereo is a continuous W.I.P.

There are two parts to wisdom:
1) Having a lot to say, and
2) Not saying it.

Just to add alittle to the Headlight dimming and the cap issue. Take the
cars charging system. Simulations lack Time Lag for the Regulator to pick
up
on a Voltage fluctuation.

Not if you make the current draw frequency low enough. You could even
attempt to simulate the PWM action by putting a high frequency in the low
freq envelope. But it's unnecessary for our purposes.

Not to mention that the Cars electrical system is
run buy the alt when running.

That's easily simulated. Just raise the voltage and modify the output Z.
Or if you want to get really fancy, put a second source in parallel.

WHen demads are high enough the Alt cannot
keep up and we have Voltage sag, which inturn drops the enitire voltage of
the charging system.

Seeing that almost all electrical components are in parallel with the Alt
and battery. That fluctuation will be felt throughout the electrical
system.
So those that say if a 50A draw causes a 1V flucuation at the amp that sag
will be produced throughout the entire system.

Correct. The fluctuation is the result of the output impedance of the
source.

Not to mention that most auto manufactures do not use the best techniques
for wiring Headlights. Their are reasons why wpoplw rewire Headlights with
Bigger Ga. Wire, Relay's and use the Head light switch wiring for Relay
activation.

Right. Many manufacturers run the headlight power all the way to the dash,
through the switches, and back again. People often modify the circuit so
this wire drives a relay. This is done to improve the total output of the
headlights. But it actually does not improve the flickering!

"Mark Zarella" wrote in message
...
At what power ratings should one start to worry about this?


some people don't realize that if you have a fully regulated amp, you
get
little to no benefits. if it's un-or-semi regulated you may/can see
some
benefits

How do you figure? Headlight dimming would be more pronounced if anything
for a fully regulated amp.

no it wouldn't, fully reg. amps put less strain on elec. systems then
un-reg. amps.

How do you figure? Headlight dimming would be more pronounced if
anything
for a fully regulated amp.

no it wouldn't, fully reg. amps put less strain on elec. systems then
un-reg. amps.

No, the dimming would be more pronounced because the regulated amp would
draw more current than the unregulated counterpart. That is, in order to
compensate for the drop in input voltage, excess current is drawn in the
regulated amp. In an unregulated amp, the current drawn is directly
proportional to the supply voltage. As a result, dimming increases with
more regulation.

"Mark Zarella" wrote in message
...
How do you figure? Headlight dimming would be more pronounced if
anything
for a fully regulated amp.

no it wouldn't, fully reg. amps put less strain on elec. systems then
un-reg. amps.

No, the dimming would be more pronounced because the regulated amp would
draw more current than the unregulated counterpart. That is, in order to
compensate for the drop in input voltage, excess current is drawn in the
regulated amp. In an unregulated amp, the current drawn is directly
proportional to the supply voltage. As a result, dimming increases with
more regulation.

no it's less pronounced the amp will change the rail voltage to compensate
for lost power.