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  #1   Report Post  
 
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Default Capacitor, how to find out what size?

Im anticipating that I will need a capacitor with my current setup. I
havent finished the install yet but I think more power will be needed.
How do you know what size cap to get? Is there a formula or something?

Ive also heard that its possible to get too large a cap. Any truch to
this? and or can a cap too big damage the amp(s)

Thx

  #2   Report Post  
MZ
 
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Default Capacitor, how to find out what size?

"http://www.mobileaudio.com/rac-faq/rac-faq_2.html#SEC21"

--
Mark
that was easy...

wrote in message
...
Im anticipating that I will need a capacitor with my current setup. I
havent finished the install yet but I think more power will be needed.
How do you know what size cap to get? Is there a formula or something?

Ive also heard that its possible to get too large a cap. Any truch to
this? and or can a cap too big damage the amp(s)

Thx



  #4   Report Post  
Scott Gardner
 
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Default Capacitor, how to find out what size?

On Wed, 10 Mar 2004 21:04:16 -0500, thelizman
wrote:

wrote:
Im anticipating that I will need a capacitor with my current setup.


You won't.

I
havent finished the install yet but I think more power will be needed.
How do you know what size cap to get? Is there a formula or something?


Many shops will tell you 1 fd / 1000 watts. Then they'll sell you one.
The latter should cast suspicion on the former.

Ive also heard that its possible to get too large a cap. Any truch to
this? and or can a cap too big damage the amp(s)


No. It won't. But it doesn't matter - you won't need a cap anyway.

--
thelizman "I didn't steal the FAQ either"


So what's your course of action when a customer complains about
flickering or dimming headlamps/dash lights, but he's not having any
battery charging problems? Do you tell him to "suck it up and live
with it", or do you sell him a high-capacity alternator or lower-ESR
battery that he doesn't really need?

I don't believe capacitors will make your system "louder", "cleaner",
or "hit harder", but I have seen small capacitors fix lighting
problems when the charging system was otherwise adequate.

Scott Gardner


  #5   Report Post  
MZ
 
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Default Capacitor, how to find out what size?

With the 100 bucks I would spend on a cap, I'd rather buy a new higher
power
alternator.

Just my 2 cents.


....which may or may not be more effective in the light dimming department
than the cap.




  #6   Report Post  
electricked
 
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Default Capacitor, how to find out what size?


"Scott Gardner" wrote in message
...
On Wed, 10 Mar 2004 21:04:16 -0500, thelizman
wrote:

wrote:
Im anticipating that I will need a capacitor with my current setup.


You won't.

I
havent finished the install yet but I think more power will be needed.
How do you know what size cap to get? Is there a formula or something?


Many shops will tell you 1 fd / 1000 watts. Then they'll sell you one.
The latter should cast suspicion on the former.

Ive also heard that its possible to get too large a cap. Any truch to
this? and or can a cap too big damage the amp(s)


No. It won't. But it doesn't matter - you won't need a cap anyway.

--
thelizman "I didn't steal the FAQ either"


So what's your course of action when a customer complains about
flickering or dimming headlamps/dash lights, but he's not having any
battery charging problems? Do you tell him to "suck it up and live
with it", or do you sell him a high-capacity alternator or lower-ESR
battery that he doesn't really need?

I don't believe capacitors will make your system "louder", "cleaner",
or "hit harder", but I have seen small capacitors fix lighting
problems when the charging system was otherwise adequate.

Scott Gardner


With the 100 bucks I would spend on a cap, I'd rather buy a new higher power
alternator.

Just my 2 cents.

--Viktor


  #7   Report Post  
EFFENDI
 
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Default Capacitor, how to find out what size?

MZ wrote:

With the 100 bucks I would spend on a cap, I'd rather buy a new higher


power

alternator.

Just my 2 cents.



...which may or may not be more effective in the light dimming department
than the cap.



Agreed. I thought I would need a cap for my system but ended up being
able to get a new alt and double the amperage for less than the
'reccomended' size cap i would 'have' to buy.

EFFENDI
  #8   Report Post  
Scott Gardner
 
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Default Capacitor, how to find out what size?

On Thu, 11 Mar 2004 09:21:24 GMT, EFFENDI
wrote:

MZ wrote:

With the 100 bucks I would spend on a cap, I'd rather buy a new higher


power

alternator.

Just my 2 cents.



...which may or may not be more effective in the light dimming department
than the cap.



Agreed. I thought I would need a cap for my system but ended up being
able to get a new alt and double the amperage for less than the
'reccomended' size cap i would 'have' to buy.

EFFENDI


I guess a lot of it depends on your car, too. For my car, $100 won't
even buy a stock-replacement 60A alternator. $120 will get you an 85A
aftermarket replacement, but that's as high as it goes unless you get
into custom brackets and the like.

Scott Gardner


  #9   Report Post  
 
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I would tend to agree that the 100 bucks or so would be better spent on
upgrading the alternator, however, in my case, GM didnt spare an inch
cramming the LS1 into the firhawks engine compartment. There literaly
is no room for a larger alternator.

  #10   Report Post  
MZ
 
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Default Capacitor, how to find out what size?

...which may or may not be more effective in the light dimming
department
than the cap.



Agreed. I thought I would need a cap for my system but ended up being
able to get a new alt and double the amperage for less than the
'reccomended' size cap i would 'have' to buy.


That's not really the point I was making. I was suggesting that in some
cases a cap is actually more effective. High output alternators often
suffer from the same limitations that a stock alternator suffers from when
idling.




  #11   Report Post  
Captain Howdy
 
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Default Capacitor, how to find out what size?

Where do you shop, $100 for a higher power alternator?

With the 100 bucks I would spend on a cap, I'd rather buy a new higher power
alternator.

Just my 2 cents.

--Viktor


  #12   Report Post  
Captain Howdy
 
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Default Capacitor, how to find out what size?


What makes you think that you need a larger alternator in size for more
output? The case size does not need to change.

In article , "
wrote:
I would tend to agree that the 100 bucks or so would be better spent on
upgrading the alternator, however, in my case, GM didnt spare an inch
cramming the LS1 into the firhawks engine compartment. There literaly
is no room for a larger alternator.

  #13   Report Post  
Captain Howdy
 
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Default Capacitor, how to find out what size?

Yup.

That's not really the point I was making. I was suggesting that in some
cases a cap is actually more effective. High output alternators often
suffer from the same limitations that a stock alternator suffers from when
idling.


  #14   Report Post  
Brandon Buckner
 
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Default Capacitor, how to find out what size?

That all depends on what was meant as "higher power". I know I can get
either a new slightly more powerful alternator or get my current
alternator rewound to a higher rating (say about 95 amp or 100 amp) for
around $100 for my Contour. It may not be a 200+ amp alt, but it'd be
"higher power" than my stock 80-85 amp.

Brandonb


Captain Howdy wrote:

Where do you shop, $100 for a higher power alternator?

With the 100 bucks I would spend on a cap, I'd rather buy a new higher power
alternator.

Just my 2 cents.

--Viktor



  #15   Report Post  
MZ
 
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Default Capacitor, how to find out what size?

That's not really the point I was making. I was suggesting that in some
cases a cap is actually more effective. High output alternators often
suffer from the same limitations that a stock alternator suffers from

when
idling.


MZ, at the same RPM a higher power alternator will produce more current

than
a lower power alternator.


Not always! In fact, some produce less current than the stock at idle.

If you have enough power coming from the alternator there will be less
problems with lights dimming since the alternator will be producing enough
current to power both your system and lights at same time.


That's right. But sometimes (certainly not always) a capacitor will
contribute more towards reducing dimming than an alt. It depends entirely
on how bad off your electrical system is in relation to the power demands of
the vehicle, as well as the type of music and listening habits of the user.

Most of the time you need more power only for the bass. The tweeters and
midranges dont need as much power. If you have xover's then the subs and
tweeters for example won't be running at the same time, so it's safe to
assume that you can get alternator to cover your subs and other

accessories.
If you don't have xover's then you have to get alternator that will cover
all speakers running at the same time (e.g. tweeters+midranges).


I'm not following this paragraph. The alternator (and capacitor) affects
all aspects of the electrical system.

Of course, if all you have is a 100 dollar bill, spend it on cap. It won't
give you more power, it will cover the surge power needed for bass.


It can deliver a sufficient amount of current in a short enough period of
time to have a noticeable effect on headlight dimming at all rpms.

And MZ, please tell both sides of story when making a point. It's easier

to
understand why they should or shouldn't choose one over other (new

alt/cap,
etc.)


I believe I have told both sides of the story. Check the FAQ.




  #16   Report Post  
thelizman
 
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Default Capacitor, how to find out what size?

Scott Gardner wrote:

So what's your course of action when a customer complains about
flickering or dimming headlamps/dash lights, but he's not having any
battery charging problems?


Bull****. If their stock electrical system can't supply the current to
keep lights from dimming, then they are having charging problems. They
need to upgrade their ground paths (hint: that stock 10 gauge to the
fender isn't helpting), sometimes the alternator, but the last thing you
should think about adding to an otherwise healthy electrical system is a
cap. Caps really only become necessary on large multi-amp systems.

Do you tell him to "suck it up and live
with it", or do you sell him a high-capacity alternator or lower-ESR
battery that he doesn't really need?



There's the keyword: "sell". There's more money to be made selling
people caps and batteries than a few feet of heavy gauge wire.


--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.
  #18   Report Post  
electricked
 
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Default Capacitor, how to find out what size?


"Captain Howdy" wrote in message
news
Where do you shop, $100 for a higher power alternator?

With the 100 bucks I would spend on a cap, I'd rather buy a new higher

power
alternator.

Just my 2 cents.

--Viktor


What I meant was spend those $100 toward a new alternator. I never said
you'll find an alternator for $100. That won't even buy you stock one, even
rebuilt stock for most vehicles.

--Viktor


  #19   Report Post  
electricked
 
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Default Capacitor, how to find out what size?


"MZ" wrote in message
news
...which may or may not be more effective in the light dimming

department
than the cap.



Agreed. I thought I would need a cap for my system but ended up being
able to get a new alt and double the amperage for less than the
'reccomended' size cap i would 'have' to buy.


That's not really the point I was making. I was suggesting that in some
cases a cap is actually more effective. High output alternators often
suffer from the same limitations that a stock alternator suffers from when
idling.


MZ, at the same RPM a higher power alternator will produce more current than
a lower power alternator.

If you have enough power coming from the alternator there will be less
problems with lights dimming since the alternator will be producing enough
current to power both your system and lights at same time.

Most of the time you need more power only for the bass. The tweeters and
midranges dont need as much power. If you have xover's then the subs and
tweeters for example won't be running at the same time, so it's safe to
assume that you can get alternator to cover your subs and other accessories.
If you don't have xover's then you have to get alternator that will cover
all speakers running at the same time (e.g. tweeters+midranges).

Of course, if all you have is a 100 dollar bill, spend it on cap. It won't
give you more power, it will cover the surge power needed for bass.

And MZ, please tell both sides of story when making a point. It's easier to
understand why they should or shouldn't choose one over other (new alt/cap,
etc.)

--Viktor


  #20   Report Post  
Scott Gardner
 
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Default Capacitor, how to find out what size?

On Thu, 11 Mar 2004 22:55:30 -0500, thelizman
wrote:

Scott Gardner wrote:

So what's your course of action when a customer complains about
flickering or dimming headlamps/dash lights, but he's not having any
battery charging problems?


Bull****. If their stock electrical system can't supply the current to
keep lights from dimming, then they are having charging problems.


I disagree. Alternators only need to be able to keep up with the
*average* current demands of the car's electrical system, and as
you've pointed out in another thread, average current draw can often
be surprisingly low.

If you can drive around all day with the headlamps on and the stereo
cranked up without draining your battery, then the alternator is
obviously keeping up with the average current demand, even if you get
some flickering of the dash lights or headlamps during short periods
of peak demand. Rather than replacing the alternator with a
higher-capacity model, one or more small, well-placed capacitors can
stop the dimming problem. However, I think we both agree that the
sound quality/SPL level won't be affected.

I think that upgraded alternators are often recommended when they're
not needed, although I agree that capacitors are needlessly installed
MUCH more often.

Scott Gardner




  #21   Report Post  
Eric Desrochers
 
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Default Capacitor, how to find out what size?

Scott Gardner wrote:

So what's your course of action when a customer complains about
flickering or dimming headlamps/dash lights, but he's not having any
battery charging problems? Do you tell him to "suck it up and live
with it", or do you sell him a high-capacity alternator or lower-ESR
battery that he doesn't really need?


The dealer would of course try to sell a cap but for the rest of the
world, understanding that a small light flickering is a non-issue and
move on seem like the sensible choice to do.

My 0.02
--
Eric (Dero) Desrochers

Hiroshima 45, Tchernobyl 86, Windows 95
  #22   Report Post  
Tha Ghee
 
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"electricked" no_emails_please wrote in message
...

"Scott Gardner" wrote in message
...
On Wed, 10 Mar 2004 21:04:16 -0500, thelizman
wrote:

Scott Gardner


With the 100 bucks I would spend on a cap, I'd rather buy a new higher

power
alternator.

Just my 2 cents.

--Viktor

I dont' know of a higher power alt you can get for $100 unless you get the
factory upgraded amp. unless a lower ESR batt. is in the plans a cap is
very cost effective.


  #23   Report Post  
Tha Ghee
 
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"electricked" no_emails_please wrote in message
...

"Captain Howdy" wrote in message
news

Just my 2 cents.

--Viktor


What I meant was spend those $100 toward a new alternator. I never said
you'll find an alternator for $100. That won't even buy you stock one,

even
rebuilt stock for most vehicles.

--Viktor

slight problem, you still need the power at idle where the lights usually
dim. for some aftermarket alts. they actually put out less power at idle
which will make the problem worse not better.


  #24   Report Post  
thelizman
 
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Eric Desrochers wrote:

The dealer would of course try to sell a cap but for the rest of the
world, understanding that a small light flickering is a non-issue and
move on seem like the sensible choice to do.

My 0.02


Here's some change: That light flickering is a symptom of unstable
voltage. Ripples in voltage can damage digital electronics, cause
malfunctions, and other problems. Ignoring this is not a sensible thing
at all.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.
  #25   Report Post  
thelizman
 
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Default Capacitor, how to find out what size?

Tha Ghee wrote:
slight problem, you still need the power at idle where the lights usually
dim. for some aftermarket alts. they actually put out less power at idle
which will make the problem worse not better.


That's why cars have batteries. If you have flicker at idle, it's
because your power and ground wires at the battery and alternator are
insufficient are insufficient.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.


  #26   Report Post  
Eric Desrochers
 
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thelizman wrote:

Eric Desrochers wrote:

The dealer would of course try to sell a cap but for the rest of the
world, understanding that a small light flickering is a non-issue and
move on seem like the sensible choice to do.

My 0.02


Here's some change: That light flickering is a symptom of unstable
voltage. Ripples in voltage can damage digital electronics, cause
malfunctions, and other problems. Ignoring this is not a sensible thing
at all.


From my Alpine CDA-9815 HU user manual :

Nominal voltage : 14.4 (11-16 volts permissible)

Looks like they can take quite a variation after all! Sensible circuits
should have filtred and regulated power supplies and I bet it's the case
in quality equipment.

--
Eric (Dero) Desrochers

Hiroshima 45, Tchernobyl 86, Windows 95
  #27   Report Post  
MZ
 
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slight problem, you still need the power at idle where the lights
usually
dim. for some aftermarket alts. they actually put out less power at idle
which will make the problem worse not better.


That's why cars have batteries. If you have flicker at idle, it's
because your power and ground wires at the battery and alternator are
insufficient are insufficient.


At idle, your alternator is still producing ~14v. So a 1.5 volt drop down
to battery voltage can still produce a noticable dimming effect. Most alts
deliver relatively little current at idle, so it's often not difficult to
get that 1.5v drop. Depending on the severity of the situation, a cap can
often alleviate the dimming effect rather substantially. The power and
ground wires at the battery and alt, as well as the general "health" of the
battery and alt should always be checked out first though.


  #28   Report Post  
MZ
 
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Here's some change: That light flickering is a symptom of unstable
voltage. Ripples in voltage can damage digital electronics, cause
malfunctions, and other problems. Ignoring this is not a sensible thing
at all.


The fluctuation every time you start your car is more severe than the
dimming associated with the audio system.

Hell, Eddie Runner calls the dimming a feature...


  #29   Report Post  
thelizman
 
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Eric Desrochers wrote:
From my Alpine CDA-9815 HU user manual :

Nominal voltage : 14.4 (11-16 volts permissible)


"Permissible". The word "permissible" in no way negates the fact that
some malfunction may occur. If you're so include, put a voltage
regulator on your headunits ground path, and limit it to 11 volts. Call
me when you learn better.

And how do you go from a cars ECM to your Alpine headunit? Are you
familiar with the term "non sequiter"?

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.
  #30   Report Post  
thelizman
 
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Default Capacitor, how to find out what size?

MZ wrote:

The fluctuation every time you start your car is more severe than the
dimming associated with the audio system.


Sorry Mark, but no. When starting, ECMs operate in open loop mode, which
requires very little current and voltage.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.


  #31   Report Post  
Eric Desrochers
 
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Default Capacitor, how to find out what size?

thelizman wrote:

Eric Desrochers wrote:
From my Alpine CDA-9815 HU user manual :

Nominal voltage : 14.4 (11-16 volts permissible)


"Permissible". The word "permissible" in no way negates the fact that
some malfunction may occur. If you're so include, put a voltage
regulator on your headunits ground path, and limit it to 11 volts.


Don't have to, there's one inside the deck.

Call
me when you learn better.


OK.

And how do you go from a cars ECM to your Alpine headunit?


The only ECMs I know of are those my sat TV provider send to diseable
hacked receivers.

Are you
familiar with the term "non sequiter"?


I'm affraid I'm not. Must be a language barrier thing.

Regards,
--
Eric (Dero) Desrochers

Hiroshima 45, Tchernobyl 86, Windows 95
  #32   Report Post  
Tha Ghee
 
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Default Capacitor, how to find out what size?

"thelizman" wrote in message
...
Tha Ghee wrote:
slight problem, you still need the power at idle where the lights

usually
dim. for some aftermarket alts. they actually put out less power at idle
which will make the problem worse not better.


That's why cars have batteries. If you have flicker at idle, it's
because your power and ground wires at the battery and alternator are
insufficient are insufficient.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.


if your batt. is weak which most times it is, it doesn't matter, what the
alt or wires are like. if your going with a aftermarket alt. it may not
work any better.


  #33   Report Post  
Tha Ghee
 
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Default Capacitor, how to find out what size?

"thelizman" wrote in message
...
Eric Desrochers wrote:

The dealer would of course try to sell a cap but for the rest of the
world, understanding that a small light flickering is a non-issue and
move on seem like the sensible choice to do.

My 0.02


Here's some change: That light flickering is a symptom of unstable
voltage. Ripples in voltage can damage digital electronics, cause
malfunctions, and other problems. Ignoring this is not a sensible thing
at all.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.


how can there be ripples in DC voltage??


  #34   Report Post  
Tha Ghee
 
Posts: n/a
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"thelizman" wrote in message
...
MZ wrote:

The fluctuation every time you start your car is more severe than the
dimming associated with the audio system.


Sorry Mark, but no. When starting, ECMs operate in open loop mode, which
requires very little current and voltage.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
other than usenet without the express written permission of the author
is forbidden.


no Mark is correct here, the fluctuation is greatest at startup of the car
and audio system. this is why most things break when you turn them off,
like light bulbs.


  #35   Report Post  
MZ
 
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how can there be ripples in DC voltage??

Because there's an AC component that derives from the alternator or
transient current draws.




  #36   Report Post  
thelizman
 
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Tha Ghee wrote:

if your batt. is weak which most times it is,


You're average car battery can put out more power than half a dozen
alternators.

--
thelizman "I didn't steal the FAQ either"

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  #37   Report Post  
thelizman
 
Posts: n/a
Default Capacitor, how to find out what size?

Tha Ghee wrote:


how can there be ripples in DC voltage??


....proof that there is such a thing as a "stupid question".



--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

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"It's about the music, stupid"

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  #38   Report Post  
thelizman
 
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Default Capacitor, how to find out what size?

Tha Ghee wrote:

no Mark is correct here, the fluctuation is greatest at startup of the car
and audio system.


You don't read engrish very well do you?

this is why most things break when you turn them off,
like light bulbs.


Light bulbs break when you turn them on. They break because over time
the filament loses mass as it is vapor deposited on the cool surface of
the inside of the bulb. When enough material vaporizes, the filament can
no longer handle the current passing through it.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
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  #39   Report Post  
thelizman
 
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Default CAFacitor Myths (was " Capacitor, how to find out what size?")

geolemon wrote:

ONLY if the -average- current draw exceeds your alternator's
capabilities do you have a -charging- problem...


That's oversimplified - and wrong. If the cables are corroded, the
biggest alternator in the world won't charge. If the connections are
corroded, the same. The alternator can supply the needs of a stock
electrical system and not give a hint of a charging problem. Its when
multi-amp systems go in that the deficiencies are borne out.

Even smallish amplifiers can yield peak current demands which will
exceed even a large alternator's supply capabilities...


"Peak" does not equal "average". Even a large amplifier - on average -
doesn't drain more than a couple of amps of current, and transients
"peaks" only last a fraction of a second. These peak current draws are
buffered by the amplifiers internal capacitor banks, and recharge demand
is handled by the cars battery, because alternators simply don't react
fast enough.

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.

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.

The capacitor smooths the transition from alternator to battery,


There is no "transition".

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.

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.

The amount of charge stored in a capacitor is huge. There's a reason the
directions advise you to charge the cap through a resistor with the
engine running. You're not going to drain a 1 or 1/2 farad cap so that
it can't deliver at least 12 volts with a car audio system.

Another downside on an alternator (besides the high expense,
possibility of it being largely ineffective without setting your idle
speed north of 2000RPM,


There's no need to idle up. A quality alternator is rated for output at
idle. Otherwise, you can just slap a larger pulley on the alternator.

and installation considerations that have been
mentioned) is the fact that a bigger alternator is a bigger drag on
your engine... and it's a bigger drag all the time, not just when you
need it.


Wrong. An alternator only requires more torque when the demand placed on
it increases.

A larger alternator is more difficult to spin, inherently. Bigger
rotor, larger magnetic forces... they can really impact your car's
performance, robbing horsepower.


Most aftermarket alternators are no larger in size than their stock
componants. The difference is in the number of turns in the coil, and
the increase in mass of the windings in negligable.

This is anywhere from "noticable" to "really bad", depending on what
kind of car you have... with most cars nowadays, you can feel a HP loss
just from switching on your air conditioning... I wouldn't want that
kind of loss on a permanent basis, much less one that was even
potentially worse...


Hope you never turn your air conditioner on.

Particularly when you consider that no matter how large of an
alternator I am able to buy, I'll likely still be able to produce a
transient burst large enough to temporarily exceed the amperage of the
alternator.


Which is what the battery is for.

And even then, that transient burst won't matter much in the grand
scheme of things...


Then why are you telling this guy to buy a cap?

You are full of information. MIS information.

--
thelizman "I didn't steal the FAQ either"

Before you ask a question, check the FAQs for this newsgroup at
http://www.mobileaudio.com/rac-faq. It contains over a decade and
a half of knowledge.

teamROCS Car Audio Forums http://www.teamrocs.com/caraudio/
teamROCS Car Audio News http://www.teamrocs.com/news/
"It's about the music, stupid"

This post is Copyright (C) 2004. Reproduction of its content anywhere
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  #40   Report Post  
geolemon
 
Posts: n/a
Default Capacitor, how to find out what size?

thelizman wrote:
*Scott Gardner wrote:

So what's your course of action when a customer complains about
flickering or dimming headlamps/dash lights, but he's not havin

any
battery charging problems?


Bull****. If their stock electrical system can't supply the curren
to
keep lights from dimming, then they are having charging problems
They
need to upgrade their ground paths (hint: that stock 10 gauge to the
fender isn't helpting), sometimes the alternator, but the last thin
you
should think about adding to an otherwise healthy electrical syste
is a
cap...*

ONLY if the -average- current draw exceeds your alternator'
capabilities do you have a -charging- problem...
Even smallish amplifiers can yield peak current demands which wil
exceed even a large alternator's supply capabilities...

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

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

Bear in mind, there's a time element involved... the time that it take
the voltage level to drop down to the 12v level of the battery... an
then another time element related to the ramp-up time of the battery
as batteries are relatively slow devices to begin giving up charge.
there's a rise time... during which voltage will actually continue t
drop below 12v.

Yes, it's less than a second, this transition...
But that's what's nice about a capacitor.

It charges up to the 14.4v level of the alternator, and begin
supplying charge immediately when the voltage falls even slightly belo
that.
There's virtually no ramp-up time, a capacitor is able to begin givin
up charge virtually instantaniously...

And before the capacitor has discharged completely, the battery will b
in the equation, able to support the alternator as required, fo
however that massive transient or bass-tone lingers.

The capacitor smooths the transition from alternator to battery, quit
dramatically even.. the results can be seen in greatly reduce
headlight dimming, as there's a nice [relatively] slow transition dow
to 12v now, rather than a temporary, sudden slam to even below 12
every time there is a large transient peak.

thelizman wrote:
*
Do you tell him to "suck it up and live
with it", or do you sell him a high-capacity alternator o

lower-ESR
battery that he doesn't really need?



There's the keyword: "sell". There's more money to be made selling
people caps and batteries than a few feet of heavy gauge wire.
*

Another downside on an alternator (besides the high expense
possibility of it being largely ineffective without setting your idl
speed north of 2000RPM, and installation considerations that have bee
mentioned) is the fact that a bigger alternator is a bigger drag o
your engine... and it's a bigger drag all the time, not just when yo
need it.
A larger alternator is more difficult to spin, inherently. Bigge
rotor, larger magnetic forces... they can really impact your car'
performance, robbing horsepower.

This is anywhere from "noticable" to "really bad", depending on wha
kind of car you have... with most cars nowadays, you can feel a HP los
just from switching on your air conditioning... I wouldn't want tha
kind of loss on a permanent basis, much less one that was eve
potentially worse...
Particularly when you consider that no matter how large of a
alternator I am able to buy, I'll likely still be able to produce
transient burst large enough to temporarily exceed the amperage of th
alternator.

And even then, that transient burst won't matter much in the gran
scheme of things...
As long as my -average- current draw hasn't exceeded the alternator'
capabilities, my battery voltage won't drop below 12v over the cours
of my drive... there won't be a -charging- problem
-
geolemo
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