Re: Do i need a capcitator?

"Mariachi" <jpgarcia153@xxxxxxxxxxx> wrote in message
news:1193511808.281763.262990@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Oct 27, 2:13 pm, "Christopher \"Torroid\" Ott" <spamtrap at
ottelectronics dot com> wrote:
"Mariachi" <jpgarcia...@xxxxxxxxxxx> wrote in message

news:1193458231.787670.17070@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

And I'm still waiting for someone with intelligence and actual
experience to comment about capacitors (I was interested myself).

I think this originated from a website and got dumped to RAC mid thread,
so
I don't know the details of the original question. As a general rule,
additional capacitance will not hurt anything. I know some people believe
large caps will drain their battery, but this isn't true as the leakage
current for even the lowest quality large caps is still in the microamp
range.

Why add a capacitor? Large car amplifiers must use a switching power
supply
to get split supplies (+\- power rails) from the +14 volt available from
the
alternator. This is a giant P.I.T.A. and is where most of the complexity
and
expense of a car amplifier is at. Generally speaking, switching power
supplies have an input capacitor bank and an output capacitor bank. The
output caps are at the voltage rails and are essentially fixed as you
have
no access to them. The input caps are needed to prevent the power supply
from drawing huge instantaneous currents from the alternator and battery.
These are mounted on the PCB inside the amp but are essentially at the
same
node as the +batt (there is usually a fuse between them). This means that
we
can increase the input caps to virtually any value we want by adding
additional caps to the +batt outside the amp. To get the maximum benefit,
these should be physically close to the amp, and the wires should be as
large as practical.

Why would we do this? There are benefits to keeping the amps power supply
voltage at the max possible. It prevents large currents from being drawn
to
compensate for the voltage dipping. This reduces heat at the power supply
FETs (which are heated by current flow, voltage is irrelevant here) and
has
a nice side effect of not putting huge instantaneous loads on the
alternator. This means your lights won't dim and because the ignition
coil
will get full voltage, the engine won't lag. Unregulated power supplies
will
see an increase in power output and both regulated and unregulated power
supplies will see a decrease in heat buildup.

Can't we just upgrade or rewind the alternator? Yes and no. If your
alternator is undersized a larger one can help, but still cannot ever
provide the instantaneous current that a cap can. A larger alternator
puts a
small additional drain on the engine all the time. Also rewound
alternators
often have a different power curve which doesn't produce much power at
low
idle. It's really about balance here. The alternator should be large
enough
to run the car, charge the battery and power your system with the lights
and
a/c on. Beefing up from there is not necessary.

Chris

Thanks for your input. I'm running probably a 420 Watt system, but
I'm probably only using half of that 95% of the time. I was planning
on adding an 8" polk momo subwoofer in a sealed box, and placing it
behind the front seat of my car (sub is rated for 30-200W).
Therefore, I'll be using around 300 W (average power) most likely for
the whole system. I just wondered if it was really necessary to
upgrade my battery and my alternator, or just buy a .5-1 Farad
capacitor for my 3 amplifiers. I have a 4 cylinder engine, so the
alternator might not be the best.

If you have trouble with the lights dimming or the bass seems to flatten out
on longer notes, than you would be an excellent candidate for a stiffening
cap. 0.5 - 1.0 would be fine. Be sure to follow the instructions for
charging it on the initial install, or you'll draw quite an arc when you
make the connection.

There was a time when a 4 cylinder meant the engine was weak, but that's no
longer true. Case in point, I test drove a Subaru WRX STI last year and it
took the rest of the day to wipe the grin off my face. ;-)


.

Relevant Pages

  • Re: Do i need a capcitator?
    ... large caps will drain their battery, but this isn't true as the leakage ... Large car amplifiers must use a switching power supply ... supplies have an input capacitor bank and an output capacitor bank. ... from drawing huge instantaneous currents from the alternator and battery. ...
    (rec.audio.car)
  • Re: How to discharge the capacitor faster
    ... and the ripple on power supply was sustained. ... > seconds for the capacitor to discharge itself, ... These caps are commonplace on PCBs with ICs on them (they are called ...
    (comp.arch.embedded)
  • Re: Do i need a capcitator?
    ... large caps will drain their battery, but this isn't true as the leakage ... Large car amplifiers must use a switching power supply ... supplies have an input capacitor bank and an output capacitor bank. ... from drawing huge instantaneous currents from the alternator and battery. ...
    (rec.audio.car)
  • Re: help with three subs
    ... alternator power to keep up with that amp. ... up to 140A, then yeah, that alternator will "keep up". ... if you haven't purchased the capacitor already, ...
    (rec.audio.car)
  • Re: "P dissipation" for caps?
    ... It's taught to make sure that doesn't exceed the resistor's power rating, ... Why is a capacitor not rated for power dissipation? ... regular ceramic caps have been known to unsolder ...
    (sci.electronics.basics)