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Get the power and performance you
never dreamed possible from your amplifiers!
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| Stiffening capacitors can help your amplifiers deliver up to
50% more output on those demanding peak bass notes. Most automotive
alternator/battery systems simply lack the ability to produce large amounts of
instantaneous power. This is exactly the type of power that car audio
amplifiers crave. Adding a stiffening capacitor to your system can add
tremendous bass punch and improve transient response. |
| Stiffening capacitors FAQ's |
| What is a stiffening capacitor? Computer grade power caps (also known as stiffening
capacitors) store energy and then very quickly release it on demand to your
power amplifier(s). The term stiffening capacitor as a generic term refers to
any large capacitor (100,000 Microfarad and larger) placed in parallel with an
amplifier and battery.
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| How does it work? A stiffening capacitor charges like a battery. But unlike a
battery the stiffening capacitor is designed to quickly release power on
demand. This quick burst of power aids your amplifier in producing deep bass
notes when it needs it. In between deep bass notes your battery and alternator
re-charge the cap allowing it to be ready for the next deep bass note. This
battery voltage assistance reduces voltage induced amplifier clipping,
increases transient response, increases bass punch, and increases amplifier
life.
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| Where should my capacitor be
mounted? Stiffening capacitors should be mounted as close to the
amplifier as possible, as is shown in the diagram above.
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| One of the other benefits of stiffening capacitors is the
ability to reduce line loss. The power cable itself creates line loss. Long
runs of power cable associated with mounting amplifiers in automotive trunks
create line loss, especially during deep bass notes. Stiffening capacitors help
maintain appropriate system voltages at the amplifier. |
| What size capacitor do I need? As a general rule we recommend 100,000 Microfarad (.1 Farad)
per 100 watts of amplifier power, or 1 Farad per 1000 Watts. Use the simple
chart below to determine what size capacitor you need.
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Total Amplifier Power: Capacitor needed:
- Up To 500 Watts .50 Farad
- 500-1000 Watts 1.0 Farad
- 1000-1500 Watts 1.5 Farad
- 2000 Watts 2 Farad
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| Can I use multiple caps? Yes, Capacitors add in value when wired in parallel.
Example: Two 1 Farad capacitors wired in parallel sum to 2 Farad. This is the
perfect size for a competition system with up to 2000 Watts of trunk-mounted
amplifiers.
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| What voltage capacitor do I need? Automotive battery charging systems typically vary between
as low as 12VDC up to as high as 14.5VDC with the average alternator output at
13.8VDC. Generally speaking stiffening capacitors these days are rated at 20VDC
average and 24VDC surge. We do not recommend using capacitors rated below 16VDC
but higher is always better.
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| Do stiffening capacitors require
special handling? Handle stiffening capacitors as you would a charged battery.
The main thing you need to worry about is initial installation charging and
discharging. Most capacitors are supplied with a charging/discharging resistor
or lamp. Capacitors draw a very large amount of current during installation. DO
NOT attempt to connect 12VDC directly to the terminals or arching and permanent
terminal damage will occur. Utilize a charging resistor or lamp in series with
the cap and follow the instructions supplied with your capacitor to slowly
energize the capacitor and eliminate arching. NEVER short the leads of a
stiffening capacitor. When un-installing a capacitor remove the source voltage
then use the same resistor or lamp to slowly de-energize it.
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| Anything else I should know? Yes,
ALWAYS install an appropriate fuse or circuit breaker
between your amplifier/capacitor in the trunk and your battery power source.
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| Capacitance (C) is the measure of a capacitor’s ability
(capacity) to store an electric charge on its plates. A
capacitor is an electrical component that consists of two conductors (plates)
separated by an insulator called the dielectric.
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| The voltage rating of a capacitor, often labeled as WVDC for
Working Voltage Direct Current, is the maximum voltage that can safely be
applied across the capacitor without arcing, or voltage breakdown, occurring in
the dielectric. The difference of potential between the capacitor’s plates
creates a stress on the atomic structure of the dielectric. If the voltage is
too high, electrons will be torn from their orbits in the dielectric material,
producing an electric arc. A small carbon path known as a puncture is created.
A punctured capacitor is not useable as the puncture creates a leakage path for
current between the plates. |
| When a capacitor is connected to a DC voltage source,
electrons accumulate on the negative plate. The other plate becomes positively
charged by electrostatic conduction. The presence of the negative charge
(surplus electrons) on one plate repels negative charges (electrons) off the
neighboring plate. Thus, the opposite plate receives an equal, though opposite,
positive charge of “holes”. A hole is a vacant spot in the valence shell of an
atom where an electron may be captured. |
| The amount of capacitor charge is determined by the amount
of applied voltage and the capacitance, in Farads, of the capacitor. When a DC
voltage is first applied, the capacitor acts like a short and demands a great
amount of current. At this first instant of time when voltage is applied, the
circuit resistance is the main limiting factor to current flow. Current flow
will be at its greatest. As capacitor charge increases, the rate of charge
decreases as the voltage across the capacitor approaches the source voltage.
When the source voltage is reached, current flow stops. Remember that there is
actually no current flowing from one plate of the capacitor to the other. There
are only free electrons moving onto and leaving the plates by the leads. As
like charges repel (electrons have a negative charge), the plate with an excess
of electrons will repel electrons from the other plate giving it a positive
charge. |
| AC Capacitor Current A capacitor is able to pass alternating
current even though there is an insulator between the plates (no actual current
path). In an RC (resistive/capacitive) transient circuit, the capacitor charge
current will flow until the capacitor is fully charged, and discharge current
will flow until the capacitor is fully discharged. When an alternating voltage
is applied to the plates of a capacitor, the capacitor’s plates are forced to
follow repeated cycles of charge and discharge. |
| The RC Time Constant It takes time for a capacitor to charge
through a circuit resistance. Capacitors do not charge at a linear rate, they
charge at an exponential rate. The RC Time Constant (t) formula is t = R·C
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| One time constant is equal to the product of the circuit
resistance times the capacitance. A capacitor will reach a full charge and show
the source voltage after a period of 5 time constants. This applies to every
capacitor in every circuit, and applies to inductors as well! For example, a 5
uF capacitor, charging through a 1 KW resistor will have a time constant equal
to 5 E-6 X 1K = .005 seconds, or 5 milliseconds. Therefore, with this
capacitor/resistance combination, the capacitor will reach full charge and show
the full source voltage in 5 X 5 milliseconds or 25 milliseconds. |
| In the first 5 ms, the capacitor will reach 66.6% of the
total charge; it will reach 86% after 10 ms, 95% after 15 ms, 98% after 20 ms,
and 99% after 25 ms. As you can see, the rate of charge slows as the capacitor
takes on charge and the voltage across the cap approaches the source voltage.
After 5 time constants, current flow stops, and capacitor voltage equals the
source voltage. |
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