Well here is some of the specs supplied for a 1 Farad cap from the
manufacture.,
# Capacitance 1 farad,+/- 5%, 20-24 Volt Surge, 105'C
# Dia. 3.54" x H 9.65"
# E.S.R. (0.0016 Ohm) Frequency? I don't care it works for me. Good enough
for me to use on a SSB amp with a 8 ' run of cable. Like I found out it just
helps
in reducing the voltage nulls during the audio peaks, and reduces the sudden
voltage drops in the electoral system. For
$59 bucks it OK to do. That's what he asked and This was my answer.
"Frank Gilliland" wrote in message
...
In , wrote:
snip
A one farad capacitor can only supply one amp for one
second at one volt. Hardly worth the expense.
It can only prevent a voltage drop on the first few peaks
of a SSB modulated signal. It's usefulness would be almost
totally drained after speaking just one appropriate word, pointless.
Then there is not much point in using them in any kind of DC power
supply, is
there? Of course there is. Do the math, Tnom:
Oranges and apples...............
P.S. you are a idiot for even equating the two
Then explain the operational difference between a power supply filter cap
and a
cap placed across the input of a load. Duh....!!!
A good car battery has, on the average, an source impedance of around
0.01 ohms
(dropping 1 volt per 100 amps, which is a darn good battery). Ten feet
of #8 AWG
has a DC resistance of 0.0063 ohms, and we'll just assume that the
negative lead
is grounded at 0 ohms. So the total source impedance at the input of the
amp is
0.0163 ohms. Now take an amp that can do 500 watts PEP. Assuming 50%
efficiency,
that means it can draw a maximum of 79.4 amps @ 12.6 volts. But since
the source
impedance is 0.0163 ohms, the voltage is going to drop 1.3 volts on the
peaks,
reducing the peak output by 50 watts or more. This is a type of
soft-clipping
and can result in some significant AF -and- RF distortion. And that's
not
considering the temperature coefficient of copper, which shows more
resistance
as it warms up from carrying lots of current, making the situation
worse.
Adding caps at the power input leads of the amp can significantly reduce
the
source impedance of the power supply. It -can't- provide more power than
the
supply is capable of providing,
But for how long........."Do the math"
.....? I said it -CAN'T- provide more power than the power supply. Are you
deaf?
but it -can- smooth the voltage ripple just like
in any other type of power supply. And what if the vehicle is running?
Do the
math: If you have a 100 amp alternator (at 13.8 volts), it has a source
impedance of .138 ohms, which is significantly higher than the battery,
so it's
not going to be much help. In fact, because it's going to be so heavily
loaded,
it's going to introduce some ripple into the power lines, ripple that
can be
reduced by using caps at the input of the amp.
How much capacitance is needed? There is no easy equation. There are a
number of
factors, such as the source resistance of the battery and alternator,
resistance
of the wire, ESR of the capacitors, average modulation percentage, PEP
watts,
etc, etc. Because of the very low impedance required by the amp, low ESR
is
paramount. Despite the advertised claims, the 'monster' caps usually
have an ESR
of several ohms, much higher than is usable. Computer-grade
electrolytics have a
much lower ESR. Using many smaller caps in parallel is better than one
big cap
because the ESR is much lower. Those are just a few things to consider.
But the
general rule is to keep adding caps until they no longer make any
improvement.
I'm really suprised, Tnom. After all the times you have shot your mouth
off and
been proven wrong on technical topics, you -still- haven't learned to
think
before you speak. Maybe next time.
One thing I am not surprised at........You will ignore the facts, like
you normally do to flame the group or express your pseudo
theory.
Present some FACTS, Tnom. I dare you!
Yeah...Right, A few farads will make a justifiable difference. You're
to funny.
What's funny is watching you choke on basic DC power supply theory (pun
intended).
=============
"...but I admitted I was wrong, Like a man! Something you and QRM
have a problem with. You guys are wrong and you both know it and
are both too small to admit it."
---- Twistedhed ----
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