From: chas <chasm@texas.net>
Subject: Re: [Amps] How do you - powering a SS amp with a capacitor?
ok, Vic
I have learned a lot from this discussion and I am glad we got into it as
there is a lot of interest in it among the newbies and those who are barely
QRO literate, as it were. I believe that a 1 or 2 farad cap would be useful
only to supplement low capacity batteries and that the money spent on same
would probably be better invested in another pair of golf cart batteries -
## The 'Joule' is the unit of energy for a cap.
### 1 Joule = 1 'watt second'. Formula for Joule is .. Voltage squared
times
uf / 2 million.
## 1 farad @ 13.8 vdc = 95.22 joules. You can suck exactly 95.22 watts CCS
CXR
for ONE second. 95.22 Watts/ 13.8 vdc = 6.9 amps...CCS CXR...for ONE
second !
On ssb [ unprocessed] you could easily suck 3 x that much current for ONE
second.
## I read all the sites, and arguments with the car audio enthusiasts a while
back. A cap
is not a battery, and a battery is not a cap. You short out a battery by
brushing 22 ga
across the posts..and u get a few sparks. You do the same with a cap, and you
get a big bang.
## a battery has high internal resistance compared to a cap [esp a 1-10 Farad
cap] . Folks with
weak alternator's and a single stock battery..with their car stereo cranked up
would find their
headlights would dim with the 'boom,boom,boom, thump, thump, thump, of the typ
heavy bass
notes. The cheap..'fix' was to put a 1-10 Farad cap in the trunk of the car,
next to the kw audio amp.
This actually works, IF the cap is big enough. Somebody started this 'rule
of thumb' whereby 1 farad
was required for every 500 watts of power.
## Trying to use caps to improve DYNAMIC regulation will work..like for ssb
..provided the
power supply is big enough. Put bigger filter caps in any AL-1500, and you
easily get another 100w
pep out of it.
with these two packs wired appropriately, we would have double the capacity
of one battery of the matched set of 4 and double the voltage of two of these
batteries. so, the problem becomes one of needing to talk with intellipower
and find out if that 9280 can charge all that lead <G>.
otoh, a cap would be useful if the discharge rate is low and slow to allow it
to charge up during a low duty cycle.
## for your emergency comms set up, you are after a good UPS set up,
so if you lose commercial AC power, you are not off the air. A 1-10 farad
cap isn't going to buy you anything. What you require is bigger battery
capacity...
and either use more, and bigger batteries, or parallel existing strings of
batteries.
thanks again... don't want to kill this as I am always ready to learn more if
anyone has more sources of articles. or discussion. I was told a year or so
ago, to go to an audio store and get an education on the linear amp power
supply system and that is still apparently, good advice.
## if u read the car audio sites, the big boys do it the right way... and
use bigger alternator[S], bigger batteries, bigger ga wire. The cap
comes dead last, if at all, in that set up. 1-10 farad caps are designed for
one thing only..to supply real short term power on music peaks... and charge
up in between those same peaks.
>
> The capacitors are available up to 1 to 5 farads. Initially they charge
> in a very short time, depending on the resistance of the wire between
> the power supply and the capacitor (which should be right at the amp). A
> capacitor like that looks almost like a dead short when it's discharged,
> so the cable can't be too fat (too low resistance) or it might keep a
> switching supply from turning on.
## try it 1st by paralleling the existing wire with same or bigger ga wire.
That's a start up problem...which may require the cap gets step started,
but I doubt it. The 1 farad cap is only a paltry 95 joules. [ A 3 kv B+
supply, like what's in a SB-220, is only 112 joules]
> You can't replace a battery with a capacitor of this size because it
> could only supply 90A for maybe half a second (that's a lot of current).
> But it could make it possible to use a smaller power source and smaller
> cables.
## a 1 farad cap @ 13.8 vdc = 95 joules = 6.9A for one second...
and 14 A for 1/2 second. 28A for 1/4 sec. 56A for 1/8 sec.
90A for .070 sec [ 70 msec]
>
> If you are interested in doing this, the place to go is one that builds
> custom audio amps for vehicles. An SSB linear has very similar
> power-demand characteristics to an audio amplifier.
>
>>
>> Vic, what is the recharge time on the capacitors? is there a measuring
>> meter for a tell tale?
## to charge up a 1 farad cap... abt a split second..depending on wire ga.
The resistance of the feeder wire and the cap itself will from a RC network.
>>
>> Not sure what the discusion about 22A power supplies was about... the
>> Cube requires a min of 40a and a max of 90A.
## Ur initial spec was to have just enough capacity..until the emergency
gen set was started. And how long is that, 10 secs, 5 mins, one hr ?? Is
the
gen set a permanent install, and fully auto...or do u have to get it out of
storage.
What happens if it doesn't start ? What happens if the fuel is all
gone...or is
stale ? Is it gasoline/or diesel. Regular car gas goes rancid after just
a few months,
even with conditioner added to it.
## I would focus on the battery capacity, and wiring..and mimimize V
drops...and
keep any proposed batteries up OFF the concrete floor.
later...... Jim VE7RF
>>
>> and yes, I am really looking forward to attaching #4 to the front panel
>> of the Cube... there is space for lugs not to exceed a MAX of .5" in
>> width. otherwise, it it off to a vise and a file <G>.
>>
>> thanks for your input. I am sure I will be hitting on you more in the
>> future.
>>
>> 73
>>
>> chas, k5dam
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