Re: general cap questions and BIG Farad caps

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Brett Miller by way of Terry Fritz <twftesla-at-qwest-dot-net>" <brmtesla-at-yahoo-dot-com>

> > You will rarely come across a 1 Farad capacitor.
> more usual values are in
> uF
> > nF or pF.
> >
> 
> 
> Actually, 0.5-1 Farad caps are much more common than
> one would think.  They
> are used all the time in a variety of
> applications although almost 99.99% of the time,
> they are low voltage <20
> Volts
> 5V, 1 Farad caps are about half the size of a 35mm
> film case.
> 
> Anyways, engineers rarely call these things caps
> once they reach these large
> capacitance values.
> 
> We basically call them batteries, although they
> behave a bit differently
> than their chemical counterparts.
> 
> Some common applications of high capacitance
> capacitors are:
> 
> 1.  High power car audio systems.  In professional
> systems, amplifiers can
> draw up to 10,000 watts continuous and even much
> more than that
>      at peak transients.  Large capacitor banks
> (1-10 Farad) are used to
> supply that extra juice when the batteries
> themselves cannot chemically
>      deliver it fast enough.
> 
> 2.  Crank radio systems.  Those crank-up radiosets
> that you see hikers and
> mountaineers using actually charge up a very large
> capacitor which acts
>      like a battery.  Because these radios need to
> operate under extreme
> harsh conditions (especially very cold
> temperatures), batteries are very
> poor
>      at low temperatures, so they use large
> capacitors instead.  The radio i
> currently have has two 5V, 0.47Farad caps in it.
> 
> 3.  Computer memory back-up and storage.  A lot of
> new computers are doing
> away with lithium batteries and using large
> capacitors as well.  Typically,
> you
>      can get a 0.47 Farad, 5V capacitor for about
> $5.00 new.
> 
> Dan

Interesting.  I'm glad you posted that.  I have seen
the 1 farad caps for use in car amplifiers and
wondered what exactly they were used for in those
systems.  When I was a kid I had a toy airplane that
you charged up with a battery for about 30 seconds or
longer, and then let it go.  It would fly for a while
using the charge stored in the capacitor.  I don't
have the plane anymore, but I bet it utilized one of
those large capacitance low voltage caps you speak of.

-Brett

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