# Re: Big Capacitor?

```Those huge caps, though, have very limited high frequency (meaning kHz in
this case) response.  At some level, the line between electrolytic cap and
rechargeable battery gets fuzzy.  A run of the mill car battery is 12V -at- 60
Ah =720 Wh  (about 1 HP/hr, btw), or just under 260 kJoule.. that's about
13 kJ/kg (figuring 20 kg mass).  Compare that to a 70's energy discharge
cap of 5 kJ in a 50 kg can...  Of course, the energy discharge cap can dump
the energy in a few microseconds, it takes 20 hours to get the rated energy
out of the car battery...

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> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Big Capacitor?
> Date: Sunday, October 08, 2000 9:31 PM
>
> Original poster: "Phillip Heslin" <pheslin-at-home-dot-com>
>
> Hi folks,
>
>   I think the key here is something that hasn't been mentioned yet. The
> size of the cap is a function of the total energy storage of the the cap
> as measured in Joules and the energy density of the particular type of
> cap. The total energy stored in a cap is calculated with the equation
> E=(F/2)*(V^2) where E is the total energy in Joules, F is the
> capacitance in farads and V is the voltage. ( I hope I remembered that
> correctly) Energy densities vary with the type of construction I.E.
> electrolytics have a different energy density than a foil cap. I believe
> that the highest energy density record is held by the relatively new
> Maxwell powercache capacitors. I have seen a rectangular cap about the
> size of a 12 oz coke can with a rating of 2500 farads, yes farads! and
> rated at 2.5V
>
> B.T.W if I mis-remembered that formula, someone please correct me.
>
>
>            Safe Coiling!
>
>            Phil Heslin
>
>
> --snip--
> > I have a question or two for any one out there. How big would a
capacitor
> > have to be, (physical dimensions), to have a value of 1 Farad? I know
that
> > voltage rating would be a determining factor, but just a ballpark
figure.
> > Has anybody ever seen one?
> > Just curious.
>
>
>

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