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From: whit3rd on 4 Jul 2010 14:47
On Jul 4, 11:13 am, "petrus bitbyter" <petrus.bitby...(a)hotmail.com>
wrote:

> ... Todays nuclear batteries
> as used in some spacecraft are low voltage.

I think there are different designs: one uses beta emitters and
generates
a kilovolt or so, one uses thermal conversion (with thermopiles)
off an isotope heat source and generates low V.
From: Nunya on 5 Jul 2010 02:56
On Jul 3, 9:18 pm, "Graeme Zimmer" <gzim...(a)wideband.net.au> wrote:
> A reverse Van Der Graph Generator ?
>
> A constantly rotating Variable Capacitor with comutator contacts to apply
> the high voltage at Min Cap and then bleed off the converted charge at Max
> capacitance?
>
> Q=CV
>
> Perhaps a cascade of them in series?
>
> ............... Zim

I think they call that a "Railgun".
From: John Larkin on 5 Jul 2010 12:20
On Mon, 05 Jul 2010 08:41:08 -0700, Fred Abse
<excretatauris(a)invalid.invalid> wrote:

>> Q=CV
>
>But E=QV,


Then it follows that E = C * V^2

which of course it doesn't.

John


From: Tim Williams on 5 Jul 2010 18:48
"Fred Abse" <excretatauris(a)invalid.invalid> wrote in message news:pan.2010.07.05.19.11.23.376684(a)invalid.invalid...
> It still implies that reducing V by increasing C involves a loss of
> energy.

So a flying capacitor converter is always 50% efficient? :-)

Cap charging (in terms of conserved charge) is an irreversible process. But just like irreversible thermodynamic processes, if you make the steps small enough, it starts looking reversible.

So the point is, you reduce the cap ripple, so the delta Q is small, and increase the frequency, so the number of transfers is high = more output current.

A solid state switched circuit may not have this advantage. For example, say you drove a wad of 1.5kV MOSFETs with photovoltaic gate drivers (through fiber optics). You will lose a lot through Rds(on) and swirching time (in the ms), so it will have to run slowly, in the 100Hz range. Rds(on), of course, dominates the loss component, but charge is still conserved, so long as the on-period is several RC time constants.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
From: StickThatInYourPipeAndSmokeIt on 5 Jul 2010 19:44
On Mon, 5 Jul 2010 17:48:35 -0500, "Tim Williams" <tmoronwms(a)charter.net>
wrote:

>Tim

snipped retardedly formatted text.

72 characters max line length, idiot. Your news client doesn't do
that? Then it is not a news client. Outhouse Unexpressive is what it
is, and what you are for using it... like an idiot... without setting it
up correctly, Mr. Useitasitcomesoutoftheboxtotalretard.
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