# Re: Big Primaries, Small Caps

```Less stored energy in the primary = shorter sparks... The amount of energy
in a given "bang" is determined by the source voltage (i.e. the NST, etc)
and the C.  Reduce the C, and you reduce the energy.

The basic process, from an energy flow standpoint, is:

Wall plug
Transformer
Primary Cap
Primary Inductor (1/4 cycle later)
Secondary Inductor (same as primary)
Spark heating..

Now, you might be able to get long sparks because you can run off multiple
bangs with a high current primary source (i.e. charge the small cap up
quickly, discharge it again) during which time the previous spark channel
may not have dissipated (I'm not real convinced of this... It cools pretty
darn fast, but still.. it's gonna be hotter, so it doesn't have to heat as
much to ionize the second time around).

The other way to fix it is raise the primary voltage, but, as you might
have noticed, capacitors are a constant \$\$/Joule.... A 1 uF, 10 kV cap
costs about the same as a 0.5 uF, 14 kV cap.. They both store 50 joules.

----------
> From: Tesla list <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Big Primaries, Small Caps
> Date: Sunday, September 03, 2000 1:12 PM
>
> Original poster: "Christopher Boden" <chrisboden-at-hotmail-dot-com>
>
> Would this mean that by twiddleing a bit more copper (say going from 15
up
> to 30 turns) I can save serious money on my MMC AND have LONGER streamers
to
> boot?
>
>
> This is too easy, what's the catch?
>
> Chris B.
>
>
>
>
>
> >Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> >
> >Hi Greg,
> >
> >	As you lower the primary inductance, the primary current increases.
> >Assuming the loss in the gap is proportional to I^2R, the higher current
> >burns off the energy as heat more in a low inductance primary then a
high
> >inductance one.  Low inductance primary circuits have to be made well to
> >minimize the loss and handle the higher current.  Large inductance
> >primaries can get away with much lossier construction.
> >
> >As I look at coils with very large primary caps, the primary inductance
> >tends to be very small.  This creates very high currents and giant
losses
> >that can eat a coil's power vastly reducing the power to the arc.  It is
> >sort of a balancing act between more stored energy on the primary cap
and
> >greater losses due to low primary inductance and high primary current
> >losses.
> >
> >Cheers,
> >
> >	Terry
> >
> >
> >
> >At 12:24 PM 8/31/00 -0400, you wrote:
> > >Dear List,
> > >
> > >I'm curious about Tesla coils with large primaries and small tank
caps.
> > >John Freau and others have articulated numerous times over the years
that
> > >coils so designed have lower gap losses and longer sparks relative to
> >coils
> > >using big tank caps and few primary turns.  I'm curious as to why this
is
> > >so.  It seems to me that the bigger bang size delivered by a larger
cap
> > >would thump the secondary harder, yielding longer sparks.
> > >
> > >Can someone in the know provide an explanation?  I'm not an engineer,
but
> >I
> > >am an experienced comm/nav technician, so I can grasp pretty deep
> >concepts.
> > > However, a side trip into Calculus land will lose me pretty quickly.
> > >
> > >Best Regards,
> > >
> > >Gregory R. Hunter
> > >
> >
> >
>
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