Re: Big Primaries, Small Caps

["Malcolm Watts" <M.J.Watts-at-massey.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Hi Jim,

On 3 Sep 00, at 15:59, Tesla list wrote:

> Original poster: "Jim Lux" <jimlux-at-jpl.nasa.gov> 
> 
> 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)

More pedantry, sorry :(  Even at ksys = 0.6 it would take half 
a cycle to transfer all energy to the secondary. This is why 
primary loss is, or should be such an important issue in spark-
making TCs where ksys is usually on the order of 0.25 or less.

Regards,
malcolm

> Secondary Capacitor (i.e. top load)
> 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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> 
> 
>