Re: Suggestion on Power Supply?

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

Original poster: "Jeremy Scott by way of Terry Fritz <teslalist-at-qwest-dot-net>" <supertux1-at-yahoo-dot-com>

John, thanks for clarifying... I didn't think your
formula had much to do with BPS at all, simply
what happens in ONE shot.

Let's see if I got this right, one shot, no BPS rate
involved:

To charge a .03uF capacitor ONCE to 20362V in under
8.3333ms requires 14400V delivering .270A of
charge:

Charge Time = Z * Cp * 5

Charge Time = (14400V / .270A) * .03uF * 5

Charge Time = .008ms

Power = V * I = 14400V * .270A

Power = 3888W

That's 3888W of power input from the
secondary side of the transformer.
The law of conservation of energy says
that the output cannot be more or less.
(we'll assume no energy is lost as heat
due to conductor resistance)

Energy at this point in the capacitor is:

Energy = 0.5 * Cp * Vp^2
Energy = 0.5 * .03u * (20362V^2)
Energy = 6.22J

The capacitor has 6.22J of stored potential energy.

The required gap conduction time is about 1.6ms
in which all the energy in the capacitor is
released. (probably less time in the real world
because some of that energy will be lost as heat
etc...)

Power = Energy / Second

Power = 6.22 J / .0016s

Power per Bang = 3888W

1.7 * sqrt(3888) = 106 inches

106 / 12 = 8.8 feet

This is regardless of how many breaks per second,
but being able to charge every 8 ms affords 120BPS
exactly.

Sorry Terry, I just don't see how I can use a 153nF
capacitor with a 5000VA pole pig:

5000VA = 14400V/.3472A

Charge Time = Z * Cp * 5

Charge Time = (14400V / .3472A) * 153nF * 5

Charge Time =  .031s

I think this is where I may be confused or just
wrong: (is it my confusion with the 8.3ms half
cycle that's the wrench in this?)

The AC half-cycle will switch polarity several times
in .031s, preventing the capacitor from charging to
it's  peak voltage. Every time a new half-cycle
starts, the voltage starts reversing on the capacitor.

If the capacitor is too big and takes too long
to charge (more than 8.333ms), we'll end up
with too low a voltage across it to do anything
with.

If you'll recall the formula for determining
the energy stored in the capacitor:

Energy = 0.5 * Cp * Vp^2

I did a quick test in pspice - I think
that a 150nF would only charge to 5000V or so:

Energy = 0.5 * 150nF * 5000^2

Energy = 1.875J

You'll see that voltage is squared, which means
it has a whole lot more impact on the amount of
stored energy than the capacitor value. So, I think
it's more important to be able to hit the capacitor's
peak voltage in under 8.3ms than it is to have a large
Cp.

Note: This doesn't apply for resonant capacitors
because they charge exponentially with time over
several half cycles. The net result is a very
high voltage in a small amount of time. V squared
is GOOD :)
































--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: "by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <FutureT-at-aol-dot-com>
 >
 > In a message dated 5/4/03 1:20:01 PM Eastern
 > Daylight Time,
 > tesla-at-pupman-dot-com writes:
 >
 > > >Their power both is equal to 4000 watts, one
 > trades
 > > >streamer length for streamer quantity, and the
 > other
 > > >vice versa... which one do you think John's
 > formula is
 > > >based on?
 > >
 > >I think John's formula is based on 120 BPS but it
 > seems to work well for
 > >most disruptive coils.
 > >
 > >Cheers,
 > >
 > >
 >
 >
 > Jeremy, Terry,
 >
 > I designed the formula for the "best fit" for both
 > large coils (of
 > any bps), and for small 120 bps coils.  It seems the
 > small coils do
 > much better at 120 bps than at higher bps.  For
 > large coils, it may
 > not be as important whether the bps is high or low,
 > but I'm not sure.
 > Smaller coils have more trouble meeting the
 > formula's predicted
 > spark length.  Perhaps this is due to the
 > proportionally greater
 > losses in a small coil.
 >
 > As far as a high bps producing many small streamers,
 > I haven't
 > really seen that effect, unless the toroid is too
 > small.  Sometimes
 > when the bps is raised, the overall power is raised
 > too, and this
 > may promote extra streamers.
 >
 > Generally, the streamers are more likely to coalesce
 > into a single
 > streamer at a high bps.  Often a rather large toroid
 > is required when
 > using a low bps, to reduce the number of streamers,
 > and to increase
 > the spark length.  The smoothness of the toroid
 > affects things too.
 >
 > John
 >
 >


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