[Prev][Next][Index][Thread]

=?iso-8859-1?Q?Re:_Ed=B4s_Amps_(was_cap_failure...)?=



Hello Ed, all

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, February 12, 1999 10:31 PM
Subject: Re: Ed´s Amps (was cap failure...)


Original Poster: Ed Phillips <evp-at-pacbell-dot-net>

Tesla List wrote:
>
> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
>
> Hello Ed, All
>
> You wrote:
>
> >Original Poster: Ed Phillips <evp-at-pacbell-dot-net>
> >
> >Example:
> >
> > The reactance of an 0.1 mfd capacitor at 100 kHz is about about 16
> >ohms; if the Q is 100, the ESR will be about 0.16 ohms.  If the RMS
> >current in the circuit is 100 amps (a pretty high value), the total
> >power loss due to ESR would be 160 watts.  This shouldn't heat a
> massive capacitor very fast.  Real high-power experts - comments
please.
>
> Why do you say 100 amps of primary current is a lot?  I would say this
> is pretty low for coiling circuits:
>
> I am presently running:
>
> 1.) a 25.5nF cap
> 2.) a 7.5kV/75mA NST
> 3.) Primary inductance is:37.85µH
>
> Eq1:) J=0.5*C*V^2
> Eq2:) J=0.5 *L*A^2
>
> solving for A:
>
> A = V* SQRT(C/L)
>
> Vgap=7500*1.414 (peak V)
> Lpri=37.85µH
>
> A = 10606 * sqrt ((25.5*10^-9F)/(27.85*10^-6H))
> = 10606 * sqrt(9.15*10^-4)
> = 320.8 Amps
>
> With a 7.5kV 75mA NST, I am certainly not running a high power coil.
> My arc length is around 41". My final setup will be running 4500VA
worth
> of 7.5kV NSTs and a 100-120nF cap into a primary designed to resonate
at
> ~98Khz. A rough calculation leads to around 1.5kA for this design.
> So, I would DEFINATELY NOT consider 100A of primary current "big".


Snipped myself

Ed:
>I agree with you.  Intended to say that 100 amps was a pretty
>conservative number for the value during the discharge cycle.  My coil
>here is also small, runs from a 12 kV 60 ma NST, and uses an 0.01 mfd
>primary capacitor.  Assuming it charges only to the RMS secondary
>voltage before the gap fires, that gives a current of about 300+ amps
>during the first part of each discharge.  The discharge rate is of the
>order of only 240 per second, however, so the net RMS current over any
>set of charge/discharge cycles is no where near that high.  I'm too
lazy
>to figure it out, but know that the primary (which is wound with #10
>solid wire) doesn't even get hot after minutes of running.

Now that last sentence was quite a surprise to me.
I am presently using a tuning coil made of 1/4" hard steel tubing
(higher losses than copper, I know). This makes adjustments
easy when changing cap sizes, however, (and also decreases
the coupling slightly).
My real primary coil is made from 3/8" copper tubing. While
the 3/8" doesn´t get warm at all, my tuning coil (which is only a
fraction of the µHs of my primary coil) gets pretty warm during
a run. After a 5 minute run it is very slightly uncomfortable to
the touch (guessing 40-45°C).  I  am running a static gap, so I
couldn´t tell you my BPS. I am guessing it is over 100 BPS (50Hz),
but I wouldn´t bet on it.

Coiler greets from germany,
Reinhard