Re: Primary Heating

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

Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bert.hickman-at-aquila-dot-net>

All,

Hmm... I've also seen this after extended runs. Perhaps "current
bunching" on the innermost turns (due to proximity effect?) so that
these turns develop higher Joule heating? 

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Coins Shrunk Electromagnetically!
http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Paul Nicholson by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>
> 
> David Rieben wrote:
> 
> > most of the heating is confined to the 2 innermost turns
> 
> and others have reported similarly.  Wonder why.  We can exclude
> a localised current max in the primary at the operating frequency
> because the self-cap of the primary is very small compared with
> the added parallel cap of the primary tank, eg 100pF/82nF < 1%, so
> that the primary current is virtually uniform [*].
> 
> David, do you have a good low-resistance connection at the inner
> end of the primary?  Perhaps you can run some 60Hz AC current through
> the primary and see if the localised heating still occurs.
> 
> If a 60Hz current doesn't reveal the same localised hot spot, then
> we might have to look for sources of HF.
> 
> > the current max always occurs at the grounded end as opposed to
> 
> We expect uniform current in the primary at Fres.  But if higher
> frequency energy is being developed in the coil anywhere (parasitic
> resonance involving the gap, secondary arcs redistributing mode
> energy, etc) then it could be interesting.
> 
> > (V and I are running 90* out of phase, I think).
> 
> Yes, I lags V by 90 degrees.
> 
> First, we should eliminate the simplest explanation - lossy connection
> to primary inner, or heat from the gap conducting through to the
> primary.
> 
> [*] providing we ignore the capacitance between primary and
> secondary.  This can be quite high for the inner-most turns, and
> the resulting displacement current adds a non-uniform component to
> the primary current.  But this component can never exceed the coil
> base current (if sec base is properly grounded), so therefore this
> non-uniform component of Ipri must be less than the main primary
> current by at least the factor sqrt(Csec/Cpri).
> --
> Paul Nicholson
> --