Re: Primary Heating

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

Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

Has anybody considered that effect may be inductive heating? A primary 
winding is pretty much the coil in an induction heater, but with a higher 
frequency. Any conductive materials in this field (especially the inner 
turns) may act as antennas and resistive losses will create heat. I have no 
working coil now, but somebody may try this. Make a few turns of copper 
tubing like your primary is made of and lay it directly on the primary 
winding with some sort of thin insulator. Does it heat up as well? 

KEN 

Tesla list writes: 

> 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
> -- 
> 
>  
>