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RE: [TCML] Greg's input on inductance



DC, please consider the simple observation that Terry pointed out.  If one measures the inductance of a primary coil with a garden-variety multimeter, the measurement is made at a very low current at roughly 1KHz.  Contrast this with how the primary coil is used in operation, at ~100KHz and hundreds of Amps.  But the inductance value read by the meter is perfectly consistent with the value that the operating coil is running with.  So I would conclude that if there is a shift in inductance due to current or frequency, it's not at all significant.

I must admit that I've lost sight of how the question of whether inductance is current-dependant, relates to the feasibility of Finn's circuit.  The issue at hand is whether Finn's circuit is able to provide a reliable timing signal to control power IGBT's over a range of operating conditions.  Finn accomplished this by using a small, LOW-POWER inductor to shift the phase of the primary current sensor.  Since the turn-on delay of the IGBT's is constant, regardless of operating frequency or current, the circuit deriving the control signal needs only provide a fixed timing advancement.  It's possible that if one were to shift the resonant frequency, one would need to re-tweak some pots to dial in a new timing value, but I've not thought about this too carefully.  It appears to be a plausible and elegant solution, to me.  The only thing that needs work IMHO is the spelling of "Predikter".

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of DC Cox
> Sent: Thursday, June 25, 2009 10:54 AM
> To: Tesla Coil Mailing List
> Subject: [TCML] Greg's input on inductance
> 
> It appears even seasoned members of the list are getting confused with the
> fundamental physics of electrical circuits.
> 
> Greg's quote: An interesting line of reasoning! Unfortunately, it is
> impossible to independently 'change either one' without changing the other;
> they will always move together, in a fixed ratio that defines the
> inductance.
> 
> 
> Consider what would happen if you could set just the Amperes value to zero.
> 
> 
> Do you really believe it would yield infinite inductance?
> 
> Now consider what he said ---  if you set the AMP value to Zero what do you
> really have.....STATIC... you have a potential difference but no current which
> means no movement and no induced voltage so...inductance does not even come
> into play until there is an EMF built up some how through a changing field
> and if you have a TON voltage but you have nothing to push then you have
> static potential energy
> 
> You can change either one independently through either constant voltage
> control or constant current control...however no one does it in Tesla coil
> work or I have never seen it done.
> 
> Dr. Resonance
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