Re: [TCML] Voltage Question

[Charles Van Neste <cwvanneste@xxxxxxxxx>]

I think Ed is correct.  Although I don't see a need to use a resistor, an air core Toroid (home made from cardboard haha) placed around the ground of the secondary will give you the current flow at the current anti-node (once the toroid is calibrated at the operating frequency of the coil).  From there it is just a matter of accurately measuring the inductance of the coil.  Then finding the reactance (wL as Ed pointed out), the resistive component can usually be neglected because it is much smaller than the reactance (my coil is only 4 ohms - after factoring in the skin depth effect).  Then you just multiply the reactance by measured current and it gives a pretty good approximation for the voltage at the top.  My coil (top load removed) starts to produce corona with a 24V peak (17Vrms) input and using the measured current and estimated inductance the top voltage comes to be about 30kV (which would be about right for the electric field to start
 producing corona).  


Cheers,
Charles



________________________________
 From: Udo Lenz <udo_lenz@xxxxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> 
Sent: Wednesday, January 25, 2012 4:18 AM
Subject: Re: [TCML] Voltage Question
 
Hi Paul,

I wonder how accurate that really is. The secondary voltage
depends on the magnetic field inside the secondary. One part of the
field comes from the secondary current. If that is the only contribution
to the field the equation you gave would be correct. But also the
field from the primary needs to be added in

Udo

> 
> Ed Phillips wrote:
> > The 'before streamers' bit is all important of course.
> 
> Yes, below breakout the secondary response is linear and
> this offers another method of calibration -
> 
> Put a small shunt resistor between secondary base and ground
> so that a scope can measure the base current.  Say 1 ohm so
> that 1 volt on the scope corresponds to 1 amp of base current.
> 
> Run the system at a drive level below breakout.
> 
> Calculate the top voltage using the effective secondary
> inductance Les obtained from JavaTC,
> 
>   Vtop = 2 * pi * Fres * Les * base_current
> 
> Observe the response of the E-field probe and work
> out the calibration factor.  With care this could be
> accurate to 5%.
> 
> --
> Paul Nicholson
> --
> 
> 
>
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