Author Topic: measure the secondary voltage of a tesla coil.  (Read 150 times)

Offline paulj

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measure the secondary voltage of a tesla coil.
« on: February 22, 2021, 11:03:51 PM »
Good evening, I was wondering if with the minimum of material, we could measure the voltage of the secondary tesla coil?
I contacted another forum which suggested that I try first with a small model, a capacitive divider, and an oscilloscope, it's just to measured a peak only.

Regards, Paul

Offline davekni

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Re: measure the secondary voltage of a tesla coil.
« Reply #1 on: February 23, 2021, 01:07:46 AM »
Tesla coil voltage measurement is a fun challenge, but not at all easy to get accurate.  A capacitive divider can work until arcs form.  Once arcs form, capacitance from the arc changes the divide ratio.  If the sensing is on the opposite side from a breakout point, it might remain somewhat close.

My preferred approximate measurement technique is measuring secondary coil current and frequency on a scope.  (Frequency changes as arcs form, so needs measuring.)  With a known secondary inductance, voltage can be calculated from current and impedance (I*2*PI*F*L).  This approximation discounts two factors.  First: Secondary coil capacitance adds current passing through only part of the coil.  Second: Primary coil current induces secondary current that is not due to secondary voltage.  This latter effect can be removed by subtracting the appropriate (for your coil) amount of measured primary current from measured secondary current.  I make an extra tap on primary CT for this purpose.  The first issue of coil capacitance is harder to deal with.  As arcs grow, some of the coil capacitance is now to the arc instead of just to top-load and ground.

With a reasonably-large top load, I think voltage by secondary current can get with +-10%.  This is based on playing at "low" voltages where my 15kV probe can measure the top directly.
David Knierim

Offline paulj

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Re: measure the secondary voltage of a tesla coil.
« Reply #2 on: February 23, 2021, 09:14:02 PM »
thank you for your feedback, I suspected that it would be complex. For other members don't hesitate to give your opinion it would be very interesting.

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Re: measure the secondary voltage of a tesla coil.
« Reply #2 on: February 23, 2021, 09:14:02 PM »

 


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