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How to measure REALLY the voltages of Tesla coils?

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LAN_403

Physikfan

Sun Jul 09 2017, 01:13PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hello Tesla friends

Please, what methods are there to measure REALLY the voltages of Tesla coils?

Patric

Sun Jul 09 2017, 04:29PM

Registered Member #2899 Joined: Wed Jun 02 2010, 06:31PM
Location: Deinze, Belgium
Posts: 255

The 'Wet finger method'?

Mr.Warwickshire

Sun Jul 09 2017, 06:30PM

Registered Member #61674 Joined: Mon Jul 03 2017, 04:01AM
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Posts: 22

You can calculate the voltage output of a Tesla coil by calculating the losses of the secondary, and knowing that the energy in the secondary's capacitance is NO larger than the energy in the primary's capacitance. This should give an estimate of the output if the coil you are calculating it for is well tuned/optimal. Here's a link which could help.

Physikfan

Mon Jul 10 2017, 01:15PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Patric and Mr.Warwickshire

The question is how close to the truth will you come with only calculating Tesla coil voltages?

How much of the energy of your primary circuit you will get REALLY into the secondary coil,
loose coupling, resonance effects, and so on..

Doing measurements, it would be interesting to see how much effort would be meaningful with nearly unlimited financial resources?

There are a lot of problems:
1. The ohmic load plus the stray capacitances of the voltage dividers on the "probe head", for example 500 kV.
2. Although it would be possible to measure with frequency-compensated voltage dividers with different resistive loads, 10 GOhm, 100 GOhm, 1 TOhm and with different stray capacitances,
3. you will have to consider that you are moving along a resonance curve, also with loose coupling.
4. All this makes linear extrapolations to 1000 TOhm load and almost zero picofarad stray capacitance of a hypothetic measuring head very difficult, not to say, almost impossible.

I'm looking forward to your answers.

Finn Hammer

Mon Jul 10 2017, 01:32PM

Registered Member #205 Joined: Sat Feb 18 2006, 11:59AM
Location: SkÃ¸rping, Denmark
Posts: 741

Physikfan,

You can try to search for Marco Denicolai, from Finland.
He constructed a water resistor to mount axially oriented, above his large Thor tesla coil. This was more than 10 years ago. Perhaps his results are still online.
He was on the Pupman list server at the time.

Cheers, Finn Hammer

hen918

Mon Jul 10 2017, 02:35PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Finn Hammer wrote ...

Physikfan,

You can try to search for Marco Denicolai, from Finland.
He constructed a water resistor to mount axially oriented, above his large Thor tesla coil. This was more than 10 years ago. Perhaps his results are still online.
He was on the Pupman list server at the time.

Cheers, Finn Hammer

I found it:

DerAlbi

Mon Jul 10 2017, 05:27PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

The problem with a TC is that its voltage is highly load dependent. A very low power TC without any sparks ignited will have the highest resonant peaking effect. As soon as sparks arise the voltage breaks down a lot.
I you want to measure it, i think one option could be to place two plates within the far field of the TC with different distances. The capacitive coupled voltages will differ from plate to plate and by that you can estimate the V/m field strength between them.. and by that maybe guess the source voltage. But you need an accurate 3D FEM model of the setup to account for all effects of the surroundings.
Another thing is using a multiphysics FEM solver. Doable in Comsol for example.. but well... you said infinite budget, right?

Hazmatt_(The Underdog)

Tue Jul 11 2017, 12:44AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

okay so you need to know a couple of things:

1. DC resistance
2. AC resistance at Fo of course
3. The impedance of the coil

Then if you are running the coil for a long time, you insert an RF ammeter at the base of the coil (I never got around to this but I have several meters), and by getting the "average" of your data set you can determine the RMS output voltage of your coil.

RF ammeters are good RMS converters for current because they map DC current to RF current and are broadband from DC to 10 MHz.

I was trying to get to this point with my goals, but I got tired of researching TC's and basically gave up/ lost interest.

I was also going to test this small scale to verify proof-of-concept but never got that far.

Uspring

Tue Jul 11 2017, 08:46AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
Location:
Posts: 711

You could use an antenna, as DerAlbi wrote. It can be calibrated by applying a known (low) voltage to the top. An arc will severely distort the electric field around the toroid and introduce errors in the measurement. So it's best to keep the arcs as far away from the antenna as feasible. Attaching a wire of the size of the arc during calibration might help.

Another way is measuring the current between the secondary top winding and the top load and also between the top load and the breakout point. The difference is the current going into the top load only. If you know the capacitance of the top load, you can calculate its voltage. I've described this here:

nzoomed

Tue Jul 11 2017, 11:48AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

All that calculus makes absolutely no sense to me! lol

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