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Tesla secondary voltage output...

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sparky

Thu Jun 07 2007, 01:41AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

I am very puzzled on how to obtain the true RMS voltage off a Tesla Coil secondary on paper. Humm, I thought that typically 1.1kV per millimeter was accurate enough, but obviously somethings wrong when people are getting 6ft (1.6m) streamers - then calling their coil a 500,000 Volt monster???

How does that work?? Sure I've been buildings for a few years now... but I never really cared about measuring the voltage output.
Maybe a few of you guys can shed some light on this issue. Does high frequency current produce longer sparks or is it that due to the higher current evolved in the Tesla Coil - sparks appear longer??

----school project coil------

My Tesla Coil that is being constructed has a secondary of 6.5" X 46" wound with 27AWG , primary is 12 turns 1/2" Copper tubing with a 1/2" spacing between coils. Input is 14.4 kV 3kVA PTs running 2.5X plate rating for 7.5KVA. Capacitor is a MMC brick 46.5KVDC 0.085 uF.

ragnar

Thu Jun 07 2007, 02:31AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

There is "streamer growth" going on... and probably other reasons which would explain why that sizeable Siberian marx generator (seen here:

) can produce 28-meter/92-foot arcs with "only" 5.2MV.

sparky

Thu Jun 07 2007, 03:20AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

--can someone shed some light on a formula that can determine the output voltage of a Tesla Coil? ...

Hazmatt_(The Underdog)

Thu Jun 07 2007, 04:25AM

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

mmm....well, I haven't proven it yet, but:

Q_primary = 2piFL / R_losses (I approximate that total as 2-3 ohms including spark gap losses)

Q_secondary = 2piFL/ R (secondary resistance)

both Q's at the same frequency where: LpCp = LsCs;

Magnification Ratio: Q_sec. / Q_primary = Q_mag.

Output Voltage = V_input x Q_mag.

Or you could do the transformer analysis using Mutual Inductance. Since the transformer is an air core resonator, the majority of the transformation comes from Mutual Inductance. You can verify that from the ARRL Handbook.

sparky

Thu Jun 07 2007, 05:43AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Well, I found out that I'm going to have 2500 turns of my secondary with 115 mH inductance while my primary comes in at 17 uH.
So I calculate:

sqrt(.115 / .000017)
82.24 = transformer V ratio
peak V capacitor discharge (20100 VAC) X 82.24 = 1653181 VAC

Hazmatt_(The Underdog)

Thu Jun 07 2007, 07:07AM

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

F is frequency L is inductance

Lp is inductance primary, Ls is inductance secondary
Cp is capacitence primary, Cs is self capacitence

sparky

Thu Jun 07 2007, 07:25AM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Thanks! I guess I'm building a 1.6 Million Volt Tesla Coil.

Terry Fritz

Thu Jun 07 2007, 01:16PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

See this paper:

ScanTesla can calculate it too far better than anyone cares :o)

Cheers,

Terry

Hazmatt_(The Underdog)

Thu Jun 07 2007, 07:45PM

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

Sounds really good Sparky,

I've already gotten the million volt mark with my 720VA coil, It's a neat feeling getting there.

Now I have yet to proove the relationship, but from what I am looking over and some I have talked with, it seems reasonable that the relationship holds true.

I would also like to point out that being able to calculate these things yourself serves to proove important benchmarks in your particular system for performance criteria. Being able to calculate the values first off serves to 'narrow the field' of your coil. You could do it the way others do it now, by tweaking a computer simulation, but to build a good coil you have to do both simulations and hand calculations.

sparky

Thu Jun 07 2007, 09:57PM

Registered Member #530 Joined: Sat Feb 17 2007, 07:56AM
Location: Victoria BC, Canada
Posts: 178

Did I also say that a group of high school students are putting the coil together... of course I'm the guy who has keys for the safety lock outs!!!
It will make the papers for sure thing and put our high school on the map!
---and make a HELL YEAH, high voltage display!

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