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Tuning a primary coil.

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LAN_403

HV Enthusiast

Tue Mar 19 2013, 06:42PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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+1 on the pancake primaries!

Anyways, for best tuning and if you want to do it methodically, you can plot input voltage vs. peak current vs. arc length.

Basically create a strike electrode say starting at 6" distance and then increasing variac voltage until it hits the strike target and at same time recording the peak primary current. Increase distance by an inch (or so) and repeat. Do this until you reach maximum spark distance.

Repeat for various tuning points.

What you will get is some nice relationships between voltage / current and arc distance.

I generally choose a tuning point where it initially it takes more current / voltage to create initial arcing, but as the arcs get longer and the coils tuning changes, the arc length grows increasingly faster with increased voltage.

I don't have it handy in front of me, but if you look in my first book, i believe i have the method i used and some example plots showing where the optimum tuning point should be for a set of measurements.

Of course, thats pretty overkill. You can just wing it like most do and thats fine. But if you do it this way, you can learn a lot about the relationship of tuning and performance.

the mad scientist

Fri Mar 22 2013, 05:30PM

Registered Member #3768 Joined: Tue Mar 22 2011, 12:46AM
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I might have to purchase your book lol, how much is it?

HV Enthusiast

Fri Mar 22 2013, 08:54PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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If you send me your mailing address, i'll send you a free copy of the tuning paper.

the mad scientist

Sat Mar 23 2013, 04:55PM

Registered Member #3768 Joined: Tue Mar 22 2011, 12:46AM
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Ok I am having some friends over today and we are going to completely rebuild the primary, should I build it pancake or conical?

Physics Junkie

Sat Mar 23 2013, 09:27PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

From what other's have said, it sounds like flat pancake would be the easiest to construct and still gives you tight coupling. It's up to you though...

the mad scientist

Sat Mar 23 2013, 09:37PM

Registered Member #3768 Joined: Tue Mar 22 2011, 12:46AM
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Alright, I will make it a pancake coil.

Physics Junkie

Sun Mar 24 2013, 08:12AM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

EasternVoltageResearch wrote ...

I generally choose a tuning point where it initially it takes more current / voltage to create initial arcing, but as the arcs get longer and the coils tuning changes, the arc length grows increasingly faster with increased voltage.

So if I'm understanding you correctly, sounds like you detune the primary till you get max arc length at a certain voltage, lets just say max voltage in which would be normal. And when you initially input voltage, the arc length will be minimal and require more current that is until you apply more voltage and the system comes into tune.. because each foot of streamer equals about 1pF which will lower your secondary+toroid resonant frequency by several kHz.

Ever try looking at a FFT spectrum and tune to where the upper pole is at its flattest point? (Does that make sense?)
Because you want to detune the primary to reduce notches in current waveform, and also to bring the system back into resonance because of the added capacitance of the sparks. Thoughts?

Uspring

Mon Mar 25 2013, 11:42AM

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

Physics Junkie wrote:

Ever try looking at a FFT spectrum and tune to where the upper pole is at its flattest point? (Does that make sense?)
Because you want to detune the primary to reduce notches in current waveform, and also to bring the system back into resonance because of the added capacitance of the sparks. Thoughts?

You needn't really a FFT to judge whether the upper pole is excited. A beating of the primary current envelope would show that nicely.

In my experience you'll see little beating once you tune the primary low for the biggest sparks. This is because you ramp up near the primary resonant frequency which is far away in frequency from the upper pole.

Physics Junkie

Mon Mar 25 2013, 07:08PM

Registered Member #7267 Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407

Uspring wrote ...

Physics Junkie wrote:

Ever try looking at a FFT spectrum and tune to where the upper pole is at its flattest point? (Does that make sense?)
Because you want to detune the primary to reduce notches in current waveform, and also to bring the system back into resonance because of the added capacitance of the sparks. Thoughts?

Makes sense too I guess. It seems that what it comes down to is that for best tuning you must keep adjusting the tap point until optimal spark performance is achieved. Keep it simple of course.

the mad scientist

Tue Mar 26 2013, 03:00AM

Registered Member #3768 Joined: Tue Mar 22 2011, 12:46AM
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Posts: 107

I need some more help constructing the primary supports, like the spacing and what not.

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