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Arcing between first few turns on secondary

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Curtis

Thu Jul 23 2009, 04:11PM

Registered Member #883 Joined: Sat Jul 07 2007, 01:02PM
Location:
Posts: 16

i second lhl's question. i have been trying to wrap my head around "half wave" and "quarter wave" for months now. i have researched as much as i can. i would appreciate if someone could explain it less in EE terms and more in "i build tesla coils in my basement" terms. Any info is greatly appreciated.

Andyman

Thu Jul 23 2009, 07:15PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

"I build tesla coils in my basement" terms are going to be somewhat EE terms because, well, they have to be. Tesla coils are not some basic, simple thing that anyone can just throw together and hope to get 30" sparks.
Wavelength and sine wave functions are basic physics. Wavelength (Î») is the distance between the peaks of an alternating current cycle and Î»=v/f where v is speed of light and f is the frequency of alternating current . If you were to imagine the ac traveling slowly down a wire, the wavelength would be the distance between voltage reversals.
I believe half wave and quarter wave are simply full waves that have another wave on top whose length is compressed into 1/2 or 1/4 of the original wavelength (higher frequency). So for every cycle of the quarter/half wave alternating current, there have already been 2 or 4 complete waves of the original frequency.
I might have this backwards, so somebody with more knowledge might be able to better answer. I'm just a freshman in college :P

And to RichM, did you sand and seal your coil form before you wound it? If there is an impurity in the form, you could be getting arcs to/through that.

HV Enthusiast

Thu Jul 23 2009, 08:31PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Curtis wrote ...

i second lhl's question. i have been trying to wrap my head around "half wave" and "quarter wave" for months now. i have researched as much as i can. i would appreciate if someone could explain it less in EE terms and more in "i build tesla coils in my basement" terms. Any info is greatly appreciated.

If you have a sinusoid, you have some wavelength which is based on the frequency. If you have a Tesla coil which resonates at 100kHz, the wavelength would be 9840 feet.

If you looked at the sine wave you would have zero at 0pi and 1pi and peaks at pi/2 and 3pi/2. The electrical (or wire) distance from 0pi to pi/2 is the 1/4 wavelength.

The electrical length can be approximated to be the wire length of your secondary. (rough estimation for this exercise)

Therefore, if you ground the base, and the Tesla coil is designed for 1/4 wavelength resonance, you would have a peak at the top of the Tesla coil.

This is WHY self-tuning Tesla coils can be exceptionally bad to secondaries. If you have a nick or other discontinuity in your secondary coil, the self-tuning will retune so the 1/4 wave peak is at that damaged point and your high voltage node will occur at that point and burn your secondary point, as opposed to a manually tuned coil which in the same case would burn at that point, but it wouldn't be the highest peak node as the 1/4 wavelength node would still be at the top.

I'm certaintly not an expert in this, so correct me if i'm wrong, but this is what my understanding it is.

coillah

Thu Jul 23 2009, 08:55PM

Registered Member #1517 Joined: Wed Jun 04 2008, 06:55AM
Location: Chico CA
Posts: 304

Just so people aren't too confused or upset over this wonderful bit of physics I'll just insert my own two cents.

Basically all coils function by this.

The only new thing going on here is the description. Dr. G is describing essentially what comprises the resfreq of a typical secondary coil, its nothing special.

When you tune your primary, you are essentially matching the resfreq of the primary circ. to the sec. circ. You get a node at the ground connection because... well ground = 0 V its pretty much a given (it takes a lot of power to make this untrue). Your coil produces an anti node at the topload, if everything is configured correctly (meaning, if the primary is tuned properly). A neat way to imagine it is, your primary and secondary are like two 1/4 sine waves. By adjusting the primary circuit you are squeezing or stretching the primary sine wave 1/4. You squeeze or stretch this waveform until the end of the primary 1/4 wave form matches up with the end of the secondary 1/4 waveform (the ends are antinodes, if this seems strange, draw a sine wave [starting at zero] and then chop it at 1/4 of the entire wave length, there's your antinode!). When those two ends match up, you have resfreq matching aka sparks!

teravolt

Fri Jul 24 2009, 02:43AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

A tesla is like a boy on a swing. 0 degreas is when the boy is at rest and when you the primary pushes the boy will go to a peak hight. That is 90 degreas or 1/4 of a full cycle or 1/4 wave length . As the boy comes back he passes through 0 on the way to -90 degreas the negitive peak of the cycle. The more push you put in each cycle the higher he goes. the tesla is the same where you are the primary and the boy is the secondary. If you look at a sign wave 90 degreas is 1/4 wave length and one peak voltage and -90 deg is the other. In your tesla if you have grounded the secondary and you still are geting arcing your secondary is out of tune with the primary.

lhl_henrylui

Fri Jul 24 2009, 05:52AM

Registered Member #1498 Joined: Thu May 22 2008, 07:08AM
Location: Hong Kong
Posts: 72

Now I understand how to make a wavelength resonance in a tesla coil.In the past, my TC were roughly designed and I haven't determined the length of the TC to form wave length resonance.So I will try to combine this knowledge with my new TC.

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