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Tesla Coil Suggestions

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Hazmatt_(The Underdog)

Wed Feb 15 2006, 08:54PM

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

I've got the blues real bad now, As I have embarked to make a Tesla Coil 'Perfect'

This is why I am asking for help.

Okay, so what's the situation?

Well, I have been working on and improving my little 720VA system as a model for the one I am designing for CSULB. I am trying to verify and prove out what works best so that when I finialize the specifications for the CSULB coil, it will be right.

Problems:

CAPACITOR
The first major problem I have is the capacitor value. I am not relying on WinTesla, because its computation does not account for internal losses. I have the following information:
V = 12,000 I = 60mA L = 700H R = 6110

Z from WinTesla is 200K but factoring in internal reactance Z is really 263,886R

WinTesla says that the cap should be .0133uF, which from its calculations is the resonant capacitor.
My calculations which match the capacitor for resonance is .010uF

I did the phasor calculations for the resonant cap, assuming that V = 12,000 < 0*
Z is then Z = 6110 - j1372 so Z = 6262 < -12.65*
I = E/Z = 1.91 < 12.65

We can see that this current draw can be terrible for the transformer to handle! its a lot more then the 60mA!

I have been using .016uF as per the 1.6X suggestion. But I think its loading down the transformer. So I am thinking of using .012uF insted, which is yes, closer to resonant, but I have looked at the calculation.

Z = 6110 + j42837 = 43270 < 81.88*
I = .277 < -81.88* which is a lot more then .060 but not nearly as bad as resonant.

The cap size presently yields (.016uF)
Z = 6110 + j98099.6 = 98289.7 < 86.4*
I = .122 < -86.4*
So basically I will draw twice the current with the .012uF cap as compared to the .016uF cap.
I would simulate, but that is where I have a lot of trouble. what do you think?

COIL
My secondary is under 1000T of #23 wire, and the problem is that the geometry as a model to the CSULB coil is totally different.
CSULB coil: H/D 8.0 6" OD by 48" L which with #22 wire may be over 1700T!
and my coil right now is
H/D 4.8-4.9 4.55" OD by 22"L and #23 wire.

I am getting some nice 2X L sparks, but the problem is I need to get every inch out of the CSULB COIL

POSITION
I'm really not sure how high the coil 'should' be above the primary. I've tried to determine this, but lowering it down to about 1" above the primary gave me racing arcs, so I doped it and eliminated the arcing. I also had primary to secondary zaps because the only insulation I put on the primary was a layer of heat shrink. I knew I would have this issue, but not this bad. Solution was natraul rubber tubing slit in half and covering the heatshrink.

The vertical position is really key to the CSULB coil because the coil form is too heavy to be supported by conventional supports, so it was decided that it would go through the primary base and attach to the bottom base, a height of about 2', exposing the rest of the 48" above for the secondary resonator. The trouble is that I have to know for sure how high to make the supports inbetween the two bases (bottom base and primary coil base). I guess that will just have to wait.

Should I widen the ID of the primary? or keep the coupling?

SPARKGAP
We are making a rotary that will have a static gap as well for the CSULB coil. Since Jim is busy fabricating the rotary, it will buy me some time for all of the stressful details.

My rotary is working, but syncing it up is a pain, so I have to make some sort of triac thing.

TOROID
I'm really concerned here because I have to get it right! So I need to know what assumptions I should use, 2X Cself?

I dunno, My coil is a good performer so far, but it needs to be improved further such that there are fewer faults. Help would really be appreciated!! I'M SERIOUS!

HV Enthusiast

Wed Feb 15 2006, 09:30PM

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

Hazmat,

It sounds as if you are at the point where your coil works good, and you just want to improve performance.

However, it is at this point where calculations and other recommendations will not help much. From here, your coil is its own entity, and you are going to have to do lots of trial and error things to improvement.

One thing if you are really interested in improving performance is to look at Gary Lau's website at

or contact him directly. He really did wonders with his latest SGTC and might be able to provide some good pointers.

Steve Conner

Wed Feb 15 2006, 11:29PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

There's no such thing as "Perfect", but if you use a 120bps sync rotary gap along with the "Sync LTR" capacitor value for your power supply, you could get close. IIRC, Sync LTR is equal to pi times the resonant value, and gives the maximum bang energy possible, which should yield the longest streamers for a given power input.

Hazmatt_(The Underdog)

Thu Feb 16 2006, 12:14AM

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

There's a major issue with using larger caps that I'm finding, which is heavy current draws.
I have tested .024uF which is 2.4X.010, which I think is my resonant value, but I cannot say for 100% sure.

I am going to go back and lock my series motor into 120BPS so to eliminate that variable! I've had-it with trying to sync things up and worrying about a misfire destroying the NST.

I will post every spec I can when I can, its just that I don't really have everything together right now.

Thank you guys!

Matt

colin heath

Thu Feb 16 2006, 08:35PM

Registered Member #123 Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162

Hi Hazmatt,
You will not get a perfect tesla coil. Either max performance or max reliability. or are you after the best compromise possible?
The best improvements once the system is built are had by trial and error as well as measurements. Small things such as surroundings will make a difference to tuning as well as streamer length itself.
little tweaks such as height of toroid above secondary can squeeze the all important few last inches of spark. Sorry if this is telling you how to 'suck eggs' but i don't know how much experience you have

cheers
Colin

Hazmatt_(The Underdog)

Thu Feb 16 2006, 11:21PM

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

I've built many before as a 'builder', like most of these guys here, just lash it up and get it going.

But now that I'm in Engineering I want to make a coil with the best comprimises possible. That's why I'm asking for suggestions.
I can get 2x WL out of my present coil, but I need more input on tweaking.

>>>>>>>>>>>>>>UPDATE<<<<<<<<<<<<<<<<<

I really wanted to thank you guys for your input!!

I'm doing more PSpice modeling and was tweaking around my charging system (including losses) and I used your suggestions for cap values.

I was really looking into this in detail and for the first time put the FFT function to use. Man what a help that was! It told me what I've been looking for all this time.

I adjusted the cap values and looked at the source characteristics, power voltage and current, but power is by far the most important to me right now.

I simulated with my value .016uF, got the power curve, took the FFT, and SPIKE, right at 120Hz, exactly what I wanted, but not quite, only 480W! OUCH! 720-480 = 240W of unrealized potential!!!!!!! This is not good!

I tried pi*Cres, but that was under 300W from the FFT, sorry, no cigar.

I went to resonant for s*** and giggles, and about 2000W #$%@#$!!!!!! well, now we know why resonant charging is bad! It's not so abstract anymore now is it!!!

So time for comprimise.

I went larger still to .018uF and got 420W, well that's no good either.

smaller .014uF HEY!!!! 600W at 120Hz BINGO!!!! I knew I had to go smaller beforehand and I was going to try .012uF!!

Seems that I have better intuition then I expected.

Please keep the Questions, Comments and Concerns coming! They are helpful!

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