Can someone help, am not getting any plasma :-) much appreciated

[Jmackie]

Ok so I've attempted to build my own tesla coil, this is what I have thus far;

10,000 volt NST directly onto two nails creating a spark gap (this works)
From one side of the spark gap into 14 series capacitors 2,000 volt and 0.15 uF (yes I know voltage is more than required but I wanted to get the capacitance correct)
From the other side of the spark gap onto the primary and from the capacitors (with bleed resistors) onto the other end of the primary.

So basically I purchased a coil with well over 1,000 turns as didn't have the time to make my own.

So my suspicions or question is:
1. The spark gaps work but there are no sparks at all from the tesla coil apart from arcing with the earth terminal
2. 14 caps in series gives me around 10 nF which is what I calculated that I need. Obviously I'm on 50 hertz at source but I'm wondering how to calculate the frequency and ensure there is resonance between both coils?

Thank you!
James

[MRMILSTAR]

Most likely you are out of tune. Enter all of your coil parameters accurately into JAVATC and see what it says about the tap point on the primary coil.

[Jmackie]

Thank you,
What's the TAP point you refer to?
Ok added the details in, seems as if the output frequency is 80 Khz, I might hook up my oscilloscope to double check.
I've also noticed small carbonisation on the lower part of the secondary which could be causing issues.

Could I pay for your time at an hourly rate to zoom call and get some help?  I really want to nail this haha.
Thanks
James

[MRMILSTAR]

The tap point is the spot on the primary coil that serves as one electrical end of the coil. This is where you will connect one pole of your capacitor(s). The primary coil is an inductor. The tap point establishes the inductance of that coil. The inductance, in combination with the capacitance, determines the resonant frequency.

Thanks for the offer but I'm not interested in any paid consultation. Just keep posing your questions on this forum. If you haven't already done so I suggest reading some of the excellent Tesla coil web sites. It sounds like you have a lot of basic questions that could be answered by these sites. I started out knowing next to nothing about Tesla coils but I was able to answer all my questions by studying various web sites.

[Jmackie]

Really appreciate your response.

So I too have spent a lot of time over the last 4 weeks, almost every day, reading websites on Tesla coils.  I've also looked at many of the old videos from Geek Group. Styropyro etc.  I haven't seen "tap" point referred to but I understand (only recently) how the secondary acts as a capacitor and the primary as an inductor.  I've taken apart many machines at home and tested step up voltage and I've created about 4 different spark gaps.  I calculated both voltage and capacitance needed from the capacitor bank and created the correct capacitor bank...

Same with the transformer, the coils etc, I feel like I've learnt a lot!  None of them actually explain how the plasma is created though but the best description I read was that if you imagine the primary coil is being plucked in the same way a guitar string is at say 1Hz, then the secondary will resonante higher the same way that the guitar string oscilates at 10 Khz.  I know we need 100 Khz or higher for the TC.

Also many websites refer to resonance in a different manner; some refer to resonance as the peak oscillations, some refer to it as the tuning fork analogy; i.e. at its material resonance.

BUT I feel like I've carried out the math correctly, and the amount of reading I am doing now, say 5 website and garner little more "new" information on top of what I already know.  So I gathered the frequency is out between the coils so I've been trying to find out how the coils are tuned...

Thanks again

[Jmackie]

MRMILSTAR can you see the attached video?

I've got sparks arcing and shorting on the secondary... I can't see visible damage on the coil but the copper wire is very thin..

I've read to create my own ground from the secondary with tinfoil.

Any ideas?
Thanks
James

[Jmackie]

So I read the primary may be to close to the secondary. I therefore quickly made a terrible looking new primary with thicker gauge copper and now I get lovely plasma shooting out randomly from the sides of the secondary...

But it doesn't hit the toroid, what would be the reason the sparks don't reach the top? As I can't imagine it not being sufficient voltage, the thing is deafening!

Thanks again
James

[MRMILSTAR]

I see several problems here. A SGTC needs to use a flat pancake-style primary coil, not the cylindrical (solenoid) type that you have. The cylindrical type provides too much coupling to the secondary coil. This is what is causing the sparking along your secondary coil. The second problem that I see is that your primary coil cannot be tapped at different places. This is how you change its inductance. You have a fixed-length primary coil which can only be tuned by adding or subtracting turns which is extremely inconvenient and imprecise.

Make a new pancake-style primary coil from copper tubing. The bare copper tubing will allow the primary coil to be tapped at any position for tuning. It will also provide less coupling to the secondary coil which is desirable for a SGTC. Use JAVATC to give you definite parameters.

[Jmackie]

Wow I didn't know that about the cylindrical primary and coupling!  Thank you...

Yes agree with tapping, I didn't think it would make much difference because I only have a few turns but now I'm reading about tapping point and how that is the best / easiest method to tune and I'll increase the turns so I can add a tap point so thanks again!

So my only remaining question is how to determine the ideal thickness of copper tubing for the primary if I have 10+kv from the transformer, 10nF from 14 x .15 uF Caps in series?  Secondary coil is 10 inches tall by 3 inches diameter with 1800 turns at 0.006 inch diameter wire.  So basically I played with JAVATC as you suggested and altering the thickness diameter of the primary coil copper tubing makes virtually no difference.

Entering the details into JAVATC it seems as if my Secondary resonant frequency is 300 Khz so I've fiddled with the secondary numbers to get to 300 Khz and basically it states I only need 2.5 turns and the thickness of the tubing is almost irrelevant.

Added the pics from JAVATC!

You can't buy HV multimeters in the UK so I'm going by spark gap, it feels as if the transformer gives far more than 10kv as the spark gap can be far larger than a few cm plus the noise is deafening.

Thanks again
James

[Jmackie]

MRMILSTAR my feeling here is that there are so many factors at play, it's not possible to workout the exact windings of the primary on paper.  I've gone with 2.5 turns and have less plasma from the secondary.

My feeling is thicker tubing and a few more turns with small gaps between the turns will work well so I've ordered that for tomorrow.  My gut is telling me (after reading non stop since your first reply maybe 10-12 hours per day) that at this point I need to use trial and error instead of formulating the rest on paper...

[MRMILSTAR]

Your coil is relatively small so just use whatever size copper tubing is available and convenient. Typically this would be the smallest diameter tubing you can get, if only because it would be the cheapest. The output from JAVATC is pretty accurate if you enter all parameters accurately. That being said, final tuning is done by experimentation. Just include a few extra turns on your primary coil to allow for tuning from the recommended point.

A 2.5 turn primary coil is going to be EXTREMELY sensitive to tuning. I would recommend lowering the capacitance to get a more reasonable number of turns on your primary coil. I would shoot for at least 10 turns although this not not a hard-and-fast number. The fewer the required turns, the more sensitive the tuning will be. Then add a few more turns to that to allow for tuning.

[Jmackie]

Hey MRMILSTAR I just wanted to say thank you for your help and here is the video I created showing my HV Tesla Coil;

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Thanks again
James

[MRMILSTAR]

It looks like you made some good progress but it appears that you are still getting unwanted discharges from the secondary coil. This is probably because you have too much coupling. If you raise the secondary coil with respect to the primary coil this will reduce the coupling. This should eliminate or drastically reduce those discharges from the middle of the secondary coil. Left unchecked, those mid-secondary discharges will eventually damage the insulation on the secondary coil windings and failure will ensue.

[Jmackie]

Thank you
I will be giving this a go today!

[ItsChloeUwU]

IMO

the primary is way too little in insulation so they would likely jump to each other and cut the primary in maybe just one spire if u are lucky to have it stay that close in the spires.. so maybe lay it down.. and maybe try to space them like 5mm to a cm apart (this would work even in a tube shape configuration but more high you put the spires more voltage rise you have so if you do this ism ore likely to have flashovers between seocndary and primary wich already happend from what i can see) .. also in my experience.. layingi t down is the best way to do it for better spark lenghts...

then i would try to put the NST circuit without a ballast (if thats whats going on there cus i cant really see) and i woul try to directly connect it to the circuit...

Another thing... the capacitors.. they are nice looking.. but try to pack them more close in a "zig-zag" way since its really really long and lice this i think it could pick up some strange interference from the coil perhaps?

Also try to look for capacitance.. in my experience around 50 to 80nf its the best for a coil with 5 to 9kV ... but might be different for you... surely around 20 or less is too little IMO even for a little coil like this..

I also saw that you are running your primary tap wire at the beginning in an arc that is going on the secondary and hitting on it with the sparks.. so you really have to put that UNDER the primary.. not over it.. also talking from experience on this...

the secondary also looks covered in resin or something.. if this is right then the resin mix i think its done wrongly wich is the problem of your arcs over the secondary not riseing to the topload... if its just a pice of tape or tube or something like this it could me air bubbles and electrostatic stuff going on wich also can make this types of arcs.. if its possible try to remove it...

lastly.. try to play with primary position tap... i always like to use my coil primary uninsulated to tap it at any point to tune it more easly.. and thats a huge plus to the coil.. once you have it tuned you could take pics and register the position to then do it with insulated already tapped one if thats the look you want!

Best of luck! Hopeing to see improvements!