Tesla coil problems.

[Ruben Schoonbaert]

Hello, my name is Ruben i'm 16 and an electronics enthusiast.
I'm actually dutch so don't mind my bad grammar.
So, i have recently tried to create my first tesla coil.
But the results are verry disapointing; (neon lightbulb barely lights up when held against the coil)
and i am kind of lost as to how i can optimise the capacity of the tesla coil.
And since i do not have an adult with the knowledge to help me in my proximity i have decided to ask the o so great internet for help.
Anyways i will leave the information i can provide below with some photos. any help would be greatly appreciated.

Secundary;
-0.1mm magnet wire
-pvs pipe is around 20cm in length and 4cm in diameter.

Capacitor;
-Its a homemade capacitor (see picture below) so im not really sure as to what the capacity is.

Powersupply;
-Basicly an AC flyback thats conected to a 12v led driver;

*So i need to know how many windings i should use for my primary coil and how big my spark gap should be.
Also i need help with my capacitor; my capacitor looks like it has enough capacity but i am not sure...

NOTE; i have tried to use online tesla coil calculators but i cant figure them out.

Any tips would be greatly appreciated!


if you need any exstra info just ask.

(battery for scale)

 

[DerStrom8]

Unfortunately Tesla coils almost never work when you simply throw them together. They actually require a strong understanding of their theory of operation and a fair amount of math in order to build them to work the way they're supposed to. In the most basic terms, you need to know two specific things:

1. The L-C resonant frequency of the primary circuit (L being the inductance of your primary coil and C being the capacitance of your homemade capacitor)
2. The L-C resonant frequency of your secondary circuit (L being the inductance of your secondary coil and C being the capacitance of your topload with respect to ground)

If these two numbers don't match, you will get very poor output, if any. There are many other factors that will have an effect but the tuning (matching of the primary LC and secondary LC frequencies) is easily one of the most important.

Resonant frequency can be calculated using the following formula:

where f is the resonant frequency in Hertz, L is the inductance in Henrys, and C is the capacitance in Farads.

 

[Ruben Schoonbaert]

Unfortunately Tesla coils almost never work when you simply throw them together. They actually require a strong understanding of their theory of operation and a fair amount of math in order to build them to work the way they're supposed to. In the most basic terms, you need to know two specific things:

1. The L-C resonant frequency of the primary circuit (L being the inductance of your primary coil and C being the capacitance of your homemade capacitor)
2. The L-C resonant frequency of your secondary circuit (L being the inductance of your secondary coil and C being the capacitance of your topload with respect to ground)

If these two numbers don't match, you will get very poor output, if any. There are many other factors that will have an effect but the tuning (matching of the primary LC and secondary LC frequencies) is easily one of the most important.

Resonant frequency can be calculated using the following formula:

where f is the resonant frequency in Hertz, L is the inductance in Henrys, and C is the capacitance in Farads.

Hello DerStrom8, thank you for the reply... Could you please explain how i am supposed to calculate the capacitance of my topoad ? thank you in advance...

 

[DerStrom8]

What do you have for a topload?

 

[Ruben Schoonbaert]

What do you have for a topload?

Honestly just a stress ball wrapped in alluminium foil, i didnt know it mattered...
Anyways i think this site should be able to help me.

https://deepfriedneon.com/tesla_f_toploadselect.htm

 

[Ruben Schoonbaert]

So if my calculations are correct my primary coil needs to have a capacitance of 13.1 MicroHenry's does anyone know how many windings i should have / how i can calculate that?

 

[DerStrom8]

Honestly just a stress ball wrapped in alluminium foil, i didnt know it mattered...

EVERYTHING in a Tesla coil matters. EVERYTHING has an effect in one way or another.

So if my calculations are correct my primary coil needs to have a capacitance of 13.1 MicroHenry's does anyone know how many windings i should have / how i can calculate that?

Check your terminology. 13.1 microhenrys is inductance, not capacitance. Capacitance is in Farads (or microfarads or nanofarads, etc).

How did you calculate a required 13.1 microhenrys? Do you know the resonant frequency you need for your primary and secondary circuit?

The calculations at deepfriedneon were not designed for Tesla coils running from a flyback transformer, so some are not applicable.

I need you to show me EVERYTHING you have done so far (the entire coil, the circuit, and all the calculations and results you have so far).

 

[Ruben Schoonbaert]

Okay,
So i used DeepfriedNeon's site to calculate the inducance from my coils and the capacitance of my topload.
I followed this tutorial for my capacitor (

)
l2=31.8mHen
C2= 3.104mfar
L1 = 0.158mHen
C1= 7.5nFar

So then i calculated the frequency of my secundary coil. that came to 0.016Hertz

So then i took the formula and rearanged it so i could calculate the inducance of my primary coil wich gave me 13.19mHenry

then i calculated that i need 21.7windings made out of 0.2cm copper wire.

This is the tutorial i used to create the power supply(

)

I tried it with 21.7 windings and the results are better but still verry low.

 

[DerStrom8]

There is a number of mistakes here and I'm going to need to break this down.

Okay,
So i used DeepfriedNeon's site to calculate the inducance from my coils and the capacitance of my topload.
I followed this tutorial for my capacitor (

)
l2=31.8mHen
C2= 3.104mfar
L1 = 0.158mHen
C1= 7.5nFar

Let's start with unit labels to limit confusion. The symbol for inductance is "H", not "Hen". The symbol for capacitance is "F", not "Far". "Milli" (1/1000) is denoted with an "m". "Micro" (1/1,000,000) is denoted using a "u" or "μ". "Nano" (1/1,000,000,000) is denoted with a "n". Please use these symbols when describing your math. For example, 1.0 nanofarad would be denoted "1 nF". 13 microhenrys would be "13 uH" or "13 μH".

Your topload (C2) is NOT 3.1 millifarads. I can guarantee it's not even 3.1 microfarads or 3.1 nanofarads either. How did you come up with that value?

So then i calculated the frequency of my secundary coil. that came to 0.016Hertz

Your calculation is way off. A coil that size will probably have a resonant frequency of between 100 kHz and 300 kHz.

So then i took the formula and rearanged it so i could calculate the inducance of my primary coil wich gave me 13.19mHenry

Are you trying to calculate what it is or what it should be? You need to start by calculating what it is. Ignore the primary circuit for now, and just focus on the secondary. Answer these questions:

1. What is the secondary coil diameter and height?
2. What gauge wire did you use for the secondary coil?
3. What is the wire's insulation thickness?
4. How many turns do you have on the secondary coil?
5. What are the topload dimensions?

Once we have this information we can move on.

 

[Ruben Schoonbaert]

There is a number of mistakes here and I'm going to need to break this down.


Let's start with unit labels to limit confusion. The symbol for inductance is "H", not "Hen". The symbol for capacitance is "F", not "Far". "Milli" (1/1000) is denoted with an "m". "Micro" (1/1,000,000) is denoted using a "u" or "μ". "Nano" (1/1,000,000,000) is denoted with a "n". Please use these symbols when describing your math. For example, 1.0 nanofarad would be denoted "1 nF". 13 microhenrys would be "13 uH" or "13 μH".

Your topload (C2) is NOT 3.1 millifarads. I can guarantee it's not even 3.1 microfarads or 3.1 nanofarads either. How did you come up with that value?


Your calculation is way off. A coil that size will probably have a resonant frequency of between 100 kHz and 300 kHz.


Are you trying to calculate what it is or what it should be? You need to start by calculating what it is. Ignore the primary circuit for now, and just focus on the secondary. Answer these questions:

1. What is the secondary coil diameter and height?
2. What gauge wire did you use for the secondary coil?
3. What is the wire's insulation thickness?
4. How many turns do you have on the secondary coil?
5. What are the topload dimensions?

Once we have this information we can move on.

Okay,
1. Diameter = 4cm Height = 20cm
2. 0.1mm copper magnet wire ( i think 38 AWG)
3.0.03mm
4.should be around 2000windings
5.its a Toroid 1.5cm thick and 8.5cm in diameter
i used deepfried neon's site to calculate it. (https://deepfriedneon.com/tesla_frame6.html)

 

[DerStrom8]

0.03mm is not a standard insulation thickness for 38 AWG magnet wire, so I am using the closest standard value (0.02 mm).

With a coil radius of 2 cm, height of 20 cm, and 38 AWG wire with 0.02 mm insulation thickness, I'm calculating only about 1093 turns. That should be fine though.

Using JavaTC (written by Bart Anderson - someone I have spoken to on numerous occasions) I am getting a toroid capacitance (based on the dimensions you provided) of about 2.267 picofarads. This is probably much too small for your coil, and will cause the resonant frequency to be way too high to be practical. Based on the dimensions you provided I am calculating a secondary coil inductance of about 8.6 mH, meaning the resonant frequency will be over 1 MHz. When you take the parasitic capacitance of the secondary coil into account it's closer to 850 kHz. While there are indeed coils that run at this speed, it is probably a bit high for your particular coil. That being said, let's carry out the remaining calculations. Your target Fres (resonant frequency) is 850 kHz. Remember that number - you'll need it.

Next let's look at your primary capacitor. You say it's 7.5 nF simply because that was the value of the one made in the video. Unfortunately that's not good enough. The value can change significantly from one capacitor to the next. You really need to know the EXACT value of YOUR capacitor, you can't simply say yours is 7.5 nF because that was the value of the one in the video. Most multimeters nowadays have a capacitance setting. I recommend measuring the capacitance of yours using a meter. From there we can calculate what you need for a primary coil.

 

[Ruben Schoonbaert]

It seems to have a capacity of 3.9 nF
About the top, i can get my hands on all kinds of foam donuts wich ill use to make a toroid top;
these are the sizes i can get:
D7.5cmW2.5cm
D10cmW3cm
D12cmW3.5cm
D15cmW4cm

 

[DerStrom8]

It seems to have a capacity of 3.9 nF
About the top, i can get my hands on all kinds of foam donuts wich ill use to make a toroid top;
these are the sizes i can get:
D7.5cmW2.5cm
D10cmW3cm
D12cmW3.5cm
D15cmW4cm

I would recommend either the 12 x 3.5 cm or 15 x 4 cm. 15 x 4 cm would probably be best.

According to JavaTC the 15 x 4 cm topload would have a capacitance of around 5.2 pF. This will drop the Fres to around 650 kHz. This is your new target.

To calculate the required primary coil inductance, rearrange the formula:

and solve for L:

where f is the resonant frequency (650 kHz) and C is your primary capacitor (3.9 nF).

Calculate your required inductance for your primary coil and then we'll start working on the dimensions.

 

[Ruben Schoonbaert]

So that would be 1.54microhenries

 

[DerStrom8]

So that would be 1.54microhenries

You're off by a factor of 10. Should be 15.4 uH.

What size wire do you want to use for your primary coil? In order to calculate the number of turns I will need to know that information.

 

[Ruben Schoonbaert]

the wire i can use right now has a metal core of 1mm is diameter and with the insulation included its 2cmm in diameter.. I can get my hands on all sorts of wires though.

 

[DerStrom8]

the wire i can use right now has a metal core of 1mm is diameter and with the insulation included its 2cmm in diameter.. I can get my hands on all sorts of wires though.

1mm wire will probably have high resistance, but let's go with that for now.

Use this calculator a friend of mine and I put together to determine your primary coil dimensions. I currently have the turn spacing set to 0.2" (5.08 mm), the wire diameter set to 0.039" (1.0 mm), and the diameter of the innermost primary winding set to 2" (5.08 cm). With the desired inductance set to 15.4 uH I get a required turn count of around 11 1/2 turns.

 

[Ruben Schoonbaert]

How big should my spark gap be ?

 

[Ruben Schoonbaert]

How big should my spark gap be ?

Also, should my primary be a pancake shape, a helical(cilinder) shape or a cone shape?

 

[DerStrom8]

How big should my spark gap be ?

Hold your horses, we'll get to that.

Also, should my primary be a pancake shape, a helical(cilinder) shape or a cone shape?

The calculator I just provided for you is for a pancake coil. You can always change it later if it seems necessary, though you'll need to tap ("tune") it differently if you do.

Start by constructing the coil as described so far with the correct topload and primary coil. I recommend using bare copper wire for the primary - it will make it easier to tune later on. Give it 20 or so turns if you can. Take photos and post them here so I can see how things turned out, and then we can go from there.