# Question about calculating the current in an Inductor Capacitor circuit

#### johnboyman

Joined Jun 1, 2019
43
Hello. I have a tesla coil for a project of mine. I have it fully built and almost ready to fire but my 15000 volt 32 milliamp transformer keeps turning on one time and firing my spark gap one time then halting, It also has a little red light on it that turns on the transformer. I think that the current may be to high in my circuit. My capacitor bank is .33uF/13 = 0.025 uF. I cannot find out how to convert farads to milliamps per second. I think that the current may be too high for my transformer so i am trying to find out how to calculate the current of my LC circuit. I cannot find any straight forward formulas on the internet. please help thanks.

#### Delta Prime

Joined Nov 15, 2019
1,311
Hello. I have a tesla coil for a project of mine. I have it fully built and almost ready to fire but my 15000 volt 32 milliamp transformer keeps turning on one time and firing my spark gap one time then halting, It also has a little red light on it that turns on the transformer

#### johnboyman

Joined Jun 1, 2019
43
Hey thanks for the response. The image of the transformer on the left, spark gap in the middle and caps on the right of that yellow box is my lc circuit. There is an inductor primary and secondary for the output of the tesla coil not in the image because its not what i am focused on. The electrical diagram below it shows how i wired it because it isn't that easy to see it in the image. Here are the specs.

-Inductance (L): 17 uH
-Capacitance (C): 0.023 uF
-Resonant Frequency(F): 254.201 KHz

-Diameter (D): 6.5 inches
-Number of Turns(N): 12
-WireDiameter (W): 0.25
-Turn Spacing(S): 0.25

Height: 7.5 inches
Length Of Wire: 282.743
Inductance: 17 uH
.33uF/13 = 0.025 uF

transformer: 15,000 volts 32 milliamps

2000 Volts each * 12 = 25,000 Volts

In the past I had my capacitor bank hooked up in series with my spark gap alone and when i ran it it would run continuously. but when I include the inductor in the circuit and hook it up fully that way it is shown in the diagram, the spark gap will only fire once and thats not because the contacts are not close enough, my transformer will turn on a red light and stop as if it blew a fuse. So i was guessing it must be the amperage. Hope you can help thanks.

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#### johnboyman

Joined Jun 1, 2019
43
I am trying to find a formula on the internet to calculate the peak current of the entire circuit to find out how much current is going through my transformer. I have found many formulas that are very close but i just can't fully get my head around this. Here are some formulas I found.

This is what someone else wrote:
Q: A 140 microfarad capacitor is connected with 250 volts, 50 hertz. What is the value of the current?
A: The impedance of a capacitor is given by Xc = 1/ (2*pi * f * C)
If there is no other component in circuit, then I = V / Xc = 250 * 2 * pi * 50 * 140*10^–6 = 11 amps.

My ideas on how to finish these formulas for my needs is to:

Vrms = 15000 volts / 13 = 1,153 volts per capacitor
C = .33 uf per cap

calculate the peak current per capacitor with the above formulas, then divide the result by 13 may equal the total peak current in the circuit. That is the direction i am moving in.

This is as far as i can find. I have one string of capacitors in an mmc string. non in parallel just 13 .33 uf capacitors in a string and a 15000 volt transformer. How can i use these equations and factor in my 13 .33 uf Capacitors to find the peak Current of My tesla coil circuit. I could just buy a 60 ma transformer and i think it would work but i need to know the math before i move on because its just driving my nuts.

Thanks alot guys.

#### Delta Prime

Joined Nov 15, 2019
1,311
A Tesla coil is a resonant transformer
You added an inductor to the secondary LC circuit , both primary & secondary together make a tuned circuit . From your specifications is designed to operate at Resonant Frequency(F): 254.201 KHz .
to keep the resonant frequancy constant L*C has to stay same. Lets say if you double L you have to divide C by 2 to keep the same resonant frequency. If only L increases Resonant frequency decrease, this is same for C. At resonance the energy will oscillate back and forth from the primary capacitor to the primary inductor and is loosely coupled to an inductor in the secondary coil attached to the top of the secondary coil is a top load that provides the capacitance for the secondary LC Network. The primary and secondary LC circuit oscillate at the same frequency to achieve maximum power transfer. The circuits in the coil are usually tuned to the same frequency by adjusting the inductance of the primary coil. You're moving in the wrong direction I really need to see your schematic.

#### DbLoud120

Joined May 26, 2014
88
Hello,
You have the spark gap wired wrong.

Have a look at the attached pdf file.

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#### johnboyman

Joined Jun 1, 2019
43
Hello,
You have the spark gap wired wrong.

Have a look at the attached pdf file.
Really. I thought about that. On the internet there are tones of diagrams of this circuit being wired and it looks different in every image i find.

Oh that is great news. Thanks a lot I will fix that and give it a try thanks.

#### johnboyman

Joined Jun 1, 2019
43
Hello,
You have the spark gap wired wrong.

Have a look at the attached pdf file.
Hey thanks. My image was actually an accident it was an older image. I uploaded the current one i have. I have. the way i wired it was in relation to the animated schematic i uploaded next to my real photo of my coil. I see your pdf i notice that the spark gap is in a different place. I see a few different versions of this schematic all over the internet it kind of confuses me. I will try to rewire it like your image thanks.

#### Delta Prime

Joined Nov 15, 2019
1,311
Could you snap a photo and send it when you get it up and running I'd love to see it in action.