Author Topic: driving a tesla coil  (Read 202 times)

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Offline GIGGINO94Topic starter

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driving a tesla coil
« on: July 10, 2024, 12:35:41 pm »
Hi i'm trying to make a tesla coil but in the process of winding the secondary i used an online calculator to calculate roughly the inductance of the secondary and it turned out to be around 0.09 uH for a secondary of 6.6 cm lenght and a 4.3 cm diameter and roughly 850 turns, so i calculated the resonance frequency of the secondary and topload to be around 160 Mhz, since i can't make a 160Mhz generator for now i was thinking of friving it with the capacitor with a spark gap that puts it in parellel to the primary  so they can resonate ( hopefully at a similar frequency of the secondary) so to generate a high voltage to charge the capacitor with i designed the circuit on the image wich is simply an astable multivibrator made with bjts an then an h bridge that powers a transformer ( i don't know if driving the transormer with a square wave is the problem but i tought that since the square wave has infinite armonics it shouldn't be a problem becouse one of that armonics will also be at the resonance frequency of the secondary of t1 and the capacitor) but the h bridge doesn't work as intended and i don't get why, there seems to be close to no current in the load ( for now i'm trying without the tesla coil itself ) i also tried with two reversed leds but they don't turn on at all, but using only two mosfets of the h bridge seems to work just fine , but then of course the capacitor would get charged at a slower rate so i think that either i didn't use the mosfets right (is the first time i'm trying to design a circuit with them ),  or i got all the idea of the driving circuit wrong.Also i wanted to ask if i should cut off the secondary of the first transformer when there is an arc to let the capacitor and primary of t2 resonate.
Details:
power source : 5v dc
mosfets:IRFZ44N
bjts: 2n2222a
voltage on the secondary of the first transformer(T1) should be around 150 v
rb of the astable :10kΩ
rc of the astable : 220 Ω
c of the astable: 4.7uF
Thanks for your attention
 

Offline mtwieg

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Re: driving a tesla coil
« Reply #1 on: July 12, 2024, 11:25:41 am »
First of all I think there must be some typo or miscalculation in your post. A secondary inductance of 0.09 uH makes no sense. For a solenoid with L=6.6cm, D=4.3cm, and N=850, I calculate about 20mH. That should bring the resonant frequency down into the <1MHz range, depending on the topload.
 

Offline gbaddeley

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Re: driving a tesla coil
« Reply #2 on: July 12, 2024, 02:28:27 pm »
6.6cm is very short. I would expect at least 20cm to achieve a useful secondary discharge length.
How did you fit 850 turns in just 6.6cm??
Glenn
 

Offline BrokenYugo

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Re: driving a tesla coil
« Reply #3 on: July 12, 2024, 02:56:52 pm »
You need a lot more than 150V for a SGTC. For further reading see "Paschen's Law" and "Paschen minimum", basically you can't have a practical atmospheric spark gap below 500+ volts.
« Last Edit: July 12, 2024, 02:59:46 pm by BrokenYugo »
 


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