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Registered Member #6857
Joined: Sat Sept 22 2012, 08:25AM
Location: Srbija, Novi Sad
Posts: 40
I finished with my exams and I decided to make a small SGTC, and of course, once it was finished it didn't work :) I mean, it did spit few sparks from time to time, but that's not what I want.
It is flyback driven, and I am using this schematic:
This is my secondary:
(It is not really large, this is not a real T-rex)
The wire is 0.2mm. I was too lazy to count turns, and I didn't have any counter, so I counted 50 turns, measured the height, and divided the final height (171mm) with it to estimate the number of turns, and it was 806T. DeepFriedNeon calculated that L=3749.219uH and C=2.577pF. The secondary form is 33mm in diameter.
I found a pot cover holder and used it as a top load. I didn't know how to calculate it's capacitance, so I estimated it to 3.933pF, which is the capacitance of a 5cm wide metal ball.
For capacitor, I used 4 8.2nF capacitors connected in series, giving 2nF at 8kV. I put 1W 10MOhm resistors across the caps.
Spark gap is made out of two screws, adjustable, nothing special.
For flyback I use 18V 3.57A laptop charger, and this is my driver: . It gives about 5cm long arcs. I intend to build ZVS, but right now I can't.
I sticked a 1m long metal rod in the ground for secondary's ground, and made a primary from 5 turns of 1.5mm wire, and I was only able to draw sparks with a metal object. My heart is broken.
Now, my questions:
-Is this secondary OK for a small, flyback driven TC? -Is estimating the top load capacitance the way I did it a big mistake? -Are secondary's and top load's capacitance connected in parallel, or in series? Will the F(res) of the secondary be: F(res)=1/(2*Pi*sqrt(L*(Csec+Ctop))) or F(res)=1/(2*Pi*sqrt(L*1/(1/Csec+1/Ctop))) -About secondary's ground, because it is not a big coil, can I ground it to wall outlet's ground? Or maybe flyback's ground? Or should I stick to my metal rod? -Are bleeder resistors a mistake with this schematic? -And my biggest problem, winding the primary: With this schematic, with cap in parallel with primary, how do I calculate the number of turns needed? I want to make a helical coil with 8cm diameter, and I have 2.4mm enameled wire prepared for it.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Is the gap sparking continuously?
Do you have a DC flyback you could try? it would give higher voltage, but I'd protect the internal diode with a resistor on the output, quite a high value one.
The topload might benefit from adding a breakout point.
(Others may have better ideas. I built this circuit, but only used it for an HF TIG welder, where it arced under argon to metal, and needed much less power)
Registered Member #6857
Joined: Sat Sept 22 2012, 08:25AM
Location: Srbija, Novi Sad
Posts: 40
Yes, it does, but the interesting thing is, it starts by making a typical TC spark gap sound (RATATATATATATATATATA) but later, 10 secs or so, the spark becomes continuous, it doesn't break anymore. That happens every time.
Yes, I am using DC flyback, but no resistor at it's output. I will try the breakout point, but even with drawing arcs with metal object, the sparks aren't big. They are minimal.
Registered Member #3114
Joined: Sat Aug 14 2010, 08:33AM
Location:
Posts: 608
Njubster wrote ...
Yes, it does, but the interesting thing is, it starts by making a typical TC spark gap sound (RATATATATATATATATATA) but later, 10 secs or so, the spark becomes continuous, it doesn't break anymore. That happens every time.
Yes, I am using DC flyback, but no resistor at it's output. I will try the breakout point, but even with drawing arcs with metal object, the sparks aren't big. They are minimal.
Sounds like not enough capacitance or the spark needs to be blown to stop it from becomming continuous, try a small fan or many small gaps
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Help needed with flyback Tesla Coil
