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Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
G'day,
My girlfriend wants to build a tesla coil with me so ive gone about designing and ordering parts, just need a once over by someone more familiar with flyback driven coils than I.
See attached photo, am i in the ball park?
I ran JavaTC and it looks ok to me, I attached the load file to this post, it will resonate at ~500kHz is that acceptable?
Is 5-7 turns on the primary of the flyback ok or should i go higher/lower?
I have bought 10x 3kV 0.1uF caps for the tank, i think 30kV @ 10nF should be ok, 30kV is a bit high i think but can pull capacitors off to lower voltage and gain capacitance yes?
I plan on using 99.5% 3.6mm tungsten electrodes for TIG welders for the spark gap, is 3.6mm too small? should i run a few in parallel?
Anything you could tell me to benefit the output or construction would be great.
Things i have thought about but dont want to play with: I dont want to setup/build a rotary gap. I dont want to use a NST.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
1. You're going to use a flyback to drive the primary tank at ~30KV? how do you plan to insulate the primary from arcing over all the time? 2. If you are charging at 30KV, then you have no safety margin for your capacitor for overvoltage 3. Primary tank circuits ringdown at 2X Vin, if charging at 30KV, ringdown is 60KV peak to peak, also insulation breakdown, should be an interesting fire. 4. I'm betting your gap is going to power-arc quite a bit, this will be a problem for optimal performance 5. Your gap will need an excess of 1", that is pretty lossy from an energy standpoint. 6. 10KV is probably more realistic for the gap/energy delivery/capacitor life/corona/insulation issues. 7. You will want an inductor between your charging system and the capacitor if using a typical flyback or the diode might go "poof"
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
Hazmatt_(The Underdog) wrote ...
1. You're going to use a flyback to drive the primary tank at ~30KV? how do you plan to insulate the primary from arcing over all the time? 2. If you are charging at 30KV, then you have no safety margin for your capacitor for overvoltage 3. Primary tank circuits ringdown at 2X Vin, if charging at 30KV, ringdown is 60KV peak to peak, also insulation breakdown, should be an interesting fire. 4. I'm betting your gap is going to power-arc quite a bit, this will be a problem for optimal performance 5. Your gap will need an excess of 1", that is pretty lossy from an energy standpoint. 6. 10KV is probably more realistic for the gap/energy delivery/capacitor life/corona/insulation issues. 7. You will want an inductor between your charging system and the capacitor if using a typical flyback or the diode might go "poof"
Just some of my thoughts.
1. I didnt say i was driving the flyback at 30kV 2. I know this, again I didnt say i was driving the flyback at 30kV, thats just the MMC rating. 3. Again I didnt say i was driving the flyback at 30kV. 4. Going to power arc? what do you mean by this? 5. 1" Gap where did you derive this from? 6. Yes. 7. Why is this inductor needed? and what typical value should it be?
Registered Member #11591
Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556
Fiddy wrote ...
Hazmatt_(The Underdog) wrote ...
... 7. You will want an inductor between your charging system and the capacitor if using a typical flyback or the diode might go "poof"
Just some of my thoughts.
... 7. Why is this inductor needed? and what typical value should it be?
When the spark gap fires, it is going to short out the charging circuit, also there will be large current spikes and high voltage with a horrible looking waveform happening in your primary tank. The rectifying diode will see a lot of that, and it won't like it! an inductor helps smooth out the current spikes that the primary tank produces.
The value will have to be guessed at but I should think you should start with something quite high, maybe in the range 1-10mH +. the only problems with high voltage inductors happen when either they don't do good enough job (the higher the better), or the turn to turn insulation breaks down, when it ends up with lots of voltage across it. To mitigate this, many smaller inductors can be put in series. The only upside to high voltage inductors is that they don't generally have to have very high current ratings, so a few cheap little ones should do the job.
Disclaimer: I have never built this circuit, so others with more experience with TCs might want to comment :)
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
I was thinking closer to 10H, but that's like an impossibility.
1" gap comes from 30kv per inch roughly.
You have to have the gap wide enough that it is not constantly "on", the system has to charge then breakdown causes it to fire when the capacitor is sufficiently charged, hence a wide gap for high voltages. If it is constantly on and not "quenching", just a bbbbzzzzaatttttt and not bang bang bang bang.. then it is power arcing.
Rotary gaps get around this problem because they close and open the gap mechanically, but as you stated, you already know all of this stuff.
You asked for input without specifying enough criteria.
You have not mentioned the arc goal either, so don't fault others when you ask for input.
Tesla coils have some 60 or more variables, so getting your design to fit what you want off of your short list is going to have a lot of input/suggestions and mismatch.
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
hen918 wrote ...
Fiddy wrote ...
Hazmatt_(The Underdog) wrote ...
... 7. You will want an inductor between your charging system and the capacitor if using a typical flyback or the diode might go "poof"
Just some of my thoughts.
... 7. Why is this inductor needed? and what typical value should it be?
When the spark gap fires, it is going to short out the charging circuit, also there will be large current spikes and high voltage with a horrible looking waveform happening in your primary tank. The rectifying diode will see a lot of that, and it won't like it! an inductor helps smooth out the current spikes that the primary tank produces.
The value will have to be guessed at but I should think you should start with something quite high, maybe in the range 1-10mH +. the only problems with high voltage inductors happen when either they don't do good enough job (the higher the better), or the turn to turn insulation breaks down, when it ends up with lots of voltage across it. To mitigate this, many smaller inductors can be put in series. The only upside to high voltage inductors is that they don't generally have to have very high current ratings, so a few cheap little ones should do the job.
Disclaimer: I have never built this circuit, so others with more experience with TCs might want to comment :)
I see, ive been looking at richieburnett's website on resonant charging, he has a formula for the calculating the charging inductor value for specified power at specified maximum BPS.
LP = 2xVDC^2 / (pi^2 x Power x BPS)
I get astronomical numbers when i use 240W, 200BPS and 10kV.
Ill have to make some inductors and try, also should i use a De-quing diode aswell?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Fiddy,
Assuming that this girlfriend is a 'keeper', Have you considered a small 'slayer' type of TC ? A USB power pack is a sufficient power source
I think that Hazmat was refering to the use of an inductor to isolate the flyback diode from the spark gap / primary resonant circuit transients and oscillations.
richieburnett's website on resonant charging is good, a good choice for a flyback powered RSGTC the peak voltage on the primary cap reaches almost 2x the dc eht supply voltage, so the strain on your flyback/inverter is much less as it provides lower, constant voltage the dc eht capacitor(s) do not need to be rated for the same current as the primary capacitor, mylar/pet/MKT/MMKT or any 'poly-' will do.
Yes you should use a de-Q-ing diode for resonant charging
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
Sulaiman wrote ...
Fiddy,
Assuming that this girlfriend is a 'keeper', Have you considered a small 'slayer' type of TC ? A USB power pack is a sufficient power source
I think that Hazmat was refering to the use of an inductor to isolate the flyback diode from the spark gap / primary resonant circuit transients and oscillations.
richieburnett's website on resonant charging is good, a good choice for a flyback powered RSGTC the peak voltage on the primary cap reaches almost 2x the dc eht supply voltage, so the strain on your flyback/inverter is much less as it provides lower, constant voltage the dc eht capacitor(s) do not need to be rated for the same current as the primary capacitor, mylar/pet/MKT/MMKT or any 'poly-' will do.
Yes you should use a de-Q-ing diode for resonant charging
Yes, the required charging inductnce is high.
Yeah id rather not waste my time with slayer or USB units, they dont have enough power for the wow factor. Also girlfriend has studied electronics. can i use the resonant charging inductor for a static gap coil?
I ordered some 15kV 550mA diodes for the de-Q-ing diode.
I will use a similar sized inductor to that of my secondary, seems to be about 10mH.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
A static gap will work using dc resonant charging but usually will not self-start without help (screwdriver across gap :)
Do not forget to provide airflow in the gap a fuzzy spark is bad, a thin bright loud spark is required for performance.
Also, the zvs topology makes poor use of ferrite (because of the resonant current which MUST be much more than the (transformed) output current for true zvs operation) I would go for flyback mode myself, preferably using the original primary winding and about 100 to 150 Vdc supply.
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
Sulaiman wrote ...
A static gap will work using dc resonant charging but usually will not self-start without help (screwdriver across gap :)
Do not forget to provide airflow in the gap a fuzzy spark is bad, a thin bright loud spark is required for performance.
Also, the zvs topology makes poor use of ferrite (because of the resonant current which MUST be much more than the (transformed) output current for true zvs operation) I would go for flyback mode myself, preferably using the original primary winding and about 100 to 150 Vdc supply.
For the spark gap I use 3 kV/mm as a rough guide.
hmmm why wouldnt it self start? Hmmm ill see how i go in continuous mode then maybe goto flyback mode.
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Building a ZVS Flyback SGTC
