Tesla Coil Build Thread

[DashApple]

Hi ,

yeah my main problem is i made the primary from the only form i had witch is to small so the gap between the secondary and primary is small aswell so i will have to remake and re tune for a larger diamiter primary to stop flash overs . ceramic would be the best materia to use .

Also need to size the grid reistor better as i burnd one out from running at full power too long

yeah ill find a 800V Mosfet and place that in the cathode - ground connection to modulate coil . Thanks

 

[Sigurthr]

I look forward to seeing the changes/results!

 

[DashApple]

I look forward to seeing the changes/results!

Hi

good luck with your SSTC , i find that i like small coils that produce Big arcs more so than big coils / massive arcs .

Thanks , I have found that with a 3" diamiter primary form running half wave supply then pulsed via mosfet is the best way to go for this coil at the moment as i dont get arc overs at half wave supply , full wave i do and the best thing is no noticable tube heating or secondary on half wave pulsed supply .

Heres a few pics with NaCl on electrode + video of it running in pulsed mode . Arcs out are 4 - 4.5 Inches , not bad for a 5 x 7cm secondary ( Red lightbulb is grid resistor )

Half wave pulsed VTTC mini coil NaCl electrode . - YouTube


SAM_0554 by TwirlyWhirly555, on Flickr


SAM_0562 by TwirlyWhirly555, on Flickr


SAM_0560 by TwirlyWhirly555, on Flickr


SAM_0564 by TwirlyWhirly555, on Flickr

 

[Cyparagon]

You should get some copper or boron salts for green streamers

 

[vk2fro]

Impressive IonLaser555 - that sized coil I'd be happy to have - its just the big ones that worry me. Can you modulate it. Singing tesla coils would be way more fun than singing floppy drives. I've seen a couple of big coils play music all the while jamie from MB is in a cage between them.

 

[Sigurthr]

I know for a fact high level anode modulation works excellently on VTTCs as I've seen it done before by the big names. No idea how it works though, haha. I have no experience with valves. I would imagine you could grid modulate as well but I've never seen it done and I'm guessing with the grid leak system VTTCs use it would be rather hard to implement.

Yes, I like small coils too. My "big SGTC" is actually considered to be medium size, and I think it is way too big. I supose it wouldn't be too bad if it was on a tiered base like most use but still it would not be what I consider optimum. One of the many reasons I am working so very hard for my little SSTC is the form factor. It will be awesome.


BTW, thank you all for contributing to this thread. I had feared it would be a one trick pony lost to obscurity save for my occaisonal bumps. It is great to see others like yourselves adding content!

UPDATE: 6-18-12
Today I was able to place the order for all the parts I will need for my SSTC driver. No skimping out on parts either. The only things I will need once this arrives is a 15 to 18V AC stepdown transformer to power the LV side of things and heavy gauge wire for the Primary. Both should be available locally (I know R.S. has the xformer).

The best part about having a job is being able to fulfil your desires with your wages. Now to save up for a scope.... lol

 

[DashApple]

Impressive IonLaser555 - that sized coil I'd be happy to have - its just the big ones that worry me. Can you modulate it. Singing tesla coils would be way more fun than singing floppy drives. I've seen a couple of big coils play music all the while jamie from MB is in a cage between them.

Thanks , Yeah I Modulate it in the cathode - ground connection with a MOSFET ,

Here are two videos of it audio modulated , sounds better in person though .

CW audio modulated VTTC Tesla coil , Mario - YouTube

CW Audio Modulated VTTC Tesla coil . - YouTube


Sigurthr , Yeah i did try Anode modulation with anothere vacuume tube as the switch , wsnt very loud but then i wasnt sure what values to use so i went with cathode modulation .

Nice , what type of SSTC will it be Full bride / half bridge , CT secondary feedback or anttena feedback ?

I Hope to start my SSTC soon , will use a ATX power supply case for the hole driver / bridge with CT feedback , hopfully after 10 - 15" arcs from it .

 

[vk2fro]

Thats pretty cool - but 1kw - thats air cooled argon power. For that little guy? wonder if you can trim it back without reducing the coils output?

 

[DashApple]

Thats pretty cool - but 1kw - thats air cooled argon power. For that little guy? wonder if you can trim it back without reducing the coils output?

Hi ,

thanks

My mistake , under audio modulation it draws 700 watts , any lower arc lengh droops

Under CW Full power no moudualtion it pulls just over 1Kw .

Just anothere audio video ,
CW audio modulated VTTC Tesla Coil , Sugar plumb - YouTube

 

[Sigurthr]

Sigurthr , Yeah i did try Anode modulation with anothere vacuume tube as the switch , wsnt very loud but then i wasnt sure what values to use so i went with cathode modulation .

Nice , what type of SSTC will it be Full bride / half bridge , CT secondary feedback or anttena feedback ?

I Hope to start my SSTC soon , will use a ATX power supply case for the hole driver / bridge with CT feedback , hopfully after 10 - 15" arcs from it .

Aye, I have no idea how to implement it, I just know that it is how it is done in large AM transmitters. As I think i said before it requries 50% of your output power as input power as modulation... so you would need 350W modulation for 700W output.

As it will only be my second SSTC and I'm taking a radically different approach with the driver I'm keeping it to a Half Bridge of IRFP260s, at least initially. Antenna feedback will be used as it is the simplest and from previous tests my little secondary puts out a rather large M-field perpendicularly to the axis of the secondary peaking at about half way up the coil - plenty far from the HV end.

I have a whole box of rather expensive MOSFETS and IGBTs I can later switch in if needed. I've also ordered at least double all the parts needed (except the TO-263 heatsinks) so if it works well I will make a second driver and expand it to a full bridge without touching/altering the first driver. That way I retain a working SSTC at all times.

The hardest part will be board layout. Minimizing stray inductances is key, and you need to have a somewhat artistic approach to get it working well, especially without a scope to monitor waveforms.

If I can get it working reliably and for long enough run times I will dismantle my SGTC. I will of course keep the secondary as it is, perhaps for a very large SSTC or DRSSTC or even a VTTC one day (wouldn't that be a sight!) but I would like to sell the huge ass primary or reuse it for another purpose (induction heater work coil, maybe), and sell the MMC (worth over $100!!!). SGTCs are just not my thing. I am glad I built it and got it to run so well and I learned a lot from it, but it doesn't get much use now due to how big it is and how much interference and noise it puts out.

 

[vk2fro]

Thats what also worries me about tesla coils - interference. I'm in a single level apartment block, and mines the dead give away with the ham radio antenna's. I'd hate to have my neighbours get upset with me due to a bit of fun with a tesla coil, and blame it on my station. Nothing would be worse than having a surprise visit from the RI's and them finding out my HF rig can do 200 watts on 11m

 

[Sigurthr]

Interference is only an issue with Spark Gap coils as the SG emanates a truly tremendous amount of interference. SSTCs and VTTCs are nearly interference free. Think of it this way; a SSTC or VTTC is nothing more than a CW radio transmitter set to a far lower frequency than any radios operate on that is fed to a resonant transformer instead of a resonant antenna. The transformer is a very poor antenna due to super short electrical length compared to the wavelength so nearly no e-field is produced beyond the range of the near field m-field.


So I built my SSTC driver the other day and I tested it on low low power DC instead of rectified filtered mains and got no output.

I went around the board checking voltages at various points with my DMM, and noticed that very little voltage is appearing at the gates of my mosfets, something like half a volt AC. I checked the UCC37322 and UCC37321 chips and both are fine, and I'm reading ~7V AC between their outputs. I figured that my DMM can't accurately measure the voltage of a PWM squarewave and that things should be just fine since the input voltages to the chips are within spec and there are no egregious circuit/design errors. With the GDT wired in I read only ~0.345B AC across any of the windings. I started to suspect that maybe my GDT is no good, but I have no scope to accurately measure and diagnose the issue further.

Then today I noticed I forgot to connect two traces in the feedback subcircuit. So I corrected the mistake by connecting the traces. I powered up the driver but did not apply any power to the HV half bridge busses. Everything looks to be about the same as before, but again, no scope.

I'm wondering if I should apply the HV DC to the half bridge and see if it works. I am thinking that it could be working fine but since there is no power applied to the Half bridge there is no output and thus no feedback to keep the oscillation going. This circuit doesn't use a starter circuit, it just relies on the UCC37321 to put out a single pulse which rings the GDT/half-bridge/primary and gets things going. So the reason I could be seeing next to no gate voltage could be that there is no ongoing oscillation as well as my crappy DMM.

What do you guys think? Could my GDT be SO BAD that everything else is ok but still I read next to no voltage between gate and source? Or is it just that I'm trying to use a DMM instead of a scope to verify the presence of a gate drive signal?

I've never made a half bridge inverter before, only an unisolated H bridge for motor controll, but everything else except the gate drive checks out ok. All passives, diodes, supply rails, ICs, and interconnects pass all tests.

 

[DashApple]

Hi ,


How many windings did you use on the GDT and whats the core size ? , Im not sure what to recomend , You could try adding power to H Bridge and limmit it ? to see if oscilates . , i was probably lucky with my SSTC

But now its clamed 6 mosfets , most recent one have gone short ( below 1 ohm ) across all pins and the only change i made the the setup was thicker wire on primary so my guess is primary current passed mosfets 16A rating some how :S , but for the gate to go short aswell i could have been Gate Overvolt so im not sure what the probelm is ,

 

[Sigurthr]

I gave it a run today and all my fears were for nothing! It ran beautifully but definitely is far from optimized.

Up next is to change the PRF of the PWM interrupter to a range outside of human hearing to remove the squeal and/or implement audio modulation. Also, I need to remake the primary with the new heavy gauge stranded wire and higher coupling. I also need to add a fan to blow over the heatsinks for continuous operation. Lastly I need to add a switch which will pull the enable pins high to the 5V rail for CW operation.

Videos:
SSTC V2.0 - Initial Testing - YouTube


SSTC V2.0 - Full Power Test - YouTube


Fets stay relatively cool with this primary on unballasted mains, at around 130F after 10mins of run time, but I'd like to keep them at less than 85F for best RdsON. This primary is 14ga and around 7 turns and it only draws about half an amp, so I have a lot of leeway. Inrush current from the 940uF of filtering is significant though, and I *think* I can hear some superimposed AM from the line frequency under the squeal, so I might need even more capacitance. I won't know for sure until I set the coil for CW operation.

Re: your coil; are you useing freewheeling diodes across the drain and sources of your bridge? SSTCs have hefty inductive kick-back which greatly increases FET heating and kills them quickly. A common hallmark is a short across all pins.

 

[Cyparagon]

Put a NTC in series with mains to fix the inrush. They're cheap.

 

[DashApple]

Nice work on the SSTC ,

The Mosfets im using have freewheeling diodes in , but i guess they are to slow , ill bypass the internal freewheeling diode with a schottky diode / ultrafast recovery diode .


Edit , got new fets = http://www.youtube.com/watch?v=Pe5gYxQqw4M&feature=youtu.be