No Output out of my E class SSTC

[corbin]

recently I put together a SSTC based of this scem( https://uzzors2k.4hv.org/projectfiles/pllsstc1/PLL Half-bridge SSTC 1.GIF ). I put everything together and powered it up with mains 120v not realizing I had to tune it first. I blew the IRFP450s and ordered some new ones. after that i realized id forgotten to put in the feedback antenna, a dumb mistake on my part. so i put the antenna on and got some new mosfets in and started it up with about 30VAC. i get no output. when i try to tune it with the pot it seems to do something though, my 30vac supply starts humming at different frequencies. since its doing that i would think i didnt fry the chips. unfortunatly i have no scope to see any of the wavelengths to see if thing are working properly. and i also dont have the money to get new chips, so incase thats not the problem is why ive posted this thread. im young and naive so im having many accidents any help would be very appreciated!

 

[DerStrom8]

Could you post a photo of your setup? I think it will help a lot.

Thanks,
Matt

 

[DerStrom8]

Also, what are you using for your main transformer? Did you make sure the two primaries have opposite polarity? That is very important. If they are wound the same direction you will not get the necessary oscillation on the Tesla Coil primary.

 

[corbin]

what are you referring to as the two primaries? Heres the pictures of the setup dont know why they are sideways

 

[DerStrom8]

Sorry, they're not primaries. I mean the two coils on the GDT, circled in the image below:

You should make sure you have the phases correct, the two coils on the right should be 180° out of phase with each other (note the phase indicator dots).

Thanks for the photos. However I'd like to see the rest of the setup (the coil itself and everything on the mains side of the FETs) if it's not too much trouble.

Thanks,
Matt

 

[JimW]

I have made roughly the same SSTC in a few configurations. The schematic you are using is likely to continue to blow the MOSFETs. Look at the protection and clamping diodes in this similar circuit:
https://www.angelfire.com/electronic/cwillis/fetcoil2.html and noted here as well: https://www.richieburnett.co.uk/sstc02.gif

As DerS. noted the primary windings of the coil itself need to wired properly. And the tuning is key. I have found that the primary tank circuit is not critical at all in the SSTC design, it is all about the self resonance of the secondary coil. Measure this with a scope and signal generator then preset your drive oscillator for that frequency and make only small changes to that.

The other thing to keep in mind is that a tower Tesla coil radiates a lot of energy into the air, and if that couples back to your drive circuit, then you will blow the MOSFETs and usually a few of the protection diodes. So shielding and short run traces are key. It is easiest to build a horizontal TC with point to point arc contacts first.

JimW

 

[DerStrom8]

Excellent point about the shielding, Jim. That hadn't even crossed my mind!

The reason I asked for a picture of the rest of the setup is so that we can see how everything is connected and how the antenna is coupled with the Tesla Coil itself. If the antenna is not set up properly it will not be in tune and you will get little to no output.

As for the scope, I believe the OP stated he did not have one. This will make testing and debugging very difficult. If the OP can get his hands on one it will make things much simpler.

Matt

 

[corbin]

Thanks DerStrom! you where right the GDT coils where not reversed! fixing that allowed me to get a very small output. Heres a video showing the complete setup, i also have two other coils, one very tiny and one skinny and really tall. i have some questions in my video, heres the link (

)

 

[corbin]

Im extremely happy to announce it works great! i hooked it up to mains after tuning it best i could and wow! first tesla coil of my own(at least successful one!) thank you guys so much for the help! Its definitely not at its finest tune wise but thatll just take some time. Im new to the way forums work, now that my problems are fixed do i close the thread? and how do i do so?

 

[DerStrom8]

Hi corbin,

I believe the antenna should be wound around with the primary. This way it will pick up the feedback and know exactly when to switch the FETs. I may be wrong, I have not built this specific coil before. It would explain why you're getting very little output though -- You're only picking up the RF noise emitted by the coil rather than the actual pulse in the primary/secondary, which would cause it to be out of tune.

Perhaps JimW could verify this, since he says he has built this type of coil before.

Regards,
Matt

 

[DerStrom8]

Im extremely happy to announce it works great! i hooked it up to mains after tuning it best i could and wow! first tesla coil of my own(at least successful one!) thank you guys so much for the help! Its definitely not at its finest tune wise but thatll just take some time. Im new to the way forums work, now that my problems are fixed do i close the thread? and how do i do so?

Congratulations on the first light! Now we're going to need a video

No need to close the thread. They generally just stay open unless there is a specific reason for them to be closed. If we leave it open it will allow others with similar questions to ask for clarification and tips and whatnot. Works much better that way, if you ask me

Regards,
Matt

 

[corbin]

well you live and you learn, i put everything into a nice enclosure. The enclosure was grounded and for some reason made everything short out. lost my mosfets, but i have extras. Sadly I dont have extra driving chips so itll be a while before i can rebuild the circuit. Pretty short lived hahaha. should I rebuild this circuit again or go with just a regular SSTC now that i have the feel for it?

 

[DerStrom8]

well you live and you learn, i put everything into a nice enclosure. The enclosure was grounded and for some reason made everything short out. lost my mosfets, but i have extras. Sadly I dont have extra driving chips so itll be a while before i can rebuild the circuit. Pretty short lived hahaha. should I rebuild this circuit again or go with just a regular SSTC now that i have the feel for it?

That choice is certainly up to you. I was looking forward to seeing another video of it working, but I can wait if you would rather build a different one

Regards,
Matt

 

[corbin]

yeah I think ill rebuild it! much cheaper haha Ill make sure to let you know when i have a video

 

[JimW]

I think that DerS. has a point about the primary in relation to the secondary. I have always had them about 1/4 of the way to the top, and supported 1" off of the secondary windings. I never tried it completely below the secondary, but I don't think you will get optimum electromagnetic coupling that way.

I have gone through many sets of FETs and drive chips with this type of design. Even with the best shielded case that I can make, I still would blow up the FET stage. I am almost certain that it has to do with coupling of the radiated signals back into the drive circuitry, but it happens fast and pretty dramatically. Usually I have it running for a half a minute or more without problems. And then only when I interact with the generated arc, then things go bad.

Driving directly from 110 VAC, with a similar push pull design, we get well over 1" of arc. But the point to point one is the only one that consistantly works. Using the same design, we built both vertical and horizontal units. Two of the horizontal are running fine, 3 versions of the vertical keep failing. The next for solving this is using two sided PC boards with a solid ground plane on one side to reduce the couple noise into the FET drive circuit.

Good luck,

JimW

 

[corbin]

I've gotten my coil working amazingly! I made a full bridge and getting about 7" streamers off the breakout. I'll post a video soon, the only problem I have is I have to use the secondaries negative to tune the coil, in order for it to arc I have to put the HV negative close to the breakout which you'll be able to see in the video, do I have my antenna in the wrong place? I've seen that some people hook the antenna to the HV Negative by a 1:30 wind around a toroid. Will that possibly help?

 

[DerStrom8]

I have seen various positions for it. Some people wind it right around the secondary with the primary coil, or I have also seen the 1:30 transformer used. As long as you keep the antenna away from the HV output, it would be good to experiment to see what gives you the best output. The idea is that the antenna is supposed to be close enough to the oscillating parts of the circuit for an alternating current to be induced in it. This AC signal is passed into the chip, which tells the FETs when to turn on and off at just the right time. If your antenna is too far away, not much current will be induced so you will get weak, if not absent, signals.

 

[corbin]

alright, so i got everything fixed, it turned out the tuning problem was the amount of primary turns, heres a link to the vid

pretty suprising how good of an output this has,

 

[DerStrom8]

Very nicely done corbin!

What did you end up doing with the antenna?

Thanks for the video!
Matt

 

[corbin]

I left it like a normal antenna just a 20cm wire coming from the driver. I guess the entire tuning issue was odly just too many primary turns