Enclosure design considerations for a DRSSTC?

[GrantV]

Hi all,

I am building my first DRSSTC and am busy designing it's physical layout.

My question is: What design considerations do I need to keep in mind for spacing and/or shielding between the bottom of my primary and the electronics below?

I know that when I was bench testing my SSTC, I had a lot of trouble with any digital equipment in the vicinity (within 2 metres) of the coil and as I am hoping to do a full acrylic build, my electronics will not have the benefit of being in a metal enclosure.

I have seen a number of other coilers do acrylic builds so I may be overthinking the issue?

Your thoughts and words of wisdom would be most appreciated 

[acobaugh]

Avoid putting anything steel within maybe 6" of the primary if you can. If you must have hardware near the primary or base of the secondary, go with aluminum, copper, or brass. Glue any wood pieces if you're using wood, and use brass screws if you must.

I highly recommend putting your driver in a metal enclosure. Depending on the overall power and proximity of the driver to other things, you'll be chasing your tail trying to make it noise resistant without a full enclosure.

[GrantV]

Thank you Andrew.

Yep, I'll def not have any steel near the components.

My primary worry was the shielding of the electronics. You mention shielding the driver but not the bridge or MMC bank?

I have added my current design to my post and I was wondering if I might have to include a shielding layer below the primary for all of the elctronics below? Maybe using strips of copper tape or similar? (laid out in a closed or unclosed grid pattern?)

Thanks for your input :-)

[acobaugh]

No need to shield the mmc or bridge, as long as the primary isn't mounted right on top of them. Is there a reason you can't shield your driver as-is? It's also recommended to put some ferrite beads on the lines going in/coming out of the driver, especially on the wires going to your GDT(s).

Here's a picture of where my driver is. There is a cover that's not shown. All wires leaving the enclosure have a clamp-on ferrite bead on them to act as a common mode choke. The GDT primary wires are looped through twice through one. Driver enclosure, driver negative, rf ground, safety ground, are all tied together at a single point.

Your picture makes it appear that, as long as you shield your driver and add some basic emi suppression to the wires coming in/out of it, you should be just fine. I take it this isn't exactly a huge coil.

It's also important to realize that nearby electronics can be affected by the radiated RF from the coil, the e-field, and EMI thrown back through the power input to the coil. You can only do so much to mitigate these effects.

[Mads Barnkob]

I will concur that the problems with induced noise / transients is something that gets worse with the power level and seems to grow exponentially

If we take a look at my small Tesla coil 400W DRSSTC it has a unshielded driver sitting almost underneath the primary coil and there has never been any issues with instability


If we then move up to my large Tesla coil 20kW DRSSTC it is a whole other story! I had to move the primary coil up on stand-offs off the enclosure to avoid heating and noise issues. I was a little worried with the heat sink sitting just underneath the primary coil. There is also some practicality in the large distance between enclosure and primary coil, like having a primary lead of three parallel pieces of 35 mm² cable, they are a bit stiff in it


So it was more a worry about induction heating issues due to proximity and as long as the driver is just in a metal box in the bottom of the enclosure, no noise issues. Be sure to do your Tesla coil grounding correct to avoid RF noise in places you do not want it.

A good example of how bad the noise can be with a large powerful coil is seen on the camera interference in this video

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Over the years I have learned that a good Tesla coil enclosure is not so much about the layout on the inside, follow the few tips above and that is fine, what is most important is that you make it easy to handle, move and storage is not an issue from things sticking out here and there. Tesla coils spend 99% of their time in storage, so give that some thought. When a Tesla coil is running, no-one is near it enough to notice any "design flaws" on the enclosure anyway

[GrantV]

No need to shield the mmc or bridge, as long as the primary isn't mounted right on top of them.

Good to know, thank you. My coil is def not large (2.5KW) and the primary will be at least 4" from the top most part of the bridge and MMC.

Is there a reason you can't shield your driver as-is?

None at all, I have an old PC PSU case that I will put my driver into so that it is properly shielded.

It's also recommended to put some ferrite beads on the lines going in/coming out of the driver, especially on the wires going to your GDT(s).

Ah yes, I had forgotten about those! Thank you, I'll get those ordered now :-)

Driver enclosure, driver negative, rf ground, safety ground, are all tied together at a single point.

Just checking: By "safety ground" you are talking about mains/house ground right? and yes, I would def tie it all onto a single ground bus.

[GrantV]

So it was more a worry about induction heating issues due to proximity and as long as the driver is just in a metal box in the bottom of the enclosure, no noise issues. Be sure to do your Tesla coil grounding correct to avoid RF noise in places you do not want it.

Agreed and thank you Mads.

Many many years ago when I built my SGTC, it was common practice to use 2 mains power line filters connected back to back. Is this still a good practice or is a single filter connected in reverse sufficient?

Talking about power line filters: Is it best to place my line filter into the circuit between my variac and the bridge? Or does it need to go into the line before the variac?
[Edit] Sorry, that was probably a stupid question. Keeping high frequency noise out of the variac is always best I guess.

Over the years I have learned that a good Tesla coil enclosure is not so much about the layout on the inside, follow the few tips above and that is fine, what is most important is that you make it easy to handle, move and storage is not an issue from things sticking out here and there. Tesla coils spend 99% of their time in storage, so give that some thought. When a Tesla coil is running, no-one is near it enough to notice any "design flaws" on the enclosure anyway

LOL thanks for this. You are of course right about it being mostly in storage and should therefore be part of the design consideration. I guess it can be quite easy to make the mistake of designing a perfectly beautiful coil which gets too easily damaged or breaks the first time you try to transport it to a teslathon