Tesla Coil Build Thread

[Down with Umbrella]

Thanks sigurthr,
Yes the secondary has three thick coats of polyurethane. However I left 1.5 feet on both ends loose so I can make what ever adjustments I need. I can coat those with some poly just to make them stick.

Secondly that box with the stainless steel cover. The two switch Frames are grounded therefore the ss cover is. so while running I should connect my wrist strap to the cover?

Another issue I thought could happen is if you look at the spark gap terminals they are about 1 1/2 in from the blower and mounting bolts which are ground to the house. Do you think any of that HV or RF could feed into that blower frame then into the house? I was already thinking about swapping some of the close bolts with 1/4 nylon threaded rod.
Thanks Jefferson

 

[Sigurthr]

Re: switchbox - yes connect yourself to it because YOU are going to be above ground potential and will get shocked when touching because you are discharging to ground. The ground strap prevents you from getting charged up.

Floating items should stay floating, grounded items should only touch grounded, etc.

The blower should be fine, the SG radiates a lot of EMI but very little in terms of power in RF.

 

[USAbro]

Right now I'm trying to find a door knob for a smoother top load. It really looks cool, but there are so many arcs and I just want one or two. I soldered the connection broken in the transformer, and filled it in with hotglue. It really looks like a good connection. But for some reason, I'm running it in my garage and the garage has a gfi and it keeps tripping but it wasn't tripping it before. Could it have something to do with my grounding?

 

[Sigurthr]

A doorknob won't help. What you want did a breakout point. A long (1/2 the diameter of the topload) piece of stuff wire or metal rod you lay across the topload with a few inches sticking out over one side.

Other than that use aluminum foil and aluminum tape to smooth out the edges and ripples.

If you change the size or shape of the topload you'll have to retune, so don't add or subtract anything more than foil and wire.

Yeah bad grounding causes GFCI to trip. See above about extension cord + metal stake for grounding fix.

 

[USAbro]

Grounding is fixed. Even with a wire though, the top load still puts out other sparks, and sparks off the wire are shorter than off the foil covered light bulb I'm using. Now I'm almost hitting 4" to air.
What is the maximum output for a 270 watt NST? Like if I ever built a bigger coil, is it possible to get 1'+ long sparks out of it?

Also, why wouldn't a door knob help? It would keep it from breaking out in multiple locations.

And another thing. It only powers cfl bulbs from 5 inches away, and my tiny one did it from at least one foot. Why? Also, it gives a hefty shock off the top load (I tried touching it). I thought a person shouldn't be able to feel much from that sized coil?

 

[Sigurthr]

My replies interspersed throughout in Green.

Grounding is fixed. Even with a wire though, the top load still puts out other sparks, and sparks off the wire are shorter than off the foil covered light bulb I'm using. Now I'm almost hitting 4" to air.
What is the maximum output for a 270 watt NST? Like if I ever built a bigger coil, is it possible to get 1'+ long sparks out of it?

16" is the theoretical maximum, but that doesn't account for various factors even besides losses, for example, the higher the frequency, the shorter the streamer for a given amount of power. 100KHz will be almost twice as long as 500KHz.

Also, why wouldn't a door knob help? It would keep it from breaking out in multiple locations.

At first I thought you were going to replace the topload with a doorknob, but now I see you have a lightbulb covered with foil on top of the topload, and the multiple streamers are coming off of the light bulb. Two things:

1) remove the light bulb. Run the coil again, you might need to retune the primary VERY SLIGHTLY. If you're getting tons of streamers out of the side of the topload, then adding things on top won't ever reduce it to a single streamer. You have to smooth out the points on the topload first.

2) after doing #1, add the breakout point wire, see if it helps any.

And another thing. It only powers cfl bulbs from 5 inches away, and my tiny one did it from at least one foot. Why? Also, it gives a hefty shock off the top load (I tried touching it). I thought a person shouldn't be able to feel much from that sized coil?

Re: Lighting up bulbs/tubes:
1) You're little flyback coil wasn't a true spark gap tesla coil, you were most likely exciting the resonator with a harmonic of the pulsing DC signal from the flyback, so you were generating more RF.
2) there is a trade off in all tesla coils; the more power that goes into streamers the less there is radiated as EM waves (which is what powers the light up tubes).

Re: feeling the output:
1) All discontinuous mode coils (DRSSTC, SGTC, VTTC w/ staccato, ISSTCC, OLTC, etc) cause nerve excitation (pain). Only CW (continuous mode) coils are painless.
2) Size of the tesla coil has nothing at all to do with how painful/painless or dangerous it is. Some of the experts build "handheld" size coils that are extremely painful and run off of lethal primary voltages. Some ten foot monster coils are totally painless and run off safe voltages.

 

[USAbro]

So how much power is required for one of those coils, you know that arcs to the ceiling and walls and stuff?

 

[Down with Umbrella]

Depends on how high your ceil is and the size and shape of your topload too. There are many factors. From the photos I have seen 1kW seems to reach pretty far but I bet if you paralled a couple 12kV 30mA NSTs you might be able to.

 

[nospin]

Usa

You need a bigger topload to store the energy longer then it will consolidate the breakout
To less more impressive arcs

You need 1kw or more to have ceiling hits of a meter or more
Mine is 2 mots 2.8kw

 

[USAbro]

I'm wondering if the 500khz frequency, could be causing the sparks to jump off many places. I placed aluminum tape around a plasma globe jar, and used a scissor edge to flatten it down so well, it is almost perfectly flat, and it still jumps off many places.

The discharges are longer off the ball, than off a breakout point.

 

[Sigurthr]

Typically kW-class is required for "environment arcs", but most folks use a MOT or MOT Bank at 1.25-5kW total for that level of SGTC. Years ago you'd see 18kV 120mA NSTs that were/are regarded as the holy grail of SGTC making, but they're no longer in production and excessively rare. It's almost impossible to get 12kV 30mA NSTs now.

I'll say this once again and in bold: YOU HAVE TO REMOVE ALL EXTERNAL EDGES FROM THE TOPLOAD FORM TO PRODUCE A SINGLE STREAMER, ADDING A SMOOTH ITEM ON A ROUGH TOROID WON'T FIX IT. Yes, it is an outstanding pain in the ass. I've only ever made one toroid because it is so much of a pain to smooth out that afterwards I decided just to pony up the cash for a professionally made one.

 

[nospin]

I'm wondering if the 500khz frequency, could be causing the sparks to jump off many places. I placed aluminum tape around a plasma globe jar, and used a scissor edge to flatten it down so well, it is almost perfectly flat, and it still jumps off many places.

The discharges are longer off the ball, than off a breakout point.

Read carefully:

The reason is: The larger topload stores more energy before breaking out.
Its a capacitor!

And when you put a breakout point on it has a place to leak out before the capacitor can charge further and develop larger singular arcs

I had this problem with my V1 4.25" secondary, to many smaller breakouts
I had a 4x18 toroid and I built a new 6x24 and the problem was solved.

Much more impressive!
I know what I'm talking about!

https://www.youtube.com/watch?v=5XVRtoRkVW4

You need a real toroid topload!

Do this, It will work!

Go get (2) 6 or 7 inch pie pans, Hold them bottom to bottom with a few pop rivets holding them, then drill a hole in the center to mount it. Then take 3 inch Al dryer duct and wrap it around the pans, then Al tape it all up and smooth the surface with a spoon with your thumb in it.

Mount it on the secondary and retune

 

[USAbro]

Thanks nospin and sigurthr. You two have guided me through this process well. Even though I've yet to smooth the top load ball out completely, I made a new, slightly bigger one that's a lot smoother, and I'm getting better output. I've been fiddling with it since I got home from school, and it's getting better.

Also, if I used a mot to power mine, would I get a lot bigger arcs?
Right now, I find running it without the fan works the best.
Also, why is the transformer getting warm? I ran for about 5 minutes straight that maybe why.
And with the mots, doesn't the spark gap have to be really small, for maybe 4kv with two mots in series, and 2k for one mot?

Edit:

Would a bigger ball like a softball work better?

 

[Sigurthr]

Thanks nospin and sigurthr. You two have guided me through this process well. Even though I've yet to smooth the top load ball out completely, I made a new, slightly bigger one that's a lot smoother, and I'm getting better output. I've been fiddling with it since I got home from school, and it's getting better.

Also, if I used a mot to power mine, would I get a lot bigger arcs?

You'd need a new tank capacitor, and then a new topload to match, and then probably wouldn't have enough turns on the primary to tune it. Stick to what you've got.

Right now, I find running it without the fan works the best.

You're still in the "workin' out the bugs stage, give it time".

Also, why is the transformer getting warm? I ran for about 5 minutes straight that maybe why.

Totally normal and safe. NSTs will get up to about 140F normally, and they're designed to run 24/7.

And with the mots, doesn't the spark gap have to be really small, for maybe 4kv with two mots in series, and 2k for one mot?

Yes, and that is one of the challenging aspects of mots in TCs. You have to either make a phased array to get the voltage up to 4kV or higher, or you have to make a voltage multiplier out of high voltage diodes and capacitors. Both ways take around $100 of parts. More importantly though, one wrong move or bad design decision with a mot... YOU DIE. It would be safer to lick your fingers and practice sticking knives into the wall socket. Seriously, they're that dangerous.

Edit:

Would a bigger ball like a softball work better?

You can use lots of various shapes for a topload, you just need to keep two things in mind:

1) it has to be free of sharp edges, that means microscopically sharp edges too. Yes, the thin edge of a piece of tape/strip/sheet counts as a sharp edge!

2) if you change the over all size or surface area of the topload you will need to retune your primary to match it, and you only have so much tuning range on your primary.

Just smooth that topload you have out first, then retune as needed without any balls or anything else on top. Smooth it gooooooooooooood. It often takes many, many layers of edge-overlapping aluminium tape to get it smooth.

Do what Nospin says, he knows his stuff.

Worst case scenario you go out and get a cheap metal mixing bowl from a kitchen supply place, look for one with a rounded outer edge, and use that. They're a freaking nightmare to tune unless you get lucky, but you're guaranteed no sharp edge issues.

 

[USAbro]

Thought I should prove I'm not trolling like Lightning Stalker says.

Let there be light.......ning

Edit: He recanted so, I take that back! lol And Stalker, thanks for the kind words.

 

[The Lightning Stalker]

This is an occasion where I'm glad to be
proven wrong! Those are some nice arcs.