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Tesla Coil Build Thread

Hiemal

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Winding for SSTC's is a lot easier; the coilform is smaller, and there's also typically fewer turns for a higher resonant frequency.

Still numbing either way though. :p

And, I'll see what I can come up with.. i DO have a motor I could use... :thinking:
 



Sigurthr

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Hehe, the SSTC secondary I'll be making will be 1000turns of 30ga on a 3.25" (3" ID) pvc coilform. The Primary is the EASY part with SSTC, helical coil wound right on another coilform just one size larger than the secondary coilform. Easy-peasy.

I very much look forward to seeing what you come up with (and your progress).


BTW... I have a very expensive DVM with a frequency counter... I'd like to measure the resonant frequency of my TC. Any ideas on how to do it without risking damage to my DVM? I was thinking getting some 5v zeners and making it so they clamp to ground if the voltage gets above 5v. I'd only have the probe in my hand far away from the TC, but still I'm paranoid when it comes to this DVM. I pretty much only have it so I can accurately measure very high or very low resistances and accurately measure capacitance. I don't want to bust it.
 

Seoul_lasers

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Roger roger. Aye, new topload is definitely on the list. Being that I am so close to the end of the tuning range I am concerned with picking too large of a toroid right now though. I've seen some right small ones (say... 2" ring on 6" total diameter) which have a nice breakout point at the center being used by the pros but I can't find any for sale. I can't remember the fellow's name but I saw it on 4HV archives and the TC mailing list archives (I'm not a member of the list) frmo posts back in the early 2000's that he made some really fantastic toroids. His site seems to be defunct now and most of the other "where to find toroids" links on the archives are also defunct. I contacted Information Unlimited about toroids as they can produce them now but was told they only stock 2 sizes and the rest are all expensive custom orders. As is, the two they stock are a bit pricy, and not all that small.

What method would you recommend? I have read in many, many places to NOT drill in to the top cap of the coilform (or the coilform) as it can lead to internal arcing between HV out and RF ground. I was thinking soldering the 30ga wire to a bit of copper with a 1/4"-20 bolt soldered to it and epoxying the copper piece to the top of the coilform. This way the toroid has a secure mount and no strain on the 30ga wire.

You're right about the pvc pipe for supports. While in the planning stage I had considered bisecting some 4" pvc (so that it stands 2.25" high and doesn't roll) and notching the round side for primary placement ridges but I couldn't find anyone around with a bandsaw. There's no way I could do that with a 5" handheld coping saw. I figure if I could cut 8 pieces of 3.5" long 1" dia pvc pipe I can use them as standoffs for the acryllic sheet I have there. But I'd still need a way of cutting the circle in the acryllic. This acryllic is weird, I've worked with plexiglass before and it always cut easily without fracturing or shattering. This stuff breaks so easy. It is quite brittle. I actually bought two sheets and was going to cut the second, but it shattered when I tried to cut it with a very fine tooth blade sawing by hand with it well supported.

I wanted to use 8ga wire for the high current side but I can't buy anything larger than 14ga locally. It's a real bummer.

Re the TC safety, yup I know. But the SSTC I have planned is less than 36VA on the primary side with the transformer Steve Ward specifies. With the transformer I'll be using initially it will be only 24VA. Hammond manufacturing makes the transformer Steve Ward uses and they don't have any in stock at the retailers so it'l be a few weeks lead time, so I'll use my 24V power supply instead (the difference is about 12V DC, enough that the mosfets will still have the minimum needed on voltage, but no more really) until the Hammond transformer comes. RF burns.. sure. You can get RF burns from 1W. Stop your heart? No. That's my definition for safe. If you know of the "slayer exciter" his MicroSSTC is similar to that. It is even less output power than the EVR SSTC1.0, just enough to light a fluorescent and give some nice corona, no streamers.


Update:

That is AWESOME Jared! Hehe, this thread is for EVERYONE's TC builds, not just mine. I'm just the main contributor right now is all. If you need any help at all or suggestions on how to wind a secondary by hand in the most insane mind numbing method possible, feel free to ask! I pretty much worked out the method for a flawless hand-wound jig-free secondary. By all means though build a freaking jig if you can, haha. My brain still feels like mush... and I'm going to wind another coil for the SSTC soon!


Sure, just highlight that just because you can't feel the electricity at TC frequencies, doesn't mean it can't do damage.

Yes, I actually hate acrylic. It's easily shattered and melts when drilling it.
IT also stinks like crazy. PVC is much more forgiving.
However, i'd trade an PVC secondary for an acrylic one any day of the weak. better dielectric strength.

About toroids. Actually they're pretty easy to build. Try dryer ducting. It's readily availible made of Aluminum and it works well. An inner tube coated with thick Aluminum foil tape will make for a nearly perfect toroid. It won't catch fire. You can fill the tube with expanding foam or you can even build the toroid by using 3M bondo for cars. Go for a small 15-20" dia tube first.
The spun toroids are expensive but for your purpose not necessary.
 
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Sigurthr

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After doing a bit of math it is clear that anything larger than a 6" toroid will be unsuable. The secondary still has a much higher self capacitance than expected and that needs to be taken in to account. As is with a soda-can topload there is only 1.5 turns extra on the primary.

I've ordered a 4" sphere from Information Unlimited (awesome price of $13 shipped, they're on ebay for $40 from TeslaStuff!) which should work well.

In the mean time may I ask help in diagnosing a problem? Peak streamer length is now 14.5", and average length is about 12.25". I suspect that the gap is not getting adequate quenching as randomly in to longer run times the streamers lose half their length and the sound of the coil changes. I will be replacing the fan with a much stronger one out of a hairdryer soon, which should help. But I'd like some confirmation.

Here is a video I just shot of the coil in operation with the new topload, and at 2:39 in to it I show three times where the output decreased. Nothing feels warm when this happens, so it isn't heating causing losses.

Sig's SGTC V2.0 - operational footage and temporary partial loss of power - YouTube

 

Seoul_lasers

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I still see some issue with your set up.
1) you've got a primary lead I assume from your cap bank
draped accoss your primary. Good way to throw off your coil
and get an primary short.
2) gap still needs adjusting. More break points.
3) use a 6" toroid. Innertube as your topload
 

Sigurthr

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I do have some left over semi-straight 1/4" copper tube to make a new gap... but I'm not sure how I would go about setting the correct gap distances with a multi point gap or how I would secure it. I don't have access to more tools than a hand drill and simple hand tools, so making an adjustable fixture like I've seen used isn't going to happen. I might be able to drill through the tubes and screw them in place on a block of wood, but I'd prefer not to use wood at a HV junction, and of course it isn't adjustable at all.

Aye, the lead is draped across, but it never gets hot and it is a HV rated wire, I don't expect any problems out of it really. It may negatively impact the magnetics but I don't see a feasible alternative. If it's insulation couldn't stand up to 11kV without any corona I would never leave it the way it is. Open to suggestions. The only thing I can think of is laying acryllic under the wire. I'll have to order some more for that though.

I went to the store (WalMart) today and they don't carry any innertubes, so that's why I ordered the 4" sphere. My local hardware shop also doesn't have any more aluminium tape, I bought the last roll a few weeks ago and it's mostly used up. I'd like to upgrade to a toroid (even DIY as you suggest) in the future, but it just isn't available up here. I also asked about dryer ducting at the hardware shop, but they only carry the plastic 5" dia stuff.

So, does the reduction in output power look like a quenching issue? After the unit has been off a few minutes it comes right back to full power, and nothing feels warm. It doesn't happen at a predictable amount of run time either.
 
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Seoul_lasers

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Hard to tell,
Remember at high frequency many insulators
Stop behaving properly. You'd be well advised to
Get the wire off the primary or you WILL eventually
have a primary arc. Also remember your peak gap voltage
is Probably 100% of your insulation rating! 11kVac = 33kvdc in insulation.
Most HV cable is rated for DC just like
Capacitors are, that is unless it specifically indicates AC.
I also suggest using some wine tubing to give extra insulation. Wine tubing is
Made of acrylic and is insanely good with handling RF at Hv.
The spark gap does sound like it is becoming too conductive.
Too hot. Like I suggested, adding another breakpoint and a much stronger blower fan might
Work better.great pics in the link of a multipoint spark gap.

http://www.deepfriedneon.com/tesla_f_sparkgap.html
 
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Hiemal

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And the reason so many insulators fail is because it effectively forms a capacitor...

The insulation acts as the dielectric, and the rest falls in place. Since it's AC, the "capacitor" doesn't charge up...thus you get some nasty problems.

It's extremely hard to insulate HVHF AC. Distance is really the only thing available to fix it.
 

Sigurthr

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Well I had some acryllic squares left over so I just placed them between the lead and the primary. It should help as acryllic seems to insulate well at this frequency.
Did not know that HV wire is rated in DC volts, this is rated for 15kV. 1.414 x 7500 = 10600, so I should still be ok if Vpk is used. If Vp-p is used I'm over rating by 50%.
Ditto there Jared, but it was my understanding that in such a case where the dielectric forms a parasitic capacitor with the circuit there would not be dielectric breakdown as no current passes through the dielectric of a capacitor. Instead you would simply have parasititc capacitance to deal with trowing off the circuit's tuning. Maybe this is just for low power stuff though, idk.

Yeah, that's the type of spark gap I was thinking of. It's a bit beyond my means of production though. That page explained how they get different spark gap settings though, which was nice.

I'm going to rip the fan out of a hairdryer and use that, so that should be a real improvement from a PC case fan. Also I may rebuild the spark gap in some 3" PVC so the fan can be mounted directly inside of it.
 

Polonium210

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Thought I would share my Solid State Tesla Coil I built


It stands 18" tall (with base) and max spark length is around 22" to a grounded object.
Secondary is 3" diameter by 7" tall wound with #30 AWG and the Primary is 4 turns of #10 AWG wound directly on the bottom of the secondary.
The driver accepts signal via fiber optics and can play music.

 
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Seoul_lasers

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And the reason so many insulators fail is because it effectively forms a capacitor...

The insulation acts as the dielectric, and the rest falls in place. Since it's AC, the "capacitor" doesn't charge up...thus you get some nasty problems.

It's extremely hard to insulate HVHF AC. Distance is really the only thing available to fix it.

yup... couldn't have said it better. AC is very very difficult to insulate against especially at
High Frequencies (Khz and beyond). the potential has a tendency to skin onto the surface of the conductor and leak (sort of like high pressure water from a garden hose) into the surrounding air. (Skin depth is extremely shallow). Insulation must be very thick to avoid losses. Check the link below.

http://ecee.colorado.edu/~ecen3400/Textbook/Chapter 20 - The Skin Effect.pdf
 
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Sigurthr

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Wow, very nice Po210! That looks more like a DRSSTC than a SSTC though as I think I saw some HV capacitors! What power transistors are you using there, and in what configuration (IGBTs / Mosfets, half-bridge, full bridge, etc).

Coincidentally I just wound a 3.5" x 7" 30AWG secondary tonight! I discovered that I can wind this size on my hand drill and get a mostly flawless coil (a few small bends in the wire, but no real overlaps or errors) in under 30min. I'm going to make Steve Ward's SSTC-6 with it as I have all the parts on hand. I may eventually go for a nice DRSSTC build like yours with it though, especially if you'd be so kind as to share specs and maybe the schematic!

photo5mj.jpg

The masking tape will be removed, it is just for clean spray painting. I learned this is needed as varathane leaves PVC sticky even after it is dry.
 

Seoul_lasers

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actually varathane requires a few hours to cure, and then about 9-10hours to completely harden. Once its dry it should be non-tacky. It takes quite awhile.

Clear coat epoxy works too.. though a kit for something this size is in $150 range. Got to work quickly with it.
 

Sigurthr

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Yeah the Varathane on the wire dried hard and non-sticky within 5 hours, but where it landed on the bare PVC caps it is still sticky days later. It says on the can "not suitable for linoleum", so I guess for non-porous and nonwicking surfaces it stays tacky.
 

Polonium210

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Wow, very nice Po210! That looks more like a DRSSTC than a SSTC though as I think I saw some HV capacitors! What power transistors are you using there, and in what configuration (IGBTs / Mosfets, half-bridge, full bridge, etc).

Coincidentally I just wound a 3.5" x 7" 30AWG secondary tonight! I discovered that I can wind this size on my hand drill and get a mostly flawless coil (a few small bends in the wire, but no real overlaps or errors) in under 30min. I'm going to make Steve Ward's SSTC-6 with it as I have all the parts on hand. I may eventually go for a nice DRSSTC build like yours with it though, especially if you'd be so kind as to share specs and maybe the schematic!

photo5mj.jpg

The masking tape will be removed, it is just for clean spray painting. I learned this is needed as varathane leaves PVC sticky even after it is dry.

Hey Thanks!

This is not a DRSSTC just a Beefy SSTC. I think the caps you are referring to are the DC blocking caps and the big blue cap is a DC buss cap.
The driver is a modded version of Steve Ward's Mini SSTC. (I will PM you about the schematic)
The power side is a half bridge of 60N60 mini bricks with a crap load of protection running on 120VAC through a full wave voltage doubler for 400VDC on the Buss.

I would suggest a two part epoxy coating for your secondary. I made a simple jig to keep my coil rotating while the epoxy cures using a microwave turntable motor. It turns just fast enough to keep the epoxy from running and makes a nice bulletproof coating:D

Another short video SMB | Flickr - Photo Sharing!

And a picture of My half bridge http://http://www.flickr.com/photos/robbyron/5541583416/in/photostream
 

Seoul_lasers

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Yeah the Varathane on the wire dried hard and non-sticky within 5 hours, but where it landed on the bare PVC caps it is still sticky days later. It says on the can "not suitable for linoleum", so I guess for non-porous and nonwicking surfaces it stays tacky.

Correct. the solvent in the Varathane is actually Kerosene. Quite penetrating but it can't do anything to the majority of plastics.
 




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