Tesla Coil Build Thread

[Seoul_lasers]

Terry filters don't protect the MMC though, I thought a primary strike can overvolt your MMC as well?

The same place I got the soft copper tubing at had some 4" pvc pipe (just not on display), so today I snagged two 22" long sections for $10 total. They couldn't cut it squarely though as their saw only cuts up to 3", so only one of the pieces has one square cut on it. I'll have to figure out how to fix the other should I ever need it as a coilform.

Yeah, there's no Home Depot or Lowes or equivalent up here, we have to make due with small businesses tailored to the normal needs of the community, which is mostly farmland. So if farmers or residential contractors don't need it, I can't get it locally.

That being said I have my new coilform and primary materials, and my spool of wire has been shipped. I'm not exactly looking forward to winding 1250-1500 turns by hand with no jig on such a large form, but hey, what can ya do? Lol. I don't have the tools (or money for them) to make a jig nor do I have the space to make it in. I don't even have a work bench, I use a 24" x 18" plastic folding table for all my projects. Sometimes living in an appartment sucks.

I'll worry about upgrading the NST/MMC later on, those are expensive upgrades. For now I have the daunting task of winding a huge (to me) secondary and making a base for the primary.

The MMC usually isn't a problem during a primary strike, due to the configuration of the circuit. The main victim is usually the transformer. MMC protection gap strongly discouraged by the Tesla Coiling community as it puts a great deal of stress on the MMC if it were to fire.

Quote from Mike Hammer
"Not sure how my name got into this discussion since Ive been
pretty much out of coiling for at least 4 or 5 years.

I still read the mailing list and still have the interest but
just dont have the time or resources anymore. Imagine the surprise
when my name jumps out at me during a quick scan of postings.

Im not sure why this person attached my name to this idea
of protecting a MMC via a spark gap. I was pretty much
out of coiling by the time MMCs became all the rage.
All of my caps were of the poly/foil type. Some flat
plate types and some rolled plate types.

To the best of my recollection I have never advocated placing
a spark gap directly across the primary cap. If such a gap
were to fire it would probably place a great deal of stress
on that cap from the very high currents involved.

I have strongly advocated safety gaps placed directly across
the transformer terminals as a fail safe of last resort as
well as a safety gap place in parallel with the main gap."

 

[Sigurthr]

Ahh, gotcha. Aye I figured the same thing that a "safety" gap across the MMC would add a lot of stress into the system and be mostly unnecessary. Likewise, a safety gap across the transformer when your main gap is across the transformer seems silly. If you're using the parallel tank cap and series spark gap circuit then yes, you would want a safety gap across the transformer, that makes sense.

Also, I have a new record streamer length (on the same old coil - I insulated the secondary to stop racing sparks and increased the coupling to energize more of the secondary (I know this stresses it more)).

 

[Seoul_lasers]

Ahh, gotcha. Aye I figured the same thing that a "safety" gap across the MMC would add a lot of stress into the system and be mostly unnecessary. Likewise, a safety gap across the transformer when your main gap is across the transformer seems silly. If you're using the parallel tank cap and series spark gap circuit then yes, you would want a safety gap across the transformer, that makes sense.

Also, I have a new record streamer length (on the same old coil - I insulated the secondary to stop racing sparks and increased the coupling to energize more of the secondary (I know this stresses it more)).

just so there is no mistake,
You should NEVER parellel a capacitor across a transformer output EVER, especially in a SGTC Tesla coil. That is a sure way to transformer destruction.

- The racing sparks sound like you still are running into a coupling issue of somesort,
try decreasing your top-load slightly... if you can hear a sputtering noise from the gap, that's a sure sign the system is out of tune. (increase primary turns by 1/2 turn until the sputtering stops- or decrease the top load)

Sounds like with the spark increase, you're hitting the coils sweet spot. Good sign.

 

[Sigurthr]

just so there is no mistake,
You should NEVER parellel a capacitor across a transformer output EVER, especially in a SGTC Tesla coil. That is a sure way to transformer destruction.

See, that is damn useful information that should have popped up sooner in other places. Everything I read said that both variants work fine with no real gains/losses over the other EXCEPT that the parallel capacitor arrangement allows HV/HF oscillations to get to the transformer and back in to the mains. It was indicated that it would be ok for non-NST transformers, but for a NST to use the series capacitor circuit.

- The racing sparks sound like you still are running into a coupling issue of somesort,
try decreasing your top-load slightly... if you can hear a sputtering noise from the gap, that's a sure sign the system is out of tune. (increase primary turns by 1/2 turn until the sputtering stops- or decrease the top load)

Sounds like with the spark increase, you're hitting the coils sweet spot. Good sign.

Aye, I think I'm pretty close to the sweet spot, if not in it now. Leaving well enough alone at this point, haha.

 

[Seoul_lasers]

See, that is damn useful information that should have popped up sooner in other places. Everything I read said that both variants work fine with no real gains/losses over the other EXCEPT that the parallel capacitor arrangement allows HV/HF oscillations to get to the transformer and back in to the mains. It was indicated that it would be ok for non-NST transformers, but for a NST to use the series capacitor circuit.



Aye, I think I'm pretty close to the sweet spot, if not in it now. Leaving well enough alone at this point, haha.

Nope, even the paralleled MMC/Cap on a PolePig is a bad idea.
Don't do it. If you have it in this setup now, change the setup. Also it will allow the discharge
of the cap to ring up the primary without as much losses. The windings on a neon are designed to be lossy to keep the current at a safe level. Combine this with RF backup and a fried neon will eventually happen. Smaller the Xmfr the faster this can occur.

The first gif on the left is the WRONG circuit. The right side shows the proper way of arranging the gap and capacitor. This way the energy is concentrated at the TC primary windings and not backing into your neon windings.

 

[Sigurthr]

Good to know! I am (and always have been) using the correct arrangement of Parallel Spark Gap and Series MMC.

I had even asked on TheGeekGroup (because 4HV was not accepting registrations) before I built this TC to see which circuit version to use but no one pointed the losses out. All I was told was that in the other (wrong) circuit you need a lot of filtering before and after the NST to keep the RF kickback out.

One question for you; what is the purpose of sanding down the pvc coilform before winding? Is it just to give the wire more grip on the coil or does it serve an electric purpose (maybe the smooth surface allows arcs to travel across it if you get racing sparks)?

 

[Seoul_lasers]

Good to know! I am (and always have been) using the correct arrangement of Parallel Spark Gap and Series MMC.

I had even asked on TheGeekGroup (because 4HV was not accepting registrations) before I built this TC to see which circuit version to use but no one pointed the losses out. All I was told was that in the other (wrong) circuit you need a lot of filtering before and after the NST to keep the RF kickback out.

One question for you; what is the purpose of sanding down the pvc coilform before winding? Is it just to give the wire more grip on the coil or does it serve an electric purpose (maybe the smooth surface allows arcs to travel across it if you get racing sparks)?

sanding down the coil forum is kind of cleaning process, so that any kind of printing or small imperfections from the coil form(PVC) get evened out. Clear acrylic tubing doesn't require this treatment. IF all you want is a quick and dirty coil form then you may skip this. Just don't expect great performance if the PVC has conductive ink or material on it....

 

[Sigurthr]

Ah, that makes sense. Thanks. No reason to skimp out on a simple step... winding the damn thing will take hours, no reason to not spend 30min sanding it imo. I was just wondering what the actual reason for it was. It would follow then that finishing with high grits are not needed, just rough grit to make sure no coatings/inks are on.

 

[Seoul_lasers]

Ah, that makes sense. Thanks. No reason to skimp out on a simple step... winding the damn thing will take hours, no reason to not spend 30min sanding it imo. I was just wondering what the actual reason for it was. It would follow then that finishing with high grits are not needed, just rough grit to make sure no coatings/inks are on.

That is correct. Winding 1200-1400x takes usually 1.5-2 weeks when done carefully by hand.
With a professional jig, possibly 2-4 days. I am including the priming with dielectric transformer quality varethane as well here. Clear coat varethane from a wood supply store also works well, but it takes several hours to dry.

 

[Sigurthr]

So while I wait for the wire to progress with my SGTC build I decided to do some research on a very tiny very inexpensive SSTC build.

I chose Steve Ward's "Micro SSTC"; parts list comes to $17. I'll order double of everything though, as I always do when buying parts for new projects, as you never know when you're going to fry something. Grenadier has all my cash right now so this will certainly have to wait, but the plans have been cemented in my mind. I'm looking forward to having a small TC I can run in my office on a table and play with that won't make my ears ring for hours or screw up electronics from far away. I have extra coilform I can use left over from my SGTC rebuild project, which will be close to the specified stuff by Ward. I'll use 30ga wire on a 3.25" form for secondary (with wind length adjusted to match the self capacitance and inductance specified) and some spare 4" form for the primary. I bought twice as much 4" form as needed for my SGTC rebuild, so that is taken care of, not that it was expensive.

Here is the schematic I'll be using: http://www.stevehv.4hv.org/SSTC6/microSSTCschematic2.JPG

Seriously, my SGTC posted above in this thread (not this post) is LOUD. VERY LOUD. I used to work in very loud environments over 95dB without needing ear protection, and I consider this coil to be very uncomfortably loud from meters away. With -43dB earplugs in it is still damn loud. I'm starting to see the appeal in DRSSTCs and VTTCs. Speaking of which, after the new SGTC and micro SSTC are done, either a 811A VTTC or a MicroBRUTE DRSSTC will be next.

 

[ped]

Hey all,
I've noticed we're lacking a central thread for TC's, not that there have been many lone threads so far (just a few throughout the forum's history), and figured I'd throw one together.

I'm currently working on my first Tesla Coil. Today I completed the NST chokes, main base, and the MMC Tank Capacitor array. Tomorrow I'm expecting my secondary and spark gap to arrive in the mail. I went with a pre-wound secondary because I don't have the space or tools to wind one myself without spending a dozen hours hand winding the coil directly on the form with no support/roller guide etc. Also, I can't get coilforms locally, lol. We have no real hardware store up here.

Pics:

You can see it dwarfs my work table and takes up half of the night tables I use as well.


Stats: (will be updated as I go along)
NST: 7.5kV 30mA nonGFCI
NST protection: 100T air-core 18AWG Chokes
Primary "Tank" Capacitor: 0.01764uF (17.6nF) 16kV MMC (24x Cornell Dubilier 942C20S47K-F 0.047uF 2kV Polypropylene Foil Caps)
Spark Gap: machined brass and steel
MMC Insulator/stand off: 1/4" Plexiglass
Primary Coil: TBD
Secondary Coil: TBD
Topload: 7.4" diameter ball of aluminium foil
Base: 3/4" CDX Plywood.
Hardware: 1/4-20 2" Bolts and Nuts

I'll be using the Series Capacitor / Parallel Spark Gap topology with a safety gap across the Tank cap. I don't plan on using Bleeder Resistors just yet, once I get the coil working well I'll add that in later if needed. They're just a safety precaution really and if you treat it as a lethal pulse cap there is no need for bleeders.

Be carefull, wood becomes conductive at high voltages, even in a mildly humid atmosphere.

Prolly allready been mentioned.

 

[Seoul_lasers]

So while I wait for the wire to progress with my SGTC build I decided to do some research on a very tiny very inexpensive SSTC build.

I chose Steve Ward's "Micro SSTC"; parts list comes to $17. I'll order double of everything though, as I always do when buying parts for new projects, as you never know when you're going to fry something. Grenadier has all my cash right now so this will certainly have to wait, but the plans have been cemented in my mind. I'm looking forward to having a small TC I can run in my office on a table and play with that won't make my ears ring for hours or screw up electronics from far away. I have extra coilform I can use left over from my SGTC rebuild project, which will be close to the specified stuff by Ward. I'll use 30ga wire on a 3.25" form for secondary (with wind length adjusted to match the self capacitance and inductance specified) and some spare 4" form for the primary. I bought twice as much 4" form as needed for my SGTC rebuild, so that is taken care of, not that it was expensive.

Here is the schematic I'll be using: http://www.stevehv.4hv.org/SSTC6/microSSTCschematic2.JPG

Seriously, my SGTC posted above in this thread (not this post) is LOUD. VERY LOUD. I used to work in very loud environments over 95dB without needing ear protection, and I consider this coil to be very uncomfortably loud from meters away. With -43dB earplugs in it is still damn loud. I'm starting to see the appeal in DRSSTCs and VTTCs. Speaking of which, after the new SGTC and micro SSTC are done, either a 811A VTTC or a MicroBRUTE DRSSTC will be next.

I thought for sure you were using plexiglass for your build. Stay far away from wood as possible like ped said.

Also, another caution, avoid sticking tubes and lightbulbs on the TC. Not only can this cause them to shatter if they get hot enough (CF bulbs) , you can start creating X-rays with lightbulbs and ESPECIALLY some kinds of amplifier tubes. (these are under a very low pressure). Some can deliver a few 10's of R/Hr, more than enough to cause some potentially serious necrotizing burns.
Below is an example of a VERY serious Xray burn. They don't heal well, and a few become Cancerous.
This picture is an example of X-ray fluoroscopy gone VERY wrong.

 

[Sigurthr]

Aye, no worries I'm well practiced in reduction of radiation based dangers and I also don't have any evacuated tubes at all. Low pressure gas tubes, such as fluorescent lamps are safe to use because the fill gas provides something for the electrons to strike instead of hard glass (which causes the xrays via bremsstrahlung).

I am aware that wood becomes conductive at high enough voltages and moisture levels. The plywood I am using for the base of the SGTC rebuild will be insulated from all HV by plexiglass sheets hot-glued down on top of it. The only point that may still touch the plywood base would be the spark gap, because only steel hardware is available to me and I don't know of a thermally stable alternative to mount the spark gap. The spark gap terminals would only see ~11kV when not "on" anyway.

In my current SGTC only three places that carry primary side HV (~11kV) are in direct contact with wood: the bleeder resistor terminals, NST feed, and the spark gap support bracket terminals. The spark gap is epoxied to the small oak wood base along with the coilforms for the secondary I bought, it cannot be removed and was not my design or construction. The Bleeder resistor terminals and NST feed terminals are the only primary side HV points that touch the plywood and are spaced far enough apart to prevent problems in dry wood. The wood has a higher resistance than the resistor anyway so that is not an issue. If the NST feed terminals were to short by the wood there would not be much danger either and I would be able to notice it immediately. I know the set up isn't ideal, but you said it yourself; it is mostly a proof of concept build.

I do not have the capability to construct using plexiglass, and only 1/8" thick plexiglass is available for purchase, which could not support the weight even if I could construct with it. Moreover, plexiglass/acryllic glue/bonder is not available locally. I tried building a display case for my flutes last year and it was a nightmare. I managed to get it done with "plastic weld" epoxy but it is ugly as hell and not structurally strong or air-tight. Also, the plexiglass supplier here cannot make perfectly square cuts (often one dimension or more is off by at least 1/8") or square edges (they're all diagonal and slightly rounded), and has a limited range of sizes available (typically smaller than 3" squared and larger than 4" squared). Without buying full sheets and having a workroom and tools of my own there is no way to build with plexiglass here.

I've been saying it the entire thread; living up here in the middle of no where one's ability to purchase materials normally taken for granted is greatly reduced, if not entirely impossible. In town we have 1 small no-name hardware store and WalMart, that is it. It is over 150miles to the next real city. I live in a 2 bedroom apartment with a shared living room, dining room, kitchen, and shared bathrooms. My workspace consists of a small heavy duty plastic 18" x 24" folding table, and I only have modest hand tools.

Btw, Ped; your pics on 4HV thread for your coil no longer work, and I'd like to see it!

 

[Seoul_lasers]

Sorry about the picture.

That's a second degree X-ray burn.

 

[ouch3994]

very awesome, maybe ill start one of these for a summer project...

 

[Sigurthr]

Sorry about the picture.

That's a second degree X-ray burn.

No problem at all, I appreciate the sentiment. =)

Heh, not the first (nor the worst) I've seen. Some radiologists at a local hospital were blasting patients with 20R instead of 20mR a while back. They got in a whole world of trouble. The Drs only suspected something wrong when one patient came back with a severe burn on their chest.


UPDATE: 4/30/12 Experienced builders; let me know what you think!

I sanded down my secondary coilform and coiled my primary coil for my SGTC Rebuild. Primary is 1/4" copper tube with 1/4"-ish spacing using about 55 feet (YES you heard right!) of tube yielding 14.75 turns. I probably won't need more than 10 but I wanted to design this with a wide tuning range and capable of upgrades. I found out my "4" pvc pipe" is actually 4.5" pipe and thus I had to readjust the turns number and H:W ratio to compensate. Sticking to around 1300 turns I come to 18" of winding instead of the earlier planned 20. Fine by me. Primary measures 24" in diameter with a center hole of 5". Secondary windings will start at 2" up on coilform and continue to the 20" mark. I am going to place one layer of 1/8" plexiglass UNDER the primary between it and the plywood board. There will also be one layer ABOVE the primary for strike protection. The center arm of the primary will be encased in 1/2" PVC tubing ontop of the top layer of 1/8" plexiglass. This is for strike protection and to keep the primary in shape. The two layers of plexiglass will be bolted down so compression holds everything. The copper is pretty work hardened already, and my hands are killing me.

Pics:

JavaTC Parameters:
J A V A T C version 12.5 - CONSOLIDATED OUTPUT
Monday, April 30, 2012 12:31:33 AM

Units = Inches
Ambient Temp = 72°F

----------------------------------------------------
Surrounding Inputs:
----------------------------------------------------
0 = Ground Plane Radius
0 = Wall Radius
0 = Ceiling Height

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
2.25 = Radius 1
2.25 = Radius 2
2 = Height 1
20 = Height 2
1364 = Turns
30 = Wire Awg

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
2.5 = Radius 1
9.481 = Radius 2
0 = Height 1
0 = Height 2
10.8395 = Turns
0.25 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.01764 = Primary Cap (uF)
20 = Total Lead Length
0.0808 = Lead Diameter

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=2.5, major=10, height=22, topload

----------------------------------------------------
Secondary Outputs:
----------------------------------------------------
205.29 kHz = Secondary Resonant Frequency
90 deg° = Angle of Secondary
18 inch = Length of Winding
75.8 inch = Turns Per Unit
0.00317 inch = Space Between Turns (edge to edge)
1606.9 ft = Length of Wire
4:1 = H/D Aspect Ratio
165.906 Ohms = DC Resistance
58247 Ohms = Reactance at Resonance
0.49 lbs = Weight of Wire
45.157 mH = Les-Effective Series Inductance
48.459 mH = Lee-Equivalent Energy Inductance
47.701 mH = Ldc-Low Frequency Inductance
13.31 pF = Ces-Effective Shunt Capacitance
12.403 pF = Cee-Equivalent Energy Capacitance
22.793 pF = Cdc-Low Frequency Capacitance
7 mils = Skin Depth
8.287 pF = Topload Effective Capacitance
236.8409 Ohms = Effective AC Resistance
246 = Q

----------------------------------------------------
Primary Outputs:
----------------------------------------------------
205.3 kHz = Primary Resonant Frequency
0 % = Percent Detuned
0 deg° = Angle of Primary
34 ft = Length of Wire
5.69 mOhms = DC Resistance
0.394 inch = Average spacing between turns (edge to edge)
1.886 inch = Proximity between coils
0 inch = Recommended minimum proximity between coils
33.585 µH = Ldc-Low Frequency Inductance
0.01763 µF = Cap size needed with Primary L (reference)
0.625 µH = Lead Length Inductance
122.077 µH = Lm-Mutual Inductance
0.096 k = Coupling Coefficient
0.131 k = Recommended Coupling Coefficient
10.42 = Number of half cycles for energy transfer at K
25.22 µs = Time for total energy transfer (ideal quench time)

----------------------------------------------------
Transformer Inputs:
----------------------------------------------------
120 [volts] = Transformer Rated Input Voltage
7500 [volts] = Transformer Rated Output Voltage
30 [mA] = Transformer Rated Output Current
60 [Hz] = Mains Frequency
120 [volts] = Transformer Applied Voltage
0 [amps] = Transformer Ballast Current
0 [ohms] = Measured Primary Resistance
0 [ohms] = Measured Secondary Resistance

----------------------------------------------------
Transformer Outputs:
----------------------------------------------------
225 [volt*amps] = Rated Transformer VA
250000 [ohms] = Transformer Impedence
7500 [rms volts] = Effective Output Voltage
1.88 [rms amps] = Effective Transformer Primary Current
0.03 [rms amps] = Effective Transformer Secondary Current
225 [volt*amps] = Effective Input VA
0.0106 [uF] = Resonant Cap Size
0.0159 [uF] = Static gap LTR Cap Size
0.0277 [uF] = SRSG LTR Cap Size
41 [uF] = Power Factor Cap Size
10607 [peak volts] = Voltage Across Cap
26517 [peak volts] = Recommended Cap Voltage Rating
0.99 [joules] = Primary Cap Energy
243.6 [peak amps] = Primary Instantaneous Current
21.7 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)
6.7 [peak amps] = Sec Base Current

----------------------------------------------------
Static Spark Gap Inputs:
----------------------------------------------------
2 = Number of Electrodes
0.25 [inch] = Electrode Diameter
0.1748 [inch] = Total Gap Spacing

----------------------------------------------------
Static Spark Gap Outputs:
----------------------------------------------------
0.175 [inch] = Gap Spacing Between Each Electrode
10607 [peak volts] = Charging Voltage
10603 [peak volts] = Arc Voltage
36459 [volts] = Voltage Gradient at Electrode
60658 [volts/inch] = Arc Voltage per unit
100 [%] = Percent Cp Charged When Gap Fires
13.315 [ms] = Time To Arc Voltage
75 [BPS] = Breaks Per Second
0.99 [joules] = Effective Cap Energy
399866 [peak volts] = Terminal Voltage
74 [power] = Energy Across Gap
22.3 [inch] = Static Gap Spark Length (using energy equation)