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Registered Member #2148
Joined: Tue Jun 02 2009, 02:22AM
Location:
Posts: 62
hi guys i designed my tc specs using tesla cad and slowly making them one by one.
i ordered 1 toroid from amazing1.com size 3"x12" i finished my secondary coil with 4.5" diameter PVC and a height of 18" using 25 AWG i have 6 home made capacitors measuring 5.5nF each. will make MMC caps soon the capacitor that i will use is 0.047uF polypropylene film axial caps. 1.5kVDC/450VAC from RSCOMPONENTS( are these are a good substitute? ?) since 942c is really hard to find.
i bought 2 15kv@30ma. i still dont know what kind of NST is. but the saleslady said that the casing of NST is metal not plastic which i think it is not a solid state??brand name is hongkong gardner. it is really hard to find good old style NST here.
heres my plan
Secondary Coil Design Diameter of secondary coil : 114.30mm Winding height of secondary coil : 457.20mm Wire diameter for secondary coil : 0.45mm Spacing between windings : 0.048mm Secondary turns : 918.00 Secondary wire length : 329.67m Secondary inductance : 21.31mH Approximate resonant frequency : 375.35kHz Secondary quarter wavelength resonant frequency : 227.50kHz Secondary self capacitance : 8.44pF Toroid capacitance required to form quarter wavelength coil : 14.53pF (16.34pF @ 3"x12" the closest)
Primary Coil Design Primary capacitance : 0.0106uF Primary resonant frequency : 227.50kHz Secondary coil diameter : 114.30mm Primary conductor diameter : 4.75mm Primary turn to turn spacing : 5.00mm Spacing between the secondary and the inside turn of the primary : 25.40mm The primary will need to be tapped between turn 11 and turn 12 to form a resonant circuit at 227.50kHz
Neon Transformer / Primary Capacitor Matching Transformer secondary voltage : 15.00kV Transformer secondary current : 60.00mA Number of transformers : 1 Primary capacitor required to form a resonant circuit at 60Hz with neon transformer(s) : 0.0106uF
ok experts i have questions regarding to this design cause some data is a lil confusing to me
1.about my primary capacitor ( tank cap,C1 etc) what value should i use? that 0.0106uF there? or something that should be calculated diferrently?
i DLed wintesla and it calculated different value for my primary cap, like 0.0112uF so im confused
2.my spark gap i made of 2 round metals but not tungsten. is it ok?
3. is it okay to make an MMC with only 1-2 strings in parallel? i think that all for now... thank you guys....
Registered Member #1548
Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61
The different cap calculation is due to the fact that you should use a LTR(Larger than resonant) cap. This is so the secondary voltage doesn't climb to high due to resonance. I believe the accepted value is about 10 to 15% higher than resonant cap value.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
enyuki -
So far, so good, except:
1. For your capacitor, .0106 is the RESONANT value for a 15/60 NST. You DO NOT want to use a resonant cap value because of potential problems with resonant "ring-up", which can generate extremely high voltages that can destroy both your NST and your capacitor. You want a larger than resonant cap value ("LTR").
You didn't state your AC line frequency, but if it is 60 Hz then you want a capacitor value around .15uF; if you live in 50 Hz land, then you want a value around .20uF.
2. Your 3" X 12" toroid is way too small to extract maximum streamer length from a 15/60 NST, but it will "work". Consider making a considerably larger (20" or 24" diameter) toroid from 4" or 6" diameter convoluted aluminum HVAC duct material.
3. WINTESLA suggests a resonant capacitor value of .0106uF for a 15/60, 60 Hz power supply, so possibly you are not using WINTESLA properly. The "Trans/Cap Match" tab is where you input your transformer and line frequency data.
4. Your spark gap design cannot be analyzed unless you provide more information beyond "two round metals not tungsten". What are the shape and dimensions of the electrodes? How are the electrodes arranged? What is the electrode material? What is the gap between the electrodes? Etc, etc.
5. You can't determine how many strings of capacitors are required unless you know the RMS and peak current ratings of the capacitors you intend to use. What is the specific model # of the RS Components capacitors you are considering? Do these caps utilize film/foil construction, rather than metallized-film construction? Are they rated for high-current pulse duty?
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
You should read this recent thread, it should answer your first two questions. 3. Yes, as long as you have a suitable voltage rating for your MMC. Using 1.5kV caps, you should have 18-20 caps in series. This will drop the capacitance down to about 2nF per string. To get it to your desired cap value, you will need about 7 strings in parallel.
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
You should read this recent thread, it should answer your first two questions. 3. Yes, as long as you have a suitable voltage rating for your MMC. Using 1.5kV caps, you should have 18-20 caps in series. This will drop the capacitance down to about 2nF per string. To get it to your desired cap value, you will need about 7 strings in parallel.
Registered Member #2148
Joined: Tue Jun 02 2009, 02:22AM
Location:
Posts: 62
Doubl3 Helix wrote ...
The different cap calculation is due to the fact that you should use a LTR(Larger than resonant) cap. This is so the secondary voltage doesn't climb to high due to resonance. I believe the accepted value is about 10 to 15% higher than resonant cap value.
Someone please correct me if I'm wrong!
i see i see now i understand! thank you very much,i dont have an oscilloscope so im depending on my rough calculations and from the experts here
Registered Member #2148
Joined: Tue Jun 02 2009, 02:22AM
Location:
Posts: 62
Herr Zapp wrote ...
enyuki -
So far, so good, except:
1. For your capacitor, .0106 is the RESONANT value for a 15/60 NST. You DO NOT want to use a resonant cap value because of potential problems with resonant "ring-up", which can generate extremely high voltages that can destroy both your NST and your capacitor. You want a larger than resonant cap value ("LTR").
You didn't state your AC line frequency, but if it is 60 Hz then you want a capacitor value around .15uF; if you live in 50 Hz land, then you want a value around .20uF.
2. Your 3" X 12" toroid is way too small to extract maximum streamer length from a 15/60 NST, but it will "work". Consider making a considerably larger (20" or 24" diameter) toroid from 4" or 6" diameter convoluted aluminum HVAC duct material.
3. WINTESLA suggests a resonant capacitor value of .0106uF for a 15/60, 60 Hz power supply, so possibly you are not using WINTESLA properly. The "Trans/Cap Match" tab is where you input your transformer and line frequency data.
4. Your spark gap design cannot be analyzed unless you provide more information beyond "two round metals not tungsten". What are the shape and dimensions of the electrodes? How are the electrodes arranged? What is the electrode material? What is the gap between the electrodes? Etc, etc.
5. You can't determine how many strings of capacitors are required unless you know the RMS and peak current ratings of the capacitors you intend to use. What is the specific model # of the RS Components capacitors you are considering? Do these caps utilize film/foil construction, rather than metallized-film construction? Are they rated for high-current pulse duty?
Regards, Herr Zapp
First of all thank you for the very precise answer.
1. So i must use Larger than resonant value capacitor. I read a lot about building tesla but never got into this LTR thing. Maybe i didnt understand at all LOL i live with 60hz 220v outlet. so maybe im using .15uF? are you sure 0.15 micro farad? or 0.15nF hehe. 0.15uF is damn large
2. is there a way how to construct a good toroid, parts used etc? because toroid seems a bit expensive. maybe i google too.
3.what do you mean im not using WINTESLA properly?
4. i think it is made out of steel(shiny) with a diameter of 1.5cm. a screw can be inserted halfway in the middle of the sphere. diameter of screw is 3mm. i'll start with a very small gap and increase it until i found the best.
5. actually i already computed how many caps i need. 300+ but i dont know if these caps can stand the force without having 942C here is the specs of the capacitor from RS Capacitance 47nF Voltage 450 Vac; 1.5kV(dc) Capacitance Tolerance 20%
Package Axial Dielectric PP Temperature Range -55 to 100°C
Over View
KP1.72 Series
* A very low loss dielectric suitable for continuous use at high voltages It will withstand high voltage, fast rise time pulses and has an excellent high frequency performance Film-foil polypropylene capacitors protected by polyester wrap and epoxy end seals.
part # is 114-474
by the way i already received my 2 NST 15kv@30ma. i think its an OLDstyle not a solid state one whew! metal case, with 2 ceramic insulator(am i correct?) on the HV output and ground. with center tap. 220v 60hz input. HEAVY!
Registered Member #2148
Joined: Tue Jun 02 2009, 02:22AM
Location:
Posts: 62
Coronafix wrote ...
You should read this recent thread, it should answer your first two questions. 3. Yes, as long as you have a suitable voltage rating for your MMC. Using 1.5kV caps, you should have 18-20 caps in series. This will drop the capacitance down to about 2nF per string. To get it to your desired cap value, you will need about 7 strings in parallel.
hey thanks. yes, because i might use 942c 0.470uF 2kv-3kv caps i ask this because some say MMC must have atleast 4-6 parallel strings.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
The RS Arcotronics capacitors are EXCELLENT for sgtc use. From my previous calculations their ratings allow them to be charged to full rated dc and discharged 100 times/sec (50 Hz) with very little stress. I used the 100nF/1.5kV and 470nF/1kV versions..the 47nF caps are even more robust.
You can use as many or as few capacitors in series and/or parallel as required for an MMC just use as required to achieve voltage handling and capacitance required.
I use one resistor per capacitor or per 'row' to 'balance' the capacitor voltages over time, and (very important to allow adjustments etc.) to discharge the MMC within a few seconds. The RS VR37 33M resistors have proved reliable for me. Now I use 33M 1W from farnell as they are better value
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Enyuki -
First, my humblest apologies - the correct "larger than resonant" capacitor value for your 15/60, 60 Hz system is .015uf, not .15uF. (Don't know where the missing zeros went....)
Responding to your specific questions:
1. Yes, it is highly recommended that you use a "larger than resonant" capacitor value. See the section on uncontrolled resonant voltage rise on Richie Burnett's website for much background on this phenomonon:
2. There are many options for constructing home-made toroids, depending on what materials you have access to. One of the most commonly used is flexible, convoluted aluminum duct material used for home heating and air-conditioning systems. This is relatively thin corrugated aluminum tubing that can be formed into a circle and secured with aluminum foil tape. In the US, this material is available in 1" diameter increments from 3" to 8". It comes in "compressed" sections about 3 feet long that can be stretched out about 1.5X the initial length. Look at many of the coils on the teslacoilwebring for examples of this construction.
3. There are two areas in WINTESLA that "calculate" the required capacitor value. First, the "Trans/Cap Match" tab calculates the RESONANT cap value for a given transformer's output voltage, current, and AC line frequency. This is just a "theoretical" value, and NOT what you want to actually use. Multiiply this value by 1.4 or 1.5 to determine a "safe" LTR value that will not be subject to extreme resonant voltage rise.
The second area where WINTESLA calculates the cap value is in the "Primary Coil" section. This calculates the actual "required" cap value to tune the resonant frequency of your primary circuit to match the resonant frequency of your secondary coil + topload. The capacitor value shown here will change (to maintain resonance) if you make any changes to the number of turns in the primary coil, or if you make any changes to the secondary circuit that changes its resonant frequency.
4. You still didn't tell us anything about the design of the spark gap. Are you using a single gap, with two 1.5cm spherical electrodes? If so, this won't quench well at all with a 60ma power supply. Consider changing to a gap design using multiple pieces of 17mm-25mm diameter copper pipe 75mm to 100mm long, mounted parallel to each other, to provide at least 5-6 series-connected spark gaps. This should be cooled with a small fan. The "single-gap" concept can work, but it requires a supply of high-velocity air at moderate pressure, or a fairly powerful vacuum-motor. See Gary Lau's "Sucker-Gap" design at: for a typical vacuum motor design. However, this type of gap is usually annoyingly noisy.
5. An MMC for a 15/60 NST-powered coil consisting of 300+ caps is absurd, both from a cost standpoint, and from physical size and mounting complexity. I'd go back and review your design (and your cap ratings) to find a more efficient solution. An MMC with 300+ individual capacitors is just not rational (or cost effective) for this coil.
The number of parallel "strings" of caps required in an MMC is determined by the peak current in the primary circuit. JAVATC and other Tesla coil design tools will calculate the peak current and help you determine the required number of strings.
Or, simply go to Terry Fritz' "MMC cap chart" at: , which will show you the required number of caps in a string, and the number of parallel strings required. (This is based on the C-D 942 series cap, .15uF at 2kV.) For your 15/60, static-gap system,, with the MMC designed to have a reasonable safety factor, you will need two strings of 20 caps each, or a total of 40 caps. This is FAR more reasonable than 300+ caps. This chart was designed with actual measurements of cap heating in an RF test setup.
You mentioned that the CDE 942-series caps are hard to find. If you go to the Cornell-Dubilier website (cde.com), you will find a "Services" tab at the top of the home page. Click this, and in the drop-down menue is a "Stock Check" option. Enter the model of the capacitor you are interested in, and it will display a listing of all the C-D distributors that have these caps in stock. Also, these capacitors are almost always available from certain eBay sources. The C-D 942C series caps are well-proven in Tesla coil service, and the RMS and peak current ratings of the 942C20P15K-F model (13.5A and 432A) are among the highest of all similar caps offered by various manufacturers.
I found the datasheet for the "RS Components" caps you are considering, which are actually the Arcotronics A72 series:
Note that the "Maximum Current vs Frequency" graphs show that the .047, 1500V cap has a maximum RMS current rating of around 5A, much less than the 13A rating of the .15uF C-D cap.
Your NSTs sound like conventional iron-core transformers, and should work well when the secondary outputs are paralleled. You will need to "phase" them correctly to get the full 60ma output.
You should also consider adding a simple R-C filter array (knoiwn as a "Terry Filter", after its developer Terry Fritz) to protect the NSTs from the high voltage "spikes" that will be generated in the primary circuit. Many, many NSTs have been destroyed in Tesla coil systems because they were not adequately protected from HV spikes & RF harmonics in the primary circuit.
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building my first spark gap TC
