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Tesla Coil Help

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LAN_403

interloper

Mon Apr 19 2010, 09:45AM

Registered Member #2801 Joined: Wed Apr 14 2010, 12:02PM
Location:
Posts: 9

Okay... this may be another supid question but can we use ceramic capacitors..? I tried my best to find polyster caps but just couldnt find it. I found ceramic caps each with 0.0033 uF kV rating (this is the most we could find, this country SUCKS). We have calculated that we need about 11 in parallel and 2 strings to give about 18.15 nF. we need about 17.2 nF (thats the static gap LTR cap value). Ill post pics and data soon

raff

Mon Apr 19 2010, 11:26AM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

interloper,

what country are you in anyway? have you considered making a DIY pulse cap?

interloper

Mon Apr 19 2010, 11:45AM

Registered Member #2801 Joined: Wed Apr 14 2010, 12:02PM
Location:
Posts: 9

we will use the salt jar capacitors if these dont work. I hope they will.

Herr Zapp

Tue Apr 20 2010, 05:15AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

interloper -

Exactly what type of ceramic capacitors were you considering? What does "0.0033 uF kV rating" mean?

Hopefullly these are not little ceramic disk capacitors .........

Even in a relatively small coil powered by a 9/30 NST, there will be very high pulse currents present in the primary circuit, possibly peak currents approaching a hundred amps or more. The capacitors used in an MMC need to capable of carrying high peak currents, and they need to use a dielectric that has low loss at high frequency (like mica or polypropylene, definitely NOT polyester!). The only commonly-available ceramic capacitors that are usable are RF-rated HV ceramic doorknob caps, and they are typically more expensive than polypropylene film/foil caps like the Cornell-Dubilier 942 series, which are well-proven in Tesla coil MMC service.

It sounds like your choices are salt-water caps, home-made rolled foil/polyethylene film/oil caps, or commercial film-foil caps. The C-D 942 caps are frequently available on eBay, if you have difficulty sourcing them locally.

Regards,
Herr Zapp

interloper

Tue Apr 20 2010, 07:44PM

Registered Member #2801 Joined: Wed Apr 14 2010, 12:02PM
Location:
Posts: 9

Today we tested the tesla coil. We made 12 salt water caps , connected em in parallel wired everything up etc. The spark gap fired off perfectly but there was no discharge from the toroid. We used this configuration-

J A V A T C version 12.4 - CONSOLIDATED OUTPUT
Units = Inches
Ambient Temp = 68Â°F

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

------------------------------------------ ----------
Secondary Coil Inputs:
------------------------------------------ ----------
Current Profile = G.PROFILE_LOADED
1 = Radius 1
1 = Radius 2
0 = Height 1
19.75 = Height 2
900 = Turns
0.019659 = Wire Diameter

---------------------------------------- ------------
Primary Coil Inputs:
------------------------------------------ ----------
Round Primary Conductor
2.25 = Radius 1
4.625 = Radius 2
0 = Height 1
4 = Height 2
4.25 = Turns
0.3125 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.02 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter

---------------------------------------- ------------
Top Load Inputs:
------------------------------------------ ----------
Toroid #1: minor=1.625, major=6, height=20, topload
Toroid #2: minor=1.625, major=8.25, height=21.5, topload

----------------------------------------- -----------
Secondary Outputs:
----------------------------------------- -----------
753.28 kHz = Secondary Resonant Frequency
90 degÂ° = Angle of Secondary
19.75 inch = Length of Winding
45.6 inch = Turns Per Unit
0.00229 inch = Space Between Turns (edge to edge)
471.2 ft = Length of Wire
9.88:1 = H/D Aspect Ratio
12.5422 Ohms = DC Resistance
16310 Ohms = Reactance at Resonance
0.55 lbs = Weight of Wire
3.446 mH = Les-Effective Series Inductance
3.969 mH = Lee-Equivalent Energy Inductance
3.968 mH = Ldc-Low Frequency Inductance
12.954 pF = Ces-Effective Shunt Capacitance
11.248 pF = Cee-Equivalent Energy Capacitance
25.106 pF = Cdc-Low Frequency Capacitance
3.36 mils = Skin Depth
8.347 pF = Topload Effective Capacitance
70.8347 Ohms = Effective AC Resistance
230 = Q

----------------------------------------------- -----
Primary Outputs:
----------------------------------------- -----------
681.96 kHz = Primary Resonant Frequency
9.47 % high = Percent Detuned
59 degÂ° = Angle of Primary
7.65 ft = Length of Wire
0.81 mOhms = DC Resistance
0.782 inch = Average spacing between turns (edge to edge)
1.084 inch = Proximity between coils
1.1 inch = Recommended minimum proximity between coils
2.723 ÂµH = Ldc-Low Frequency Inductance
0.01639 ÂµF = Cap size needed with Primary L (reference)
0 ÂµH = Lead Length Inductance
13.948 ÂµH = Lm-Mutual Inductance
0.134 k = Coupling Coefficient
0.123 k = Recommended Coupling Coefficient
7.46 = Number of half cycles for energy transfer at K
5.41 Âµs = Time for total energy transfer (ideal quench time)

------------------------------------------- ---------
Transformer Inputs:
------------------------------------------ ----------
220 [volts] = Transformer Rated Input Voltage
9000 [volts] = Transformer Rated Output Voltage
30 [mA] = Transformer Rated Output Current
50 [Hz] = Mains Frequency
220 [volts] = Transformer Applied Voltage
0 [amps] = Transformer Ballast Current
0 [ohms] = Measured Primary Resistance
0 [ohms] = Measured Secondary Resistance

-------------------------------------- --------------
Transformer Outputs:
----------------------------------------- -----------
270 [volt*amps] = Rated Transformer VA
300000 [ohms] = Transformer Impedence
9000 [rms volts] = Effective Output Voltage
1.23 [rms amps] = Effective Transformer Primary Current
0.03 [rms amps] = Effective Transformer Secondary Current
270 [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
18 [uF] = Power Factor Cap Size
12728 [peak volts] = Voltage Across Cap
31820 [peak volts] = Recommended Cap Voltage Rating
1.62 [joules] = Primary Cap Energy
1090.8 [peak amps] = Primary Instantaneous Current
23.7 [inch] = Spark Length (JF equation using Resonance Research Corp. factors)
27.8 [peak amps] = Sec Base Current

The above calculations assume that the total capacitance is 0.02 uF, which is probably wrong. We calculated the capacitance using a formula we found on the net. Therefore the detuning is way more than 9%. Either that or the toroid is not good enough. We're gonna test it with a can tomorrow and see what happens. Suggestions?

Some Pics-

Yeah, I know the primary is kinda screwed up but we tried to straighten it as much as we could. We used a traffic cone to wind it.

raff

Tue Apr 20 2010, 11:38PM

Registered Member #2315 Joined: Tue Aug 25 2009, 02:35AM
Location: Leyte, PH
Posts: 161

try to use an LCmeter to get the capacitance of your cap... it also helps to measure the primary winding inductance...

Herr Zapp

Wed Apr 21 2010, 04:08AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

interloper -

1. If there are no other serious construction flaws, it is probable that your coil is just way out of tune. It looks like you have MANY extra feet of wire in the primary circuit; we can't even see where the salt water capacitors are, or the spark gap. Relocate the capacitors and the spark gap as close to the primary as possible, and make all connections as short and direct as possible. If you measure the length of all your extra primary wiring, add that to the length of the actual primary coil, and plug the resulting length into JAVATC, you'll see that the primary resonant frequency is much lower than you think.

2. How are you making electrical connection to the salt water electrolyte inside your bottles? Your photos do not appear to show completed capacitors.

3. You need to get a more accurate determination of the actual capacitance value of your salt water capacitors; can you borrow a multimeter with a capacitance range from someone?

4. You have connected your salt water capacitors in parallel, correct, and not in series? Put them all in a bucket or metal pan, and arrange them in a circle with all the wires from the electrolyte tied together in the center of the array to keep the interconnecting wiring as short as possible.

Can you post some close-up photos of your spark gap and capacitor bank, as connected to your coil?

Regards,
Herr Zapp

lpfthings

Wed Apr 21 2010, 05:27AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Those salt water caps look like they don't even have an internal electrode! That could be the cause of your problems ..

Goodchild

Wed Apr 21 2010, 05:31AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

lpfthings wrote ...

Those salt water caps look like they don't even have an internal electrode! That could be the cause of your problems ..

ya it looks like you don't even have wire or any thing inside the bottle.

Mads Barnkob

Wed Apr 21 2010, 07:55AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Herr Zapp wrote ...

Can you post some close-up photos of your spark gap and capacitor bank, as connected to your coil?

We need either complete pictures of the whole setup that shows every connection in your coil setup, or you could also draw a schematic, use google documents for an easy shareable drawing program.

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