Author Topic: mini tesla (hopefully not a fail)  (Read 1400 times)

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #20 on: November 15, 2020, 07:08:34 PM »
Yes, many capacitor types overheat with high-frequency AC use.  The polypropylene MKP10 0.22uF part should be good.  Do you have 4 or 5 of them?  Soldering a string of capacitors in series reduces capacitance.  Four 0.22uF caps in series will be 0.22uF / 4 = 0.055uF.

Thank you for sharing gate and drain scope traces.  Gate signal looks clean.  The TC4426 is managing to drive all four FETs.  I expect it is getting hot, or will get hot once frequency gets to 141kHz.  Temperature can be reduced some by gluing a small piece of aluminum or copper to the top of the IC as a heat-sink.

These latest scope images show oscillation at about 48kHz (21us period), even though the scope is reporting 147kHz.  The scope must be counting some of the ringing in its frequency measurement.  I suspect primary capacitance needs to be significantly lower, probably less than the 0.1uF I'd suggested previously.  Polypropylene capacitors are best for this use.  Mica is a possible alternative, but will run hotter.

Do you have design parameters for this larger coil?  If so, enter them in the "JavaTC" online program:
http://www.classictesla.com/java/javatc/javatc.html
It will output frequency and lots of other useful information.
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #21 on: November 16, 2020, 08:08:47 AM »
So, i made some tests with 4 and 6 caps, the IC is barely warm to touch, so that is not a problem...yet, however i will look for a tiny heatsink, also i have thermal double sided tape so that should be good.

"These latest scope images show oscillation at about 48kHz (21us period), even though the scope is reporting 147kHz.  The scope must be counting some of the ringing in its frequency measurement."
That can be because of the Chinese oscilloscope, i can't afford a better one unfortunately...
 I tried using javatc, but they ask for a ton of parameters and i get lost within the numbers and i quit very quick.

The following tests are made with a 12v PS, and the arcs are gone from 3 caps up.

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #22 on: November 16, 2020, 06:47:10 PM »
Even fancy scopes can't magically differentiate between intended cycles and noise spikes when measuring frequency.  They may have a low-pass-filter option to help.  The cleaner gate waveforms appear to report the correct frequency.

37nF (0.22uF / 6) looks like it's hitting your expected frequency well, and the upper halves of the primary voltage appear like inverted sine-waves.  Thus I think that's a good capacitance.  What is the current draw from 12V supply for this 6-series-caps case?  What current draw did 1 and 2-cap cases have?  If the current is low with 37nF (6 caps in series), it may just need more voltage.  The most efficient case may have higher impedance, so need more voltage at less current for the same power.

I also suggest trying phase reversal (switching primary coil leads) again with 37nF.  Now that it's in tune, the optimum may not be the same as it was running at a harmonic.  (With the previous larger caps, the secondary was likely resonating at the 3rd harmonic of primary drive.)

Can you share what information you have for your coils, primary and secondary?  Diameters, heights, number of turns, wire gauge, top load diameter?
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #23 on: November 17, 2020, 08:58:40 AM »
The test at 12V with 1 cap draws @5A, and with 6 caps draws @0.72A. And after i switched the primary it draw @1A, but also the IC gets warm for a few seconds into the test, i am assuming it will get toasty within a minute, but other interesting stuff happened after i flipped the primary, like the frequency shoot up to almost 500kHz. As for the coil, it is almost time to go to work, but i will disassemble the coil tomorrow and measure everything. Also since i had laying around 4 more capacitors, i put those to test as well.


Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #24 on: November 17, 2020, 07:50:51 PM »
Looks like your primary coil was the preferred polarity.  500kHz with the leads reversed isn't useful on this coil.

0.72A at 12V and ~140kHz looks nicely tuned.  The primary is a parallel L/C tank circuit, so will draw minimum current when tuned to the drive frequency.  I recommend leaving 6 0.22uF caps in series and increasing voltage above 12V.  However, the 100V IRFP140 FETs limit input voltage to ~30V.  24 or 30V may be sufficient to get some sparks.  Efficiency will be better this way than 12V and a single 0.22uF cap.

As you can see on the 500kHz gate waveform, the TC4426 is struggling to drive 4 paralleled IRFP140 gates.  At 835kHz it will be worse and get hotter.  It might work at 835kHz driving a single FET.  (If I understand your intent correctly, you are building this slayer circuit as a test for eventual use with your tiny coil.)

To get longer sparks, a Tesla coil needs to be driven for short periods with gaps between each period.  This is what interrupters do.  During each enable period, the power can be higher, as the gaps keep the average power reasonable.  Simple circuits use a 555 for interrupting, pulsing the driver chip's enable pin high for short times periodically.
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #25 on: November 18, 2020, 11:31:52 AM »
Ok, i will try to raise the voltage tomorrow, do i need to protect the input of the IC since it is connected directly with the other end of the secondary ? A zener at least ? Unfortunately this IC does not have an enable pin...i will look for alternatives, and does it has to be inverted ?? i don't quite understand why. and you have the measurements of my coil in the bottom, one thing i forgot to take a photo is the secondary diameter, which is 110mm, same as the inside diameter of my top load.
 

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #26 on: November 18, 2020, 07:48:24 PM »
Do you have a separate 12V supply for the driver chip as shown in the PowerMax slayer circuit you copied?  That is necessary once higher voltage is used for the primary coil.  D1 and D2 are there (one to 12V and one go ground) to protect the driver input.

A non-inverting driver will work fine with reversal of the primary coil leads.

Another option is to keep your existing TC4426 driver and add a PFET between the 555 interrupter and driver input.  I'll sketch a schematic of that option if you are interested.  The PFET would pull the driver input high when disabled, forcing the IRFP140 gates low (off).

Does the foil tape at the bottom of the secondary coil make a full turn?  If so, that shorted turn will load the coil and hurt efficiency.  Similarly, most designs have the top-load spaced above the top of the secondary winding.  Otherwise the top-load also acts as a shorted turn.  That is less of an issue being at the top of the secondary.  A shorted turn at the bottom is more of a problem.  (Is the ring that holds the bottom of the secondary made of plastic or other non-conducting material?  Looks OK, but I can't tell material for sure from images.)

I guessed 72cm as the length of your secondary tube.  Winding appears to start about 2.5cm up, so 69.5cm of winding.  Using that, here's the JavaTC results for your coil.  I adjusted secondary turn count to get resonant frequency close to your 141kHz result, ending up with 2100 turns.  The images suggest finer wire and more turns, but it's hard to tell.  If the bottom tape is making a shorted turn, that would explain some of the difference.

For this 141kHz coil, the standard SSTC 1 circuit you started with should work fine.  So, another option is to go back to that circuit and figure out what was causing issues.  The only reason I suggested slayer was for your 835kHz tiny coil.


J A V A T C version 13.5 - CONSOLIDATED OUTPUT
11/18/2020, 10:45:04 AM

Units = Centimeters
Ambient Temp = 68ºF

----------------------------------------------------
Surrounding Inputs:
----------------------------------------------------
999 = Ground Plane Radius
222 = Wall Radius
255 = Ceiling Height

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
5.5 = Radius 1
5.5 = Radius 2
2.5 = Height 1
72 = Height 2
2100 = Turns
0.025 = Wire Diameter

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
7.6 = Radius 1
7.6 = Radius 2
1 = Height 1
13.6 = Height 2
14 = Turns
0.25 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.037 = Primary Cap (uF)
80 = Total Lead Length
0.2 = Lead Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
140.37 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
69.5 [cm] = Length of Winding
30.22 [cm] = Turns Per Unit
0.08095 [mm] = Space Between Turns (edge to edge)
725.71 [m] = Length of Wire
6.32 [:1] = H/D Aspect Ratio
252.8064 [Ohms] = DC Resistance
52168 [Ohms] = Reactance at Resonance
0.317 [ kg] = Weight of Wire
59.15 [mH] = Les-Effective Series Inductance
70.635 [mH] = Lee-Equivalent Energy Inductance
71.54 [mH] = Ldc-Low Frequency Inductance
21.734 [pF] = Ces-Effective Shunt Capacitance
18.2 [pF] = Cee-Equivalent Energy Capacitance
50.389 [pF] = Cdc-Low Frequency Capacitance
0.2156 [mm] = Skin Depth
14.097 [pF] = Topload Effective Capacitance
309.9564 [Ohms] = Effective AC Resistance
168 [Q] = Quality Factor

----------------------------------------------------
Primary Coil Outputs:
----------------------------------------------------
169.41 [kHz] = Primary Resonant Frequency
17.15 [% low] = Percent Detuned
90 [deg °] = Angle of Primary
668.53 [cm] = Length of Wire
23.48 [mOhms] = DC Resistance
0.65 [cm] = Average spacing between turns (edge to edge)
1.962 [ cm] = Proximity between coils
0 [cm] = Recommended minimum proximity between coils
22.792 [µH] = Ldc-Low Frequency Inductance
0.0539 [µF] = Cap size needed with Primary L (reference)
1.061 [µH] = Lead Length Inductance
373.356 [µH] = Lm-Mutual Inductance
0.292 [k] = Coupling Coefficient
0.13 [k] = Recommended Coupling Coefficient
3.42 [half cycles] = Number of half cycles for energy transfer at K
9.56 [µs] = Time for total energy transfer

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=12, major=34, height=72, topload
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #27 on: November 20, 2020, 09:54:33 AM »
Yes i have a separate power supply for the IC. Yes the foil at the bottom also on the top makes a full turn and is shorted. The wire i used is 0.1mm i removed the tape at the bottom and i made some more solid connections for the capacitors, and i had a big surprise, my frequency on the gate is 44kHz...sometimes i feel i am followed by a curse or something. Can the foil at the bottom have an effect that big ? do i need to start over and find the frequency of the secondary and go trough all the process again ?
If i want to go back to previous circuit for this coil i need to order new IC from China, that was the only place i found them, and i don't fully understand the gate drive transformer, i am walking into 2 unknown territories.

Online costas_p

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Re: mini tesla (hopefully not a fail)
« Reply #28 on: November 20, 2020, 08:31:34 PM »
Hello bogdan,
I am not trying to seem smart or something, but I can say , that I have successfully replicated the 'SSTC on steroids' , with DS0026 (from ebay) and a 240 to 24v transformer, utilizing a voltage doubler for around 71V, also I made the full circuit (with the 555 interrupter) and produces around 5cm sparks at 120W

I am reading and replying from my mobile since I am out of house for the weekend, at Monday I can help you as much as you like about this circuit, and make it work.
Papadakis Costas

Offline plasma

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Re: mini tesla (hopefully not a fail)
« Reply #29 on: November 20, 2020, 09:05:11 PM »
I think 6 caps at 0.72A is good for 12V ,the resistance would be low, like said above more source voltage will mean more circulated current, I'm guessing a Q of 20 for the large inductor minus resistance, you should have 20A if you measure the current between the secondary and top load, measuring the voltage across a 1 ohm resistors should give a value to workout current, the bandwidth should change though, so more source current will be supplied.

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #30 on: November 21, 2020, 02:20:00 AM »
Removing the foil tape will lower frequency, but not from 141kHz to 44kHz.  Perhaps to 120kHz.  Did you remove tape at the top too?  If not yet, I recommend removing top tape and raising the top-load a few cm with some kind of non-conductive spacer.

Was my 720mm secondary height close?  Can you measure roughly how many turns per mm your secondary coil has?  With 0.1mm wire, 7 turns per mm would be reasonable.  That would be about 5000 turns, which might get you close to 44kHz.

I agree that it makes sense to get this slayer circuit working first.  Then you can consider upgrading to the half-bridge version once other issues are resolved.
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #31 on: November 21, 2020, 03:31:31 PM »
Any help is welcomed, i want to understand as much as possible about this resonant frequency and how to troubleshoot the coil. only at the bottom, t the top hopefully i will do in next week, it's a bit more complicated. Measured with a digital caliper and a magnifying glass, your 7 turns/mm was spot on :), with 74cm total height of windings, that would make for 5180 turns...+- a few. So the plan for next week is to remove the top load and put it higher than the last turn, and build a simple slayer to check for new frequency. Am i on the right track ? If the wire is too thin, i have 2 spools of wire, 0.25mm and 0.4mm if you say it will be better i can rewind the secondary with no problem.

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #32 on: November 22, 2020, 12:02:41 AM »
With secondary of 5180 turns and 74cm long, JavaTC estimates 58kHz.  That should be close to accurate once the upper shorted-turn is removed.

Yes, eventually larger wire with fewer turns will be more optimum for that size coil.  That will result in a higher resonant frequency closer to your original 141kHz result.  However, I'd suggest experimenting with this winding before changing.  The lower 58kHz makes debugging drive circuitry a bit easier.

Do you have any sort of signal generator, even a home-made 555 circuit with potentiometer for adjusting frequency?  That's the best way to find secondary resonant frequency.  Connect the bottom of the secondary winding to the signal generator and adjust frequency slowly until a peak in signal amplitude shows up on a scope probe hanging in the air near the top-load.
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #33 on: November 22, 2020, 09:43:41 AM »
Yes, i have a signal generator, up to 2MHz...or so they say, but for my range of frequency should be enough. Ok i will use this method as well to check for the resonant frequency once i lift up my toroid and remove the shorted tape at the top as well. Question, can i use a conductor, like a threaded rod to lift up the toroid, or use some wood or something isolating for the support as well ?

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #34 on: November 22, 2020, 09:09:32 PM »
I've seen a single threaded rod in the middle used before.  Multiple rods could work if they are insulated at one end or the other to avoid making any shorted loops.
David Knierim

Offline bogdan

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Re: mini tesla (hopefully not a fail)
« Reply #35 on: Today at 05:09:54 PM »
So, my mom took care of raising the topload... when she bumped into the coil and it fall down. That reduces the windings to 60cm. the lower foil is gone, the top foil is gone, i now have a bit of pvc pipe between the last winding and the toroid, but i had to turn the coil, since the damage was on the lower part. With the signal generator method i get 3 significant resonances, a small one, at @44kHz, a big one at 138kHz and another one exactly the same at 277kHz. Which one do i choose ?
Since the 138kHz was close to my original 140kHz i said i would give it a try with 12V, i also flipped the primary since my secondary was also flipped after the accident, but it did not liked that, it stayed at 500 and something kHz and did not moved no matter what capacitor i used. So i went with the original orientation of the primary and 5 caps, the results were in 140kHz on the coil, @50kHz on the gate and a current draw of 4A, also a bit of corona forming on the topload. Why is this difference happening, and why is the curent draw so high compared the the old secondary?
Tomorrow hopefully i can get some pictures of the coil and gate frequencies.

Offline davekni

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Re: mini tesla (hopefully not a fail)
« Reply #36 on: Today at 07:35:55 PM »
Removing turns is one way to get space to the top-load:)

Let's figure out the secondary resonant frequency before trying to run the coil.  For that test, leave the primary unconnected.  Otherwise primary resonant frequency will complicate the results.  Can you post scope images of your peaks at 44, 138, and 277kHz?  Some of those may be harmonics from the signal generator.  Can the signal generator be adjusted in steps finer than 1kHz?  The peak at 44kHz might actually be much stronger at 44.5kHz or some other slight change from 44kHz.  The top-load signal picked up by the scope-probe near by should look like a sine wave even if the signal generator output is a square or other wave shape.
David Knierim

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Re: mini tesla (hopefully not a fail)
« Reply #36 on: Today at 07:35:55 PM »

 


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[Dual Resonant Solid State Tesla coils (DRSSTC)]
Mads Barnkob
November 22, 2020, 11:08:49 PM
post Re: mini tesla (hopefully not a fail)
[Beginners]
davekni
November 22, 2020, 09:09:32 PM
post Re: Peak Primary current in small DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
AstRii
November 22, 2020, 06:33:02 PM

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