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2022-01-22, 14:04:18
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Author Topic: Dally, Shark & Ruslan workbench  (Read 84499 times)

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   So you are saying that the house AC ground and the water pipes are one and the same? Wow, that can change things.
   Got any old radiators, you can bury?  Just kidding...
   

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I was doing some testing on a smaller ferrite gizmo which has a 10:5 turns ratio which i had seen on one of stalkers video's, see picture.

I used the nanoVNA in both directions (10:5 and 5:10) to see if there is a difference, but there is almost none, see screenshots.

It seems that the low pass cutoff is somewhat earlier as the bigger 5:5 ferrite gizmo.


Itsu

   

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It seems that the low pass cutoff is somewhat earlier as the bigger 5:5 ferrite gizmo.
Yes, it acts as a low-pass filter but with a slightly different passband characteristic.
Varying the gap between the two windings changes this characteristic but the electric length (wrt. standing waves) remains largely unchanged, so the nodes and antinodes should stay in the same place.
   

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As mentioned earlier i have reinstalled the Grenade L5 / Inductor L4, but still have removed the ferrite gizmo.

I decommissioned the DECT telephones for the time being to be able to do some measurements.

I still run with continued pulses into the MOSFET driver and optimized the frequency to match the kacher/antenna resonance frequency which at the moment without the ferrite gizmo seems to be 1.5Mhz (45% duty cycle).

Push pull DC output is 213V and lights a 25W bulb.

Kacher output seems better as i can pull 0.4mm purple streamers from a screwdriver.

With kacher active the push pull DC output drops to 209V, so the kacher seems to have some influence.

24V input to Kacher MOSFET pulls about 2A causing the MOSFET to reach about 45°C, but the 2 Ohm drain resistor reach 70° C or so.

Video here:  https://youtu.be/qAQmUmsdPB8


Next video shows some probing using the 2 led / pickup coil (H field) and the neon (E field), but i think the light is to bright for the latter to be seen.

We still have the node somewhere above the middle of the kacher secondary coil.

Video here:  https://youtu.be/ZdgtlMvueIw

Itsu
   

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Hi Itsu,

Please consider following pictures.
First is a battery powered Tesla coil setup. I measured 1-2 amp peak-to-peak current in the ground wire and 50 volts relative to wall socket ground at the circuit common wire.
Second picture for PSU powered setup as I understand it from your description.
My point is that PSU probably creates some unwanted connection in the ground wire.

Regards,
Vasik


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Hi Vasik,

i see what you mean, but the simple 24V switched PS is not connected to ground.

But i can see if i can test with a 24V battery stack.

Itsu
   

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Still without the ferrite gizmo, i captured the FFT output of the kacher signal picked up by the blue probe:
1) when laying close by the top secondary, see screenshot 1, and
2) when laying close the the Antenna end, see screenshot 2

It shows a difference in cleanliness of the both signals already (base signal at 1.55MHz).

Almost no harmonics on the secondary kacher signal (the blue picked up signal seems lower in amplitude and more erratic).
Clearly visible harmonics at 3.1 (2nd), 4.65 (3rd), 6.2 (4th) and 7.75MHz (5th).


Will see if the ferrite gizmo has any influence on both the output of the kacher and the cleanliness of the picked up signals.


Itsu
   

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I re-installed the ferrite gizmo and toke similar readings as yesterday when without it.

I had to re-tune the pulse frequency to get max. amplitude, its now somewhat lower then yesterday (1.44MHz).

Below screenshot 2 show that the FFT signal has less harmonics visible, so it looks like the ferrite gizmo is indeed functioning as a low pass filter.

Output of the kacher looks the same as i still can pull some 0.4mm purple streamers from secondary / antenna.

Itsu

   
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Hi All,
Things are beginning to move forward here.
The kacher was resonating too low in frequency so I removed a few turns and it is near the 1.2 which will be altered later if required.
Powering it with a cmos oscillator and fet at 12 volts supply it produces a 10mm arc.
The driver coil is a few turns thrown together so this will need to be replicated shortly. Its quite sensitive to the driving frequency which indicates a reasonable Q factor.
I'll put some pics up once it's a completed unit.
   

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Powering it with a cmos oscillator and fet at 12 volts supply it produces a 10mm arc.
10mm with 12V. I think that's more than Nick got ...and Itsu.

I look forward to seeing your primary current waveforms as well as coil geometry details and grounding layout.
Also, please put a neon bulb on a stick like Itsu has done here and show us the E-field nodes along the coil and ground wiring.

Schematics don't interest me much, ...unless they have a novel FM and PM block.
VSWR interests me a lot, though.
   

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I had to re-tune the pulse frequency to get max. amplitude, its now somewhat lower then yesterday (1.44MHz).
I think that's because the gizmo contains much longer wire than its substitute.

...so it looks like the ferrite gizmo is indeed functioning as a low pass filter.
The turn direction reversal between the TC/Kacher secondary and the aluminum antenna should suppress the higher overtones, too (see this).

If making another aluminum wire antenna is not difficult for you, you could demonstrate this effect to yourself and others by making another coil-antenna with the opposite direction of turns ("opposite" to the direction you have now, even if it is inferior) and comparing the overtones to the case with the other coil-antenna (identical in all respects except the direction of turns).

P.S.
I am using the word "overtones" and not "harmonics" on purpose. This is because the helical secondaries of Tesla coils do not propagate all frequencies at the same speed :o.  This is known as a dispersive propagation media.  Because of this, the overtones do not occur at exactly the multiples of the fundamental frequency.  If they did - I would call them harmonics.

   

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Hi All,
Things are beginning to move forward here.
The kacher was resonating too low in frequency so I removed a few turns and it is near the 1.2 which will be altered later if required.
Powering it with a cmos oscillator and fet at 12 volts supply it produces a 10mm arc.
The driver coil is a few turns thrown together so this will need to be replicated shortly. Its quite sensitive to the driving frequency which indicates a reasonable Q factor.
I'll put some pics up once it's a completed unit.

Hi szaxx,

thanks for the update, sounds good, looking forward to some pictures.

Do you have a ferrite gizmo and antenna attached to the kacher secondary?

If not, the 1.2MHz sounds really low as my kacher resonates at around 2.5MHz without them.
Also the ferrite gizmo and antenna will dampen the output (lower the Q?).

Thanks,  itsu
   

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I think that's because the gizmo contains much longer wire than its substitute.
The turn direction reversal between the TC/Kacher secondary and the aluminum antenna should suppress the higher overtones, too (see this).

If making another aluminum wire antenna is not difficult for you, you could demonstrate this effect to yourself and others by making another coil-antenna with the opposite direction of turns ("opposite" to the direction you have now, even if it is inferior) and comparing the overtones to the case with the other coil-antenna (identical in all respects except the direction of turns).

P.S.
I am using the word "overtones" and not "harmonics" on purpose. This is because the helical secondaries of Tesla coils do not propagate all frequencies at the same speed :o.  This is known as a dispersive propagation media.  Because of this, the overtones do not occur at exactly the multiples of the fundamental frequency.  If they did - I would call them harmonics.


I think your link is not going where you want it to go.

I have some aluminum wire for the antenna left, so i could make another one with opposite direction.

Thanks for the harmonic versus overtone description, i did not notice any difference in the frequency of the multiples of the fundamental yet.

I wonder how to measure the VSWR of a tesla coil, or should it be calculated?


Itsu
   

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I think your link is not going where you want it to go.
Where does it go to ?
   

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OK, it attached a PDF in the background, got it.

Itsu
   
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Hi szaxx,

thanks for the update, sounds good, looking forward to some pictures.

Do you have a ferrite gizmo and antenna attached to the kacher secondary?

If not, the 1.2MHz sounds really low as my kacher resonates at around 2.5MHz without them.
Also the ferrite gizmo and antenna will dampen the output (lower the Q?).

Thanks,  itsu


Not yet, I have ferrite rods from radio's and a couple of the required mains filter type, one of these  I'll wind once recovered. I'm currently looking for aluminium wire and may have to buy some more.
The frequency will drop and I'll remove turns to compensate once it's all put together.
In the meantime I'm waiting for the regulators hence 12 volt testing.
I hope the arc is good too once assembled. I'll test this without the kacher and see how it performs. Maybe a photo too with a few scope shots.
   

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I toke some days off from the bench to enjoy the summer season, and will be doing so probably the next weeks from time to time.

Meanwhile i have changed the kacher MOSFET driver to handle higher voltages by using a 1.2KV MOSFET NVH4L160 and ditto drain diode C4D02120A.
Still the drain source 440V TVS KE440CA is installed as is the 18V TVS from gate to source.

Voltage on the drain is increased to 93V and with 4 pulses duty cycle i have the below screenshot 1 antenna output signal (blue) and drain signal (yellow).

We still see the steady state increase during the pulsing, but it fairly quickly drops down somewhat again, see screenshot 2

The antenna shows a moderate 0.2mm sparks pulled from a screwdriver.


Itsu
   

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   Do you notice any interaction with the induction circuit, yet? Hand movements on the antenna, ringing noises, etc...
   

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No, things are fairly stable, just some stinging when touching some metal nearby.

Itsu
   

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We still see the steady state increase during the pulsing, but it fairly quickly drops down somewhat again, see screenshot 2
This means that you have high energy loss per cycle (low Q).
This can be caused be variety of factors, i.e.: wire insulation dielectric properties, carcass dielectric loss, the TVS dissipation, high primary to secondary coupling coefficient (k), etc...

If you count the full cycles of the oscillations after the primary driving pulses stop but before the secondary's oscillations amplitude decays to 4%, then you will obtain the numerical value of the Q.
« Last Edit: 2021-08-17, 13:18:25 by verpies »
   

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Thanks, "the TVS dissipation" may be a good candidate to do check on.


Itsu
   

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So what is your Q if you count the cycles according to Fig.12.8 ?
   

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Quote
So what is your Q if you count the cycles according to Fig.12.8 ?

Looking at the screenshots in my post #1769, i count roughly 14 full cycles after the primary driving pulses stop but before the secondary's oscillations amplitude decays to 4%  which means a Q of 14.

But i will double check that again.

Itsu
   

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Here another screenshot 1 with both the drain pulses (yellow) and picked up antenna signal (blue).

There are roughly 22 full cycles between the last drain pulse and the 4% of 355Vpp = 14Vpp ringing signal.

So here the Q would be 22, but the length of the ringing and the fluctuating of that ringing in the lower parts can be influenced by several things like moving the primary etc.


So the Q of the kacher / antenna system would be between 10 and 20.


But i understand from the massive amount of info given by Vasik that the kacher signal as being picked up should look like the screenshot 2 below.
So very little ringing, only 4 or 5 full cycles.

This points then to a very low Q coil or could this capping off of the ringing be done be some other means?

Itsu
   

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The only way of discovering the limits of the possible is to venture a little way past them into the impossible.
   
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