Author Topic: New small SSTC (Read 15972 times)

Bambinz · « **on:** March 18, 2019, 11:46:18 AM »

Hi all,
First of all I would like to thanks you for any help!

I would like to build a small SSTC in order to obtain a spark length of max 4-5cm. The power supply will be 24V.
The reference project is the followings:

To semplify the discussion you can find below the schematic created by Tefatronix, that I would like to thanks for the availability to support me during the project.

Now, I am build my version of this tesla and works but I obtain a spark of 1cm.
The main difference is that my primary has the followings characteristics:
- Diameter 4cm
- Heigh 6cm
- Wire diameter 0.25cm
- Turns: About 150
I think that the resonant frequency is too high (I have measured it and is about 2.5MHz).
Instead the authors secondary coil has the following dimensions:
- Diameter 3.2cm
- Heigh 5.5cm
- Wire diameter 0.1cm
- Turns: About 550

I think that a resonance frequency so high reduce the overall system efficiency and with high frequency is impossible to obtain ramified sparks. Is it correct?
In addition I have used a IRFP4110 that probably has too high gate capacitance, I have ordered the IRFZ44N.

Another questions: In this type of teslacoil with small size and small supply voltage, which coupling factor I should use? Higher as possible? Like 0.5-0.7 or in any case I should reduce the coupling factor?

Thank you again for your time and help

Bambinz

Mads Barnkob · « **Reply #1 on:** March 20, 2019, 01:23:52 PM »

That is a great little coil to start with, I do not think I ever saw that video before.

You should match the secondary coil specifications, to obtain a similar resonant frequency. Your gate drive circuit will simply not be fast enough to drive those MOSFETs at 2.5MHz and even if it was able to, your MOSFETs would spend too much time in the linear region and the high switching losses generates more heat than you dissipate with a small passive heat sink.

Generally low voltage and SSTC needs high coupling due to the lower peak currents in the primary circuit.

Bambinz · « **Reply #2 on:** March 20, 2019, 03:52:15 PM »

It is possible to trasform this mini-tesla in a DRSSTC by adding a capacitor in parallel to the primary?

Now I have ordered the material necessary to build this little tesla.

Mads Barnkob · « **Reply #3 on:** April 01, 2019, 10:43:53 PM »

Quote from: Bambinz on March 20, 2019, 03:52:15 PM

It is possible to trasform this mini-tesla in a DRSSTC by adding a capacitor in parallel to the primary?

Now I have ordered the material necessary to build this little tesla.

Secondary base current feedback for a DRSSTC was never a success, as you need as close to perfect primary circuit feedback as possible to avoid blowing up your silicon.

Let this circuit be a low voltage SSTC and if you want to build a simple DRSSTC, look at Steve Wards universal driver 1.3b to start with.

Bambinz · « **Reply #4 on:** April 02, 2019, 08:16:49 AM »

Thank you!
Why the base current feedback not work with DRSSTC?

First of all I will test this minitesla, and then I try to implement a DRSSTC with the same secondary to compare the performance

I hope that in the next day arrives the wire so I can start to build the tesla.

Mads Barnkob · « **Reply #5 on:** April 02, 2019, 12:21:17 PM »

Quote from: Bambinz on April 02, 2019, 08:16:49 AM

Thank you!
Why the base current feedback not work with DRSSTC?

First of all I will test this minitesla, and then I try to implement a DRSSTC with the same secondary to compare the performance

I hope that in the next day arrives the wire so I can start to build the tesla.

You do not use the feedback in a DRSSTC to tune the driving frequency to match the secondary circuit, you manually tune a DRSSTC with moving the tapping point for best performance.

You need primary current feedback in a DRSSTC to be able to limit the peak current with a OCD circuit and to obtain the best possible ZCS to lessen losses in the IGBTs.

Bambinz · « **Reply #6 on:** April 02, 2019, 08:26:00 PM »

A ok

Thank you very much.

Now, I will wait the material and then I will update you with my progress

Thank you again!

Bambinz · « **Reply #7 on:** April 06, 2019, 02:56:53 PM »

Questions:
To varnish the secondary coil, could I use vinyl glue (wood glue)? I can made many layer of glue.

Bambinz · « **Reply #8 on:** April 07, 2019, 11:36:26 AM »

There are someone?

AndreiRS · « **Reply #9 on:** April 07, 2019, 09:54:45 PM »

I think that glue is water based. It would be better then to use wood varnish, clear ones without color.

Bambinz · « **Reply #10 on:** April 10, 2019, 03:06:02 PM »

At the end I have used a acrylic transparent wood varnish.
You can find the picture of the secondary below:

I would like to varnish 5-6 layer, now I'am at 4

Bambinz · « **Reply #11 on:** April 16, 2019, 06:45:24 PM »

I have measured the coil:

Without the topload, frequency 1.28MHz

With topload, frequency 1 MHz

Bambinz · « **Reply #12 on:** April 16, 2019, 06:55:02 PM »

Questions: How I must choose the capacity of the topload?
I have used a disk of 7.5cm of diameter.

Mads Barnkob · « **Reply #13 on:** April 18, 2019, 10:28:28 PM »

SSTCs likes big topload, it generally gives larger sparks. But there is a tipping point where it becomes too large a load for the inverter, not something I know more about in detail than that.

I would say that adding a topload that has a major diameter even to your windings length of the secondary and a minor diameter even to the secondary coil diameter will give you a good all-round solution.

Bambinz · « **Reply #14 on:** April 19, 2019, 08:23:49 PM »

Today I have mounted the tesla-coil, but doesn't work

The spark appears only if I bring a screwdriver close the topload. Why?
I have forgot to connect the GND to the earth, this mistake can cause the problem described previously?
The previous version works also withouth the earth connection, but the resonace frequency was very high, therefore I think that probably works like an RF transmitter, therefore the earth connection is not needed.
Unfortunately, this evening and tomorrow I can not work on the teslacoil.

Fumeaux · « **Reply #15 on:** April 19, 2019, 08:53:35 PM »

Quote from: Bambinz on April 19, 2019, 08:23:49 PM

Today I have mounted the tesla-coil, but doesn't work

Quote from: Bambinz on April 19, 2019, 08:23:49 PM

The spark appears only if I bring a screwdriver close the topload. Why?

The spark doesn't have enough voltage to break out itself.

Quote from: Bambinz on April 19, 2019, 08:23:49 PM

I have forgot to connect the GND to the earth, this mistake can cause the problem described previously?

Could be, but probably isn't the reason.

Quote from: Bambinz on April 19, 2019, 08:23:49 PM

The previous version works also withouth the earth connection, but the resonace frequency was very high, therefore I think that probably works like an RF transmitter, therefore the earth connection is not needed.

Can you film it?

Bambinz · « **Reply #16 on:** April 20, 2019, 08:50:54 AM »

Thank you very much for your help!

This evening, probably, I can make some other test and I verify some things.

Can be that the tesla coil not start to oscillate, and when I touch the topload with a screw driver or other type of metallic part start a little and short oscillation?

Bambinz · « **Reply #17 on:** April 21, 2019, 09:39:16 AM »

Now works!!!!
I have made the followings changes:

- Changed the primary, I have used the old primary.
- Increase capacitance C12 from 1nF to 3nF.
- Added a BIG capacitor on the power supply!
- Added the interrupter with a duty-cycle of about 5%

Now the power consumption is about 24V 1A
The results:

I think that with only 24W is a very good results, no?

Fumeaux · « **Reply #18 on:** April 21, 2019, 10:52:08 AM »

Looks good! Maybe when you play around with the value of C12 more, you can get bigger sparks.

Bambinz · « **Reply #19 on:** April 21, 2019, 05:34:09 PM »

trying to fix up the "box" of the teslacoil, ... I have broken the connection between the secondary and the ground (I didn't see before turn on the tesla coil) and one mosfet it died.
Therefore I have unmounted all tesla circuit and remounted with a new mosfet and then the other mosfet it died. Why? Now doesn't works and kill mosfet like Terminator

Why the mosfet die?

High Voltage Forum · « **Reply #19 on:** April 21, 2019, 05:34:09 PM »

Author Topic: New small SSTC (Read 15972 times)

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