High Voltage Forum

Tesla coils => Solid State Tesla Coils (SSTC) => Topic started by: Bambinz on March 18, 2019, 11:46:18 AM

Title: New small SSTC
Post by: Bambinz on March 18, 2019, 11:46:18 AM: Hi all,
First of all I would like to thanks you for any help! ;D

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.
(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2Ftefatronix.g6.cz%2Fimages%2Fsstc4_schem.png&hash=b6db99e68480d14b6472722a3e6a0f39d0e2d601)

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
Title: Re: New small SSTC
Post by: Mads Barnkob 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.
Title: Re: New small SSTC
Post by: 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. ;D
Title: Re: New small SSTC
Post by: Mads Barnkob 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. ;D

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.
Title: Re: New small SSTC
Post by: 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.
Title: Re: New small SSTC
Post by: Mads Barnkob 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.
Title: Re: New small SSTC
Post by: Bambinz 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!
Title: Re: New small SSTC
Post by: Bambinz 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.
Title: Re: New small SSTC
Post by: Bambinz on April 07, 2019, 11:36:26 AM: There are someone? ;D ;D
Title: Re: New small SSTC
Post by: AndreiRS 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.
Title: Re: New small SSTC
Post by: Bambinz 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:
(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2Fi63.tinypic.com%2F2w2luu0.jpg&hash=4741be4dc76aca3d3ba84f34109e920fd6b76bae)

I would like to varnish 5-6 layer, now I'am at 4 ;D
Title: Re: New small SSTC
Post by: Bambinz on April 16, 2019, 06:45:24 PM: I have measured the coil:

Without the topload, frequency 1.28MHz
(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2Fi63.tinypic.com%2F1zdql8j.jpg&hash=5f59eeec572a94d883cfca9ebc85d292801e82d7)

With topload, frequency 1 MHz
(https://highvoltageforum.net/proxy.php?request=http%3A%2F%2Fi68.tinypic.com%2F15ejyhl.jpg&hash=d597ea49c629526feb89e906059ec9094ce786ec)
Title: Re: New small SSTC
Post by: Bambinz 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.
Title: Re: New small SSTC
Post by: Mads Barnkob 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.
Title: Re: New small SSTC
Post by: Bambinz 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.
Title: Re: New small SSTC
Post by: Fumeaux 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?
Title: Re: New small SSTC
Post by: Bambinz 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?
Title: Re: New small SSTC
Post by: Bambinz 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?
Title: Re: New small SSTC
Post by: Fumeaux 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.
Title: Re: New small SSTC
Post by: Bambinz 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?
Title: Re: New small SSTC
Post by: Bambinz on April 21, 2019, 08:59:56 PM: News, now works, bad but works xD
The problem was the layout, I have made some connection too long duringe redesign (The connection between the capacitor and the primary coil). Now I have shorted all connection (are shorter also respect the first version). In addition, now the coil is above the coil and not away like in the version of the video.

However now I obtain a little spark and absorbe very high current, about 5-6A. Probably is due to the poor tuning of the C12 because I have used the old capacity, but the inductance of the connections and the parassitic capacitances are varied due to the change of layout.

Tomorrow I continue with the test!

Thank you very much !!!
Title: Re: New small SSTC
Post by: Bambinz on April 23, 2019, 08:18:17 PM: Now work like in the first video, little bit better.

I have noticed that without interrupt the coil produce only 3mm-4mm of spark and consume a lot of current like 7-8A. The coil work very well with a low duty-cycle (betwen 0-10%).

I think that is due to the very low inductance of the primary coil (Only 1 turns) that results in an high peak-current because the reactance at the risonance is very low.

I think that this mini tesla coil work very well because:
1. Low inductance of primary coil = High primary current and High ratio L2/L1 -> Higher voltage gain
2. Very high coupling, probably will be in the range of 0.7-0.8. Therefore results in a very high efficiency and then the high coupling not cause problem because we use small power.
Title: Re: New small SSTC
Post by: Bambinz on April 24, 2019, 11:48:59 AM: Today I have start-up again the tesla-coil without change anythings and .... MOSFET it dies :(

Therefore I have decided to reproject the driver, the new versions will be base on the the leonsocean schematic: https://www.loneoceans.com/labs/sstc2/ but with some modifications.

- 1) The secondary will be the same
- 2) The primary will have the same size and 1/2 turns (not 1+1 because will be used an half-bridge driver)
I will use an high coupling and a very low primary inductance to have an high voltage gain and an high primary current. I think that is the key to obtain a good spark from this small
teslacoil
- 3) Use an STM32F1 to control all the system
- 4) The inductance of the primary will be in the range of 0.1uH -> At 1 MHz will be a primary reactance of 1 Ohm, therefore with 24V of supply will obtain like 24A that is to mouch, therefore I
will limit the duty-cycle to about 10% to have an RMS current in the range of 2-3A maximum.
- 5) I would like to add a mosfet protection(Snubber and short-circuit protection) to not kill to many mosfet xD
- 6) Use a better mosfet that support higher voltage, to prevent the destruction. Therefore the driver will be drive an high capacitance mosfet respect the actual mosfet.

Other suggestions? Can be works?
Title: Re: New small SSTC
Post by: Bambinz on April 28, 2019, 08:30:39 PM: I'am starting to project the new tesla-coil driver with some interesting features.
If you want and if you are interested I can open new thread with the description, schematic, layout and the software.
Title: Re: New small SSTC
Post by: Mads Barnkob on April 29, 2019, 10:43:03 AM: Quote from: Bambinz on April 28, 2019, 08:30:39 PM
I'am starting to project the new tesla-coil driver with some interesting features.
If you want and if you are interested I can open new thread with the description, schematic, layout and the software.

Yes, please do start a new thread for a new project, instead of updating your first thread :)
Title: Re: New small SSTC
Post by: Roit on September 24, 2019, 03:53:08 PM: Hi

I hope it's okay to ask a question. I've built the same coil but haven't been able to test it yet, my problem is getting the Hex code down on Attiny13. i have tried with arduinoisp unsuccessfully. How did you program your chip?
Title: Re: New small SSTC
Post by: Bambinz on April 18, 2020, 04:18:10 PM: Hi all,

The minitesla still working ;D
Now I would like to do a PCB to minimize the parasitic inductance!
Instead of driving the mosfet with the feedback transformer, can I use a gate driver ic like the UCC27425?

I would like to try to do use this system: https://www.loneoceans.com/labs/sstc2/sstc2schematicv10.jpg but to drive the push-pull configuration. To reduce the number of components :D

In addition I have realized the configuration in the link with a bigger coil, but with a 50W transformer (24VAC 2A) I obtain only spark of about 3-4cm. Probably due to the low input power :D
Title: Re: New small SSTC
Post by: Mads Barnkob on April 22, 2020, 09:10:39 AM: Quote from: Bambinz on April 18, 2020, 04:18:10 PM
Instead of driving the mosfet with the feedback transformer, can I use a gate driver ic like the UCC27425?

I would like to try to do use this system: https://www.loneoceans.com/labs/sstc2/sstc2schematicv10.jpg but to drive the push-pull configuration. To reduce the number of components :D

You need the GDT (gate drive transformer) between your UCC driver and the MOSFETs for isolation between logic and power sections. If you want to omit the GDT, look into "high side mosfet drivers", but that is often more complex than a simple passive component like a GDT.
Title: Re: New small SSTC
Post by: Bambinz on April 24, 2020, 10:25:44 PM: Quote from: Mads Barnkob on April 22, 2020, 09:10:39 AM
Quote from: Bambinz on April 18, 2020, 04:18:10 PM
Instead of driving the mosfet with the feedback transformer, can I use a gate driver ic like the UCC27425?

I would like to try to do use this system: https://www.loneoceans.com/labs/sstc2/sstc2schematicv10.jpg but to drive the push-pull configuration. To reduce the number of components :D

You need the GDT (gate drive transformer) between your UCC driver and the MOSFETs for isolation between logic and power sections. If you want to omit the GDT, look into "high side mosfet drivers", but that is often more complex than a simple passive component like a GDT.

I want to use the Push-pull configurato, therefore the two mosfet is refered to ground. In this way I Can drive it with the ic, no?

EDIT:
I would like to increase the power of the mini SSTC. I have a transformer of 150VA 2x15V.
I have think at two topology, half-bridge with voltage doubler like the loneoceans configuration to have +-42V on the inductor.

Or a push-pull with a voltage doubler to have +-80V on the inductor. The advantage of the push-pull is that doesn't require the GDT and I will have higher voltage but the layout is more more critical.

Which configuration is better for my application?
Title: Re: New small SSTC
Post by: Magneticitist on April 27, 2020, 03:48:34 AM: This is a really cool coil that got me into that circuit a little while ago. I haven't tried making anything as small as his but I've had some pretty cool setups using the mosfet stage alone. The long arcs only occur when biasing the fets just right and getting the GDT just right. Doing initial research on coiling I wouldn't have thought something like that would be able to operate so clean just from a little GDT and no gate drivers. I've made several of them without replicating the Skori or Tefatronix circuits exactly but I've noticed the push-pull stage in general is a pretty handy way to drive pretty much any small coil so long as the high currents are kept in mind. I've tried even IRFP250's with what I consider some success and even have a couple that use pulled 1:1's as GDT's. The interrupter is pretty essential but I find running some of them from around 15-20v continuous to be manageable for short periods pulling hot arcs. To get anything close to a 6 inch discharge I need to run them at 24v at least but really closer to 30v or 35v is where I like. I also had one which ran beautifully from 2.5v and under lighting floros quite nicely from a good distance, something like close to 3 feet and at that voltage it pulled about an amp. It was using IRFZ44N's which is actually what Tefatronix ended up using in his finalized build, not the logic levels IRL's. Someone had commented to me that he tried the same setup with similar goals as yours in mind and while I'm not sure where he ended up he told me he was able to drive it at around 100vdc by adding more turns to his primaries. The GDT is of course the critical component here being that it's doing all the high speed switching work.

My most successful test build ran at about 1.4mhz and crapped out on me due to the GDT arcing at the windings, the downside of using a pulled 1:1 with thin insulation and not running the thing legit grounded. It gave me about 6 inch discharges with the right topload and interrupting from 33v and I could actually run it from a little boost module from a 12v lithium pack. I learned that was a bad idea later when the little 35v output caps on the module popped. It was very simple though.. just the two 250's, couple 15v zeners, a 10K pot, one cap, and the GDT. With something like a 3x2.5 inch coil it pulled about 3-4A at 12v with a relatively loose primary coupling. Pulling arcs would bring it to 10A or so, nice hot yellow ones. The tight primary coupling is something I just haven't been able to do because I can't insulate it from the secondary well enough at voltages exceeding 24v or so. The arcs WILL find a way through or around without an extremely effective insulation. Only enough air space seems to do the trick along with some insulating. I ended up turning that build into one which gave a nice little decent bushy CW discharge with some power to it at about 30V 5A.

The only difference in how I run mine is that I started off using a master PWM which drives the circuits instead of interrupting them by pulling the gates low. I use a TL494 to get variable frequency and duty and inject audio signals into the coils through that. My favorite one now is one almost identical to the one which crapped out, and I've been using it for wireless transfer testing after noticing I was accidentally transmitting to a nearby coil on my table. I couldn't figure out why my coil sounded like it was arcing somewhere in the circuit instead of out at the breakout point until noticing the small spark coming out of the nearby coil. It will drive a 12v automotive blower wireless pretty good from around a foot away at around 30-45watts.

Right around when I was really starting to get into trying to build a better one I started getting into the Steve Ward circuits and got lost in trying to troubleshoot my way through his Mini SSTC.