Attempting the Kaizer sstc II

[CCX191]

First of all I would like to thank Mads for sharing this circuit out and also inviting me to this forum.

It has been about 3-4 days of building the circuit. I have very minimal understanding on circuitry/ electronics so I will be posting some of my progress here and some questioning.

My first question might be quite stupid but.. how do I power the circuit? I have done the entire driver except the bridge and would like to test my GDT. At which point where my power is supposed to be connected?

At the image attached is the circuit so at the top left I can understand that I will put in 12VDC and the ground as negative. So how about the arrows pointing upwards with 12VDC do I put in 12v in there too? And then the ground arrow at the interrupter is where I connect my negative?

[futurist]

Connect the driver to 12 V like you wrote, the driver and bridge are powered independently and you can test the driver without the bridge
Keep in mind that you have to have GDT connected, otherwise you'll blow up the MOSFET drivers

[CCX191]

Thanks! So does that mean I put in 12v on the part where there's an arrow pointing upwards with 12v?

[futurist]

Yes
How do you plan to test the driver?

[Mads Barnkob]

All arrows pointing up with a voltage reference, if the number is the same, they share the same supply, it is just to make it easier to draw the schematic without too many crossing lines

As futurist points out, it is important to have a load connected to the MOSFET driver ICs, if they are running open loop they can oscillate at a very high frequency and burn themselves down. Connect the GDT and also connect the MOSFET gates to the secondary side of the GDT, this way you will have a more realistic waveform to check.

I normally use a simple 555 timer or a signal generator for the feedback circuit/antenna to test the driver alone.

[CCX191]

Ah thanks! I just burnt my UCC3732Xs so I guess I will get back when I get my replacement

Edit: And also does that mean the interrupter does not require another power in?

[Mads Barnkob]

Ah thanks! I just burnt my UCC3732Xs so I guess I will get back when I get my replacement

Edit: And also does that mean the interrupter does not require another power in?

I had it all mounted in the same enclosure, as you can see in the pictures on my website, they shared the same 12V 2000mA power supply.

[CCX191]

Would putting in 12v 10A work then? I can't risk another set to burn down it's very costly here

[futurist]

Power supply has to be DC, and if it is, 10A rating will be more than enough

Don't worry about blowing up components, it happens to everyone - doublecheck your connections before powering anything
Also be very careful when powering the bridge with mains power, it is deadly

I would buy few spare UCCs, they are not that expensive
https://www.aliexpress.com/item/Free-shippin-5pcs-lot-UCC37321P-UCC37321-DIP-8-Bridge-Drivers-new-original/32553627093.html

Do you have an oscilloscope available?

[CCX191]

I have bought some spare UCC37322 from AliExpress last week but not UCC37321 yet but as far as getting from Farnell(element14) it costs 3x more and I can get them within two days  Yes I do have an oscilloscope but it's those cheap DSO138 oscilloscope kit which I think might work.

Edit: I have two bridge rectifiers, GBU1004(400V 10A)& KBPC3504(400V 35A) and I've ordered a 1500uf 450v capacitor which one should I use? And the variac used is 2000W.

[Mads Barnkob]

Unfortunately the UCC driver ICs are expensive, but they are also some of the best that was available when Steve Ward made the universal driver 1.3, maybe there are better and cheaper alternatives today, but just not pin compatible, one of the costs lies in the enable input, not all drivers got this.

The DSO138 has a low sampling rate and should not be used for signals over 100 kHz, so it has some real limitations, but it is also cheap, but you should be able to build a SSTC with help from it

I suggest that you use the 35A bridge rectifier, because of the poor power factor of a SSTC, the 10A might get too hot.

Variac is perfect, variacs can even be overloaded by 300% for some minutes

[CCX191]

While I wait for my variac, capacitor and UCCs to arrive I've decided to use a metal box (painted) to house everything. I suppose I have to avoid the the Tesla coil from striking it's driver & bridge  and from it's the EM field So I assume that everything should be insulated. Is there anything I should be aware on the enclosure? Like grounding and etc.

In Mads post I see that there is a metal sleeving on the secondary and another wire, is it due to the fact that one connects to mains ground and the other to "ground" or the striking rod?

I also have some questions regarding the audio interrupter. I see that it uses a 9v supply which I assume I can get a separate power source or a step down circuit for that right?


Edit: Does polarity matter in the GDT? If so how do I determine :/

[Mads Barnkob]

While I wait for my variac, capacitor and UCCs to arrive I've decided to use a metal box (painted) to house everything. I suppose I have to avoid the the Tesla coil from striking it's driver & bridge  and from it's the EM field So I assume that everything should be insulated. Is there anything I should be aware on the enclosure? Like grounding and etc.

In Mads post I see that there is a metal sleeving on the secondary and another wire, is it due to the fact that one connects to mains ground and the other to "ground" or the striking rod?

I also have some questions regarding the audio interrupter. I see that it uses a 9v supply which I assume I can get a separate power source or a step down circuit for that right?


Edit: Does polarity matter in the GDT? If so how do I determine :/

You should ground everything to the same ground point, in a star ground manner, just google "star ground".

It is correct that I had a black wire going to house mains ground, but today I would not do that again! The copper mesh sleeves goes to a strike target that I used for measuring spark length, so it is just everything grounded together. I believe its better to make a artificial ground from aluminium foil, kitchen foil, to cover a whole table where the Tesla coil stands on top, instead of using house ground.

I think I just used a 7809 regulator for the audio interrupter supply. From the 12VDC supply for everything else.

Polarity is very important in a GDT, its a regular transformer. You need to drive the MOSFETs with opposite polarity to make it switch any current into the primary circuit. Before you wind the transformer, mark all the wires black in the same end, then when you twist the individual wires to a stand-alone winding, you have a black mark on one of the ends.

If you take a look at my DRSSTC1, you can find this picture of the GDT:

[CCX191]

Thanks, that was very insightful!  Time to redo my GDT and purchase a LM7809. I just completed my full bridge and I'm wondering what's it meant by resistive load on the GDT? Like for testing the GDT waveform.I understand I cannot simply just power it to avoid it from oscillating to death as to what happened on my first attempt and even for you on the Kaizer SSTC-1. Can I just simply connect it to the bridge and power it on without the bridge being powered? And as for the polarity of the GDT, the positive end for the primary would be the one that's connected to the cap(C4)?

Hopefully my variac can arrive by this week 

Edit: Just redid my GDT

And oh how do I enable CW mode? By simply detaching the interrupter and put in 12V ?

[Mads Barnkob]

Yes, you can test the driver with MOSFETs connected to the secondary side of the GDT and with no power on the bridge. That is better than making a resistive load on the GDT just for testing.

Polarity of the primary side of the GDT does not matter, it only matters that the polarity of the MOSFETs are opposit so that it switches the correct MOSFETs on to lead current through the primary coil.

I know I wrote on the schematic that disconnecting the interrupter made it run in CW mode, but other people have had problems recreating this behavior, so to run CW mode you have to keep the UCC driver ICs enabled, check the datasheet of your drivers if you have to pull it to GND or +12V to keep them on all the time.

[CCX191]

So.... I got it to work for a short bit... And the .68uf caps on the full bridge started to burn down as I increase the voltage... Anything I did wrong here?..

Here's a picture.. am I even using the right capacitors?

[Mads Barnkob]

You actually managed to blow up the DC blocking capacitor in series with the primary circuit?

It looks like a regular MKP (polypropylene) capacitor, which is the right type to use, but it is rather small.

It is very hard to see in your picture what is what, could you please upload some more detailed pictures of your whole setup, test and coil etc.

[CCX191]

Uh.. I have taken it apart but I will try to get some pictures

This is how the whole driver + bridge looks like without the capacitor attached yet


This is kinda how my bridge looks like

[Mads Barnkob]

Your heat sinks are floating at MOSFET Drain potential, if they touch each other you will have short circuits or other conditions where your bridge will not be able to oscillate properly. So if they are all mounted on those two steel bolts going through the side of the box, that is your first problem to fix.

Also, ground that box as the first thing, to save yourself from getting shocked if there is any other wrong wiring.

[CCX191]

What do you mean on the floating heatsinks? The mosfets are already insulated with insulator sheets and I have checked that there is no current flowing through the heatsink so I assume they are fine? And the box is already grounded through the screws of the power supply so I guess it's quite safe?