Kaizer DRSSTC VII

This is a summary of the whole project from design, to building and to test the “10 minute design DRSSTC Tesla Coil”. This article will eventually be populated with the information, from the underlying posts of design and building progress.

• Designing: Designing A Complete DRSSTC Tesla Coil In 10 Minutes
• Building part 1: Building the 10 Minute DRSSTC Part 1: Finding the Components
• Building part 2:

Introduction

The idea to design a DRSSTC dates back to 14th February 2021, following a brainstorm session on what projects/videos to make, it did however strand on my TODO list for quite some years. The design video was recorded on the 8th February 2026, almost 5 years after the idea was scribbled down!

Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

Read this document about safety! http://www.pupman.com/safety.htm

Specifications

	Description	Amount
Supply voltage	230 VAC ~ 320 VDC
Bridge topology	Full-bridge 2x parallel PCB	1
IGBTs	TO-247, 40N60, 600 V, 80/120 A	8
Rectifier	25 A full-bridge	1
Driver	UD2.9 pulse skip PCB	1
Interrupter	555 timer based PCB	1
Secondary coil	230 x 75 mm, 1000 windings, 0.2 mm	1
Topload	300 mm major, 75 mm minor diameter	1
Resonant frequency	Around 300 kHz
Primary coil	4-5 turns of 5 mm copper brake line	1
MMC	CJE 0.1 uF, 3000 VAC, 80 A MKP capacitor	1
DC bus capacitors	1500 uF, 450 VDC, electrolytic capacitor	6
Snubber capacitor	2.2 uF, 275 VAC / 450 VDC, MKP capacitor	1

For indepth knowledge on Tesla coils and DRSSTC in particular, I recommend reading the entire guide: https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/ For the purpose of this video / project, to design something really fast, I will skip to selected parts of the guide.

A Tesla Coil is primarily defined by its secondary coils characteristics. So the first goto is the DRSSTC Design Guide part on secondary coils: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/secondary-coil/ and scroll to the header “How to find the right secondary coil size and ratio”, select a size suitable to your needs and available components. Scroll further down to “How to find the right secondary coil wire size and number of turns” for selection of impedance, according to chosen wire size and number of windings. I chose a secondary coil with diameter of 75 mm, 1000 turns of 0.2 mm diameter copper wire, resulting in a winding that is 220-230 mm long.

The easy way to choose a toroid topload, that I find to have the “right” proportions”, is to use the secondary coil dimensions for the topload as well. Secondary coil diameter = topload minor diameter and secondary winding length = topload major diameter. I chose a toroid topload with minor diameter 75 mm and major diameter 300 mm.

Calculate the toroid topload capacitance: https://deepfriedneon.com/tesla_f_calctoroid.html which comes out to 13 pF.

Verify your secondary coil numbers in the helical coil calculator and use the topload capacitance to get the resonant frequency of the secondary system: https://kaizerpowerelectronics.dk/calculators/helical-coil-calculator/ . Resonant frequency comes out very close to 300 kHz.

I wanted to use the DRSSTC PCB pack from profdc9 ( https://highvoltageforum.net/index.php?topic=353.0 ), as it contains interrupter, UD2.7c and UD2.9 drivers and 4 different bridge layouts. I went with the largest, full-bridge of parallel TO-257 IGBTs.

Choose an IGBT. Follow the guide for the complex calculations or rip it with finding a IGBT with similar ratings to 40N60 for TO-247 devices (400 A) or if choosing bricks, you can go with 2-3 times its pulsed current rating as your maximum design goal. I want to use a full-bridge of parallel IGBTs, so I bump my peak rating up to 600 A. With parallel devices, you can never assume do double the current handling, due to possible uneven current sharing.

Select a resonant capacitor size, also called a MMC, if its constructed from multi mini capacitors. https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/mmc-tank-capacitor/ scroll down to “How to choose the value of the MMC capacitance?” and find a suitable range for the size coil you went with for the secondary coil. Low capacitance equals high impedance, long on-time, thinner sparks, higher losses and cheaper construction. High capacitance equals low impedance, short on-time, thicker sparks, less losses and expensive construction. I chose to go with 0.1 uF

Select a primary coil size, I have prior used 2.5 mm² copper wire for a small tesla coil and 10 mm copper pipe for the DRSSTC 1. Seemed reasonble to go with something in between, like copper brake line that is 3/16″ / 5 mm in diameter. Use the Spiral Coil Calculator ( https://kaizerpowerelectronics.dk/calculators/spiral-coil-calculator/ ) to find the outer/major diameter and to check windings needed to hit a resonant frequency where it can be down to 10% lower than the resonant frequency of the secondary circuit. More turns = lower resonant frequency.

Use JavaTC ( http://www.classictesla.com/java/javatc/javatc.html ) to calculate the tuning point, by entering all the above numbers and design parameters from the chosen parts. I ensure to have 20-30 mm free space from secondary coil to primary coil. Distance between primary coil turns should be sufficient for tap point to not short circuit two turns. Let the primary coil sit a bit lower than the secondary coil winding start, to have a good coupling start point. The closer proximity, the better energy transfer, but also higher risk of flash-over that will destroy secondary coil. Use the Auto-tune to find the resulting primary inductance. Is this case its 3.3 uH.

Design the MMC with MMC Calculator ( https://kaizerpowerelectronics.dk/calculators/mmc-calculator/ ) and enter the resonant frequency and primary inductance from JavaTC. Enter the peak current, on-time and BPS as your design limits or worst case scenario. Choose a capacitor or enter data from your own. Use the capacitors in series to get higher voltage rating, use the strings in parallel to get better current handling. Now find a amount of capacitors where temperature rise, voltage handling and both peak and RMS current is within recommendations in the calculator.

DC bus capacitors can now be found ( https://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/dc-bus-capacitor/ ) Find a suitable DC bus capacitor and capacitance from calculating the inverter ripple and RMS current demands. Needed capacitance can be found from a MMC burst energy estimation and to keep a ratio of 20-50 times higher to the DC bus capacitance, to avoid excessive voltage sag during bursts of long sparks. Scroll down to “Calculating the ripple current and RMS current” and enter your design limit parameters and supply voltage. I will go with 320 VDC, from rectified 230 VAC mains. 200 us on-time and 200 BPS, at 280 kHz and 3.3 uH primary inductance, results in worst case 14 A ripple current and 5 A RMS current.

Scroll further down to “DC bus capacitance needed in regard to expected performance of the DRSSTC” and calculate the MMC burst energy from your design parameters. I would have around 12 joule burst energy in my 0.1 uF MMC. A 4700 uF / 450 VDC electrolytic capacitor stores 240 joules and there is thus a ratio of 20. This will work, but using two of these very standard sized power electronics capacitors would give a ratio of 40 and smaller capacitors to suit the above peak / RMS current demands could be easier met.

Schematics

The UD2.9 through-hole pulse skipping driver and dual TO-247 IGBT full-bridge PCB originates from the profdc9 DRSSTC PCB package that is freely available with schamtics, project files, bill og materials and gerber files here: https://highvoltageforum.net/index.php?topic=353.0

Construction

Firstly choice of materials, was aimed to be ones that are widely available and non-excotic, in order for most people to be able to build this project. Secondly choice of materials was to be something that I already have in my posession. This is to use some of all the stuff I have saved through the years, to promote repurposing and not just support the buy-new-culture every time a single piece is missing, better to find a free alternative. The different choices are described above and finding them is shown in the Part 2 video.

15th March 2026 to 12th April 2026 was spend finding components I already owned, sourcing materials needed and placing orders for the rest.

DRSSTC Components

The drivers and interrupters printed circuit boards were ordered from a PCB manufacturer, by using the free gerber files in the DRSSTC PCB package. Quality is very good. Silkscreen has no errors or missing prints. Feed-through sticking between layers is perfect as well.

The secondary coils do feel a bit thin, with only two layers of thin varnish. It is not a thick layer of heavy flowing polyurethane, feels like its spray on varnish. The wire is secured in both ends with electrical tape, which makes no difference for operation, but does not look great. I did not try out the mounting set and topload holder yet.

The toploads are very high quality! Very thick material, so very sturdy and resistant to bumps and dents. There is however only the center hole to make it completely round, it can easily skew a bit if a too small screw is used, or the two parts are pushed opposite directions.

For the primary coil, the brake line copper tube is perfect for this sized Tesla coil. Its 3/16″ diameter (4.76 mm) has all the advantages of the large copper tubing, like being hollow, so skin effect is much smaller, than if we used solid wire. Normally solid wire would easily be used in a coil of this size.

The rectifiers from International Rectifiers, type 36MB20A is not something I can use afterall. I misinterpreted the ratings from the model name, it was not 20A at 350V, but the other way around 35A at 200V, the voltage rating is too low! The rectifiers would have been easy to mount with cable shoe legs, especially with some reused wires from my huge collection of teardown wires :D. I was lucky to find some other rectifiers of the same package type, the KBPC2506 bridge rectifiers, rated for 25A at 600V.

I chose to use two different kinds of IGBTs, mostly due to not having 16 of one kind. This is perfect for evaluating the performance of the “same” rated die in two different packages. The Fairchild FGH40N60SFD comes in a TO-247 package and the Ixys IXGR40N60C2D1 in a ISOPLUS247 package, which is essentially the same, without mounting hole.

From the evaluation, below in the table, my verdict is that the Ixys IXGR40N60C2D1 is better suited for a 300 kHz resonant frequency. The higher switching frequency, the more we have to pay attention to gate charge (how much energy we need to drive the IGBT on) and the switching speeds/losses. Another aspect is not just losses, but also how to dissipate that energy. The flange of the Fairchild FGH40N60SFD is not isolated, so insulating pads a needed, to not short circuit the legs of the bridge. This makes power dissipation worse than the direct contact the Ixys IXGR40N60C2D1 can make with the heat sink.

	Fairchild FGH40N60SFD	Ixys IXGR40N60C2D1
Flange	Collector potential	Isolated
Saturation Voltage VCE(sat)	2.3 V	2.7 V
Pulsed Current ICM @ 25 oC	120 A	200 A
Maximum Power Dissipation PD @ 25 oC	290 W	170 W
Gate Charge QC	120 nC	95 nC
Turn-On Time td(on)	24 ns	18 ns
Rise Time tr	43 ns	20 ns
Turn-Off Time td(off)	120 ns	130 ns
Fall Time tf	30 ns	80 ns
Turn-on Switching Losses	1.14 mJ	0.6 mJ
Turn-off Switching Losses	0.48 mJ	0.5 mJ

For the current transformers (CT) and gate drive transformers (GDT) the same type and size ring cores can usually be used. I chose a Epcos B64290L0647X830 which is made from N30 material with a 5630 AL value. Most cores / materials with a AL value around 5000 is suitable.

The heat sinks is two different types. I think that the flat heat sink for the ISOPLUS247 package is the original heat sink from the Ixys IXGR40N60C2D1 that was used in a induction stove / cooker. The other type is in two parts, a block for the IGBT mounting and a part with fins to go on top of that.

The power supply for the driver, I chose a ABB SD821, 24 VDC at 2.5 A industrial power supply, with 230 VAC input. It just takes up less space than a transformer (also I did not have any suitable transformers), and I can skip having the rectifier / capacitors on the driver board itself.

6x 1500 uF Epcos ALC10 electrolytic capacitors in parallel, is used to make a 9000 uF at 450 VDC bank for the DC bus capacitance. It is able to deliver high peak currents from the 6 capacitors in parallel and withstand around 60 A ripple current.