# Again!

So I have picked up this project again circa 2018. My sister has asked me to look into making a small tesla coil for her haunted house. Enough to be scary but not too dangerous.

# Design Parameters

• secondary
• height: min, max
• width: min, max
• wire_size: min, max

# Work Log

## 10 Oct 2018

• interrupter work

It gets a little messy around here when I’m this close to a deadline:

## 09 Oct 2018

• mostly framing work: using nylon bolts to attach various components together

## 08 Oct 2018

Made a toroidal topload from 8" dryer duct wrapped in aluminum tape. I also have a 4" duct if I need more capacitance (probably).

## 11 Jul 2012

I haven’t done much these past couple of weeks. I made the primary coil supports. Made the MMC bank. Finished the control board. I just have the last bit of contruction to do. Then it will be time for first light! I still have to test the control board. It is a new design afterall.

A note on the controller board: the 9 Volt power line was bridged to the two outputs of the UCC27423. I noticed this only after I had completed my board. I just sanded off the connection. I fixed the problem on the Eagle board file, but not the transfer. I will get to that in a little bit.

## 20 Jun 2012

I finished ordering the components for the controller board from mouser. Click here to access the order. I might have ordered some extra things or forgot something, but that should give you a good idea what to purchase.

I ordered some 942C20P15K-F capacitors today. I was looking at $8.35 a piece from mouser. Thankfully, I found a better place: Online Components. Woohoo for$3.75 each. Plus the minimum order is 1. I feel much better now. I guess we will see if they are a good supplier.

I plan on using 4 in series and 5 in parallel for a total of 188nF at 6000 VDC. I will add some 940C20s that I bought earlier by mistake to increase the capacitance to 263nF. Hopefully they won’t feel ashamed by their bigger cousins.

## 15 June 2012

#### Controller Board

I finally got the controller board done. It is based on Steve Ward’s universal driver 1.3, but it is modified slightly. The schematic is the same, but I made the PCB more suitable for the Toner Transfer Method for PCB manufacture. A note on PCBs: don’t use Ferric Chloride! It is terrible for the environment. Use copper chloride instead.

I would suggest looking over this instructable for an idea how to use Eagle. For some reason whenever a board file is saved, the polygon doesn’t show up when you reopen it. If you want to edit the board, make sure you use the Ratsnest button to show the GND planes. If you just want to straight copy the board, you can use the transfer page. It is just a pdf file with two copies of the top and bottom of the board to be used in the Toner Transfer Method. The parts list is the same (nearly) as Steve Ward’s. Some of the parts are obsolete so you might have to substitute. I will try and post a copy of the order I placed with Mouser.

### Simulations

Scan Tesla was developed by Terry Fritz in order to simply simulate a tesla coil (both solid state and original) using lumped circuit elements. Basically you just input the possible dimensions of your coil (secondary and primary inductance, tank capacitance, etc.) and Scan Tesla runs through each possibility and spits out the best one. Pretty neat software I must say. So anyway, here is the input text file and here is the output I get. I ended up winding 43.75" before running out of space. That works out to be about 3000 turns of wire. Quite a bit higher than you usually see. Scan tesla suggested that the benefits of a higher inductance outweighed the increase in resistance. I guess we will see… I measured the resistance of the wire using a standard digital multimeter. The inductance calculator I used suggested that my resistance should be around 1300 ohms. It was 289 ohms. Something is wrong here. Maybe the inductance calculator includes some reactance from the inductor as well? They do ask for the design frequency which would suggest they did. I am hoping that 289 ohms is right. My output drops significantly if the secondary resistance is 1300 ohms, obviously. The expected resistance for 27 AWG wire is about 51 ohms per thousand feet. That gives about 315 ohms resistance total. Much closer to what I measured. Skin depth is greater than the conductor diameter (below 130 KHz anyway).

I might try and modify Scan Tesla to include some practical design considerations. If you want to find the ideal number of turns in your coil you have to run separate simulations because secondary resistance and inductance are not linked. The program would just use the lowest resistance and highest inductance. Hardly a real world situation.

### IGBTs

I am using the IXYS 60N60C2D1 brick IGBT. A lot of people say that it is underpowered for DRSSTC work, but it was cheap and still available on Mouser. It isn’t that hard to adapt a system to a different IGBT if I want to upgrade later. I ran into this article on IGBTs. It is a great read and very helpful. I would suggest at least browsing through it.

### Gate Driver Transformers

The HvWiki on GDTs is very helpful. Check thedatastream.4hv.org link at the bottom of that page for some more info on GDTs. So now that I have an IGBT, I can start calculations on the GDT. I choose to use B64290L618X38 toroidal ferrites from Epcos. Probably should buy the next size up to increase the cross sectional surface area, but they work for now.

• Drive Voltage = 12V
• Frequency = 67.7 KHz
• AL = 10,700 nH/N2
• XSA = 51.26 mm2

This means that I need more than 8.3 turns to avoid saturation. With 10 turns… The inductance is 1.07 mH. The magnitizing current (rms) is 48 mA. The gate current is 13 mA. The total current a driver must supply is 61 mA.

## 10 June 2012

For those of you who have been doing these kinds of projects you know what happens when you really get into one. Everything else just kinda falls by the wayside. Unfortunately for you this means that I don’t update the site all that often. I do however have a few websites that you should read up on.

## 15 May 2012

So I built my first DRSSTC in the past few weeks. I had to do a final project for my PHSX 536: Electronic Circuit Design and Measurement class. I didn’t choose a wimpy LED flasher circuit or anything like that…. I chose a Dual Resonant Solid State Tesla Coil. In retrospect, probably not something that should be done in a few weeks. It never officially worked. While taking some voltage measurements one of the 40n60 IGBTs blew up in my face. Scary… but no permanent damage. I wrote a nice paper on it however. There might be some things wrong with it. I kinda had to BS a little about the things I didn’t understand. Hopefully my teacher doesn’t understand either and skips over those parts. You can read it to get a good understanding of the schematic I used. Thanks Steve!

## 5 May 2012

I didn’t get an internship this summer. :,( On the positive side, now I have nothing to do but everything I want to do. I made a list of things that I want to accomplish this summer. One of them is build an audio modulated DRSSTC with an arc length longer than I am tall (~6’). All my classmates told me to call them when it was finished. Of course I am going to show off!

### Secondary

So I have an idea of the arc length that I want. I started browsing around to get an idea of the size I would need to achieve 6’. I again came to Steve’s website and his DRSSTC-2. So apparently I am looking at a secondary form size of between 6" and 8“. The local Home Depot sells 4 inch drain pipe (OD=4.215”). This definitely would not suffice. So I settled on the 8" cardboard concrete tube. I have seen multiple websites with various suggestions for aspect ratios. Most stick between 1:3 to 1:5. I will go for 1:4 because its in the middle. The 4Hv Wiki suggests a wire size between 22-28 AWG for an 8" form. I went with 27 AWG because that is what I could find surplus for a decent price.

• Diameter = 7.75"
• Length = 43.75"
• 27 AWG wire
• N = 3020 Turns
• L = 295 mH
• C = 17 pF
• fres = 71,190 Hz

# Bibliography

Craven, Richard M., Ivor R. Smith, and Bucur M. Novac. 2017. “Significant Practical Features of Tesla Transformers.” https://dspace.lboro.ac.uk/dspace-jspui/handle/2134/28067.

1. http://en.wikipedia.org/wiki/Q_factor#RLC_circuits

2. http://en.wikipedia.org/wiki/Parasitic_capacitance