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Help with My First DRSSTC

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gloverp14

Wed Jun 08 2011, 10:51PM

Registered Member #3937 Joined: Wed Jun 08 2011, 10:40PM
Location:
Posts: 3

After talking with Steve and Joe at Maker Faire 2011, I now am interested in building a solid state tesla coil. I just want to know what I'm getting myself into. Regarding HV experience, I have built a VDG generator, coil/rail guns, but in general I have built pulsed HV devices. As far as tesla coils go, I haven't built a spark gap TC yet, so would you recommend jumping right into a DRSSTC? Ultimately I want to put a MIDI signal through it. I fully understand the concepts of how a TC works, and the concept of switching the coil on/off at the frequency that each note is played. And if I built a one (1-2ft spark), would it be a significant investment?

Dr. ISOTOP

Wed Jun 08 2011, 11:41PM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Building a DRSSTC requires significant power electronics experience; if you've never worked with oscillators, gate drivers, etc. before you might consider starting with a standard SSTC.

doctor electrons

Thu Jun 09 2011, 12:38AM

Registered Member #2390 Joined: Sat Sept 26 2009, 02:04PM
Location: Milwaukee Wisconsin
Posts: 381

I say go for it! It is something you can spend small amounts of money on for supplies as you can afford them.
If that is a route you are willing to go. I personally cant wait that long to see the results, but i am hooked and
have been for some time. One benefit is that its a serious crash course in drsstc technology. As long as you are well
aware of the safety concerns and the other issues involved. you will surely learn a great deal in a small amount of time.
Be aware that these things are highly addictive and can get expensive!! The rewards outweigh the costs though in my
case. If its something you are interested in and you love electronics,,,,, BY ALL MEANS, GET TO IT MAN!!!!
DRSSTC's are nothing shy of amazing! There is a wealth of knowledge here (some of the masters hang out here) and
almost everyone here is happy to help! Just remember the rules

Remember, you gotta get your feet wet weather you just jump right in or weather you just dip your toe in the pool!!!

gloverp14

Thu Jun 09 2011, 01:56AM

Registered Member #3937 Joined: Wed Jun 08 2011, 10:40PM
Location:
Posts: 3

Thanks for the encouragement. And two questions,
If I use PWM to play a MIDI signal through it, what gets better results? The normal SSTC or a DRSSTC?

I am willing to spend up to $1000 all in all. Will that get reasonable results?

Dr. ISOTOP

Thu Jun 09 2011, 03:56AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

$1000 will let you build a full strength DRSSTC with all the goodies - a bridge of CM600's, CDE942 MMC, nice 12" secondary, etc. It'll do 10' if you do it right

Go for it!

gloverp14

Thu Jun 09 2011, 05:40PM

Registered Member #3937 Joined: Wed Jun 08 2011, 10:40PM
Location:
Posts: 3

I'll build it, but in general does one design have better results than the other?

StevenCaton

Thu Jun 09 2011, 09:35PM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

I'll build it, but in general does one design have better results than the other?

Based on that statement, I believe you are not ready to attempt a DRSSTC.

Considering that you have never built a tesla coil, I would highly recommend you start with a simple SSTC first. If you attempt a DRSSTC right at the start, it will most likely result in failure and many blown parts unless you get a very extensive amount of help from a more experienced friend.

So, my personal recommendation would be to use $X dollars of your $1000 and build a sstc. Get it working, and then go for the drsstc.

iceowl

Sat Jul 16 2011, 06:32AM

Registered Member #2834 Joined: Thu Apr 29 2010, 02:04PM
Location:
Posts: 22

Coiling is a very interesting sport in that it can be as expensive or cheap as you like. At this point, I have seen people build coils from $50 worth of stuff they pulled out of garage sales and flea markets and eBay, and then multiple 1000s of dollars with top end gear.

I can offer my own experience which is that I have built several coils over the past year or so. I've made spark gap coils starting with static gaps. Static gaps with blowers powered by NSTs. SRSGs. SRSGs with various spinning electrode methods from garolite disks to whirling tungsten propeller rods. ARSGs made from vacuum cleaner motors and treadmill motors. Then NSTs paralleled to give up to 300ma (in 60ma increments) And pig driven ARSGs, at the end of it. Recently I made 2 DRSSTCs, first with sort of dumb interrupters, and then with MIDI control.

There are some constant parameters to all those coils. First, you have to decide on your design parameters. This can be made as easy or as difficult as you like. The easy thing to do is to check out the dimensions of other people's coils you can find on the web, and then go to JavaTC on Bart Anderson's website and type in the parameters to see what you get in terms of frequency of operation, max theoretical spark length, etc. Then tweak to suit your taste.

When you have a design that you think will work, you have to come across a resonator somehow. I've not seen many complete resonators for sale on eBay, or anywhere else, and most coilers don't give their old ones away because of bizarre emotional attachments. The trick is, if you build the right resonator you can run it with a spark gap and then swap out the spark gap for a DR motor. I have done this one 2 occasions. It doesn't yield optimal results, but it can be made to work if you choose a low enough f0 and build your gear with growth in mind. That is - no matter how big the sparks are in your first coil, you will find yourself on a seemingly endless trail to ever larger output. So build your first primary/secondary/topload with that in mind.

All of which is to say that no matter what type of power supply/interruption you choose, be it NST or Pole Pig or DC bus and IGBT, you need to wind a secondary to the right frequency, choose and obtain a top load, and create a primary tank circuit. So my amateur recommendation would be to first do that and don't build anything quick and flimsy.

Once you have the resonator, the absolute simplest and cheapest thing to do is to build a static blower spark gap driven by an NST or a MOT. If you use a MOT you have the added issue of needing a ballast to limit current and you possibly will want to create a voltage doubler, but even that's not so hard. An NST is self limiting and generall if you stick to a 12k or 15kv output you're fine, but you may wind up having to spend up to $100 for a 15/30 from eBay. MOTs can be had cheaper. If you use an NST you may want to build a Terry protection "filter" as well. I've run my NST coils with one always, and never had a problem. Others have reported frying their NSTs without one.

You will need caps for your tank circuit. If you stick to the CDE 942 series, or those like it recommended here by Steve Ward, you can pretty much use the same ones for a spark gap coil as you use for a DR coil. You will need to change parallel/series combinations - spark gap coils might want higher voltage toleration and less overall capacitance than your DR depending on the design. But you can use the same type of caps. I've recycled my spark gap caps in my DR coils.

I built my first spark gap coil with a 3"x22" secondary. I subsequently built a 6"x30" secondary, an 8"x42" secondary, and a 12"x58" secondary. I've tried solid turned aluminum toploads (which are prettiest), as well as dryer duct (ugly, but cheap and just as functional), and finally, hoops, which look weird and work very well.

Each type of coil has it's own problems that will require debugging, but by far the easiest to get working was the static gap. The SRSGs were more problematic in that they have to be phased correctly to get any output, the ARSGs were easier, but generally speaking you get some result when applying voltage to all the spark gap coils.

DR coils can be frustrating, in that they sort of either work or they don't. And when they don't there can be a lot of reasons for it. So I would suggest building and debugging the problems in a spark coil first, if you never built one before, so you can get the feel of what things look and sound like when they're going right, and what things look like, and sound like, and smell like, when they're going wrong. Do that first before you have to start worrying about whether you have the right gate resistance or wound your GDT on the right kind of ferrite...

Anyway, just some thoughts.

Cheers,
Joe

Killa-X

Sat Jul 16 2011, 04:09PM

Registered Member #1643 Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039

I would agree with the majority. few years ago I wanted to build a DRSSTC after just making a SSTC (which performed horribly). I was then told by my friend Arcstarter that I shouldnt make one because I dont have the famous clue what I'm doing. So I kept with SSTCs for awhile, learning by experimenting along with his help. Started to understand it my self, and went on my own, building a fullbridge SSTC. I'm still maxing my mosfets out at 400V, with 24-28" sparks. Then I attacked DRSSTCs recently, and most things made since to me. I didn't find it that hard, as much as I just needed assistance with knowing what waveforms looked good, and what to look for, along as fixing ringing..ZCS..etc (Thanks Kizmo).

As many said, DRSSTC is a whole new thing. It requires a lot of knowlage, its not something you can just whack together. You need to understand how to calculate things out so you have a good tank capacitor, figure out capacitance reactant to figure the voltage of your capacitors, and so forth. Its best to start with a SSTC so you have an understanding of the whole system and the waveforms. All you do is just plug it in really. A DRSSTC your tuning the primary and tank capacitor, not to forget coupling too.

But, i found DRSSTCs easier now that I have an understanding of SSTCs, and so far the build is going good, I have already done induction tests at 340VDC 600A without failure on CM300s. As Iceowl said, you decide the cost. Some people use wood as its cheap, or due to personal feel. I prefer acrylic, and I like my stuff looking very clean, neat, and organized. Because of that, I spend a lot on my coils. I could have just done wood for my DRSSTC, but no, I smacked on $50 worth of 1/8" black lexan on top of the wood just because i thought it looked cool.

Whatever you decide, good luck! I cannot dictate you to be a SSTC or a DRSSTC builder. All I can do is give my own suggestive reasons why I think you should start with a SSTC, if you feel you know a lot about building power inverters and fully understand the whole entire DRSSTC schematic, Have fun. It would just suck to build a DRSSTC, and find out that it doesnt work, and then have you not the famous idea where to even start debugging. That's mainly why i suggets a SSTC, if it doesnt work, its usually due to very few things. DRSSTCs, well, a bit can go wrong. Bad waveforms can lead to expensive bricks exploding too.

Maurizio Valvo

Sun Jul 31 2011, 11:01PM

Registered Member #3219 Joined: Mon Sept 20 2010, 09:06PM
Location: LeinÃ¬ (Turin), Italy
Posts: 23

I can say that after lots of reading, studying, simulating, planning, building and testing, I have had very good success with my very first TC, which is indeed a full bridge DRSSTC running from 230V mains (>300Vdc bus voltage). It took me more than a year since I started reading on websites, with no previous knowledge of the matter (thanks to all people of the TC community who have shared their valuable experiences and knowledge!), till I had the first circuitry under test. I have good knowledge of electronics, but I had never worked before with pulsed power circuits. I just read and studied a lot and expecially I tested every piece of circuit (using very modest test equipment: homemade oscilloscope and frequency counter, multimeter; I also realized a very simple oscillator, based on a 555, to provide the input signal for testing the driver circuitry, GDT and bridge board) before starting experimenting with the complete system; also I started with very low bus voltage using a 50W transformer with 12, 24 and 48V outputs. Thanks to this very careful way of going, I haven't burnt anything till now.

I have reached 120cm sparks (2x the coil height); I am a bit limited by the current specs of my IGBTs (ixgr60n60c2d1). I have used Steve Wards 2005 driver and burst mode interrupter (with few adaptations; the new version was published after I started my project); the OCD function makes the driver very robust, I haven't killed any IGBTs and I am now probably around 50% over their current limit.

I am very satisfied already with the current results, but I still want to experiment and tweak a bit to maybe get even better ones.

My thought is that if you have good electronics experience, have no hurry and do everything in small steps, testing and verifying before moving to the next one, you will have very good chances to get successful results. Just be aware, apart from all electrical safety issues, that DRSSTCs can be unbelievably loud!

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