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I need help with a DRSSTC, in everyway possible?

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Guyfrom7up

Fri Jun 19 2009, 07:24PM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

Hi, I've built a few SGTC before, but I've never built a DRSSTC before. I've been searching the net for a while, but some I have some questions that I couldn't find answers for. If you have any good links for me, that'd be great.

-How many turns should the secondary have, about? For SGTC it's ~1000, what is it for DRSSTC?
-Why don't people ever just use one microcontroller (such as an AVR) instead of a bunch of discrete components and somewhat hard to find chips?
-does audio modulation come from the audio signal pretty much controlling the interupter? How does this work, because most music is clearly not just an on/off state.
-how does one go about driving IGBT's for tesla coils? I see a lot of little transformers, but how many volts/current do most IGBT's require?
-What should the voltage rating for the capacitors/IGBT's be if the main powersupply is just a voltage doubler off of ~120 vac? I read somewhere that you should have like 10x the voltage rating, but that seems a bit high.

any other tips in general would be greatly appreciated. This is going to be a project for me and several friends to work on this summer, and audio modulation is a must. I'm all about electronics, and none of my friends get electronics. So they would build the secondary and topload while I (with the help of you guys :D) design the electronics/control hardware. And they want music :P.

Thankyou!

StevenCaton

Fri Jun 19 2009, 11:48PM

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

-How many turns should the secondary have, about? For SGTC it's ~1000, what is it for DRSSTC?

More, such as 2000+, including a fat toroid. Remeber, fine wire and many turns + fat toroid give a really low Fo, which is what you want.

DRSSTC's cant play full on music. (depending on your definition of music) They reproduce tones, which is done by changing the break rate. (example, 100Hz, or 300Hz)

-how does one go about driving IGBT's for tesla coils? I see a lot of little transformers, but how many volts/current do most IGBT's require?

For small IGBT's, gate drive transformers, larger IGBT's, such as CM600's require a dedicated gate driver circuit with its own power supply.

What should the voltage rating for the capacitors/IGBT's be if the main powersupply is just a voltage doubler off of ~120 vac? I read somewhere that you should have like 10x the voltage rating, but that seems a bit high.

IGBT's should be rated for 2X input voltage to bridge.

And they want music :P.

If this is your first one, its going to be a hell of a lot of work, so they may have to resort to a CD player in the meantime.

Good luck

Dr. Drone

Sat Jun 20 2009, 12:10AM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
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Posts: 1673

Guyfrom7up

Sat Jun 20 2009, 02:29AM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
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Posts: 15

-SteveC
Thanks, those are exactly the answers i was looking for, thankyou so much

-Dr. Spark
I've been searching a lot, and what I've mostly been seeing is people blindly following other people's designs, but I don't see a lot of theory, like igbt drivers and stuff, just a lot of schematics without explanation of why or anything. I've been searching these forums for DRSSTC information, and I only asked questions I couldn't find definite answers for.

StevenCaton

Sat Jun 20 2009, 03:50AM

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

Look at the DRSSTC page in the HV wiki

Guyfrom7up

Sat Jun 20 2009, 04:41AM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

yeah, the hv wiki is great. It's been like my main source of information for DRSSTC because it covers a lot of things that is rarly mentioned elsewhere on the internet.

Update: I figured out a way that I should be able to convert normal audio into what I guess you could call 1-bit sound using just 1 small cheap microcontroller. This data will be transferred via fiber optics to the coil.

Andri

Sat Jun 20 2009, 04:24PM

Registered Member #1533 Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46

Guyfrom7up, could you share that method you have figured out to convert music to single bit sound?
I've been wondering how to do this as well. So far I've only written a perl script to play old nokia ringtones through the serial port which I have connected to my tc driver through an opto coupler and a coaxial cable.

Guyfrom7up

Sat Jun 20 2009, 07:09PM

Registered Member #817 Joined: Mon Jun 04 2007, 01:33AM
Location:
Posts: 15

My way is based off of the way that the plasmasonic boards convert the sound my comparing the incoming audio to a higher frequency triangle wave. If the input signal is higher than the triangle at a certain point, then the output is a 1. If the input signal is lower than the triangle wave at a given point, the output is a zero. I think the plasmasonic boards achieve this by using a signal generator, a comparator, and some other chips (I'm not sure, I haven't really gotten around to looking at their schematic). My way would be taking an audio signal, inputing it into a microcontroller (probably attiny25/45/85, depending on the program size, they all cost under 2 dollars), and then using a program I'm going to write, compare it to a sort of virtual triangle wave, and output the signal to an LED which then goes through fiber optics to the Tesla Coil. I'm making everything fit inside of an altoids tin to protect against the TC (even though it would be fairly far away, but it couldn't hurt) along with a 9volt battery.

I'll post code/schematic/boards when I make sure it works, I don't want to post faulty stuff :D. I'm ordering parts from mouser today, so I should have a working/non-working board by next weekend.

Andri

Sat Jun 20 2009, 09:05PM

Registered Member #1533 Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46

What you are describing does not sound like 1-bit sound to me. It's PWM sound. It's been in use for quite a while now in high efficiency audio amplifiers (Class-D). Basically, the power to the speakers is determined by the pulse width, which is variable. The frequency of the pulses must be at least twice the highest frequency the human ear can detect. All frequencies above ~20kHz are then filtered out so that power won't be wasted driving the speakers at the "sampling frequency".

If I wanted to build a TC with clear sound, I guess I could just build a big class-D amplifier without an output filter and with the sampling frequency tuned to primary resonance.

Steve Conner

Sun Jun 21 2009, 09:31AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Dr. Spark wrote ...

To blast a Post â€œNeed someone to send me 5,000 emails and 200 phone calls to build my coil for me and then hey lets audio modulate itâ€

This kind of sums up my feelings too. If you need your hand held through every step of building a solid-state Tesla coil, you probably don't deserve to have one. They are advanced projects for people who already know what they're doing and want to take their soldering-fu to the next level. That's probably why you won't find any noob friendly construction guides, because high voltage power electronics just fundamentally isn't noob friendly. I believe that if you have enough skills to succeed at building one, then the information available online will be all you need.

Having said that, try searching the Pupman archives to read about the early DRSSTC experiments. And you may well get help from forum members younger and less cynical than me.

Andri: The older musical SSTCs like the Plasmasonic used this "Class-D amp" PWM method, and it does produce clear sound. But it doesn't work for DRSSTCs, because they need to run at high peak power and low duty cycle to make the cool-looking sparks, but PWM implies a continuous carrier. So the usual method for DRSSTCs is to let off one bang per zero crossing of the audio signal. This is indeed like a 1-bit ADC.

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