Tesla Coil + PIC Microcontroller

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jrz126

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I'm currently working on building a solid state tesla coil, and I'd like to use a pic to handle the control. However, the emf generated by the coil plays havoc with any digital circuit near by.
The Coil: **broken link removed**
The IGBT, 2500V and 1700A continuous: **broken link removed**

Now I'm hoping to be able to shield the PIC in an aluminum enclosure, but I'm not sure if that will work? Anyone have any suggestions/tips for shielding?

Also, is there a way to detect if the PIC has reset itself? or isnt functioning correctly due to the emf? I need to build in a shutdown circuit for this situation.

BTW, When the coil is operational, I should be able to get 6-7' (yes, feet) sparks off of it.
 
optoisolators would probably come in handy - they isolate a circuit via transferring signals with light
 
jrz126 said:
Also, is there a way to detect if the PIC has reset itself?
Click to expand...

You could save a setting in the EEPROM upon a user initiated start, and check for it in your initialization part of your program to see if it has already been set, and its only cleared upon shutdown etc.. If the setting was already saved, that means the program has reset, and not followed through correctly.

or isnt functioning correctly due to the emf?.
Click to expand...

Make one pin a dedicated output for a signal that’s controlled via an interrupt, producing an on off state every 10ms, connect it to a crow and check that the output is correct, and that the timings are exact and not altering. That would indicate that the internal clock is functioning correctly.

I've heard that EMF can alter internal settings on a PIC, so update internal registers on a regular basis to be sure they are of known values.

And dont be in the room/anywhere near it when you 'test' this device!!!!
 
A metal box connected to earth ground will have no electric field inside, and this is a good thing. Ah..., but the magnetic field with its ability to induce currents in conductors will rise up to bite you. The optos won't help with currents that can be induced on either side of the opto. They do a wonderful job of eliminating common mode ground differences. The only way to reduce the effect of magnetic coupling is to reduce the area of the loops; if you can even identify the loops. If every conductor is a shielded twisted pair you'll have a chance, and don't forget the power cord or cabling to a battery.
 
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I have a 250,000 volt Tesla Coil, and suspected it had something to do with computer problems on the far side of my house. It killed several digital watches, and a pager (little brother doesn't listen too good...). I would never have consider putting anything static-sensitive in the same room. High voltage at High frequency travels on the surface of the conductor, not through it. Insulation... not as useful as you would think... Just my personal experiences, I'm no expert on this stuff, just played with it for a couple of years.
 
Have you tried all the usual stuff like enclosing all the drive electronics in a steel box and using filtering on the power supply and output leads?

Opto-isolation is a must; buiding a circuit like this without it is very foolish.
 
I havent attempted anything just yet, I was trying to get some ideas of what to try.
I did try building a syncronous dc motor (functions just like a sync. ac motor, but using a DC motor and a PIC) for a neon sign transformer based TC. I had it working great in the lab at school, but it started going crazy the moment I started applying a small amount of power to the TC.

I am planning on getting some pretty big arcs out of this coil. Steve Conner (one of the biggest TC experts) built a similar coil using some weaker igbts and was able to get 5-6' arcs.
 

What frequency are you switching the IGBTs?
 
jrz126 said:
Also, is there a way to detect if the PIC has reset itself?
Click to expand...

check out your PCON register (see attachment)

I'm guessing the watchdog is what you'll want to use

instead of optoisolators chips, consider fiber-optic isolation ... couple your control circuit to the drive circuit via a 25ft piece of inexpensive home-audio fiber optic ... IR emitter on one end, IR diode on the other.
 

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This will definitely help with the induced currents in the box which is 25' away from the coil. Your problem will not be solved by the box alone. You must consider the size and location of the loops, since that is the mechanism of magnetic coupling.

Careful layout and construction of ANY circuitry in the vicinity of the coil will be critical.
 
If you've gotten to this point in making tesla coils you need to rethink where you're running it. Like completly enclosing the generator room in metal cladding to prevent this kind of EMF interference nearby. Wouldn't the kind of metalic shielding they use in computer speakers be ideal to enclose the PIC in? It'd act both as a faraday cage and a magnetic barrier.
 
Jeff, you should read the Wikipedia entries on Faraday Cages and Electromagnetic Shielding, if you haven't already.
BTW, Faraday cages do not need to be connected to earth ground to be effective.
 
Just what function does the PIC even serve? The SSTC I made once out of a TV flyback had me wind a tertiary winding for the transistor bases and IIRC it self-resonated. A fixed freq is not a great idea. Esp since when you play with the coil by loading it, it will shift the resonant freq slightly.
 
I'll be switching the igbt at a variable rate, anywhere from 60-500Hz. The coil itself resonates at 35kHz. I have a 20.4uF 2400V cap bank

The Pic will be used to monitor the current flowing through the IGBT via current transducer. Then it will switch the igbt off at the right time (before the current goes negative). It also should be able to provide overcurrent and overvoltage protection.

The pic isnt absolutly necessary. Steve Conner sent me one of his blank PCB's that he made up using some 555 timers and voltage comparators. I'm not the greatest when it comes to debugging analog circuits though. It'll still require another circuit to trigger the IGBT remotely. So maybe I'll use the PIC there.

Anyone have a part number or name for the fiber optic connector used in home audio stuff? I found the toslink cable on ebay, but I need 2 connectors for it.
 
just use some shrink-tubing ... fiber in one end, led / detector in the other

google search for sharp (or toshiba or sony) toslink receiver transmitter, lots of audiophile type sites sell them
 
I ordered the parts, should be here friday

I also was able to talk to the guy that made the circuit that I'm using. He helped me out quite a bit. I still need to tune it, but I'm getting a pretty cool effect from the florescent lights right now **broken link removed**

I might not need the Microcontroller after all.
 
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