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Topics - sjsimmo

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1
Solid state Tesla coils / My First SSTC
« on: November 21, 2018, 11:43:46 PM »
Hello!

This post is just to provide some documentation of my old SSTC, which I completed about a year ago.


The SSTC was based on this coil: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?172138
And the finalised circuit looks like this:


The driver circuit is a direct copy of the coil linked, except that the 555 interrupter has been replaced with a simple Audio one that I designed. Some minor faults include the fact that I used a comparator as an op amp (I believe this causes some oscillations, which reduce audio quality). And the current limiting circuit has a small fault, which means that higher input voltages reduce the operating current. This was later modified with a capacitor across the current sensing resistor, to allow more peak current (dodgy, but it works ).
The driver circuit was etched on a hand drawn PCB using a permanent marker, and ammonium persulfate etchant:


And the case was made from 1.5mm aluminium sheet, bent in a vice (with a rubber mallet). For the interrupter I drew the PCB design in MS paint (never could get used to PCB CAD programs... ), and used the toner transfer method to etch the PCB:


The secondary was wound on an automated winding jig (unfortunately I never took a photo of the robot, before it was disassembled), with wire from one of the brake mechanisms in a laser printer. The coil is 90x30mm and has approximately 600 turns.

The primary coil was originally allowed to touch the secondary, until I noticed the racing arcs between the 2 coils , at which point I made the small isolating blocks out of perspex.


The final result was a very small SSTC capable of low quality audia, and about 1-inch sparks with 50 VAC input (the faulty current limiter causes sparks to reduce in length above this voltage).



So that was my first SSTC... now back to the DRSSTC
Feel free to ask if you have any questions (I probably left some stuff out...)
- sjsimmo

2
Dual Resonant Solid State Tesla coils / My First DRSSTC
« on: November 20, 2018, 05:31:36 AM »
Hello again,

I'm working on a DRSSTC, but am having some problems. Any help would be appreciated  :)

The current Specs:
- FGY75N60SMD full bridge
- 400x90mm secondary, ~2000 turns
- 7 turn primary
- primary resonant frequency ~140khz
- my own driver design (I know, should have just used one of the UD designs...)
- 500hz interrupter 10-200us on-time (will later be replaced with a fibre optic based midi interrupter)


The driver:
The driver is primarily based on the onetesla Gen-1, but I have modified it to include OCD.



The problem:
I am currently operating the coil with the secondary not in place, but primary connected.
When I inject a 100-200 kHz square wave into the driver feedback CT input, the gate drive waveforms seem ok, and the circuit operates as normal, OCD works when current is applied to the OCD CT inputs, system shuts off at zero crossing point when the interrupter goes low etc.

However, when I connect the CT's and apply voltage to the bus, the circuit starts oscillating below 12VDC, but at the wrong frequency! It seems to oscillate at about 250-300 khz (maybe the 2nd harmonic  ??? ). In addition to this, the output of the GDT becomes horribly triangular. placing an oscilloscope probe on the primary coil, shows that the primary circuit voltage isn't ramping up, but is just a constant AC (as expected, considering it's not oscillating at the resonant frequency). The same thing happens as input voltage is ramped from 0-120VDC input (the waveform just grows stronger with larger input voltage).

On a side note, when I tried applying 24VAC to the bus, without slowly ramping the voltage up, the UCC37321 blew up violently :-[ . I have ordered replacements (not sure when they will arrive) , but am not sure why this happened...

I don't have any scope shots of GDT outputs, primary current etc. at the moment, as I blew up the driver before thinking to save them...

Anyone have any ideas/suggestions?

thanks in advance, sjsimmo[/attachment]

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