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Registered Member #1931
Joined: Thu Jan 15 2009, 03:11AM
Location: Hobart Tasmania
Posts: 6
My musically inclined friends have been begging me to build a Tesla coil capable of being audio modulated since seeing my SGTCs in operation and viewing the numerous YouTube videos of audio modulated coils. Plus I've been looking for a new project for a while.
There are a couple of short, not particularly good, videos of my SG coils here: if you are interested.
I've read Dan's excellent DRSSTC book and most of the relevant posts here. I have some experience in power electronics (e.g. recently designed and built a 70kA 8/20us lightning impulse test generator) and feel that this project is certainly within my capabilities, but would appreciate any input you may have regarding my early thoughts below, as I have little to no experience in using IGBTs.
I'm still not completely certain if I should be designing a large coil for outdoor concert use or something like the minibrute that can be used on a stage indoors. Both have their own appeal, but in the end it will be decided by price.
I will have 2.4kVA available (Australian 240V 10A standard single phase GPO) and would like to use as much of this as possible to make arcs. However price and availability of IGBTs is a sticking point at the moment. I can get HGT1N40N60A4D minibricks for about $93AUD each or BSM100GB60DLC dual IGBTs for $76AUD (including delivery). I like the terminal layout of the BSM100 as it would easily lend itself to a low inductance DC bus, but wonder if it is capable of delivering enough power at about 100kHz (Ptot of this half bridge device = 445W compared to each 1N40N60s Ptot of 298W). I plan on using a full bridge configuration. Both devices have similar VGE(th) and timing parameters, necessitating little or no change to Dan's DRSSTC II design if I go for the half bridge devices.
Also designing for a product that is no longer manufactured (HGT1N40N60A4D minibricks) does not seem very wise in a device that can be prone to popping them, so I am leaning away from using these.
Are the TO-247 devices capable of handling the switching losses at this sort of power level? I noticed in other posts that say they have been used effectively in minbrute designs, but for switching 2.4kW?
Would I be better off using CM300s (~$115AUD delivered) and aiming for a lower resonant frequency / larger coil?
Ok it's way too late here and I've just deleted a couple of paragraphs of rambling questions. I'm going to sleep on it and check back tomorrow. Thanks in advance for any advice you can offer at this early stage in my design.
Registered Member #2040
Joined: Fri Mar 20 2009, 10:13PM
Location: Fairfax VA
Posts: 180
I can vouch for the CM300s, I have two of the half bridge modules set up for a full bridge, running at ~70KHz and ~800A. Gate drive is via a full bridge of fets and a massive GDT, with relatively good rise times. I would have to recommend the GDT method over four individual igbt drivers, I've tried it both ways and the GDT is simpler and just as good performance wise, not to mention cheaper too.
Registered Member #1931
Joined: Thu Jan 15 2009, 03:11AM
Location: Hobart Tasmania
Posts: 6
Thanks for the feedback (terrible pun, sorry) and GDT recommendation. Though coming from a lightning protection background I keep reading that acronym as "gas discharge tube".
I have been playing around with Barton B. Anderson's JAVATC designer to get a feel for the size of the secondary coil in the 70kHz range - it's huge!
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Preliminary DRSSTC design help required.
