High Voltage Forum

Tesla coils => Dual Resonant Solid State Tesla coils => Topic started by: Marty on July 12, 2018, 08:14:38 PM

Title: DRSSTC impedance
Post by: Marty on July 12, 2018, 08:14:38 PM
Hi everyone!

After a lot of reading, learning, doing calculations etc. I chose these specs for my medium DRSSTC:

Secondary coil: 20x80cm (8x32"), 0.5mm (24AWG), about 1454 turns, with toroid 81kHz and 48.5kOhm impedance (I want "smaller", but with low frequency about 70-80kHz)
I will be using CM300DY-24H, so I need low frequency to lower switching losses.
I wanted to use 16cm dia secondary, but the frequency will be a bit to high and if I use for example 0.35mm wire dia (27AWG) the frequency will be about the same, but impedance will be far away from "magic 50k".

But I saw other coilers (loneocans etc.) using 16x70cm secondary with 0.35mm wire (1850turns,f=80kHz, Z=61kOhm), so
I´m asking what is better, lower impedance (about 50k) or higher with more turns and more suitable h/d raito ?

Thank you for answers
Title: Re: DRSSTC impedance
Post by: Teravolt on July 13, 2018, 03:22:21 AM
a 4:1 is a good ratio and 80KHz I have calculated as 1/4 wavelength   http://www.procato.com/calculator-wavelength-frequency/     when you add a toride to the top and take in consider the distributive capacitance it will be less. when you have an arc from the top it will bring it down farther if you are concerned you could add another foot to the 8" coil or use smaller wire. At resonance your measured impedance should be the resistance of the wire witch is around 25.6 ohm per 1000 Ft. In reality it will be more    https://www.allaboutcircuits.com/textbook/alternating-current/chpt-6/q-and-bandwidth-resonant-circuit/

 I would use a tesla calculator to find your baseline coil and build the secondary and then tailor a primary with the resonant frequency to match using a o-scope and a sweep generator. there is plethora of projects hear
Title: Re: DRSSTC impedance
Post by: Hydron on July 13, 2018, 09:08:00 AM
Everything will still work if you don't hit the "magic" 50k - this is not an exact number by any means. The 160*700*.35mm type design worked well for me with the exact same IGBTs (pre "magic 50k" knowledge).

If you have the 20cm pipe though then bigger is better!
Title: Re: DRSSTC impedance
Post by: Marty on July 13, 2018, 12:45:17 PM
Thanks for your reply,
I didn´t buy the pipe yet because they dont have it (maybe some sign :D ).. so if the impedance is not that crucial, I will use 16x70cm and nice skeleton toroid which will also lower f and Z... Again, thank you for helping me with understanding this mystery :D
Title: Re: DRSSTC impedance
Post by: Mads Barnkob on July 13, 2018, 09:00:52 PM
Hi Marty and welcome to HVF

You got a good plan, known and proven to work components.

For a DRSSTC, a coil with a impedance around 50k is just a well-proven design and the performance is documented from numerous builds. Something like the high impedance and arbitrary waveform driven QCW coils really show that the impedance is by far not a determining factor for the performance.

As long as you don't get outside +/- 25k of the 50k, you are in the "safe" zone where it will be able to produce sparks, getting outside these boundaries should only be with experimentation in mind and not to build a well performing DRSSTC.

Looking forward to see much more about your build, please keep us update :)