Hi Jay,
To match the 8 bridges to 1 primary circuit, there are 8 ferrite core
transformers in an assembly. Each bridge drives a 10-turn primary winding
on 1 core. The secondary then winds through groups of 4 transformers at a
time (basically winds through all 8 cores, serially). The effective turns
ratio for each transformer is 10:3 (though my pic shows a 4 turn secondary,
it was replaced by 3 turn). Since all the secondaries are in series, you
get 10:3*8 or 10:24 total turns ratio. I think the optimal match is
actually with 2.5 secondary turns, and there is a method for achieving this
by using turns that go around the outer posts of the EE cores and get wired
in parallel. By optimal, i mean that my electronics can deliver maximum
power to the tesla coil. As it exists now, i can only ramp up to 350V into
the H-bridges before i exceed their current limit. By lowering my turns
ratio i should be able to operate with 450V on the bridge, at the same
current, which is 28% more power.
This method of matching really isn't needed, but the parts were available
and it does offer some robustness and the ability to ground my primary
circuit, which is good in the event of a flashover... which is much more
serious on a coil like this.
Steve
On Sun, Nov 16, 2014 at 8:35 AM, Jay Howson <jhowson4@xxxxxxxxxxx> wrote:
> Pure excellence =)
> Seeing such massive arcs from a little secondary is awesome!
> Keep up the Good work!
>
> Looking over your set up. I am wondering if you could describe the
> impedance matching. I'm trying to wrap my brain about what you have going
> on.
>
> Are you feeding each each ight into it's own winding on a ferrite? Like a
> common mode choke kind of? Or , what?
>
> Just curious.
>
> Jay
>
> Sent from a tiny phone with a tiny keyboard.
>
> ----- Reply message -----
> From: "Steve Ward" <steve.ward@xxxxxxxxx>
> To: "Tesla list" <tesla@xxxxxxxxxx>
> Subject: [TCML] "Fat Coil" QCW Double Resonant SSTC
> Date: Sat, Nov 15, 2014 10:03 PM
>
> Hey Guys,
>
> I've been playing with larger arrays of fast-switching IGBTs for growing
> huge arcs from "tiny" coils. The idea is that hotter plasmas can be
> achieved at lower voltages by upping the frequency. At ~350Khz and above,
> its noted that the plasma tends to grow in straight segments which helps it
> reach further still... A dramatic demonstration of this effect is shown
> here with an 8" long coil with just 165 turns of wire producing maybe
> 100kVAC at 300khz is jumping 11 feet to the shop ceiling.
>
> https://www.flickr.com/photos/kickermagnet/15705193211/in/photostream/
>
> More pics at:
>
>
> http://forcijo.smugmug.com/Events/Teslathons/Philthon-2014/45663076_MtFqHw#!i=3689589842&k=M8Crsgs
>
> For those into the specs on components and such, I'll link my 4HV.org post
> from earlier today:
>
> http://4hv.org/e107_plugins/forum/forum_viewtopic.php?167363
>
> This coil is waiting for a 40kW power supply before it can sustain the 10+
> foot performance at high duty cycle. For now its limited to bursts at any
> power level over 15kW (which can only produce about a 5-6 foot discharge at
> 50% "on time" or about 25% duty cycle considering its a triangular
> modulation signal). Maximum peak power so far is 190kW. The maximum i'd
> bet my power electronics can handle is 260kW peak, so i think 13-14 foot
> sparks may be possible from my 8" tall winding... i'll set it up with more
> space next time and see :-).
>
> Steve
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