Re: Air cored Tesla coils for high voltage?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Terry,
          I am presently in the throes of constructing a 100W 25kV
flyback supply for cap testing etc. and looked at the possibility of
using a GMHEICSLR in a resonant topology. Things that counted against
it were weight and at the 100W level, wire size (read excessive
heating). At a lower power level, the mass of that coil is simply too
great for the proposed use. Epoxy is pretty heavy. In principle I
think an air-cored coil would be highly desirable but the geometry
and potting material would require careful consideration to give it a
significant advantage over a a ferrite transformer, the tradeoff
being core mass vs copper mass. I'd be prepared to place a bet that a
well engineered air-core design would win easily.

Malcolm

On 2 Jul 2005, at 15:14, Tesla list wrote:

> Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi,
>
> If you made it like a "continuous" DRSSTC driven by say a small motor
> H-bridge IC.  There is a "chance" you could make it "lighter"...  The
> coupling would probably have to be more optimal (0.6) which could be a
> problem...  An epoxy impregnated air core like the GMHEICSLR would be
> nice since the epoxy solves a lot of HV clearance issues.
>
> I have a design for a few amp little charged pumped H-Bridge that is
> very small and light.  About the size of a quarter using surface mount
> ICs and such.  I could dig it up...  I think it could run at 100kHz++
> It would need primary current feedback added and brought to the
> input...  The rail voltage would be pretty low which might be a
> problem...  Best to go for high battery voltage at lower current in
> that case.
>
> Nice to know this thread is about Tesla coils ;-))
>
> Cheers,
>
>          Terry
>
>
> At 06:00 AM 7/2/2005, you wrote:
>
>
> >>  So my question could you make the transformers to
> >>power a tesla coil be air cored?
> >
> >Yes. It's possible to make completely air-cored solid state Tesla
> >coils. There is no HV transformer needed- the coil itself is the
> >step-up transformer and it could run directly off 30V DC. The high
> >frequency inverter that drives it can be very small and light too.
> >
> >However, they may not be the best solution. An air cored transformer
> >needs to be resonant, and that implies higher current flow for the
> >same output. A Q of 6 is usual, and that means the wire is carrying 6
> >times more current than a non-resonant transformer or C-W multiplier
> >would. So it needs to be thicker, hence heavier, if it's not to burn
> >out.
> >
> >Ferrite transformers will work well even if non-resonant. So, while
> >ferrites are heavy, I would bet they would save more than their own
> >weight in copper. These are calculations _you_ will have to do if
> >you're interested in getting an autonomous lifter off the ground ;)
> >
> >But I notice that military and space HV supplies- where weight really
> > counts- are all made with a HF inverter driving a ferrite
> >transformer that drives a C-W multiplier stack.
> >
> >
> >>  Then another question is could you make the toroid on
> >>the tesla coil be lightweight?
> >
> >You don't always need one. Sometimes the self capacitance of the coil
> >is enough, if not you can add a series string of small ceramic disc
> >caps. If you use a ferrite transformer then you definitely don't need
> >one ;)
> >
> >Steve Conner
>
>
>