RE: air-core resonator

["Dale Hall" <Dale.Hall-at-trw-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Chad, Steve, 

Some air-ferrite core clarification/refinement:
The ferrite core increases the amount of inductance for 
a given coil of wire.
Magnetics usage results a smaller xfmr (Vs air) with less 
wire for a given inductance, reducing DC resistance loss 
which reduces heat assuming the core material composed of
small insulated magnetic particles is able to switch efficiently 
at the operating frequency else the core produces heat.
A core closes and confines the magnetic path assuring all 
flux lines cut each turn optimizing coupling.
A cut core gap provides a high reluctance section allowing flux 
to bulge out increasing the current where a core would otherwise 
saturate sacrificing a bit of the ferrite advantage.

An air core xfmr could be wound but it would be much larger,
possess more DC resistance, and possess less coupling but since
there is no core to saturate increasing current increases the field.

Steve, below, assumes the same winding which would have much less
inductance requiring a much higher frequency for the same reactance.

A FW rectifier would be inneffective for the single transistor flyback.
For FW the drive must be push-pull or half bridge.
(Two switches providing drive in two directions, V to gnd or V to V)

If you want long power arcs (38"+ 7kV .2uF 4.9J)instead of more 
but smaller streamers and are willing to wait a second or so between 
bangs from a flyback TC see my recent DCTC "ion gen" postings & pictures.
It consumes much less DC power as well, <1 watt from 12v .05A (batt)!
Vs your 60 Watts (3A 18v)

Regards, Dale

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Wednesday, August 02, 2000 5:28 PM
To: tesla-at-pupman-dot-com
Subject: Re: air-core resonator

Original poster: "Steve" <Steve-at-g8cyerichmond.freeserve.co.uk> 

You've got a good start for flybacks. The ferrite is needed to maintain the
magnetic circuit. Actually there are air gas in the ferrite ring, usually
formed from  thin pieces of silicone sheet. The resonant frequencies of
these transformers are in the 15-20kHz range (it depends on a number of
variables). I have built a number of flyback (in the UK they are often
called LOPT) circuits, and use them to drive small Tesla coils. The commonly
used drivers with either 2N3055s or 2N3055s with 555 timers wouldn't work
with air cored transformers as the frequencies needed would be too high for
the 2N3055..

Basically to drive a small Tesla coil, I take the output via a high voltage
rectifier to feed the primary circuit. Either EHT rectifiers reclaimed from
TVs or a string of 1N4007s are ok. My best effort so far has been 6" sparks
using a small LOPT with a pair of 2N3055s, feeding a primary circuit with
8.3nF MMC and a helical primary 4" dia. 18swg wire, 6turns 1" high (ok a
pancake would be better). Secondary is 2" dia 12" high 850 turns close
wound. Topload 2" x 9.5" toroid. The secondary is really a bit too long and
thin. The flyback circuit draws about 3A -at- 18V peak.
I could probably improve things by using a larger flyback transformer, and a
bridge rectfier rather than half-wave.
Steve.
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, August 02, 2000 12:04 AM
Subject: air-core resonator

> Original poster: "sundog" <sundog-at-timeship-dot-net>
> Hi all!
>  I'm looking at flyback drivers for giggles and experience, and am
> wondering... I've seen a lot of methods of re-wiring them with a new
> primary, and a feedback winding to make it self-oscillating.  Please
excuse
> my ignorance, but will this method work on an air-core resonator, or is
the
> ferrite core needed?  I'm guessing it is needed.  I've got a 16v
> some-ungodly-amperage transformer to push it with (the thing is
> center-tapped, and about 3"x4"x4"!), and a good 5lbs.  Don't need caps to
> explode wire, I just short that thing out, and *poof!*.  Anywho, I've got
a
> good high-amperage supply, and plenty of 2n3055's to toast.  Got good
> heatsinking also.  Eventually i'd like to take a crack at a solid-state
> sillycon powered TC.  I believe flybacks would be a good place to start
> learnin'.  Less noise than a sparkgap too :)
>
>   Another question...A base-fed TC...that's just a secondary that's having
> high-powered RF pumped into it, right?  I'm assuming a primary isn't used,
> and the normal RF ground is used as the input.  What are the normal ranges
> for input power, and how exactly do you feed it?
> Caio! Shad