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Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Hi folks!
This thread is just what I need! Perhaps somebody can offer an opinion on the following:
I'm presently working on an oil-immersed secondary. Why? It's just one of those "because I can" and "because I want to" things Anyway, the containment vessel is a four-foot-tall, 18" OD ceramic insulator. All goodness so far, except that the end caps are these big 16"-in-diameter .25" thick aluminum discs.
My first thought was something along the lines of, "Ok, so, I'll use only about half the height of the thing so that I can keep the primary and bottom of secondary away from the bottom end cap." Now, after reading this, I wonder if my fears are really justified? How close is *too* close? Should I not be too worried about coming within, say, one foot of the bottom?
Ultimately, the bottom of the primary will be sitting on small-gauge copper pipe that's connected to the bottom end cap, which will then be connected to ground.
My hope is that this arrangement, once filled with oil, will enable me to play with higher-than-average coupling and high streamer-to-secondary length ratios. In addition to the oil insulation, the secondary is actually wound on a piece of 8"OD PVC which has been threaded on a lathe using a special jig, so the windings are actually spaced slightly so as to let the oil surround them almost completely. Should be fairly impervious to flashovers.
EDIT: Secondary is not wound yet, but I have threaded 36" of PVC, and was planning on cutting 12" off. I guess I'm wondering whether I should do so, or keep the 36".
Registered Member #29
Joined: Fri Feb 03 2006, 09:00AM
Location: Hasselt, Belgium
Posts: 500
Keep in mind that immersing your secondary in oil will probably lower its resonant frequency significantly..
If the primary is wound near the base of the coil, moving the ground plane away will have two effects:
1. It will likely lower the resonant frequency a little, 2. It will increase coupling somewhat (as hads been observed by BP and others).
Both of these effects are because the field at the base of the coil is mostly magnetic (electric field is not so strong). Moving the ground plane away from the base a little increases the magnetic field energy stored in the fields at the base of the coil (which are like increasing the inductance). The coupling increases because magnetic coupling grows stronger when the primary current interacts with the reonator field where the resonant mode field is strongest. (EM field theory buffs will recognise immediately the "electromagnetic reaction theorem" at work here.... )
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
WaveRider wrote ...
Keep in mind that immersing your secondary in oil will probably lower its resonant frequency significantly..
Yesssss. The lower the better!! As it is, my winding technique somewhat limits the number of turns I can use (since I'm not tight-winding), so I'll be using a larger-than-average topload to [partially] compensate.
WaveRider wrote ...
If the primary is wound near the base of the coil, moving the ground plane away will have two effects:
1. It will likely lower the resonant frequency a little, 2. It will increase coupling somewhat (as hads been observed by BP and others).
I'll give myself some extra primary turns to account for the suspected lower-than-air-core resonant frequency. As for the coupling, a bit more than usual shouldn't hurt here, given the better-than-average standoff the secondary should have when immersed.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
I've no idea if it will be significant; if you are operating at fairly high magnetic flux and frequency, the magnetic forces will try to pop the ends off..
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Sulaiman wrote ...
I've no idea if it will be significant; if you are operating at fairly high magnetic flux and frequency, the magnetic forces will try to pop the ends off..
The big steel bolts should prevent that, although they may induction-heat a little... Oh well! Never said I was after record-breaking efficiency
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Resonators in enclosed spaces
Anyway, the containment vessel is a four-foot-tall, 18" OD ceramic insulator. All goodness so far, except that the end caps are these big 16"-in-diameter .25" thick aluminum discs.
As it is, my winding technique somewhat limits the number of turns I can use (since I'm not tight-winding), so I'll be using a larger-than-average topload to [partially] compensate.