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Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843
@Patrick
That's the "fullwave" low frequency, frequency domain solver, p/o CST EM Studio.
I "cheated" a little bit in that I didn't simulate any "coils" per se, but I instead represented the coils as conductors, to which is applied HV AC at 30 kHz. The capacitive coupling to the core and resultant Efield should be very similar.
(Being that I didn't use coils, I could've also used the "EQS" (i.e., electroquasistatic) solver, rather than the "fullwave" solver, but I was experimenting with what they call "voltage path" excitation, which isn't available with the EQS colver).
I may try it later on using actual coils, but that would be more involved.
@Ash
For my experimental coil, I made the ID of the bobbin a little bigger than the core, so I have some room for a capacitive shield, which will be a piece of foil between two pieces of polyethylene or polystyrene film.
And yes I think using multiple cores physically separated from each other (each with one "tall and skinny coil) would be one solution (although maybe not the most practical one). Also it would be minimized if you use just one single "tall and skinny" coil on a single core. But if you use multiple "tall and skinny" coils on the same core (with the core having a square cross section), you would have to shield the core I think.
(BTW I think Patrick was referring to the coil windings themselves having a square profile, which would probably also result in field enhancement).
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
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Posts: 4245
jpsmith123 wrote ...
For my experimental coil, I made the ID of the bobbin a little bigger than the core, so I have some room for a capacitive shield, which will be a piece of foil between two pieces of polyethylene or polystyrene film.
Is a capacitative shield the same thing as an electrostatic shield? I have some experience with electrostatic shields.
Would it be necessary to sandwich the foil in polyethylene/polystyrene sheet before wrapping around the core to avoid creating a one turn shorted winding?
Do you recommend polystyrene as an insulator? I did some googling and it's insulation properties seem ok, but couldn't find anything more specific. I've been experimenting with 1mm polystyrene sheet as a square section coil former, but have found that when I use polystyrene cement on the edges it doesn't seem to harden to the same hardness as the rest of the sheet. I can only assume some of the solvent remains in the seam, and I'm concerned this may affect the insulation properties. (The idea was that polystyrene cement is supposed to produce a 'welded' seam. I was actually thinking of constructing my own enclosures in this manner too, similar to your idea in this thread, but 'made to measure'.)
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Is a capacitative shield the same thing as an electrostatic shield? I have some experience with electrostatic shields.
Yes.
Ash Small wrote ...
Would it be necessary to sandwich the foil in polyethylene/polystyrene sheet before wrapping around the core to avoid creating a one turn shorted winding?
Yes, a shorted turn must be avoided at all costs.
Ash Small wrote ...
Do you recommend polystyrene as an insulator? I did some googling and it's insulation properties seem ok, but couldn't find anything more specific. I've been experimenting with 1mm polystyrene sheet as a square section coil former, but have found that when I use polystyrene cement on the edges it doesn't seem to harden to the same hardness as the rest of the sheet. I can only assume some of the solvent remains in the seam, and I'm concerned this may affect the insulation properties. (The idea was that polystyrene cement is supposed to produce a 'welded' seam. I was actually thinking of constructing my own enclosures in this manner too, similar to your idea in this thread, but 'made to measure'.)
Polysterene has excellent dielectric properties and is often used in good quality capacitors.
I have used methylene chloride for welding polystyrene to good effect. I believe that commerical solvent welding gunk contains a mixture of methylene chloride and tetrahydrofuran. Methylene chloride evaporates in a jiffy, so you must be ready to place your materials accurately at once or your plans will come unstuck! It is also possible to infiltrate methylene chloride into a clamped joint by capillarity - by dropping the solvent into the seam with a pipette. As with contact adhesives, it is very difficult to recover from a first mistake.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
Ash Small wrote ...
Is a capacitative shield the same thing as an electrostatic shield? I have some experience with electrostatic shields.
Yes.
The electrostatic shields I'm familiar with have slots in (to allow RF through). Would this application be better with slotted shields or without?
Proud Mary wrote ...
Polysterene has excellent dielectric properties and is often used in good quality capacitors.
Now you mention it, .........
Proud Mary wrote ...
I have used methylene chloride for welding polystyrene to good effect. I believe that commerical solvent welding gunk contains a mixture of methylene chloride and tetrahydrofuran. Methylene chloride evaporates in a jiffy, so you must be ready to place your materials accurately at once or your plans will come unstuck! It is also possible to infiltrate methylene chloride into a clamped joint by capillarity - by dropping the solvent into the seam with a pipette. As with contact adhesives, it is very difficult to recover from a first mistake.
My (fairly extensive) googling on this subject only returned butanone (methyl ethyl ketone) as the solvent used in the commercial stuff. I bought different types of commercial stuff, each with a different viscosity (the thinnest has an applicator like a hypodermic needle for capillary application, the middle one has a brush applicator, and the thickest is in a 'toothpaste' tube) from the local model shop to experiment with.
I've just read the the instructions on the boxes and it seems they will also glue ABS and some other plastics, so I'm now wondering if they do contain other substances. (I'd assumed the thicker ones were just MEK and dissolved polystyrene)
I've just found that the Humbrol poly cement contains butyl acetate. I can't find anything else on the Revell products.
I'll have to try and get hold of some MEK and DCM to try.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
The electrostatic shields I'm familiar with have slots in (to allow RF through). Would this application be better with slotted shields or without?
Shield efficiency falls as frequency rises because of the shield capacitance. Slots, holes, etc allow the shield to continue working as a Faraday Shield, but reduces both its capacitance, and any tendency to form circulating eddy currents.
Here are some handy circuit diagrams:
I'm no authority on solvent welding, Ash, and there may well be better solvents than methylene chloride, which I used because it is inexpensive and easy to get.
It is recommended for use with polystyrene - as is methyl ethyl ketone (MEK) - in this here commercial technical bulletin on bonding polystyrene:
I would expect that thickneners are added to some commercial products to prevent the solvent from running off before it has had time to act, as we find in Nitromors paint stripper, for example.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
jpsmith123 wrote ...
I wish I could find a plastic (ABS) box a little smaller than the one I have.
Something like 4" x 4" x 2" to 2.5" deep, would be perfect for the RTV-potted-teflon-wire-wound HV secondary.
Then once I see how well the Qsil12 RTV works, I'll make another one that also incorporates the multiplier.
You could make one, as I descibed above, out of clear polystyrene CD cases and MEK/DCM, exactly as you describe avove, but with a sealed lid (put on after filling with RTV, possibly with a vent hole for expansion. As I pointed out above, it would be 'made to measure'. I cut the CD cases to size by repeatedly scoring them with a Stanley knife.
You could even use sheet ABS with a suitable solvent/adhesive.
EDIT: I seem to remember that solvents make ABS brittle.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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I might have to do that. Although I hate the thought of the hassle. One of my problems is that I'm sort of a perfectionist, and if it's not perfect, I'll throw it right in the garbage, even if it took me all day to make it.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
jpsmith123 wrote ...
I might have to do that. Although I hate the thought of the hassle. One of my problems is that I'm sort of a perfectionist, and if it's not perfect, I'll throw it right in the garbage, even if it took me all day to make it.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
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Well I'm leaning toward the idea of trying to make some kind of a box, but I think if I do I'll make it out of 1/8" CPVC sheet, since I can get it fairly inexpensively from McMaster-Carr, and since I have a little bit of experience with that stuff.
I just have to figure out how to go about doing it...
It would probably be easier if I had a milling machine, but all I have is a sloppy Ryobi drill press and a sloppy cross-slide vise.
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A New Idea For Ferrite HVHF Transformer Construction
It is also possible to infiltrate methylene chloride into a clamped joint by capillarity - by dropping the solvent into the seam with a pipette. As with contact adhesives, it is very difficult to recover from a first mistake.
