Foam Insulated Wire

On the other hand, it suggests a resonant approach might be quite handy...

BTW, I've taken apart VCR power supplies with this really thick insulated wire inside for the primary. It's triple insulated, so like, enamel and plastic on the wire, plus mylar tape between layers. They didn't use any varnish, which I guess was the point.

Tim

:> Your foamed wire is trading capacitance for leakage inductance. Surely not :> a great thing at 1MHz. : :On the other hand, it suggests a resonant approach might be quite handy... : :BTW, I've taken apart VCR power supplies with this really thick insulated :wire inside for the primary. It's triple insulated, so like, enamel and :plastic on the wire, plus mylar tape between layers. They didn't use any :varnish, which I guess was the point. : :Tim

I don't think the use of extra insulation is intended to compensate for lack of varnish. Properly built transformers use varnish under vacuum impregnation mainly to prevent the ingress of moisture which can cause breakdown under high voltage conditions. Secondly, the varnish prevents any movement of the conductors thus minimising magnetostrictive noise, particularly in smps transformers. Even with the extra insulation techniques in your VCR psu the transformer would have benefitted from vacuum impregnation. However, this step does involve a further costly process which is probably considered unwarranted in some brands of consumer equipment.

In the case of lowering inductor loop to loop to loop etc. capacitance, there's no lower dielectric than air (practical). Creating the air spacing in my case seemed like more work than just winding with teflon insulated hook up wire.

I did dream up putting blobs of glue every few mm on magnet wire so that windings would be spaced apart. But there's no way of getting perfect spheres that are centered. And thought about using tiny plastic beads (jewelry) but guessing this will be a pita to find.

The chances of it ever being more than a prototype reduce unless there are pretty serious performance benefits, in use.

You do get some interesting options when you start winding film-wrapped foil on these cores, with 3xFEP magnet wire or litz in a slab-like structure, ignoring the center post as a magnetic path. When power levels and core cross-sections start to dictate close to unity turns, it gets real interesting, but you need real manufacturing skill in-house and a real application to get any joy out of it. Wallace et all at WEMPEC and Steigerwald at GE fooled with these shapes for a while in the 90s.

RL

I might Google around to see if I can dig up some low-capacitance inductor constructions.

RG-196 is close. So is 0.086 inch semirigid / RG-405. First page,=20 google is your friend.

The big guys do it by spacing the windings with splints of wood, but this is done to increase voltage capacity and allow the circulation of cooling oil. Could always be something analogous, but *shrug*...

Tim