When winding OP-transformers, keeping parasitic inductance and stray capacitance at low values is a good thing.
If there's room to spare inside the lamination window, adding extra layers of insulation would help lessen stray capacitance between layers.
-Would this also result in less coupling between primary and secondary layers, thereby increasing parasitic inductance?
Next question: -Will adding copper foil (electrostatic shielding) between layers decrease stray capacitance?
Transformer design is very much like the ocean, giving with one hand and taking away with the other.
If there's room to spare inside the lamination window, adding extra layers of insulation would help lessen stray capacitance between layers.
-Would this also result in less coupling between primary and secondary layers, thereby increasing parasitic inductance?
Next question: -Will adding copper foil (electrostatic shielding) between layers decrease stray capacitance?
Transformer design is very much like the ocean, giving with one hand and taking away with the other.
Adding copper shield will only redirect the elctric field E to other direction, but still will be there. Never saw such shield in outpit trafos, but in any case I don't see why not to try it.
You're absolutely right. Especially designing an OT always is a compromise. Your idea of decreasing inter and intra winding capacitances by adding more insulation material, for example, also decreases the transformer efficiency, as the windings' DCR increases.
Best regards!
It may well be that increasing insulation by an amount as not to increase DCR too much may not give a useful decrease in capacitance.
These are the things the old guys at the plants who wind good OP-transformers most likely know.
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No because coupling is magnetic; as long as they are wound on the same core ...... no big deal.
But separation will be small anyway and insulating material might have higher dielectric constant than air, so increasing the problem.
There will be a change in coupling coefficient because not all of the flux is confined to the core. Some of it goes through the air, and that amount that’s in common has changed. Not by much but it does change. The better “confined” to the core the flux is (higher effective mu) the less it does change. Tends to affect SE trafos more, because the air gap tends to let more of the flux “leak” in the first place.
The flux that goes thru the core couples both windings. Any flux that circles just one coil (air path) causes leakage inductance. So tight spacing between windings is the general rule (except minimum insulation required for V difference). The great untapped (except for one famous OT manufacturer) technique for reducing leakage L is using a "long" E or going to a toroid. A long air path makes the high mu core much more attractive to the escaped flux. Cut toroids with one or two short bobbins lose that advantage. Long E lams may still be available for "constant V" xfmrs, but their days are long gone with switching supplies these days. Some long E lams have dimensions that will fit TWO standard bobbins on their length, like the one shown below made by Tempel. Some old Kepco power supplies used long E xfmrs to keep a low profile. All the commercial OTs out there use standard "scrap-less" short E laminations, so have to use a high number of interleaves (which by the way make each winding section relatively long and thin) to achieve low leakage L.
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You mentioned using a "long" E laminination, but those are hard to come by, so, is it possible to use two regular E's like this?
For a SE transformer an air gap would be needed and they would also need to be clamped tightly together, which is doable.
One could use two bobbins or fabricate one twice the length.
For a SE transformer an air gap would be needed and they would also need to be clamped tightly together, which is doable.
One could use two bobbins or fabricate one twice the length.
Should work for SE, Make sure the lams are neatly packed with a flat surface for the gap spacer. Probably will need to pack them into the bobbin tightly to avoid buzzing lams. Maybe a big hose clamp around the outside to keep them together tightly.
For P-P it would likely give poor performance unless the lams could be ground perfectly flat and polished. Has to avoid making a short across the surface too.
For P-P it would likely give poor performance unless the lams could be ground perfectly flat and polished. Has to avoid making a short across the surface too.