It adds a bit of leakage inductance, but can still transfer lots of power. Resonate both windings.
I was thinking opposite sides, no added core, resonate the inductors. Rotate one 90 degrees about the common axis so their pads don't align.
Same side has PCB surface leakage/tracking hazards.
I designed an electric meter that could be read if the line power was off, for a country with unreliable power. I transferred about 100 mW over an inch gap with resonated ferrite bar inductors. Sent the data over the same link.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
A single-turn secondary could be enough in some applications. Add a small step-up transformer or a series LC on the high side if the voltage is too low.
60 Hz transformers get around 1 volt per turn. High frequency ones can be a lot more.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
snipped-for-privacy@highlandsniptechnology.com wrote in news: snipped-for-privacy@4ax.com:
Not a great idea though. Ideally one wants to keep the volts per turn pretty low. 1 or 2 volts is good. If it climbs up too much a lot of other considerations have to start being made.
I used it 40+ years ago on some TVs that had cracks in the molded plastic parts in the HV supply that couldn't be replaced. It stopped them from producing Ozone. It didn't dry out, and properly applied, I've never heard of it failing.
snipped-for-privacy@highlandsniptechnology.com wrote in news: snipped-for-privacy@4ax.com:
A 'one turn secondary' would be a serious step DOWN in most cases. It is, of course a direct ratio to the primary turns count.
Step up secondaries, in particular, should not have that high a volts per turn number. Mag wire insulation matters and turns at the end of a winding getting near turns at the start will result in a fail... often.
John Larkin wrote in news: snipped-for-privacy@4ax.com:
You don't get it. A 1500 turn secondary has to have the turn managed such that NO earlier turns get anywhere near ANY upper count turns. 1500 turns of #43, not your impossible insulated wire application. So the volts per turn add up. Too high and the transfomer incessanlty arcs and fails 3 out of 4 builds. Reduce the volts per turn to 1.5 or less and the transformer works, without failure, unpotted. And that is at 58kHz.
But you also have to be smart enough to know how to build an HV transformer with 1500 turns on the secondary that operates unpotted. You cannot simply 'scatter wind' it. It is not merely about the separation of the end nodes of the winding, the turns also have to be kept away from the younger bretheren. 1500 turns was 10 150 turn layers with a 1 mil transformer tape layer between each.
You are not going to get 30kV from one turn. And you would never need 30kV insulated wire on asmall form factor transformer. They likely do not use it in the larger form factor power realm either. The insulation takes up too much space, and usually has thermal issues since the insulation insulates. That is why they too have polymide coated mag wire in use.
The problem under discussion is powering a bit of gear that's sitting way off ground. So one secondary turn has to make a few volts out but be *insulated* for kilovolts.
John Larkin wrote in news: snipped-for-privacy@4ax.com:
Just use two turns or three or four. Use the insulated wire, sure, but you'll get better core couple from a few spaced turns. Also 'powering a bit of gear' from one turn?
Martin Riddle wrote in news: snipped-for-privacy@4ax.com:
Winding to winding capacitance, sure, but not interwinding capacitance.
But no. I know what was being discussed and I know what volts per turn are.
You obviously do not simply because you attempted to "tell what I was talking about".
The winding is layers so that early turns do not come into proximity with later turns. Do the math. 1500 turns at 1 volt per turn means I can put about 150 turns on each layer before the mag wire insulation strength is approached. What you cannot do is allow any of those early layer conductors to get close to later ones. The layers even start inboard so that the layer egdes do not have exposed turns and none "fall down" to lower layers while you wind. Both result in a fail.
TAPE ^_________ ------- ^wire turns
They are 'flat wound' (one layer of turns) so the layer stack is not that great, and the primary goes on the outside. That is the example I was describing. 10 stacks of 150 turns is 1500.
A linear segmented transformer bobbin is similar in that each segment holds some wire, then the winding steps over to the next segment and continues. This is done to limit the number of turns per segment so that first turns do not get near later turns.
If you have never tested or examined transformers in failure and documented failure modes, you may not understand that the first turn is lots of volts separated from the last when there are lots of turns to speak of.
But yeah, I got his post where he is talking about a single turn.
Single turn, smingle turn. OK, consider my single-turn transformer, RIS-480. This had a single turn 2-inch wide copper strip primary, which was powered at 300kHz with 200V. A 38-turn litz-wire secondary, with Q = 1000, pushed 7.5kV into a coax cable and electrode load, with the help of a 15kV glass resonating vacuum capacitor, see some photos:
You only have to insulate against ADJACENT windings, though; with a 30 kV goal, thirty layers (with tape) or adjacent buildups (with disk or air separators) will work fine with the worst insulation (500V) one can get off-the-shelf on the WIRE, the rest of the insulation in spacers and careful structural design. And occasionally some spaghetti insulation... and a LOT of attention to any conductive magnetic elements and fasteners.
The easiest way to make a mass-produced transformer doesn't look like a HV transformer, though.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.