Hello, which is the most correct orientation for an air inductor positioned (glued) above a laminated EI transformer (or better laminated EI choke) for the less mutual inductance: A, B or C?
I would say C but not sure.
I would say C but not sure.
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C. Why?
A is wound the same direction as the coils inside the transformer, on the central core rotational axis. The Laws of Magnetics however theoretically exclude the net magnetic path at A from having any net coupled induction vector. Problem is, in the real world, magnetic fields leak, and do not leak perfectly symmetrically. The asymmetric magnetic field leak gives rise to the A coil picking up signal.
B is actually somewhat worse than A because it is a 90° rotation of the internal transformer windings, also paralleling the 90° turn of the interior magnetic field itself. For any leaking (again, asymmetric not by design, but happens chance) field, B can pick it up well.
Ultimately C is the best because the 'turning field' of the core is running in the same direction as the pickup coil windings, which by magnetics 'right hand rule' doesn't induce a net coil voltage thru the center of the pickup coil.
And al of this is moot … once you take a real pickup coil and move it around next to a live transformer, to see how it all works. There will be many null points in different directions and placements, depending on the asymmetric fields of the transformer's manufacturing real-world short-comings.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
A is wound the same direction as the coils inside the transformer, on the central core rotational axis. The Laws of Magnetics however theoretically exclude the net magnetic path at A from having any net coupled induction vector. Problem is, in the real world, magnetic fields leak, and do not leak perfectly symmetrically. The asymmetric magnetic field leak gives rise to the A coil picking up signal.
B is actually somewhat worse than A because it is a 90° rotation of the internal transformer windings, also paralleling the 90° turn of the interior magnetic field itself. For any leaking (again, asymmetric not by design, but happens chance) field, B can pick it up well.
Ultimately C is the best because the 'turning field' of the core is running in the same direction as the pickup coil windings, which by magnetics 'right hand rule' doesn't induce a net coil voltage thru the center of the pickup coil.
And al of this is moot … once you take a real pickup coil and move it around next to a live transformer, to see how it all works. There will be many null points in different directions and placements, depending on the asymmetric fields of the transformer's manufacturing real-world short-comings.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
You want as many of the intersecting field lines to be as ortogonal as possible. Field lines come out straight of inductors hole but comes back in a loop... so I suppose it matters how far away they are from each other... get the iron shavings (?) on a paper and place the offenders - study the patterns. Dont miss on the hight 👍 axis ;-)
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The answer to this question stems from Physics. Magnetic lines of force form a closed loop. In a EI cored transformer, the flux loop passes through the central leg in the E core part, this usually has some sort of bobbin with insulated copper coils wound around it. The direction is in parallel to the central leg in E with flux being directed to the other two legs to return back to the central leg. This means, any leakage flux flowing through air must also pass through the bobbin. The flux form an imaginary fountain of flux with its 'water source' as the central leg of the bobbin. Leaking magnetic flux should be, therefore in parallel with the central leg in the E. However, this depends on other factors like the presence of magnetoferric materials which offer a path of very low permeability for the leakage flux.
In a few words, the most obvious choice is to put the axis of the external inductor at right angles to the path of leakage magnetic flux. Although, this seems like an easy task it can easily result in the inductor picking signals from the transformer. The induced voltages in the inductor must be such as to completely cancel out, and this is extremely difficult to achieve with an inductor next to a transformer.
In a few words, the most obvious choice is to put the axis of the external inductor at right angles to the path of leakage magnetic flux. Although, this seems like an easy task it can easily result in the inductor picking signals from the transformer. The induced voltages in the inductor must be such as to completely cancel out, and this is extremely difficult to achieve with an inductor next to a transformer.
Run the trafo as intended. If its also a filter componenet, run something trough it with a generator. Take inductor and hook up a volt meter. Position inductor and read meter... reposition.... optimize 🙂
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C is the least worse. They all risk coupling substantially to the leakage field I reckon. I'd mount the inductor in front of the transformer with a horizontal axis. There are ways to measure the coupling with headphones and a signal generator (assuming everythings disconnected). The T-junction of an EI core and the corners are where I'd expect field leakage to be strongest. Getting away from the iron is good news.
(you will directly involve the transformer core in your inductor if its near the iron, changing its inductance).