Core lamination

[AndrewT]

Originally Posted by pieter t

Longer cores, required for longer coils, mean longer magnetic path length too......

Pieter.
This is not an attack against what you have posted. I simply quote it because it is a good example of 3 "longer" that are being confused by at least me and seemingly a few others.

Too many "longer".
For the winding, surely the layer is one wire thick or for a 2layer winding, two wires thick.
For the width of the layer, it should be the number of wires laid side by side.
For the length of the winding we should be measuring the wire length used to wind around the core, times the number of turns in that layer.

When referring to magnetic path length, the longer is in a different direction to the longer (of winding) just defined. I see it as the path length around the core that the flux has to travel to get back to the start point for the measurement.

As for longer in respect to core, I don't know what this could be.

Window area and window shape: Let's define what we mean.

Hopefully all confusion will disappear if we agree on what we are actually discussing.

[pieter t]

OK,
Here are the most important abbreviations used in "magnetics" and known to people who are into the matter:
- lfe = mean iron path length (yes mean path length around the core);
- Afe = net iron cross-sectional area (not the same as height x width!);
- Mfe = mass of iron core;
- ha = height of winding space;
- ba = width of winding space;
- lcu = average length of coil winding (average length of one turn);
- Acug = geometrical copper cross-section (ha x ba).
Source: "Strip wound cut cores" by Vacuumschmelze.

[iko]

Which in books written in English might more often appear as:

F = window width [cm]
G = window length [cm]
MPL = magnetic path length [cm]
MLT = mean length turn [cm]
Ac = effective iron area (D x E) [cm^2]
Wa = window area (F x G) [cm^2]
Wtfe = iron weight
Wtcu = copper weight

[pieter t]

Of course there is no standardization in terms.
Ikoflexer: effective iron area is not D x E but about 80 - 90 % of that product (depending on core size).

[Tony]

Longer cores, required for longer coils, mean longer magnetic path length too.

and lower magnetizing current as well....

[pieter t]

Originally Posted by ikoflexer

Which in books written in English might more often appear as....

Well, the Vacuumschmelze "Strip wound cut cores" is also in English as the title already suggests

[pieter t]

Originally Posted by ikoflexer

F = window width [cm]
G = window length [cm]
MPL = magnetic path length [cm]
MLT = mean length turn [cm]
Ac = effective iron area (D x E) [cm^2]
Wa = window area (F x G) [cm^2]
Wtfe = iron weight
Wtcu = copper weight

"ha" and "ba" are more accurate parameters.
F and G are geometrical core dimensions; F and G do not take into account the loss of space by the bobbin.
For example, for an SG89/51 double c-core Vacuumschmelze specifies ha being 20,1 mm, whereas without bobbin there is 22,2 mm of space.

[gorgon53]

Originally Posted by Tony

^well said Gorgon53, i agree with what you expounded re OPT's....

Thanks Tony

[gorgon53]

Originally Posted by pieter t

Longer cores, required for longer coils, mean longer magnetic path length too.
With longer magnetic path length however the primary inductance will suffer compared to a shorter core (same core area and number of windings).
Not a completely free lunch therefore; to reach the same inductance on a longer core more windings are required leading to higher capacities.....

Sure pieter t, no free lunch ever, it is all about compromises. But the 4:1
rated window is still on the short side and will hardly be to long for a audio OPT. The capacity-thing....
The squared effect of the lower voltage/turn of a longer coil givs smaller effective capacitance dispite that more windings are required. The more stretched out coils outside-diam/inside-diam ratio is of advantage.
Less Rac copper losses, less interleaving, less capacitance between layers.
Less interleaving, higher voltage between layers, higher effective capacitance.
Choose your poison ;o)

Anyway, high BW does not really leave to much choice, the coil has to be stretched out more than the EI 3:1 window allows. This is one of the reasons M-cores where introduced in the first place. To be more "universallly" usable
than what allready existed and surely never was intended for audio use.

You clearly get higher BW and lower Rac-losses with the more stretched out coil despite the fact that you need more windings (as is easely confirmed by the high BW toroids can achieve).

[AndrewT]

Gorgon,
what is your "longer"?
A diagram or description maybe.