Em~~~~inner hole about 25mm, outer circle about 40mm, 10mm height.
The inductance is about 22mH, 50 winds.
Toroid cores are great!!!
You just need to know what compound that the toroids are made of.
Yellow/White is type 26, good from DC to 800kHz.
Green/Blue is type 52, good from DC to 1MHz.
I am currently working with some T250-52 Toroids from micrometals.com
They have been very helpful with all their information.
Check, Pace | Calculator for toroid calculations if you know the AL of the toroid.
If not check, Micrometals, Inc. - Power Cores for the AL specs and plug them into the powermagnetics site for ratio with the AL provided from micrometals.
Toroids are great since you need less wire to make a similar value inductor.
I recently built an air core .4mh inductor from 22 awg wire; It took 26 ft of wire. Two days later I built the same inductor with a T130-52 toroid and it took 8.6 ft of 22awg.
I am learning about Toroid cores myself.
Jantzen is producing toroid "C-Core" inductors with values from 1.5-18mH.
They have to be worth it if the commercial sector is willing to put R&D into it.
I would stick to type -26 and type -52 for x-over use since they are intended for use from DC "0hz" to up to 1MHz.
You just need to know what compound that the toroids are made of.
Yellow/White is type 26, good from DC to 800kHz.
Green/Blue is type 52, good from DC to 1MHz.
I am currently working with some T250-52 Toroids from micrometals.com
They have been very helpful with all their information.
Check, Pace | Calculator for toroid calculations if you know the AL of the toroid.
If not check, Micrometals, Inc. - Power Cores for the AL specs and plug them into the powermagnetics site for ratio with the AL provided from micrometals.
Toroids are great since you need less wire to make a similar value inductor.
I recently built an air core .4mh inductor from 22 awg wire; It took 26 ft of wire. Two days later I built the same inductor with a T130-52 toroid and it took 8.6 ft of 22awg.
I am learning about Toroid cores myself.
Jantzen is producing toroid "C-Core" inductors with values from 1.5-18mH.
They have to be worth it if the commercial sector is willing to put R&D into it.
I would stick to type -26 and type -52 for x-over use since they are intended for use from DC "0hz" to up to 1MHz.
Type T cores are powdered iron core, "better for audio" type 26 & 52.
Type FT are for RF chokes in radio communications MHz range.
Using an FT in a T role will result in quick saturation "distortion" due to leakage & saturation. If you are using a type T "powdered iron" toroid and you are saturating you might look into fracturing the core into two identical halves and epoxying them back together. This break in the physical toroid can increase the saturation limit but it will also lower the AL value "mH/turn" of the toroid so more turns will be required.
Check out the LC100-A inductor/capacitor meter for $33 on eBay to get rough measurements of toroids that you build yourself.
Type FT are for RF chokes in radio communications MHz range.
Using an FT in a T role will result in quick saturation "distortion" due to leakage & saturation. If you are using a type T "powdered iron" toroid and you are saturating you might look into fracturing the core into two identical halves and epoxying them back together. This break in the physical toroid can increase the saturation limit but it will also lower the AL value "mH/turn" of the toroid so more turns will be required.
Check out the LC100-A inductor/capacitor meter for $33 on eBay to get rough measurements of toroids that you build yourself.
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You want to watch it using powdered iron and other powder materials for crossover inductors. The inductance coefficient of the higher perm powdered iron materials like Micrometals 26 and 52 tends to vary quite a bit as a function of AC flux density The curves are available at the Micrometals web site. Of course, this will have an effect on crossover frequency as a function of excitation level. Mix #8 is better for in terms of this effect, as it has lower permeability. The down side is that more turns are required, and the spray flux will be worse, as the lower perm materials won't tend to confine the flux as tightly.
^ what? You mean like an air core wouldnt confine flux as tightly either. If large stray field is ok when using air cores, then what of it? Ferrite is fine, just get the largest rated u can, to avoid saturation, and dont try hooking up a chain of smaller ones to get high values. Anything TOO large and id be tempted to use a transformer instead though.
No, an air core inductor is not necessarily ok, especially parked too close to another inductor in the crossover. Crosstalk between air core inductors is well documented. This can be mitigated to a large extent by orienting the air core inductors orthogonal to help minimize the coupling - distance helps, too.
The larger concern for the powder materials is the permeability modulation of the high perm powder materials vs. drive amplitude, something you don't get with air core or a properly designed ferrite inductor. For example,a largish ferrite E core with a center leg gap will have a stable inductance value vs. drive level if properly designed (it'll saturate if not), and the center leg gap is shielded by the windings to a large extent, so spray is not a big concern. The inductance is set by the air gap, and the ferrite just completes the magnetic circuit.
Lower permeability powder materials (such as Micrometals mix 8) do not exhibit a large amount of permeability variation vs. drive level. The down side is that mix 8 is less than half the permeability of the higher perm materials like 26 and 52, so you need 1.4-1.5X the turns for a given inductance (it's also more expensive). The spray can be mitigated to a large extent by using toroids instead of E cores - the geometry and even winding distribution around the core help a lot. Toroids are a pita to wind, but that's the breaks...
The motivation behind using a core material anyway is to reduce the amount of copper necessary for a given inductance, reducing the resistance (also enabling a more compact inductor if done right, and reducing the tendency of coupling between filter elements). The copper resistance will reduce the power delivered to the load, and soften the filter characteristics if significant. The lower the speaker impedance, the more significant this effect.
The larger concern for the powder materials is the permeability modulation of the high perm powder materials vs. drive amplitude, something you don't get with air core or a properly designed ferrite inductor. For example,a largish ferrite E core with a center leg gap will have a stable inductance value vs. drive level if properly designed (it'll saturate if not), and the center leg gap is shielded by the windings to a large extent, so spray is not a big concern. The inductance is set by the air gap, and the ferrite just completes the magnetic circuit.
Lower permeability powder materials (such as Micrometals mix 8) do not exhibit a large amount of permeability variation vs. drive level. The down side is that mix 8 is less than half the permeability of the higher perm materials like 26 and 52, so you need 1.4-1.5X the turns for a given inductance (it's also more expensive). The spray can be mitigated to a large extent by using toroids instead of E cores - the geometry and even winding distribution around the core help a lot. Toroids are a pita to wind, but that's the breaks...
The motivation behind using a core material anyway is to reduce the amount of copper necessary for a given inductance, reducing the resistance (also enabling a more compact inductor if done right, and reducing the tendency of coupling between filter elements). The copper resistance will reduce the power delivered to the load, and soften the filter characteristics if significant. The lower the speaker impedance, the more significant this effect.
mutual coupling you mean, rather than crosstalk... I am very aware of this, but you miss my point.
Air cores: large stray field, need most Cu, least saturation if all else equal.
Hi perm ferrite: small condensed field, least Cu, easiest to saturate.
Point being: a ferrite with low perm, medium Cu, and large field LIKE AN AIR CORE,
is a GOOD thing, since it is the best compromise between sat and Cu. Anyone with any sense will orientate coils at right angles, ferrite or not.
Air cores: large stray field, need most Cu, least saturation if all else equal.
Hi perm ferrite: small condensed field, least Cu, easiest to saturate.
Point being: a ferrite with low perm, medium Cu, and large field LIKE AN AIR CORE,
is a GOOD thing, since it is the best compromise between sat and Cu. Anyone with any sense will orientate coils at right angles, ferrite or not.
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a bit late, but please have a look of the pics
my inductor for the low pass was in pics, it was good in inductance, but only brings distortion.
If the core is made from Micrometals type 52 material and of the size previously described, you would require several hundred turns to obtain an inductance of 22mH.
If your inductance meter is giving you the correct reading, I can only imagine that the core material is made from a high permiability ferrite like those used in push-pull SMPS transformers. This type of material is not suitable for high current/low frequency applications.
Regards
Peter
Micrometals - Iron Powder Cores
If your inductance meter is giving you the correct reading, I can only imagine that the core material is made from a high permiability ferrite like those used in push-pull SMPS transformers. This type of material is not suitable for high current/low frequency applications.
Regards
Peter
Micrometals - Iron Powder Cores
I ain't familiar with the types of cores, so I can't tell if it was type 52.
So, are you meaning that the distortion was caused by core saturation?
And can u explain how does the saturation bring noise?
Thanks for this enlightened post. Its not often that I learn something here at DIY but this discussion was useful. I'll stick with steel laminates.
COIL2M2/2.8/T4
I think you need to be careful here. Most general coils are made for use in SMPS switched mode power supplies like in your PC.
Gentle Ferrites and steel laminates are used in audio. I found the ferrites increased inductance about 4 fold over air core when I did some testing. But even so, a decent 1mH coil gets about 100 turns at a guess. Inductance is the square of the number of turns, so it doesn't get too unmanageable in practise.
So the OP's homebuilt 50 turn 22mH coil is clearly using a much higher permeability material, and it's saturating and not working well:
For interest, below is a 1mH ferrite coil I tested near a metal ground plane. The effect on inductance was dramatic, as was the ability to hear 1kHz test-tone crosstalk on a nearby badly aligned 0.2mH aircoil connected to a tweeter. As you probably know, coils should be aligned at right angles, and kept away from each other for least crosstalk. Film capacitors, happily, were immune to stray magnetic fields when I tested them.
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