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Old 13th October 2011, 04:43 PM   #1
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Default a ferrite inductor for x-over

i made a round ferrite inductor for a power x-over in my sub, but the inductor produced a very high distorsion, can anybody tell me why?

was it a problem caused by the ferrite core or round shape?

thank.
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Old 13th October 2011, 05:04 PM   #2
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Probably because the core saturated.
What size and type of inductor did you use?
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Old 14th October 2011, 02:41 AM   #3
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Quote:
Originally Posted by Einric View Post
Probably because the core saturated.
What size and type of inductor did you use?
Em~~~~inner hole about 25mm, outer circle about 40mm, 10mm height.
The inductance is about 22mH, 50 winds.
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Old 14th October 2011, 03:21 AM   #4
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22mH that's a BIG value. I'd say yes it almost certainly saturated. So you used a toroidal core?
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Old 14th October 2011, 04:05 AM   #5
Einric is offline Einric  United States
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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.
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Old 14th October 2011, 04:15 AM   #6
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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.

Last edited by Einric; 14th October 2011 at 04:18 AM.
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Old 14th October 2011, 05:05 AM   #7
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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.
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Old 14th October 2011, 06:20 AM   #8
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^ 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.
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Old 14th October 2011, 06:56 AM   #9
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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.
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Old 14th October 2011, 08:54 AM   #10
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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.
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Last edited by mondogenerator; 14th October 2011 at 08:56 AM.
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