Sizing Inductors, current capacity

[Ed LaFontaine]

Is there a rule of thumb for sizing inductors?

I am asking with regard to contour shaping elements:

Low mH values, 0.05 up to 0.35 mH, used in mid-range, tweeter or full range networks.

Can I consider inductors in the 0.8 to 1.5 A capacity range? I understand dcr plays has a role here.

[whgeiger]

Originally Posted by Ed LaFontaine

Is there a rule of thumb for sizing inductors?

I am asking with regard to contour shaping elements:

Low mH values, 0.05 up to 0.35 mH, used in mid-range, tweeter or full range networks.

Can I consider inductors in the 0.8 to 1.5 A capacity range? I understand dcr plays has a role here.

Ed,
See
Passive Crossover Network Design
This is the best article I have ever read on passive c/o design.
In general the larger the wire cross-section, the better; and where you start depends on the max. current to be carried. DCR increases with temperature.

Regards,
WHG

[whgeiger]

Originally Posted by Ed LaFontaine

Is there a rule of thumb for sizing inductors?

I am asking with regard to contour shaping elements:

Low mH values, 0.05 up to 0.35 mH, used in mid-range, tweeter or full range networks.

Can I consider inductors in the 0.8 to 1.5 A capacity range? I understand dcr plays has a role here.

...within reason. See
Passive Crossover Network Design
Regards,
WHG

[speaker dave]

Are you talking about air core or iron core? I thought you were worried about iron core saturation, a complex matter.

For air cores I've never worried about it. Most of the inductors I've used have wire way bigger than voice coil wire. Guess which burns out first?

For iron core (of all types) the core is rated for a saturation flux. Induced flux is then proportional to ampere turns (i.e. more turns of a higher inductance value means closer to saturation for a given signal current). Remember that inductance is proportional to turns squared.

David S.

[Ed LaFontaine]

Thanks for the link. I'm reading.

I'm considering whether ferrite core power inductors are a cost effective and suitable alternative to air core inductors...I may be reminded of the folly of my intended frugality (sp?)...I'm learning things I should know at the same time.

[Paul W]

Hi Ed,
Where I've found it can make a difference is the bass XO. Higher resistance in the series inductor(s) can increase box Q/size...you can see this in UniBox etc.

For the mids & up, smaller wire air-core/higher resistance usually becomes part of the overall XO design.

[wakibaki]

Have a look at these:- Inductors Solen S14

...they call them 'Perfect Lay Hexagonal Wound', and I guess you can't get better.

w

[Ron E]

Originally Posted by Ed LaFontaine

Is there a rule of thumb for sizing inductors?

I am asking with regard to contour shaping elements:

Low mH values, 0.05 up to 0.35 mH, used in mid-range, tweeter or full range networks.

Ed, a listening test is where the rubber meets the road and is what I would suggest. if you are talking the usual RL baffle step type circuit, the resistor carries most of the current at high frequencies. how much can you save going ferrite in a 0.05mH coil anyway?

[Ed LaFontaine]

Waki, I have some of those in the x-over I built for Lynn Olson's ME2's many years ago. They continue to satisfy.

Paul, I don't expect to have an audio arena as described in your link for myself...maybe I can build one for my son someday.

The loads on inductors in higher frequency ranges are less than for bass or sub's, No?

One of my questions I hope will be answered here is to determine the suitability of ferrite cored inductors such as this:

SDR1806-221KL Bourns Power Inductors



Or this:

PM2120-221K-RC J.W. Miller Power Inductors

Now, both of these should have ~the same effect on the frequency response. However, the differences in dcr must be taken into account. Also, giving due appreciation to Mr. Elliott, they both contain iron cores, which is way down the spectrum from perfect lay hex coils.

The speakers in mind for this exercise may never see more than 10-15 watts in normal day to day use..

Where in the power spectrum does "saturation" become a concern?

How does saturation manifest itself?

Am I asking the wrong question?

edit: Ron E, I am learning to listen better as I go. Not necessarily baffle step, though good to be an included topic. Wide rangers often benefit from contour shaping at "higher" frequencies.

[speaker dave]

Originally Posted by Ed LaFontaine

The loads on inductors in higher frequency ranges are less than for bass or sub's, No?

One of my questions I hope will be answered here is to determine the suitability of ferrite cored inductors such as this:

The speakers in mind for this exercise may never see more than 10-15 watts in normal day to day use..

Where in the power spectrum does "saturation" become a concern?

How does saturation manifest itself?

Am I asking the wrong question?

If you are only going to send 10-15 watts to a speaker then your inductor requirements are quite mild. I would think you could get by with modest sized inductors.

Work on the issue this way:
What inductnace do I need?
What DCR do I need?
How much will that cost in an air core?
If thats too much, then which iron core?

Saturation forces permeability to drop towards the permeability of air.

A core give you "bonus" inductance for a given number of turns. If you push too much current through (ampere turns) then the bonus inductance drops and you fall back to the air core inductance.

So power supply chokes are rated as "so many milihenries at X current". At low current they would be higher.

Since this is a real time effect it becomes distortion on heavy waveforms. It isn't necessarily just a bass effect although the large series inductors of woofers frequently need low DCR and are the more difficult positions. Tweeter network inductors are often low L and more typically can be made as an air core.

Hard to generalize and I have measured networks where I had to calculate power across each component. You don't always get the result you expect.

Still, for 10-15 Watts I wouldn't loose sleep over core size, although I'm sure others will advise you that compromise equals disaster!

David