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I've been trying to design this inductor for some time now

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Jimmy154

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I'm trying to design these inductors for some speakers that are almost done, except for these 2 - 12 mH inductors.

I have some 12 AWG (2.05 mmin diameter) wire I want to use for these inductors, but I can't seem to find a suitable core. I'm not sure of the current going through them. I made an air core inductor that's 12 mH, but it weighs 8-10 lbs and has a somewhat large .6-.8 DCR. I was thinking of making them with some CRGO (silicon?- don't know what that means) steel laminations made into EI-cores, but they wound up being really expensive and difficult to make. I have just resently heard that some people use large ferrite or iron powder toroid cores for this application, but I'm not sure what kind or if this is the right core. I thought toroids were just doughnuts and then I went to www.dtmagnetics.com and they have "common mode toroids" and they seem to be rectangular, when looking at their dimensions and now I'm all confused about what the core I'm looking for looks like.

All this possibly senseless writing brings me to my question. Does any one know what kind of core I should use?
 

stevez

Active Member
Jimmy - I have a hardcopy design guide published by Amidon Associates. They and a couple of other companies (Palomar might be one) are pretty "hobbiest friendly" and just might have the info you need. Inductor design, including core selection, is pretty involved however design info that you might obtain from Amidon, Palomar (do they exist?) or DT Magnetics might help. I would not hesitate to call or email the suppliers. I've been pleasantly surprized on occasion with the attention given to the small customer.

FYI - from an abbreviated reference I found that an iron powder toroid made with 41 HA material appears to be recommended for low frequency (less than 100 kHz) use. Why that and not something else is unknown to me.
 

hamfiles

New Member
:!: You're using 12 guage wire for the coils? Thats serious heavy duty. I assume your shooting for close to zero ohms dc resistance.

I'm sorry to say I really can't be of much help, as I haven't ever made any high performance speakers. But I will say this. When you wind your own inductors, often the calculated inductance is somewhat different than what you end up actually having. If you're not using an inductance meter, there is a basic field expedient way to measure an inductor to make sure it has the value of Henrys you are looking for.

Just in case you need it, here's a link for how to do this.

http://www.geocities.com/hamfiles/MeasureInductor.htm
 

Jimmy154

New Member
I ran across www.palomar-engineers.com. It never accorded to me to e-mail them though. I will go ahead and do that and also amidon, although I think it talked to some one from amidon already.

For formula I use: "The current in the resistor is simply I = V-resistor/R
Also I= V-inductor/(2*3.1415*L*frequency) = (V/2*pi*F*L)", for frequency I was told by the desinger of my x-over to use 200 Hz and also to use that 12 gauge wire. The resistors are to 1% tolerance 20 ohm resistors wired in parellel to give me an even more accurate 10 ohm, I figure.

I'd like to use CRGO steel laminations for the core I think. It's just obtaining them at a reasonable price that's the problem. I already ordered the wrong cores twice from bytemark.com. I don't want to pay $50 for a set of EI steel cores that might not even work.

Anyway thank you for your help I will e-mail those companies and take a look at the link that shows how to measure inductance. Never hurts to double check if I got the right inductance on my other 10 air core inductors. Which were a piece of cake and turned out beautifully, by the way. Inductances of those: .5, .7082, and .9 mH.

Can you post pictures on in this forum, if they're not URL? Maybe some one could tell me why the inuductors I made out of steel laminations I got out of 2 washing machine motors has an inductance of .08 mH and I could go from there.
 

Jimmy154

New Member
I think I found some toroidal cores

I think I found some toroidal cores that might be good for my application. It's made out of silicon-iron aluminum alloy which is good I think. I'm not sure if toroid cores are good for my application, but the dimensions and material they're made out of is good. The diamensions are 1.84" OD; .95" ID; .71 Height; and permability is 60. It's 77439-A7 on this page http://www.arnoldmagnetics.com/products/powder/pdf/cross_ref_super_mss.pdf

I'm having problems calculating how many mH I can get out of one of these cores. I'm hoping to get at least 2 mH from one core. I don't know if this is possible Duraflux makes the same core and it has a AL of 135 nH.

My two questions are can I use a toroidal core inductor as a passive speaker x-over component? And how many mH can I get out of one of these toroids or 2 toroids stacked on top of each other.

Oh yea, almost forgot none of those companies I e-mailed really told me anything. One told me that "Most audio transformers use Silicon Iron laminated transformers which we do not offer." These toroidal cores are silicon iron, but like I said I don't know if toroids are good for this application and if I can get the inductance high enough. Any one know?
 
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