Toroidal inductors as crossover parts

[Chuck H]

Any drawbacks to this?

I'm working on an attenuator and the some inductors I've found that fit my criteria are toroidal. There is a current thread about pros/cons for toroids as transformers. What are the drawbacks as inductors? They seem to be affordable, smaller in size and lower in DCR than other types.

Thanks

Chuck

[dai h.]

for a reactive dummy load? Are you referring to the Jantzen ones? Sorry I can't answer your question but I spotted those (if those are what you had in mind). Stumbled on some "ERSE" inductors also which looked low cost and apparently avail. in some high mH values.

[Chuck H]

Thanks Dai,

These:

http://www.bourns.com/data/global/pdfs/7100_series.pdf

...And one other similar from the same MFG.

Chuck

[Enzo]

If you are talking about crossovers as in speaker crossovers, check out Parts Express. They have a large selection of inductors for crossovers - as well as the caps, circuits boards, jack plates etc - in a variety of values as well as a variety of sizes for current handling. Very heavy wire ones available for 500 watt crossovers if desired even.

I think the ones in your link are dual inductors used for power line filtering.

From Parts Express, typical air core and iron core inductors:

[Chuck H]

Originally Posted by Enzo

I think the ones in your link are dual inductors used for power line filtering.

What is a "dual" inductor?

Is there a problem with using "power line filtering" inductors in other applications?

I'm not being glib or antagonistic. I actually would like to know if these things have drawbacks. By the specs I thought they would be good candidates. Low DCR, lower field should reduce unit coupling, affordable and compared to the 12mH units I bought from Madisound these are compact. Now I need 25mH. I'd have to series two very large, expensive units from Madisound or Parts Express to get that. I need to spec a part that will keep cost down and be available in bulk.

Chuck

[Enzo]

Steve Connor would probably be far more qualified to discuss this. But those LOOK like what they put in the mains power entry to like switching power supplies. Not just an inductor, it is two on a single core, and since the mains wires running through it are of opposite polarity, any transient something on one will buck the other... or something. It rejects common mode noise. I don;t see why you couldn't use one winding of it, in the same way you can use one winding of a transformer as a choke. But I don;t know.

25mHy is pretty large, are there caps involved? Larger caps are cheaper than larger inductors aren;'t they?


You might find this interesting:
http://colomar.com/Shavano/inductor_info.html

[Merlinb]

Originally Posted by Chuck H

Any drawbacks to this?

I'm working on an attenuator and the some inductors I've found that fit my criteria are toroidal. There is a current thread about pros/cons for toroids as transformers. What are the drawbacks as inductors? They seem to be affordable, smaller in size and lower in DCR than other types.

Thanks

Chuck

In short, no, there is no disadvantage to using a toroid core. Use what you like for trannies or chokes.
Only on these amateur forums do you ever get these threads asking about the difference between toroid v EI core transformers (I suspect it's because most people are used to seeing EI trannies in old equipment). They're all the same- one is a doughnut, the other is a brick, but they do the same thing the same way.

Toroids are smaller and more efficient. They are also cheaper to make nowadays, but usually more expensive to buy (go figure...) because they're so much better than EIs.
Toroids can be run closer to saturation without leaking all over the place, so you can use less metal for a given VA rating, IF you are sure you won't accidentally overload the core. Of course, if you're not sure, you could just use an oversized toroid couldn't you, it'd still be more compact than an EI!
I suspect EIs will have more-or-less vanished from the market in 100 years time, since there's nothing much to recommend them over toroids.

[Steve Conner]

Well, there are toroids and there are toroids.

The parts Chuck H. linked to are indeed what Enzo called "Dual inductors", though the official name for them is common mode chokes.

To be sure, they have high inductance, but they aren't actually designed to store energy. In the intended application, the 60Hz line current flows in opposite directions through the two windings, so the magnetic field from it cancels out, and it sees no inductance. Any RFI trying to leak out of the equipment has to go through the two windings in the same direction, and so sees the full inductance of the choke.

I imagine the DC current rating in the datasheet is for this condition, which would make it a purely thermal rating, not a saturation current, as the current doesn't generate any magnetization. The actual saturation current, if you tried to use it as an inductor, is likely to be very low, because the toroid core is ferrite with high permeability and no airgap. That means non-linear inductance that varies a lot with signal level.

I guess here I'm invoking Murphy's Law of datasheets: Any property of the component that isn't specified on the datasheet will turn out to be worse than you can possibly imagine. And these things are not specified for use as actual signal-carrying, energy-storing inductors.

As a possible alternative, check out the inductors used to suppress RFI in lamp dimmers, they have powdered iron cores that can store a reasonable amount of energy without saturating. I don't imagine these would be linear enough for audio use either. Air cores, or laminated iron with a generous airgap, seem to be where it's at for audio.

[Merlinb]

Originally Posted by Steve Conner

To be sure, they have high inductance, but they aren't actually designed to store energy. In the intended application, the 60Hz line current flows in opposite directions through the two windings, so the magnetic field from it cancels out, and it sees no inductance.

Of course, you could wire the two coils in series for more inductance and no cancelling (provided you got the phasing right), but I don't think they have enough inductance to be useful for audio(?); they're normally for RF supression.

[dai h.]

chuck, there are the ERSE ones I saw:

http://www.erse.cc/coils/superq/supe...ortby=ARC#list

they list a 25mH that appears would work if doing the Aiken reactive load thing (low freq. tank portion)

http://www.erse.cc/coils/results.asp.../superq/sq.jpg

they are cored coils, which appear to be the only way to go (usually) since a 25mH air core with low DCR would be darn HUGE

[Chuck H]

Thanks guys. Enzo, that link went directly to "my favorites" for quick access. Taking a tip from your reference to big caps being cheaper than big inductors I've trimmed down to a 12mH and increased the cap size. The only drawback is that the new arrangement has a slightly narrower bandwidth in the impedance rise. Should be fine though.

Dai, the Erse products look like the most affordable "viable" product. Thank you for sharing. The cost of the Erse product is only about five bucks US over the cheap alternative I THOUGHT I'd found. So that's no bad.

Steve, your absolutely right about the unmentioned parameters. One thing you can count on from advertisers...If you don't see it, it ain't there. Yours and Enzos greater knowledge of the application of specific products helped me avoid a problem here. Thank you.

This is the greatest place. This forum.

Cheers

Chuck