Do power inductors having an aluminum winding (or a light weight winding) exist? [closed]

Question

I need the lightest power inductors possible. Do inductors having aluminum windings (or any light-weight winding) exist?

I would also consider hollow-core wiring to be used at very high frequencies, like 2 MHz. At those frequencies, it would make sense to have the metal where the current is going to flow anyway.

Mattman944 wrote:

So, your real goal is light-weight power (voltage) conversion. Operating at a very high frequency is a great way to minimize your inductor size. That is how they get the phone chargers to be so small. Look around for devices that already have solved this problem.

That's a good idea, Matt, but I've already done that. I've been taking apart all kinds of converters for years, so I agree with you -- try to learn from existing practice. But I have an extreme use case, and don't have a spare airplane to take apart.

In the question, "Why don't we use 7075 aluminum Ethernet and USB cables?" a comment by Harper - Reinstate Monica under an answer stated:

When you compare by weight, Al is twice as good a conductor as Cu.

So I know I'm not off-base here.

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EDIT 1

Since I asked this question, I have found one Microwave Oven Transformer (MOT) where both windings were aluminum (obvious as I cut the secondary off). Also, 3 MOT primaries that I removed were all aluminum (the one pictured is about 790uH and <500mOhm).

Two views of one of the aluminum MOT primaries:

My thinking in including these pictures as evidence for question validity follows:

If an aluminum-wound power transformer exists, then that is close enough to suggest the existence of an aluminum-wound power inductor.

I know that this is a transformer winding, but in its air-core form, it is an inductor all by itself, and I believe, efficient enough to be considered a power inductor, even if it is air-core.

Answer 1

I'm not aware of aluminum being chosen for on-board inductors, but perhaps they are out there.

The gains from pushing to higher frequencies, are far greater than the gains from using different materials. Broadly speaking, inductor Q goes as sqrt(F), so you can shrink the inductor by maybe 30% by doubling the frequency -- although this reduces its surface area as well, so it'll get hotter, and the real reduction might be more like 15%. Or if you quadruple frequency, that might put it closer to 30%. Compare a 260kHz LM2671 to a 2MHz MP2457, along with all the support components required (there are savings in smaller capacitors, too!).

Whereas the savings from wire alone, are 40% for the wire in and of itself, but there's insulation, core material (an air-core coil will be MUCH heavier for the same specs at these frequencies!) and the whole rest of the build, to consider; all together, that 40% improvement might be diluted to a couple percent. It has no effect on core size, nor capacitors or anything else. And the component will be physically larger, which may be of some consequence to EMI (i.e., it's a larger antenna -- by maybe just a couple dB, but still, "strictly worse").

There may also be advantage in using other construction methods (e.g. litz cable versus solid wire), though this won't really be applicable at these frequencies or scales (but is very helpful in the 200W+ and 300kHz+ range, particularly for DCM/BCM operation, or resonant converters). And, not that this is exclusive to copper, but you will have an even harder time finding aluminum wire usable this way(!).

So, in short: the gains from material choice are nearly negligible, whereas there are much larger potential gains from just designing it better. Still, when you're spending millions of dollars putting something in space, say, you reach for even the highest-hanging fruit, so maybe these are used in aerospace -- but don't expect to find them off the shelf, at least not for any price you'll want to pay(?).

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The other major use case, is anywhere low frequencies are stipulated -- military and aircraft often use 400Hz AC for example. You're stuck on miniaturization, you can't design your way out of that -- at least, not without a lot more work and compromise. In that case, it's a great choice. Such iron-core transformers and inductors also need quite a lot of wire, and there's no support circuitry, it's just a dumb part, so the gains aren't diluted as much.

Pushing flux density up is also a priority (minimize core weight/volume), which also means losses need to be kept minimal (and/or allowing higher operating temperatures -- higher class insulation), so I would expect amorphous/nanocrystalline materials are of interest here, or at least much finer laminations/stripwound cores of lower-loss alloys.