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Lightweight air core transformer?

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LAN_403

Uspring

Sat Aug 20 2016, 08:54AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

says densities are around 5 g/ccm. The data sheets, search e.g. in

will give you the physical dimensions and/or volume from which you can calculate the mass. The 43813 has about 10 ccm.

Robert Clark

Sat Aug 20 2016, 02:35PM

Registered Member #58454 Joined: Thu Feb 18 2016, 06:33AM
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Posts: 23

Based on this, the core should weigh approx. 50 grams. Assuming the core takes up most of the weight, then even when you include the wiring the weight will still be approx. 50 grams.

On page 9 of that report:

is also given the wattage rating from 200 watts to 1,000 watts dependent on frequency. But I don't see the voltage rating, i.e., what's the voltage input and output.

Bob Clark

Dr. Slack

Sat Aug 20 2016, 04:20PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The core only determines the maximum voltage in a quite complicated way, not as simply as for power.

In simple transformer theory, you can use any number of turns, and the more turns, the more voltage. In practice, the more turns, the higher the self capacitance of the coil, and the lower the frequency it must run at. A lower frequency reduces the volts per turn for the same B field, but it does allow you to use a higher max B field, which is usually limited by core loss induced temperature rise of the core. There are several different ways to wind the coils, needless to say the simplest has the highest self capacitance. The maximum voltage you can obtain will be effectively impossible for the core manufacturer to tabulate.

It would be good to study a small TV flyback transformer, and see how far that can be pushed in power before it smokes. That way, the difficult job of winding and insulating a low capacitance secondary has already been done for you.

It might also be worth experimenting with driving a transformer in resonance, which uses the coil self capacitance as a useful component rather than a troublesome stray. You can also get a significant voltage rise with resonant operation, and it also allows you to use lower coupling, which improves primary to secondary insulation.

Assume that *anything* not designed specifically for low weight flight will have excess mass that can be designed out. While it might be helpful to get ideas from general purpose components, there will always be scope for weight loss.

DekuTree64

Sat Sept 10 2016, 03:16AM

Registered Member #54596 Joined: Fri Mar 06 2015, 11:31AM
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Posts: 19

I've pondered the idea of air core transformers for this as well. Possibly a Bitter electromagnet made from aluminum foil.

Seems the basic concept of a switching power supply is to store up energy in a magnetic field and then cut the loop and catch the voltage spike. So the objective is to store as much magnetic energy in the smallest mass possible. If you can store it in air, that's about as light as it gets :) But if I understand things correctly, the permeability of air is so low that it ends up being better to use iron anyway.

There are two main avenues for thrust improvement that I know of: much higher DC voltage, or carefully timed AC waves like a linear particle accelerator. Either way, you get to use each ion for a longer period of time, which gives better efficiency.

Reaching 200+kV is a challenge, so the AC version may be the better way to go. But very tricky to get the timing just right so the ions "surf the wave", being slowed down from collisions with neutral air particles, but pulled forward equally by the local E field.

Tesla coils can generate very high voltages without too much difficulty, but I don't know any way to rectify it. It may be possible to generate the AC wave with a Tesla coil, but I'm not sure it's ideal for that either, since I don't think you need really high voltage if you get the timing right. And Tesla coils are built for a specific frequency, whereas it would be better if you could vary the frequency to find the maximum thrust point.

klugesmith

Sat Sept 10 2016, 08:16AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714

Hurrah for Francis Bitter!

DekuTree64 wrote ...
...Seems the basic concept of a switching power supply is to store up energy in a magnetic field and then cut the loop and catch the voltage spike.

That's the basic concept of a flyback converter. It's used in only the simplest, least-powerful SMPS designs (and, uh, television sets, and engine ignitions).

Ordinary transformers, whether for mains frequency or switchers, receive power into primary and deliver it out of secondary concurrently (pun intended). They would have no energy in the magnetic field if their cores were infinitely permeable. Core saturation would still put a limit on volt-seconds per turn per cycle.

HiVi

Thu Sept 29 2016, 04:17PM

Registered Member #57532 Joined: Sun Oct 18 2015, 03:19PM
Location: Slovenia
Posts: 4

Bob, i suggest you to read following document, there is already a study on weight optimisation of transformer:
Development of High Frequency Low Weight Power Magnetics for Aerospace Power Systems
Also ferite core and highest frequencies are not answer to everything.

Long story short, i can assure you air core will not bring you anwhere near power efficiency and density for working autonomous lifter.

I suggest next time to post such thread to High Voltage section, or maybe move it there. I didnt see it till now.

Sulaiman

Thu Sept 29 2016, 04:44PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

not quite what is wanted but could be useful;

instead of Al foil for the lifter lower electrode, wind a single layer solenoidal coil of many fine turns
use the output of this coil with a C-W type voltage multiplier for the corona wire eht
remotely power the craft from below using an eBay 1000W zvs inverter.

Nik

Fri Sept 30 2016, 01:55AM

Registered Member #53 Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638

This isn't necessarily the safest way to power a remote controlled device BUT, could a microwave generator and rec-tennae be used? I have seen them used in a space elevator demo, from what I gathered the rectified microwaves gave a pretty high voltage. Maybe something like a combination antenna/CW multiplier could get it up to the voltage required for the lifter. If so it would be a lot of light diodes and maybe a few medium sized caps, the rest of the power supply could sit on the ground (in a well shielded enclosure). Any thoughts?

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