Re: Lightweight air core transformer?
Sulaiman, Fri Aug 12 2016, 09:33AM

have you looked here ?

a few random thoughts;

how will you stabilise a free-floating lifter ?
could you consider a helium baloon to neutralise most of the weight, and give stability?

copper wire is dense, consider aluminium or carbon ?

how will you remotely control the power?

I believe that the power-to-weight ratio of a high frequency ferrite=cored transformer is better than air-cored,


everyone knows that UFOs get their power from the mothership,
maybe 'wireless power transfer' is practical at short-range?

Re: Lightweight air core transformer?
Robert Clark, Fri Aug 12 2016, 01:14PM

Thanks for the response. That link you provided is one that all researchers on the lifters have read. In that page, like with all other researchers, they use iron cored transformers to get the high voltage. But these are too heavy for the lifters to raise.

You can stabilize the lifter by actively varying the angles of the collector plates at the bottom.

The air core transformers look light to me because all they consist of is wires, no iron core. But perhaps this results in low power efficiency.

I was not aware you could get a high frequency iron core transformer. I thought air cored was used for that.

Do you have an example of an iron core that can get better than 1 watt per gram power to weight ratio?

Bob Clark

Re: Lightweight air core transformer?
Mads Barnkob, Fri Aug 12 2016, 01:56PM

You would have to build a high frequency high voltage switch mode power supply, that could use a small planar high voltage transformer with multiplier stages after.

High frequency implies that you do not use iron core transformers anymore, but ferrite cores of different material composition depending on your switching frequency. But you are properly most likely to be with the spectrum of MnZn cores.

Re: Lightweight air core transformer?
Finn Hammer, Sat Aug 13 2016, 05:13AM

Robert,

It would help a lot if you would come forward and describe what you want the lifter to do, for example: "I want to build a lifter that can fly by itself and be remotely controlled".

Since you are so concerned about the weight of the power supply, I assume that you want to float it on the lifter.
Is this a correct assumption?.
In that case, you also have to float the power source, batteries, they are heavy too. Have you considered that?
And grounding of that power supply? Drag a ground wire after the lifter?

Cheers, Finn Hammer

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 13 2016, 06:46AM


Thanks for the response. Yes, I want a lifter that can fly independently without being attached to a power supply left on the ground. This would be a completely new, practical form of transportation. Silent, with no moving parts, completely emission free.

I have looked at the batteries part of the equation. Surprisingly, high power density batteries do exist. They are used for example for radio controlled airplanes and helicopters where you need high power at lightweight to drive the propellers or rotors. I've seen battery power(watts) to weight(grams) ratios of better than 10 to 1, i.e., these batteries can put out more than 100 watts of power at only a 10 gram weight.

Since the lifters can raise in the range of 1 gram in weight, i.e., the thrust, per 1 watt of power input, this would be well within the requirements to get an independently flying lifter.

It's the high voltage power supply that is the stumbling block to getting them to fly independently. Do a google image search on "lifters", "power supply", and "high voltage". You'll see the lifters are quite light, in the range of a few grams, but the power supplies are large and heavy in the range of a few kilograms.

Bob Clark

Re: Lightweight air core transformer?
Finn Hammer, Sat Aug 13 2016, 09:02AM

Bob,
When The typical power supply is heavy like a brick, it is only because The Random experimenter does not know better.
Try to have a look at The supply nested inside a taser stick, The small handheld units that advertise megavolts, but dont deliver close to that, still, rectify, and you might be flying.

Cheers, Finn Hammer

Re: Lightweight air core transformer?
Sulaiman, Sat Aug 13 2016, 09:04AM

can you specify the eht psu a little better ?
e.g. voltage and current and weight required

I suspect that mechanical movements to achieve stability is a poor choice because
. it will add significantly to the overall weight
. the craft will no longer have no moving parts
. for a triangular lifter you could use three separate inverters with variable outputs

Finn : I believe that there is no need for an earth wire,
it is just the p.d. between corona wire and the rest that is required

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 13 2016, 01:49PM


The specs of the lifters built by one lab are here:



You see the best thrust to power they could manage was about 1 gram thrust per watt of power. For instance the basic triangular Super Cell V1.0 lifter listed there got .15N thrust, about 15 gram-force, using 14 watts of input power.

This particular one used rather higher voltage though of 54 kV. So the amperage was 14W/54,000kV = 0.25 mA.

Bob Clark

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 13 2016, 01:55PM


I think these work by using capacitors which are known to be able to put out high power but only for a short pulse for a few seconds. We need a power supply to work for several minutes continuous.

Bob Clark

Re: Lightweight air core transformer?
Hazmatt_(The Underdog), Sat Aug 13 2016, 05:27PM

Hi Bob,

This is a 300V (can go to 450V if you're not careful) SMPS I'm designing for a friend of mine. Runs off of 9-15V, 86% efficiency at the moment, should be higher soon, and it is VERY HEAVY for 20W.

Many people have tried, but the major problem is the power source, ultimately a battery, is very heavy.

and trying to get 50-75KV out of a compact SMPS is a challenge.

Instead of trying to make the supply smaller, you are going to have to make the lifter surface area larger.

If you do the calculations for the energy required (I have not), I would bet you a can of coke that to get 15 min. run time of a self-contained lifer, that is battery and SMPS, the power source would probably weigh no less than 10 lbs, and the lifter would be nearly the size of a Football field.

I'm not trying to be mean or anything, just realistic.

Re: Lightweight air core transformer?
jdub1581hv, Sat Aug 13 2016, 08:59PM

how bout a small flyback (lopt) xfmr such as those used in plasma globes and those from small crt tv's (5" or less) / 1980's cam-corder eyepieces?
drive it with a SMT mazzilli zvs driver (logic lvl mfets) from a single 18650 lipo (high discharge rated)...
Smallest thing I can think of... and still going to be heavy for the ionocraft

Re: Lightweight air core transformer?
Sulaiman, Sat Aug 13 2016, 09:24PM

I thik that 10 lbs. is very pessimistic,

since batteries seem to be around 0.2 g/W
the most obvious solution seems to be many many small LiPo cells in series
impossible to get more W/g


do not ask me how to switch it on/off without electrocution

P.S. regarding stability:
the lower vanes can be simply operated by a central pendulum connected by a thin metal rod.
one pendulum can control multiple surfaces.

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 13 2016, 09:54PM



I looked at small transformers available for purchase and they had worse than 1 to 3 power(watts) to weight(grams) ratios. I would think if these commercial products such as plasma globes had very light for their power transformers then such would be available for purchase, but I haven't seen any. Remember it's not just they be light weight, but also high power for that light weight.

See for example the small sized high voltage converters here:



In the example of the plasma globe it's likely the transformers are small but the power requirements are smaller.

Bob Clark

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 13 2016, 10:28PM


The weight of the batteries is not really the problem. Batteries of high power for the weight already exist because they are needed for small electric powered airplanes and drones. See for example the batteries here:



They already get multiple times better than 1 watt power per gram of battery weight.

Many amateurs have built tesla coils (air core transformers). What are some of the power to weight ratios for those?

Bob Clark

Re: Lightweight air core transformer?
Hazmatt_(The Underdog), Sun Aug 14 2016, 04:19PM

A 1 KG lifter, total weight, 1m off the ground for 10 min. requires 600W of electrical power at 100% efficiency, or 720W at 80% efficiency.

So if you can manage 720W/KG, that's what you need.

Re: Lightweight air core transformer?
Uspring, Tue Aug 16 2016, 01:35PM

Robert Clark wrote:

But how lightweight can an air cored transformer be? Less than 1 gram weight per watt power output would be ideal.

From a formal point of view, there is no weight/power ratio for air cored transformers. Imagine a transformer loaded by some resistance with an input voltage of say 10 V. There will be some current in the windings causing losses due to the copper resistance. Now apply a 100V. Then currents will be multiplied by 10. Input power will be multiplied by 100. Losses will also be multiplied by 100. So the loss to power input ratio i.e. the efficiency will stay the same. Your transformer might go up in smoke, but that is a cooling issue not one of efficiency.

You will want, of course, the transformer to be efficient, aside from the power it can handle. That's an interesting question by itself, so I went through the math initially neglecting skin effects. The result is surprising. For a toroidal shape, the power loss fraction depends solely on the mass of copper m, frequency f and the size of the toroid s. The result is:

Ploss/Pinput = 20000 kg * s / (m * f), s in m and f in Hz.

So for a 5cm toroid and a frequency of 50kHz, the power loss would be about 10% for 200 g of copper. That is quite a bit and since I neglected skin effects, the efficiency could be significantly worse. A large frequency increases efficiency only up to a certain point, since the skin effect will limit efficiency gains.

I believe you will be better off with a ferrite core. That will reduce the amount of copper needed so that its weight becomes insignificant compared to the weight of the core. There are cores in the 10s of grams range, which can handle a kW of power at say a 100kHz. It probably makes sense to add a Greinacher multiplier stage behind the transformer in order to alleviate insulation issues.

Re: Lightweight air core transformer?
Robert Clark, Tue Aug 16 2016, 02:40PM


Thanks for the informative response. Perhaps switching to aluminum wires would save on the weight of the wiring? Aluminum weighs 1/3rd as much as copper.

About iron or ferrite core transformers the best I could find in power to weight ratio were in the range of 1 watts per 3 grams. But the lifters can only manage about 1 gram-force thrust per 1 watt of power input. So we would need to improve the power to weight ratio of the transformers by better than 3 times for this to work.

A transformer you mentioned at only 10's of grams weight able to handle a kW of power would work if it can go into say the thousand volt output range. Do you have a link for it?

Bob Clark

Re: Lightweight air core transformer?
Uspring, Wed Aug 17 2016, 08:37PM

There is a table in here along with other useful info. I think the 43813 weighs less than 100g. But there may be better ones.

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 20 2016, 05:49AM

Thanks for that. I looked at the link, and while it did give equations for calculating the wattage of a transformer, it didn't give any weights. The 1 watt per gram goal is a severe constraint.

Bob Clark

Re: Lightweight air core transformer?
Uspring, Sat Aug 20 2016, 08:54AM

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.

Re: Lightweight air core transformer?
Robert Clark, Sat Aug 20 2016, 02:35PM

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

Re: Lightweight air core transformer?
Dr. Slack, Sat Aug 20 2016, 04:20PM

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.

Re: Lightweight air core transformer?
DekuTree64, Sat Sept 10 2016, 03:16AM

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.

Re: Lightweight air core transformer?
klugesmith, Sat Sept 10 2016, 08:16AM

Hurrah for Francis Bitter!

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.

Re: Lightweight air core transformer?
HiVi, Thu Sept 29 2016, 04:17PM

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.

Re: Lightweight air core transformer?
Sulaiman, Thu Sept 29 2016, 04:44PM

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.

Re: Lightweight air core transformer?
Nik, Fri Sept 30 2016, 01:55AM

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?