Inductive Coupling through a Steel Enclosure

I am trying to inductively-couple, for the purpose of charging a battery (capacitor bank), across a 5mm space. On each side of the gap is mild steel channel stock of approximately 10mm thick. The inductive coupling frequency is around 1 MHz. While the coupling works on the bench, the steel greatly affects the field. Is there any technique for lessening the affects? Any links or hints would be greatly appreciated.

Thanks.

Reply to
Ms.Malamu Habavir
Loading thread data ...

As steel is a ferromagnetic material I don't see any change other than to change the frequency up and use a grid of metal. You should think of another mechanic system here.

What is the reason for the steel plate?

- Henry

"Ms.Malamu Habavir" schrieb im Newsbeitrag news:OWV8h.29$ snipped-for-privacy@newsfe22.lga...

steel

frequency

Reply to
Henry Kiefer

Thank you for your comments.

The Steel can be thought of as two steel boxes. Each box has a 20mm hole which are aligned. The coils are set in to the steel and made flush with the surface. The steel is unavoidable. A higher frequency you say?

Malamu

Reply to
Ms.Malamu Habavir

Hm. I don't really realize what you mean in mechanical sense. Is there a NDA requirement?

If you have 20mm holes where you can transmit thru the power, then it would be possible to send the electromagnetic wave if the frequency is high enough. Think of a microwave oven, where you see a fine metallic grid in the front door. The wavelength of the microwave (2.45GHz) cannot pass the small holes in the grid. If you make the holes bigger, the wave will pass!

What is the power requirement? mW, W or kW?

For high-power rf amplifier Class E is interesting. I've done work with it.

If you only want to electrostatic shield the capacitor bank, there would be an Al-foil enough to do. With Al in-between you can even couple magnetic without great problems! Shielding is different in terms of magnetic and electrostatic.

- Henry

"Ms.Malamu Habavir" schrieb im Newsbeitrag news:MBW8h.30$ snipped-for-privacy@newsfe22.lga...

the

to

battery

greatly

Any

Reply to
Henry Kiefer

You need to minimize the reluctance of the magnetic circuit that includes just your cores while maximizing the the reluctance of the magnetic circuit through the steel channels.

First step, shape your cores to maximize the cross sectional area and minimize the magnetic path length that passes through air. One possibility is a horseshoe shape, but better still might be a pot core such as this:

formatting link

Second step, maximize the magnetic path length through air to the steel by making as large a hole as possible, deeply chamfering the inside, and filling it in with a plastic insert (which might also be used to mount your coil).

-- Joe Legris

Reply to
J.A. Legris

Yes, I'm trying not to disclose too much information to protect myself and the company.

I have tried an aluminum shield around the coils with some success. I am using a class E amplifier. I was trying to stay below 1 Mhz for FCC reasons. I came across some literature that the FCC allows inductive coupling in the

13 MHz region.

So I should get better performance at the higher frequency?

Reply to
Ms.Malamu Habavir

The exact frequency is 13.56MHz wordwide. It is almost free to use for anything. There is another at 6.8MHz. At the moment I don't know if this is worldwide.

13.56MHz is a common frequency for power, even class E.

If the mechanic is as I wrote it, then YES, you get more power. If you place a ferrite rod in the hole, or two narrow fronted, then you always get good coupling. The primary ferrite broken in two part with an air-gap and the same as secondary will give even more couping. But I think this is a little tiny in

20mm hole.

Are you primary power limited on the transmitter side?

You can reach me by snipped-for-privacy@gmx.net

- Henry

"Ms.Malamu Habavir" schrieb im Newsbeitrag news:QyY8h.144$ snipped-for-privacy@newsfe14.lga...

reasons.

the

hole

with

than

mild

Reply to
Henry Kiefer

I'd say using a split pot core for the coil would work. That would keep the field out of the surrounding steel and would fit a round hole.

Thomas

Reply to
Zak

Any time a magnetic field passes through a hole in a conductor, a potential is generated around the hole (1 turn's worth) that causes eddy current to encircle the hole. If you could pass two equal and opposite fields (or any even number of pairs) through the same hole, the voltages they generate would add up to zero, eliminating the circulating current.

Reply to
John Popelish

Is it possible to cut a thin radial slot in the steel and fill it with a non conductive material?

Reply to
Homer J Simpson

Picture two hollow stell boxes each with a 20mm hole drilled in them at the same location. The thickness of the steel is aprox. 5mm. The boxes are 9cm cubed. The coils, facing each other, sit flush with the surface of the steel. The boxes are aprox. 5mm apart.

What do you mean by a radial slot?

Reply to
Ms.Malamu Habavir

Thank you for your comments. Is there a paper or website that might discribe the properties of the split pot core in terms of the field control that you might know of?

Reply to
Ms.Malamu Habavir

So basically, two coils with signals 180° out of phase. One coil generating a negative pulse when the other is generating a positive pulse?

Reply to
Ms.Malamu Habavir

rating=20

That is the idea, though you can accomplish the same thing=20 by bending the flux from the inside end of the coil, and=20 sending that back through the hole beside, or around the=20 original flux. A common way to do this is to add a high=20 permeability core to the coil, that has both a center post,=20 and a surrounding shell. When the post is the north pole,=20 the shell is the south pole, and vice versa. A matching=20 core on the receiving side captures the flux from these two=20 poles and wraps it around and through the second coil.

Google [pot core].

Reply to
John Popelish

5 mm is an exceptionally long distance for even an unshielded inductive coupling. Especially if large amounts of energy are to be efficienty transferred.

This is called the "electric toothbrush problem" and it has yet to be satisfactorily solved.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

You will have as much luck inductive coupling through steel as you would light.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

From the center of each 20 mm hole, saw as fine a slot as you wish in one direction away from the coil. Fill with epoxy etc. I expect this would cut a lot of the eddy currents which reduce the coupling between the coils.

Reply to
Homer J Simpson

Yes. It's damn near 1/4" and that's a big gap. Even in a big electric motor that would be excessive, and their magnetic system is designed to work effectively.

Reply to
Homer J Simpson

The usual reason for inductively coupled charging is to pass energy through a container is to maintain the sealed integrity of that container. If you can have holes in it, I suggest putting a plug in one and a socket in the other.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
 Click to see the full signature
Reply to
Paul Hovnanian P.E.

=20

The distance you can transmit energy with a pair of poles=20 depends on the spacing between them. The larger the gap=20 between the opposite poles, the further out the field=20 fringes. This means that the pot core may not give the best=20 performance. See this page for some pictures of different=20 core shapes that are commonly available.

formatting link

If you could find a U or C core whose poles just fit in the=20 hole, you would have a pair of magnetic poles further apart=20 than you would get with a pot core that would produce=20 slightly further reaching fringes. If you could actually=20 place the core in the hole, so that the air gap between=20 halves was very much smaller, then the pot core would be=20 better, because of its symmetry and ease of winding.

Reply to
John Popelish

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.