Maker Pro
Maker Pro

Inductive Coupling through a Steel Enclosure

M

Ms.Malamu Habavir

Jan 1, 1970
0
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.
 
H

Henry Kiefer

Jan 1, 1970
0
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
 
M

Ms.Malamu Habavir

Jan 1, 1970
0
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
 
H

Henry Kiefer

Jan 1, 1970
0
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
 
J

J.A. Legris

Jan 1, 1970
0
Ms.Malamu Habavir said:
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.

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:

http://www.mag-inc.com/ferrites/ferrite_pot_cores.asp

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).
 
M

Ms.Malamu Habavir

Jan 1, 1970
0
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?
 
H

Henry Kiefer

Jan 1, 1970
0
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 [email protected]

- Henry
 
Z

Zak

Jan 1, 1970
0
Ms.Malamu Habavir said:
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?

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
 
J

John Popelish

Jan 1, 1970
0
Ms.Malamu Habavir said:
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?

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.
 
H

Homer J Simpson

Jan 1, 1970
0
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.

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

Ms.Malamu Habavir

Jan 1, 1970
0
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?
 
M

Ms.Malamu Habavir

Jan 1, 1970
0
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?
 
M

Ms.Malamu Habavir

Jan 1, 1970
0
So basically, two coils with signals 180° out of phase. One coil generating
a negative pulse when the other is generating a positive pulse?
 
J

John Popelish

Jan 1, 1970
0
Ms.Malamu Habavir said:
So basically, two coils with signals 180° out of phase. One coil generating
a negative pulse when the other is generating a positive pulse?

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

Google [pot core].
 
D

Don Lancaster

Jan 1, 1970
0
Ms.Malamu Habavir said:
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.

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
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
D

Don Lancaster

Jan 1, 1970
0
Ms.Malamu Habavir said:
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
You will have as much luck inductive coupling through steel as you would
light.


--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com
 
H

Homer J Simpson

Jan 1, 1970
0
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?

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.
 
H

Homer J Simpson

Jan 1, 1970
0
5 mm is an exceptionally long distance for even an unshielded inductive
coupling. Especially if large amounts of energy are to be efficienty
transferred.

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.
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
Ms.Malamu Habavir said:
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?

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.
 
J

John Popelish

Jan 1, 1970
0
John said:
Ms.Malamu Habavir said:
So basically, two coils with signals 180° out of phase. One coil
generating a negative pulse when the other is generating a positive
pulse?

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

Google [pot core].

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

http://en.wikipedia.org/wiki/Magnetic_core

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