copper bracket for inductor coil??

[Guest sbalfour]

Today I fashioned a piece of copper strip about 3/4" wide into a

bracket that I used to fasten a .55mH coil to the circuit board.

(I know that a steel bracket might be a problem, but steel isn't

very magnetic, so it would be a small problem. I wished to

avoid it nonetheless). When I measured the coil on the board, the

inductance had risen from .55mh to .68mH! So I removed the coil with

bracket from the board, and cleared the work area, in case I might be

exciting a mutual inductance with one of the other coils on the board

or some piece of equipment nearby. The coil with bracket still measured

.68mH; without the bracket, it was .55mH. Coils are expensive, scrap

bits of copper are cheap. I've got a .68mH coil for the price of a.56mH one. I've never seen this technique/error mentioned anywhere. So what

have I got.. eddy currents? I don't suppose a plastic bracket would do

this, bzzzzzt.

Stuart

[dynaco_dan]

>Today I fashioned a piece of copper strip about 3/4"

>wide into a

>bracket that I used to fasten a .55mH coil to the circuit

>board.

>(I know that a steel bracket might be a problem, but steel

>isn't

>very magnetic, so it would be a small problem. I wished to

>avoid it nonetheless). When I measured the coil on the board,

>the

>inductance had risen from .55mh to .68mH! So I removed the

>coil with

>bracket from the board, and cleared the work area, in case I

>might be

>exciting a mutual inductance with one of the other coils on

>the board

>or some piece of equipment nearby. The coil with bracket

>still measured

>.68mH; without the bracket, it was .55mH. Coils are

>expensive, scrap

>bits of copper are cheap. I've got a .68mH coil for the price

>of a.56mH one. I've never seen this technique/error mentioned

>anywhere. So what

>have I got.. eddy currents? I don't suppose a plastic bracket

>would do

>this, bzzzzzt.

>

Stuart

Hi Stuart;

Steel coil brackets was used by AR to mount their copper coils.

Later brackets included a foam insulation, I assumed it was for a resonance reduction.

[soundminded]

>Today I fashioned a piece of copper strip about 3/4"

>wide into a

>bracket that I used to fasten a .55mH coil to the circuit

>board.

>(I know that a steel bracket might be a problem, but steel

>isn't

>very magnetic, so it would be a small problem. I wished to

>avoid it nonetheless). When I measured the coil on the board,

>the

>inductance had risen from .55mh to .68mH! So I removed the

>coil with

>bracket from the board, and cleared the work area, in case I

>might be

>exciting a mutual inductance with one of the other coils on

>the board

>or some piece of equipment nearby. The coil with bracket

>still measured

>.68mH; without the bracket, it was .55mH. Coils are

>expensive, scrap

>bits of copper are cheap. I've got a .68mH coil for the price

>of a.56mH one. I've never seen this technique/error mentioned

>anywhere. So what

>have I got.. eddy currents? I don't suppose a plastic bracket

>would do

>this, bzzzzzt.

>

> Stuart

>

Careful, steel is highly magnetic and will increase the inductance of a coil if it is nearby. Copper is non magnetic but you have to be very careful not to inadvertently turn the bracket into the secondary winding of a transformer. Personally, I'd uses something electrically and magnetically inert like plastic. Tie Wraps are very useful for a wide variety of purposes. I've also seen coils held together with a variety of tapes and films, even shellacs and varnishes. Those are chosen carefully so as not to be flamable or toxic or for the adhesive in tapes to break down if they are going to get warm. Good Luck.