Hi
in a toroidal coil core. where is the N pole and the S pole?

thx

 

Practically speaking, there are none. The magnetizing current sets up a flux in the core, but it is confined to the core. That is an advantage to using toroids - they tend to keep that magnetic flux confined. If you need poles, which are discontinuities in the magnetic core that allow the field lines to emerge, you will have to saw out a section of the torus.

 

Which is used for devices like tape recorders. The gaps are extra sensitive to magnetic variations.

 

Which is used for devices like tape recorders. The gaps are extra sensitive to magnetic variations.

Do you remember when they tried to manufacture ceramic magnet balls with one pole in the center and the other pole on the outside? It was an attempt at "anti-gravity". Unfortunately the dice of the universe seem to be weighted against this. They were never able to manufacture this.

eric

 

Dang, and I thought I had thought of that first. It was a "pseudo monopole" in my mind.

 

Practically speaking, there are none. The magnetizing current sets up a flux in the core, but it is confined to the core. That is an advantage to using toroids - they tend to keep that magnetic flux confined. If you need poles, which are discontinuities in the magnetic core that allow the field lines to emerge, you will have to saw out a section of the torus.

What if the toroidal core is made off multiple pieces semicircle stuck together? how can I avoid flux leaks?

 

how can I avoid flux leaks?

It may be in the accuracy of the fit. There may be some further source with experience you can consult. And you can always try an experiment - recall that iron filings will show magnetic flux lines. A piece of paper and some filings will show problems at a joint.

 

It may be in the accuracy of the fit. There may be some further source with experience you can consult. And you can always try an experiment - recall that iron filings will show magnetic flux lines. A piece of paper and some filings will show problems at a joint.

why is it then that manufacturers make coil core out of many laments "sheets" of metal instead of just one solid piece? do those have flux leaks or 100% flat fit?

 

Toroidal core = apple

Laminated E core = orange

Which is to say that the principles are different.

http://www.allaboutcircuits.com/vol_2/chpt_9/1.html

 

why is it then that manufacturers make coil core out of many laments "sheets" of metal instead of just one solid piece? do those have flux leaks or 100% flat fit?

The reason for the laminations is to cut down on eddy current losses. The eddy currents are proportional to the steel circuit thickness. In other words, each lamination has its own little eddy current. Eddy currents are like the little water eddies in a flowing river current. They are separate from the main current as eddy currents are separate from the main magnetizing current of the transformer. Eddy currents cannot be eliminated from any magnetic circuit...only minimized.

Cheers, DPW [ Spent years making heaters out of op-amps.]