I tried building a toroidal inductor with the following parameters:

OD= 1.400 in / 35.55 mm +/- 0.75 mm

ID = 0.900 in / 23.0 mm +/- 0.55 mm

Ht = 0.500 in / 12.7 mm +/- 0.50 mm

Wire: solid insulated copper 14G

Data sheet for the material: https://www.fair-rite.com/43-material-data-sheet/

enter image description here

For some reason inductor the is not working when a connect it to a battery (doesn't work as a magnet). I was expecting to get more than 100 micro Henry out of it.

Is it possible that is not working because the wire is insulated with thick plastic? What are other possible reasons for it not working? Thank you!

  • 2
    \$\begingroup\$ How did you measure the inductance? Looks ok so far. Link to toroid data sheet? \$\endgroup\$
    – Russell McMahon
    Jan 13 '21 at 6:16
  • 2
    \$\begingroup\$ how does one measure inductance with a battery? \$\endgroup\$ Jan 13 '21 at 6:38
  • \$\begingroup\$ Maybe your measurement technique is not correct. Can you please edit your question to add detail about how you measured the inductance? If it was not over 100uH, how many uH was it? \$\endgroup\$
    – mkeith
    Jan 13 '21 at 6:46
  • 4
    \$\begingroup\$ @RodionDegtyar The toroid core you have, type 43, is nice for discontinuous switchers. But it is not so nice for electromagnets. And the shape is a closed loop, so there is no place where you can get direct access to lots of Teslas (webers per square meter) even if you could make them. \$\endgroup\$
    – jonk
    Jan 13 '21 at 8:35
  • 1
    \$\begingroup\$ To get a measurable magnetic field with this inductor, grind a gap in it with a cutting wheel on a Dremel, to make a C shape with the smallest gap you can. (May take several cutting wheels!). Then you may be able to detect a magnetic field concentrated in the gap. The reluctance and thus the inductance will reduce, it'll be dominated by the width of the gap. \$\endgroup\$ Jan 13 '21 at 13:16

The magnetism you see from that coil will be very low. The main reason is that the wire is wound on to a ring. That means that the magnetic field has no need to leave the ring. Electromagnets are normally rods, or U-shaped.

The other reason is that you don't have many turns of wire. Electromagnets have a large number of turns. The insulation on the wire isn't a problem.

  • \$\begingroup\$ for use as magnet, doesn't matter how many turns of wire he adds . . . \$\endgroup\$
    – Pete W
    Jan 13 '21 at 13:48
  • 1
    \$\begingroup\$ @Pete W Yes, but if He uses a I, U core, or gap the existing one - inductance will drop, and to get the same as before more turns will be needed. \$\endgroup\$
    – fifi_22
    Jan 13 '21 at 17:50

re: "doesn't work as a magnet"

Magnetic field outside a toroid is (in principle) zero.


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