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I’m trying to generate a special sort of field in a spherical spinning iron core using two orthogonally oriented coils.

One single-layer coil of 18 AWG magnet wire is wrapped directly onto most of the surface area of the 1” iron sphere that is to be spun, with its direction perpendicular to the spin axis. Some commutators and brushes will be used to deliver direct current to this coil. I’ll refer to this as the rotor of the field generator.

Another single-layer coil of 18 AWG magnet wire is then wrapped onto a fixed hollow spherical shell (not much larger than the rotor, let’s say it has an OD of 1.5”) surrounding the rotor, with its direction parallel to the spin axis. This is the stator.

What is the easiest/simplest/cheapest/most reliable way to go about supplying an alternating current to the stator coil? Getting an exact frequency and amplitude aren’t a concern, as I can simply tune the spin frequency/wattage of the rotor coil to match. But of course ensuring the amplitude is low enough to not damage anything is important.

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  • \$\begingroup\$ Is direction along the axis of a coil (of parallel windings?), or along its conductor? \$\endgroup\$
    – greybeard
    Commented Apr 20, 2023 at 20:44
  • \$\begingroup\$ @greybeard Direction refers to the axis (length) of the coil in relation to the spin axis of the iron sphere. \$\endgroup\$ Commented Apr 20, 2023 at 20:48
  • \$\begingroup\$ So the direction of the length of the rotor coil is perpendicular to the spin axis of the iron sphere (which the coil spins with, since it’s directly attached), and the direction of the length of the stator coil is parallel to the spin axis of the iron sphere. \$\endgroup\$ Commented Apr 20, 2023 at 20:55

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Simple and reliable should be a transformer from 60 Hz or 50 Hz mains to a pretty low voltage - 18 AWG suggesting not too many turns.
In the old times, I might have picked a 6 V incandescent bulb as a crude current limiter.

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    \$\begingroup\$ (There was a "trick" not to burden what was to be fed a limited current with the "cold filament current": start with a closed switch parallel to the load, open the switch for turn on.) \$\endgroup\$
    – greybeard
    Commented Apr 20, 2023 at 21:01
  • \$\begingroup\$ So something like a Variac, right? How should I go about connecting the two ends of the magnet wire to the ‘standard wall outlet’ featured on such variable transformers? I assume I’m not meant to simply scrape the enamel off and shove the two ends into the live/neutral slots… \$\endgroup\$ Commented Apr 20, 2023 at 21:02
  • \$\begingroup\$ Getting an exact frequency and amplitude aren’t a concern: I thought of a 5, 6, 6.3 or even 3 V transformer, relying on some sort of series resistance to not overload the stator winding. \$\endgroup\$
    – greybeard
    Commented Apr 20, 2023 at 21:13
  • \$\begingroup\$ Is that like… a product I can buy off-the-shelf? I’m no electrical engineer. \$\endgroup\$ Commented Apr 20, 2023 at 21:35
  • \$\begingroup\$ When I google “5v ac transformer” I’m met with a gaggle of products that range from wall adapters with barrel plugs, to whacky looking chunks of unidentifiable metal with 5-6 wires poking out. I assume the latter is what I need, but how do I plug the thing into my wall, and then plug the other end of the thing into the coil? And what is “some sort of series resistance” supposed to be? Sorry, I’m very new to all this. \$\endgroup\$ Commented Apr 20, 2023 at 21:47

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