Energy Harvester Core Selection

I wish to make an electromagnetic energy harvester for a project. The placement of the harvester will be near a circuit to light a 12 V 0.5 W LED or alternatively charge a 12 V battery. I wish to use a cylindrical inductor for this purpose due to the ease of wrapping the coil.

I ordered from DigiKey 10x Fair-Rite rods which supposedly have an initial permeability of 2300.


To test the inductance capability of one of the rods, if you wrap 40 turns around the rod and use any generic inductance equation you would seek to get 32.8 mH…

However I only get 151 uH or 0.151 mH.

That would equate to a relative permeability of 11.

The final goal would be to wrap all of those rods together within a 600 or 700 turn coil, and so on. However it is pointless to do that until I believe I can achieve a large inductance value close to what I need in order to produce 12 V emf or 0.042 mA.

An example test circuit would be a line current of 10 A and harvester would be placed 3 inches away as shown here:

Please advise and thank you for your time.

Welcome to the Digikey tech forum. Sounds like an interesting project but beyond my realm of experience. I’m sure you’ll assistance from other contributors with your application.

Hello dc87,

There may be other considerations including:

  • rod geometry
  • coil spacing

May I encourage you to consider using calculators such as this one provided by Fair-Rite.

Best Wishes,


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