Specialized Transformers and Inductors for Downhole Magnetics

Down Hole Magnetics

As a custom transformer and inductor manufacturer for 50+ years, we have built downhole magnetics for a variety of downhole customers.

We are experts in designing downhole magnetics that operate in extreme environments. Our custom magnetics are designed to meet our specifications on temperature, size and shock vibration.

Today, most of our downhole designs are for 200C and 220C although we have some that operate at 240C temperatures as well. As the downhole market continues to drill deeper, the operating temperatures have continued to increase.

Design Elements

The downhole industry, as with the aircraft industry, requires high reliability under extreme environments as a key element of the design. Custom Coils regularly delivers to customers who expect zero defects found. Materials used in downhole designs are very critical. Using the proper materials for the specific operating temperatures is imperative.

Hi-Temp Cores

  • Powdered Iron (200C)
  • MPP (200C)
  • Ferrite (300C)

Small Geometries

  • Toroids down to 4mm
  • EE5 ER9.5 E-cores
  • Potcores down to 7x4mm

Hi-Temp Wires

  • MW35-C (200C)
  • ML16 (240C)

Insulation Materials

  • Kapton (180C)
  • Teflon (200C)
  • Nomex (220C)
  • Teflon/GC (260C)

Flying Leads

  • Teflon type E

Solder Types

  • Lead-free (230C)
  • HMP (300C)


  • Ripley's 468-2FC (220C)
  • Dolph's BC346A (220C)
  • RTV-xx Hi-Temp (260C)

Related Products



  • MWD (Measurements While Drilling)
  • LWD (Logging While Drilling)
  • Rotary Steerable Motors
  • Wireline
  • Completion Equipment

Have a question about a transformer or any other custom downhole magnetic assembly?

Ask our skilled experts can solve all your queries!

Contact Us At 605.934.2460


Custom Coils
PO Box 348
109 Iowa Street
Alcester, SD 57001-0348

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