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Materials and Equipment Required


Material listings are for a complete set of three inductors:

  • 58908-A2 High Flux Toroid core. 26µ permeability, 79mm OD, 48mm ID, 17mm high, 37nH/T2 AL. Quantity required: 3. Supplier: Magnetics Incorporated,

  • Litz wire, 30x 0.335mm diameter strands, 'single' insulation, around 2.6mm2 total copper cross sectional area. Three of these litz wire bundles will be used in parallel, giving almost 8mm2 total cross-sectional area. Quantity required: approximately 50 metres.
    Supplier: varies, see below:

  • Kapton or Polyester transformer insulation tape: Quantity required: a few metres. Supplier: Your local catalogue electronics supplier, eg Element14 (formerly Farnell), part number: 753-014

  • Transformer Varnish or low viscosity potting compound: Generic, use a local supplier. If using a vacuum chamber, a solvent-free varnish must be used to avoid boiling when the vacuum is pulled on the chamber.

  • Connectors: PowerPole 75A Red or M6 bolt lug terminal. Quantity Required: 6 housings, 6 crimps. Supplier: Anderson Power Products or their local distributor, part number 5916G7 for the housing, 5900 for the crimp. Bolt lugs, if used, are available from local electrical supply shops.

The Litz wire is the most difficult component to source. It is also the component that can tolerate the largest variation in specification and does not have to be an exact match to the size given above. Finer strands give smaller eddy current losses, but also poorer fill factor (the amount of copper contained in the cable) as a bundle of very fine strands will be as much insulation as copper. Larger strands have proportionally less insulation and will give lower resistance for a given bundle diameter.

Smaller size wire strands than approximately 0.25mm diameter can be used, however this does not improve eddy current losses to any significant degree, and it will worsen the fill factor and therefore the resistance of the wire. Strands larger than 0.5mm diameter will begin to see an increase in eddy losses and are not recommended.

Multiple bundles of litz are used in parallel. This is to make construction easier, as winding three small 30 strand bundles together is easier than winding one large 90 strand bundle. However, if sourcing a different wire construction is easier, than almost any combination is OK, but may require more effort to wind on the core. The construction listed above is known to produce good results.

The wire strands are only required to be insulated to 'single' thickness insulation. Choose a 'solderable' insulation with the highest temperature grade available easily. This will usually be 155°C Polyurethane or similar.

Litz wire is available from specialised manufacturers, use a web search to find a supplier close to you, as copper wire is heavy and shipping charges will be high if not purchased reasonably locally. One example supplier in the US is the New England Wire Company.


  • Solder pot: Required to strip insulation from ends of litz wire.

  • Fume hood and personal protective equipment to use with solder pot: Wire insulation fumes can be toxic, depending on the insulation material.

  • Vacuum chamber: Recommended to use when applying transformer varnish or epoxy coating to inductors, to remove trapped air bubbles. It is possible to perform this step without pulling a vacuum on the inductors, but much better results will be achieved with it.

  • Crimp tool: Required to crimp the PP75 connectors or M6 bolt lugs onto the ends of the wire after soldering.

  • Gas torch: Required to reflow the solder into the PP75 crimps or bolt lugs after crimping. This step may be possible with a high-powered hot air gun (paint stripper), but a gas torch will be guaranteed to work properly.