The term “Litz” is derived from the German “litzendraht” meaning woven wire. Litz wire is constructed of individually insulated magnet wires bunched or braided together in a uniform pattern so that each strand takes all possible positions in the cross section of the overall conductor.
What is the benefit of Litz Wire?
The primary benefit of Litz wire is in reducing AC losses in high frequency windings due to the “skin effect”. Current in a solid conductor is concentrated at the periphery. As frequency rises, the current migrates to the skin. The multiple strand construction of Litz allows current to divide uniformly between strands. The AC to DC resistance ratio then tends to equalize which is desirable in high Q circuit applications.
Determining the operating frequency of the application is the most important question to consider when designing a Litz wire. The operating frequency will determine both the Litz construction and the individual wire gauge. The following table shows the recommended strand gauge versus frequency for most Litz constructions.
Because of low electrical losses and ease of soldering, the magnet wire insulation most commonly used is polyurethane or polyurethane top coated with nylon. Litz wires are often insulated with an overall single or double wrap, or serve, of nylon textile that affords additional abrasion resistance and a space factor in the winding.
Operating frequency is the most important question to consider when specifying Litz wire. The operating frequency will determine both the Litz construction and the individual wire gauge. The following table shows the recommended strand gauge versus frequency for most Litz constructions.
Applications for Litz Wire
There is a tremendous variety of Litz wire applications, from small lighting ballasts to huge wind turbines. Each with distinct technical requirements.
Antenna Systems
Bottling Equipment
Electric and Hybrid Vehicles
EV Charging Stations
Electric Motors
Florescent Lighting Ballast
Florescent Lighting Ballas
Plastic Mold Injection Machinery
Power Transformers
Toroidal Transformers
Solar Inverters
Magnetic Resonance Imaging (MRI)
MRI
Industrial Motors
Maglev Trains
Medical Electronics
Microwave Transmission
Motor Drives
Oil & Gas Equipment
Specialty Audio Interconnections
Wireless Transmission Systems
Wind Turbines
How is Litz Wire Constructed?
Litz wire is made with individually insulated strands that range from 28 to 48 AWG. MWS’s standard magnet wire film insulations include polyurethane, polyurethane/nylon in single or heavy build. As a custom option we can provide solderable polyester, solderable polyester/nylon, polyester/polyamide-imide and polyimide – which are used to insulate each strand.
The outer insulation and the insulation on the component conductors, in some styles, may be servings or braids of nylon. Polyester heat-sealed polyester, polyimide and PTFE tape wraps along with extrusions of most thermoplastics are also available as outer insulation if the applications dictate special requirements for voltage breakdown or environmental protection.
How Litz wire “skin effect” reduces AC losses?
AC current flowing through a single wire conductor increasingly pushes the current toward the surface “skin” of the conductor as frequency increases. This physical phenomenon accelerates the wire’s AC resistance in direct proportion to the frequency of the current. Over 98% of the current will flow within a layer 4 times the skin depth from the surface. This behavior is distinct from that of direct current which usually will be distributed evenly over the cross-section of the wire.
Designers can virtually eliminate the skin effect with Litz wire. The key is to choose the diameter of individual wire strands twisted into the Litz construction that are like the skin depth for the given frequency. Doing so causes current to flow through nearly the entire cross section of each wire, thus minimizing AC resistance and heat losses.