Litz Wire Details

Litz Wire

Single Wire Diameter vs Range of Frequency

range of frequency [kHz] dominal diameter of single wire [mm]
from to from to
0.06 1 0.4 0.254
1 10 0.254 0.2
10 20 0.2 0.127
20 50 0.127 0.102
50 100 0.102 0.079
100 200 0.079 0.063
200 350 0.063 0.05
350 850 0.05 0.04
850 1400 0.04 0.03
1400 3000 0.03 0.02

Influence of Litz Wire Parameters on Litz Wire Freatures

  construction parameters
conductor material nom. diameter single wire ØSW no. of single wires nSW no. of bundles & bunching steps length of lay SL per bunching step pitch direction SR per bunching step thickness of enamelling
litz wire features electrical total cross section litz wire AConductor,Litz; direct current resistance RDC X X X        
high frequency resistance RAC; RF-losses X X   X X    
current density J = I/AConductor,Litz   X X        
filling factor litz wire AConductor,Litz/Atot,Litz   X   X X X X
breakdown voltage UBDV             X
mechanical (AConductor,Litz = const.) outer diameter ODLitz;total cross section litz wire Atot,Litz X X X X X X X
dimensional stability   X X X X X  
flexibility   X X X X    
flexlife performance X X   X X    
max. tensile strength X            
surface structure, roundness   X X X X X  

Main influencing parameters for HF-coils

      construction parameters
      nom. diameter single wire ØSW number single wires nSW number bundles & bunching steps length of lay SL per bunching step pitch direction SR per bunching step
litz wire features electrical total conductor cross section AConductor,Litz; direct current resistance RDC X X      
resistance at high frequency RAC; RF-losses X   X X  
mechanical outer diameter litz wire OD Litz; total cross section litz wire Atot,Litz X X X X X
flexibiliy X X X X  

Optional Litz Constructions and Features

litz wire construction pitch direction SR length of lay SL [mm] bunching factor VF features
270 x 0.071 mm (54 x 0.071 mm) x 3 S,S 20;26 ≈ 15 good RF-performance, rough textured three-sided litz wire profile
((30 x 0.071 mm) x 3) x 3 S,S,S 20;26;26 ≈ 20 good RF-performance, compact bunching
((18 x 0.071 mm) x 3) x 5 S,S,S 20;26;26 ≈ 20 good RF-performance, compact bunching, evenly surface and litz wire profile
((18 x 0.071 mm) x 3) x 5 S,S,Z 20;20;26 ≈ 15 fine litz wire structure/-surface
(39 x 0.071 mm) x 7; concen. S+Z,S 20+20;24 < 13 very round, dimensional stable litze wire profile, high flexibily

Litz Wire Design for HF Coil with Specific Winding Window

practise-related approach
frequency [kHz] 50 125 200
total no. of windings NW,tot 30 30 30
no. of layers NL (winding layers) 3 3 3
no. of windings per layer NW,L 10 10 10
outer diam. litz
wire (grade 1)
ODLitz [mm]		 with servg. 2.19 2.19 2.19
without servg. 2.32 2.32 2.32
nom. diameter single wire
ØSW [mm]		 0.100 0.080 0.063
filling factor
litz wire
FillLitz [%]		 with servg. 48.2 47.7 46.1
without servg. 47.0 46.5 44.9
filling factor
winding window
FillWind [%]		 with servg. 25.9 26.3 24.9
without servg. 29.1 29.2 27.2
typ. litz wire
construction		 with servg. 225 x 0.100 mm
5x(45x0.100mm)		 360 x 0.080 mm
5x(4x(18x0.080mm))		 550 x 0.063 mm
5x(5x(22x0.063mm))
without servg. 255 x 0.100 mm
5x(51x0.100mm)		 400 x 0.080 mm
5x(4x(20x0.080mm))		 600 x 0.063 mm
5x(5x(24x0.063mm))

Comparison of The Design Approaches

practise-related approach approach acc. Ch. R. Sullivan
frequency [kHz] 50 125 200 50 125 200
total no. of windings
NW,tot		 30 30 30 30 30 30
no. of layers NL (layer winding) 3 3 3 3 3 3
no. of winding per layer
NW,L		 10 10 10 10 10 10
outer diameter litz wire (grade 1)
ODLitz [mm]		 2.19 2.19 2.19 2.17 2.18 2.19
nom. diameter litz wire
ØSW [mm]		 0.100 0.080 0.063 0.071 0.050 0.040
filling factor litz wire
FillLitz [%] 		48.2 47.7 46.1 46.9 46.1 45.2
filling factor winding window
FillWin [%]		 25.9 26.3 24.9 25.3 25.0 24.6
typ. litz wire construction 225 x 0.100 mm 5x(45x0.100mm) 360 x 0.080 mm 5x(4x(18x0.080mm)) 550 x 0.063 mm 5x(5x(22x0.063mm)) 440 x 0.071 mm 5x(4x(22x0.071mm) 875 x 0.050 mm 5x(5x(35x0.050mm)) 1350 x 0.040 mm 5x(5x(54x0.040mm))

LW Spools

Spool and Packaging for Litz Wire

Spool Types

Spool Types Diagramm Wire Sizes Characteristics
Biconical 1 37 - 58 AWG 0.010 mm - 0.114 mm Biconical spool for fine and ultrafine wire, superb de-reeling capability, ideal for high speed  winding machines
Cylindrical 2 31 - 50 AWG 0.050 mm - 0.511 mm Straight barrel spool, solid traditional design
Tapered 3 24 - 38 AWG 0.102 mm - 0.511 mm Stable winding due to tapered barrel spool for heavier sizes
Container Container for large spools

European Spools

Spool Type d1
[mm]		 d4
[mm]		 I1
[mm]		 I2
[mm]		 Spool weight
[g]		 Filling weight unserved litz wire* [kg] Filling weight served & taped litz wire* [kg] Filling weight extruded litz wire* [kg] Spools per box Spools per pallet max
125K 125 16 125 100 200 2.0 1.3 ** 4/6/9 216
160K 160 22 160 128 350 4.8 3.2 2.0 4 96
200K 200 22 200 160 600 8.9 5.9 3.9 2 42
250K 250 22 200 160 1050 16.6 11.0 7.3 1 36
355K 355 36 200 160 1850 32.4 - ** - 12
VMV630 630 56 475 361 18500 214.0 178.0 ** - 1
VM 710 710 52 250 180 18000 - 81.0 (taped) ** - 4
400/56-275 400 56 275 241 4590 81.0 67.5 (taped) ** - 4

Dimensions of the spool

d1 ➡ Flange Diameter

d4 ➡ Core diameter

l1 ➡ Overall width

l2 ➡ Traverse

* Approximate values valid for copper, for other metals please inquire.

** The extrusion machines only work with spools bore diameter of 22 mm / 0.87 inch.

Other packages on demand.

American Spools

Spool Type Flange
diameter
d1
[inch] 		Bore
diameter
d4
[inch] 		Overall
width
I1
[inch] 		Traverse
length
I2
[inch] 		Spool weight
[lbs] 		Filling weight
unserved
litz wire*
[lbs] 		Filling weight
served & taped
litz wire*
[lbs] 		Filling weight
extruded
litz wire*
[lbs] 		Spools per box max. Boxes per pallet max.
3x3" 3.15 0.63 3.15 2.52 0.16 1.23 0.82 ** 24 N/A
4x4" 3.94 0.63 3.94 3.15 0.28 2.21 1.43 ** 6 N/A
5x5" 4.92 0.63 4.92 3.94 0.54 4.41 2.87 ** 6 216
6x4" 6.00 0.63 4.33 4.32 0.75 7.06 4.63 ** 6 125
6x6" 6.30 0.87 6.30 5.04 0.8 10.58 7.06 4.85 4 96
8x8" 7.87 0.87 7.87 6.30 1.35 19.62 13.01 8.60 2 42
250K 9.84 3.01 7.80 6.22 3 N/A N/A N/A 1 36
355K 13.98 1.42 7.87 6.30 4 71.44 59.54 ** N/A 12


Spool Type Flange diameter
d1
[mm] 		Bore
diamter
d4
[mm] 		Overall
width
I1
[mm] 		Traverse
length
I2
[mm] 		Spool weight
[kg] 		Filling weight
unserved
litz wire*
[kg] 		Filling weight
served & taped
litz wire*
[kg] 		Filling weight
extruded
litz wire*
[kg] 		Spools per box max. Boxes per pallet max.
3x3" 80 16 80 64 0.07 0.56 0.37 ** 24 N/A
4x4" 100 16 100 80 0.125 1.00 0.65 ** 6 N/A
5x5" 125 16 125 100 0.245 2.00 1.30 ** 6 216
6x4" 152.4 16 110 109.7 0.340 3.20 2.10 ** 6 125
6x6" 160 22 160 128 0.35 4.80 3.20 2.20 4 96
8x8" 200 22 200 160 0.6 8.90 5.90 3.90 2 42
250K 250 76.5 198 158 1.461 N/A N/A N/A 1 36
355K 355 36 200 160 1.85 32.40 27.00 ** N/A 12

Dimensions of the spool

d1 ➡ Flange Diameter

d4 ➡ Core diameter

l1 ➡ Overall width

l2 ➡ Traverse

* Approximate values valid for copper, for other metals please inquire.

** The extrusion machines only work with spools bore diameter of 22 mm / 0.87 inch.

Other packages on demand.

Asian Spools

Spool Type d1 (mm) d4 (mm) l1 (mm) l2 (mm) d14 (mm) Spool Weight (g) Filling Weight unserved litz wire* (Kg) Spools per box Boxes per pallet max
PT-4 124 22 200 170 140 270 6 4 24
PT-10 160 22 230 200 180 620/420 12 2 30/40
PT-15 180 22 230 200 200 550 18 1 45/36
PT-25 215 32 280 250 230 1000 28 1 24
P-30 300 30 160 130 300 1230 20 1 24
K200C 200 22 200 160 200 625 8 2 24

Dimensions of the spool

d1 ➡ Flange Diameter

d4 ➡ Core diameter

d14 ➡ Flange diameter

l1 ➡ Overall width

l2 ➡ Traverse

LW Determination of Winding Tension

Litz Wire

Determination of Winding Tension on Litz Wire

The following table shows the maximum applicable winding tension on the single litz wire strands. The maximum feasible winding tension for litz wires can be calculated by multiplying the number of single strands by the appropriate winding tension of the single strand. Regardless of this calculation, for litz wire diameters thicker than 5 mm tension limits of (420N) for hard metals and (270N) for copper and soft metals are recommended.
 
These values are guidelines and can deviate significantly depending on the manufacturing process.

  Cu, Cu/Ag
[mm] AWG nom. [cN] ± 20 % [cN]
0.018 53 1.6 0.3
0.019 52.5 1.7 0.3
0.020 52 1.9 0.4
0.021 51.5 2.1 0.4
0.022 51 2.3 0.5
0.023 50.5 2.5 0.5
0.024 50.5 2.6 0.5
0.025 50 2.9 0.6
0.026 50 3.1 0.6
0.027 49.5 3.3 0.7
0.028 49 3.5 0.7
0.030 48.5 4.0 0.8
0.032 48 4.5 0.9
0.035 47 5.4 1.1
0.036 47 5.7 1.1
0.040 46 70.0 1.4
0.045 45 8.8 1.8
0.050 44 10.9 2.2
0.056 43 12.4 2.5
0.060 42.5 14.3 2.9
0.063 42 15.7 3.1
0.071 41 19.8 4.0
0.080 40 24.9 5.0
0.090 39 31.1 6.2
0.100 38 38.0 8.0
0.112 37 47.0 9.0
0.120 36.5 53.0 11.0
0.130 36 62.0 12.0
0.140 35 71.0 14.0
0.150 34.5 80.0 16.0
0.160 34 91.0 18.0
0.170 33.5 101.0 20.0
0.180 33 113.0 23.0
0.190 32.5 125.0 25.0
0.200 32 137.0 27.0
0.210 31.5 150.0 30.0
0.220 31 164.0 33.0
0.230 30.5 178.0 36.0
0.240 30.5 193.0 39.0
0.250 30 209.0 42.0
0.260 30 225.0 45.0
0.270 29.5 241.0 48.0
0.280 29 259.0 52.0
0.290 29.5 276.0 55.0
0.300 28.5 295.0 59.0
0.310 28 314.0 63.0
0.320 28 333.0 67.0
0.330 27.5 353.0 71.0
0.340 27.5 374.0 75.0
0.350 27 395.0 79.0
0.360 27 417.0 83.0
0.370 26.5 439.0 88.0
0.380 26.5 462.0 92.0
0.390 26 486.0 97.0
0.400 26 510.0 102.0
0.420 25.5 560.0 112.0
0.430 25.5 586.0 117.0
0.450 25 639.0 128.0
0.470 24.5 695.0 139.0
0.480 24.5 724.0 145.0
0.500 24 783.0 157.0

LW Connection Technologies

Litzwire

Connection Technologies for Litz Wires

Due to the many stranded nature of litz wires, terminating them often poses a challenge. The following table advises the connection technologies which are generally applicable for various insulations. Only the most important factors of influence have been classified. Many others, such as enamel type and insulation thickness of the single strands, heat resistance of the additional insulation, the stranding construction (tight/compact or wide/flexible), have not been addressed.

  Litz wires without additional insulation Litz wires with additional insulation
overall diameter < 1.0 mm overall diameter ≥ 1.0 mm Serving Extrusion Taping
Connection technology many fine single strands* few heavy strands** many fine single strands* few heavy strands**
Soldering dip/flow/hand/wave soldering dip/flow/hand/wave soldering dip/flow soldering dip/flow soldering dip/flow soldering dip/flow soldering dip/flow soldering
Mechanical skinning -- brushing -- brushing taking off serving, brushing if necessary stripping off coating, brushing if necessary off/opening the tape, brushing if necessary
Crimping (pre-stripped) possible possible possible possible possible possible possible
- welding
- thermocompression
- resistance
- ultrasonic sound		 thermo-compression, ultrasonic sound thermo-compression, ultrasonic sound, resistance thermo-compression thermo-compression, ultrasonic sound, resistance Thermocompression (nylon) thermocompression mechanical removal of additional insulation recommended

* nom. diameter ≤ 0,100 mm

** nom. diameter > 0,100 mm


Please contact us if the conductor metals are alloys.

Please contact us directly for futher assistance.

LW Abbreviations

Abbreviations

Abbreviations 
AConductor,Litz = total conductor cross section of litz wire
Ages,Litz = total cross section of litz wire
ODLitz = outer diameter of litz wire
ODBundle = outer diameter of bundle
nsw = number of single wires
Øsw = nominal diameter of single wire
VF = bunching factor
SL = length of lay (bunching length)
SR = pitch (bunching) direction
RDC = DC resistance
RAC = AC resistance
f = frequency
ρ = specific resistance of conductor
µO = permeability of free space
δ = skin depth
J = current density
UBDV = breakdown voltage
b = width of winding window
h = height of winding window
NW,tot = total number of windings
NL = number of winding layers
NW,L = number windings per layer
FillLitz = copper filling factor of litz wire
FillWin = copper filling factor of winding window
ne = recommended total number of single wires
n1,max = number of single wires of basic bundle in 1st bunching step
k = constant according Ch. R. Sullivan

LW Smartbond

Smartbond Litz Wire

General

Products for multimedia applications are increasingly equipped with wireless charging devices. ELEKTRISOLA's Smartbond OSP18 has been developed to meet the needs of these specific charging systems. This self-bonding litz wire combines excellent bond strength with good windability, fast soldering, and very good hot air bonding characteristics.

The hot air bonding process is environmentally friendly compared to solvent bonding process, allows faster winding, and has potential for process automation. Very thin coils can be produced with Smartbond`s unique construction giving additional space for designers or to help to achieve miniaturization goals.

Features and benefits of Smartbond litz wires

  • excellent bonding strengths with hot air bonding
  • high winding speed
  • solderable without pre-stripping of insulation
  • environmentally friendly automated process due to elimination of solvents
  • thin walled overcoat allows small coils
  • customized wall thickness possible per customer specification

Technical properties of Smartbond litz wire

Standard Litz Wire Served Litz Wire Selfbonding Litz Wire Smartbond
Stability of coil - good medium good
Flexibility / windability soft more stiff soft soft
Bonding process - solvent hot air hot air
Mechanical protection avg good avg good
Surface and haptic - rough avg smooth
Second adhesion step
without additional adhesion		 no no limited yes

Diameter of litz wire and copper fill factor

Dimensions
Diameter of single wires 0.020 - 0.500 mm
Outer diameter of litz wires 0.500 - 3.500 mm

Applications

  • transmitter coil for wireless charging
  • receiver coil for wireless charging
  • wireless power charger
  • coreless coils in different applications

LW Served

Served Litz Wire

General

High frequency litz wire served with natural silk, polyester, or nylon is characterized by increased dimensional stability and mechanical protection. The optimized serving tension ensures high flexibility and splicing- or spring up prevention during the process of cutting the litz wire. This splicing effect can cause handing and contacting of the wire ends more difficult in post processing.

Features and benefits of served litz wires

  • Additional protection against mechanical stress
  • Excellent dimensional and physical stability
  • High flexibility
  • Splicing prevention
  • Good solderability above temperatures of 410 °C
  • Improved impregnation
  • Optimization of winding capacity
  • Serving material allows optimization of insulation distances

Technical properties of served litz wires

Technical values of serving material

Serving materials1) Silk Nylon Polyester*
Thermal properties
Recommended permanent use temperature 110 120 120 °C
Melting temperature - 250 - 260 250 - 260 °C
Elektrical properties
Dielektric constant ℇr 1.4 3.4 3.2
Mechanical properties
Elongation at break (dry) 13 - 25 25 - 46 20 %
Moisture absorption (65% rel. humidity, 21°C) 9 2.5 - 4 0.2 - 0.5 %
Other
Color white, green white white

Dimensions

Serving materials1) Silk Nylon Polyester*
Diameter of single wires2) 0.020 - 0.300 0.020 - 0.300 0.020 - 0.300 mm
Number of single wires3) 2 - 25,000 2 - 25,000 2 - 25,000 pcs
outer diameter of litz wires 0.071 - 4.0 0.071 - 10.0 0.071 - 4.0 mm
Number of layers (typ.) 1 - 2 1 - 2 1 - 2

* Available in Asia only
1) customized solution on demand (thermo adhesive yarns)
2) other diameters on demand
3) depending on number of single wires

Applications

  • HF transformers
  • HF in-/converters
  • HF transceivers
  • HF chokes
  • Inductive charger

LW With Strain Relief

Litz Wire with Strain Relief

General

Some of the ultrafine litz wires are impacted by high mechanical forces during further processing and over their lifetime. Litz wire constructions starting from an available single conductor diameter of 0.01 mm (AWG 58) can be designed implementing strain reliefs to improve the resistivity of the litz wire against tensile stress. It is typically used in applications where litz wire is used not wound in a coil, but used like a cable.

Features and benefits of litz wires with strain

  • Excellent increase of tensile strength and flex life performance
  • Different strain relief materials can be selected for individual applications
  • Protection of super fine litz wires against mechanical stress
  • Strain reliefs can be used in all other litz wire constructions

Properties of litz wires with strain relief

Comparison of properties with a typical litz wire

Technical values of strain relief materials

Materials Polyester
PES		 Polymer
LCP		 Polyamide
Aramide
from
Gram per 10,000 m dtex 30 110 110
Tensile strength N 1.5 29.6 26.7
Elongation % 9.8 3.3 3.9
to
Gram per 10,000 m dtex 450 440 420
Tensile strength N 29.4 99.2 49.7
Elongation % 12.4 3.4 4.2

Dimensions of litz wire with strain relief

Dimensions
Diameter of single wire 0.020 - 0.500 mm
Number of single wires 2 - 5,000 pcs
Outer diameter of litz wire 0.020 - 2.5 mm

LW Profiled

Profiled Litz Wire

General

Profiled (mechanically shaped) litz wires allow optimal utilization of available winding space due to the superior filling factor of  rectangular or square litz wire cross sections. In comparison to a standard round cross section construction, profiled litz wire can increase the filling factor up to 20%.

The design advantages of profiled litz wire can only be fully realized using products with consistent and precise dimensions. This dimensional stability is only possible with exact control of each process step.

Features and benefits of profiled litz wires

  • Increased filling factor of up to 20 %
  • Constant winding performance requiring tight dimensional tolerance and good flexibility
  • Profiled dimensions to customer specification
  • Profiling also possible with outer insulation

Technical properties of profiled litz wires

Increasing filling factor by profiling

Available insulation materials of profiled litz wires

For served litz wire:

Nylon

For taped litz wire:

Polyester (PET)

Polyethylene Naphthalate (PEN)

Polyimide (PI)

Dimensions
Smallest sizes (width x height) 1.2 x 1.2 mm
Biggest sizes 15.0 x 15.0 mm
Ratio (width x height) 1:1.7 mm
Tolerance (±) 0.1 mm
Diameter of single wires 0.050 - 0.500 mm

Other dimensions and materials on demand.

Applications

  • Wireless charging
  • Induction cooking hobs
  • HF transformers
  • HF transducers
  • E-motors

LW Taped

Taped Litz Wires

General

Taped high frequency litz wire constructions are mainly suitable for applications requiring high break down voltage. Taping improves the capability to withstand flexing and mechanical stress. Adhesive taped litz wire can be achieved by using thermally sealed or self adhesive tape. This ensures protection against re-opening during and after manufacturing processes and thus secures the compliance with defined creepage distance. 

Some tapes can be thermally sealed when used in conjunction with certain wire enamel types.

Excellent adhesion and bonding characteristics to the individual wires are possible. A wide range of thermally sealable tapes can be selected for special applications all promoting various degrees of flexibility and mechanical protection for the litz wire construction.

Features and benefits of taped litz wires

Variants Dielectric strength Flexibility Splicing Contacting
Standard high very good good very good
Thermally Sealed elevated medium very good very good
Self-Adhesive very high good very good good

Technical data sheet of different tapes

Taping materials PET PEN PI
Description Polyester Polyethylene Naphtalate Polyimide
Color transparent transparent brown
Standard PET PEN PI
Insulation class (UL) °C 105 (A) 180 (H) 200 (C)
Insulation class (VDE) °C 130 (B) - 200 (C)
Dielectric constant ℇr 3.3
(VDE 0345)		 2.8
(JIS C 2318)		 3.4
(ASTM D 150-92)
Flammability 400
(VDE 0345)		 VT-M
(UL 94)		 V-0
(IEC 60695-11-10, UL 94)
UL-file no., tapes E53895 E206562 E39505
Processing fusible fusible mechanical stripping
Thermally Sealed
Insulation class (UL) °C 13 - 25 - 20
Insulation class (VDE) °C 9 - 0.2 - 0.5
Dielectric constant ℇr 3.25
(ASTM D 150-81)		 - 3.4
(ASTM D 150-92)
Flammability n.a. - V-0
(IEC 60695-11-10, UL 94)
UL-file no., tapes E93687 - E39505
Processing fusible fusible mechanical stripping
Self Adhesive
Insulation class (UL) °C 130 (B) 180 (H) 180 (H)
Dielectric constant ℇr 3.2
(JIS C 2318)		 2.8
(JIS C 2318)		 3.3
(JIS C 2318)
Flammability - flame retardant
(internal test acc. UL 510)		 flame retardant
(internal test acc. UL 510)
UL-file no., tapes E515235 E515235 E515235
Processing fusible fusible mechanical stripping
Custom materials can be arranged

Degree of overlapping

The degree of overlapping of two adjacent tape windings is defined by the gradient angle between tape and litz wire during the taping process. The overlapping determines the number of tape layers located on top of each other and thus the thickness of the insulation.


Dimensions
Diameter of single wires 0.040 - 0.700 mm
Outer diameter of litz wire 0.5 - 20.0 mm
Overlapping (typical) 50 or 67 %
Number of tapes (typical) 1 - 2

Applications

  • EV (Electric Vehicles)
  • OBC (Onboard charger)
  • DC/DC converter
  • Wireless charging
  • Charging piles
  • SMPS (Switch Mode Power Supplies)
  • HF transformers
  • HF transducers
  • HF chokes

Special constructions with VDE-approval for high voltage applications available:

GotoEFOLIT®-product family

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