Round Enameled Copper Wire is a kind of winding wire, usually made of copper or aluminum, insulated with enameled wire, used to make windings and coils.

Enameled copper wires with round cross-sections are widely used in windings of small and medium-sized motors and transformers, as well as other electromagnetic devices, such as sensors and actuators.

Litz wire is usually made of enameled copper wire.

Despite its simple appearance, enameled wire is a complex product. The enameled wire must withstand the mechanical stress caused by bending and stretching during the winding process of the coil, which is usually carried out at the fastest possible speed to increase productivity.

In addition, during normal operation (and overload events), mechanical forces, thermal stresses, and chemical and environmental conditions require wires and their insulation materials to have a certain level of performance so that a reasonable service life can be expected.

For example, for round enameled wire, define or control the following parameters:

Size (diameter)
insist
Mechanical flexibility ( *** resistance of enamel)
Elongation (due to the tension required during the winding process)
Thermal shock resistance
Rebound (after bending)
Dielectric breakdown strength
(Tooth enamel) fully cured
Solderability (easy to apply solder directly through enamel)
Thermoplastic flow (cut in)
Solubility
Transformer oil resistance and hydrolytic stability
key
Heat resistance
Scratch resistance of enamel
Quality loss
resistance
Lap shear bond strength
Enamel performance
In addition to electrical insulation, enamel can also prevent corrosion or oxidation of copper wires.

The typical electrical strength of enamel is about 170-220 V/μm, which is why a relatively thin layer of enamel can withstand high voltages. For example, the 0.375 mm wire with a cracked enamelled wire shown above has a breakdown voltage of 4.35 kV even though the enameled thickness is only 0.0275 mm.

The life of electrical insulation is related to its use temperature. The typical shortest life of enamel at its nominal temperature is about 20,000 hours.

There are several nominal temperature ranges (heat levels), which list the basis for making enamel, such as:

155-180°C-Polyurethane (good solderability at 370-390°C)
180-200°C-Polyesterimide (good heat resistance and chemical resistance, can be soldered above 470°C)
220°C-Polyamideimide (good heat resistance and mechanical properties, not solderable through enamel)
240°C-Aromatic polyimide (very good heat resistance, chemical resistance and radiation resistance, can not be welded by enamel)
welding
The enameled wire of this common mode choke coil is directly soldered to the PCB using the “self-melting” characteristic of the enameled, without the need to remove the coating by any mechanical means.

The presence of enamel hinders welding (compared to bare copper). For this reason, the chemical properties of the enameled wire are optimized to facilitate soldering (especially for enameled wires rated up to 200°C), which can be achieved by applying heat and solder directly to the outer surface of the enameled wire.

The enamel will dissolve or evaporate, exposing the copper underneath, and to some extent provide even some fluxing or self-melting properties.

Enamel with a higher temperature rating does not support the function of direct welding to copper. Instead, the coating must first be removed by some mechanical means.

Self-adhesive enameled wire
There are also special grades of enamel for specific applications. For example, there is a “self-adhesive” type of enamel, which has an additional layer of adhesive.

After winding into a circle, the formed wires can be bonded to each other by using solvent-activated adhesives or heating components. The coil can be heated by the thermal method (depending on the type of adhesive), usually to around 120-220°C: *** hot air on the component, put it in the oven, or through the “resistance method” (make current Heating by coil).

Using the solvent method, the adhesive can be activated by applying (brushing, spraying or wicking) a suitable solvent (such as denatured alcohol (ethanol or methanol)) during the winding process. The solvent can be diluted with water as needed, but it will reduce the adhesive strength.

score
Enameled wire is usually divided into three “levels”, the number of which is related to the thickness of the enameled bag (usually assumed to be the number of coatings):

Class 1-Thinnest insulating material, single layer
Class 2-Medium insulation, double layer
Class 3-the thickest insulating layer, three layers
Class 3 enameled wire should not be confused with triple insulated wire.

For example, the size comparison of 0.5mm Rectangular Enameled Copper Wire is shown in the table below. Higher levels of voltage breakdown increase significantly, but at the expense of thicker insulation and the outer diameter of the wire (so fewer wires can be installed in the same cross-sectional area of ​​the winding).