What material is used for winding resistors

Wire-wound resistors are a type of resistors made by winding resistance wires on an insulating framework and then undergoing insulation packaging treatment. resistance wires are generally made of nickel-chromium, manganese-copper alloys with a certain resistivity. The skeleton generally adopts ceramic, plastic, and metal skeleton coated with an insulating layer. It has the characteristics of small temperature coefficient and high accuracy.

Working principle of wirewound resistors

Wire-wound resistors are a type of resistors made by winding resistance wires on an insulating framework and then undergoing insulation packaging treatment. As shown in the figure, resistance wires are generally made of nickel-chromium, manganese-copper alloys with a certain resistivity. The skeleton generally adopts ceramic, plastic, and metal skeleton coated with an insulating layer. It has the characteristics of small temperature coefficient and high accuracy. Among the wire-wound resistors, there is a high-power wire-wound resistor that uses ceramic as the skeleton, and the outer layer of the resistor is coated with glaze or other heat-resistant and good heat-dissipating insulating materials. The characteristic of the wire-wound resistor is high power dissipation. , Up to hundreds of watts, mainly used as high-power load, can work in the environment of 150 ℃ ~ 300 ℃ temperature.

The very old domestically made RXJ coil is wound on a porcelain skeleton with resistance wire, which is larger in size, and later it is a small one wound on the bakelite skeleton.

The non-sealed wire wound, the resistance wire is directly exposed to the air, although the production cost is low, but it is easily affected by the weather. It is common in early domestic instruments and multimeters.

The following resistors are also non-sealed wire wound. The outer ring is made of paper, which serves as an identification and aesthetic effect and is not sealed. Such resistors are common in older instruments.

Small-scale sealing wire windings usually use a thin aluminum shell, and both ends are sealed with epoxy. The common domestic models are RXJX (old model) and RX71 (new), and there are also RX12 vertical models. The resistance is small, it is bound to use thin wires under the same resistance value, so that the withstand power and characteristics will be affected to a certain extent, but the wire winding is a wire winding after all, which is stronger than the metal film, and because of its small size, it is widely used.

The deviation is generally 0.05% to 0.5%.

Even if they are all RX71, the size may vary greatly. RJ71 has 1W, 0.5W, 0.25W and 0.125W points.

This vertical type has a small footprint and is suitable for higher density packaging

Epoxy packaged wire wound, cylindrical shell and end are generally made of glass fiber epoxy material, and then sealed with epoxy glue. Commonly used domestic RX11 (old model) and RX70 (new) precision resistors, the power is 0.25W (common), 0.5W (more common), 1W (occasionally), 2W, 3W. This is the best mass-produced resistor made in China. The maximum can reach 0.01% (customized can reach 0.005%). There is no indicator for aging, but it can generally be 25ppm/a typical value, and the temperature coefficient can be <15ppm/C. The main purpose is various high-precision instruments. Although the above vertical type is also epoxy encapsulated, its size is too small and its performance is not as good, so it is not put here.

RX9-20 is a high-resistance wire wound resistor with three specifications of 0.5W, 1W and 2W. The new model is RX-78. The following resistance can achieve 0.02% on 10M, which is quite difficult. However, because the high-resistance wire is very thin and needs to be wound many times, the production cost is high and the rejection rate is high.

WireWoundResistor

Wire-wound resistance is to wind a nickel-chromium alloy wire on an alumina ceramic substrate, and control the size of the resistance one by one. Wire-wound resistors can be made into precision resistors with a tolerance of 0.005%, and the temperature coefficient is very low. The disadvantage is that the parasitic inductance of wire-wound resistors is relatively large and cannot be used for high frequency. The volume of the wire-wound resistor can be made very large, and then an external heat sink can be added to be used as a high-power resistor.

In the case of very small resistance, someone asked whether it can be replaced by copper wire, enameled wire, or wire?

The conclusion is not possible, because the temperature coefficient of resistance of copper is very large, reaching about 4000ppm/℃. Therefore, copper resistance is often used for temperature measurement or compensation. In fact, the temperature coefficient of resistance of pure metals is very large. Only a few resistance alloys have a small temperature coefficient and a large resistivity, which is suitable for wire wound resistors.

Regarding wire-wound resistance wires, most of them are precision manganese-copper enameled wires. The temperature coefficient of resistance of manganese copper wire is very small and the resistivity is relatively high, which is an ideal material. Constantan was used in the past, but the thermoelectromotive force of constantan is very large, which is not suitable for precision applications. There is also a new constantan called New Constantan, which is low cost but not very suitable for precision occasions.

The temperature coefficient of resistance refers to the percentage increase in resistance when the temperature increases by one degree.