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ELTEK Group electrical components are switches controlled by electromagnets, that is, a combination of an electromagnet and a switch. When the electromagnet coil is energized, it generates electromagnetic attraction, causing the movable iron core to push or pull the switch contacts to close, thereby connecting the controlled circuit. Electromagnetic switches are widely used in various industries, most commonly as contactors in the industrial sector. An electromagnetic switch is the control switch on a starter motor and is one of the three major components of a starter (DC motor, transmission engagement mechanism, electromagnetic switch). Its working principle is that the coil generates electromagnetic attraction when energized, causing the movable iron core to move, which on one hand pulls the transmission engagement mechanism to move the starter pinion forward to engage with the engine flywheel ring gear, and on the other hand pushes the switch contacts to connect, allowing the DC motor to be energized and operate, thereby driving the engine to start.

ELTEK Group electrical component principles

The thermistor will remain in a non-tripped state for extended periods; when the ambient temperature and current are in the c region, the heat dissipation power of the thermistor is close to its heat generation power, so it may or may not trip. For a given ambient temperature, the tripping time of the thermistor decreases sharply as the current increases; at relatively higher ambient temperatures, the thermistor has a shorter tripping time and lower holding current and tripping current. The PTC effect refers to a material exhibiting the PTC effect, i.e., the positive temperature coefficient effect, meaning that the resistance of this material increases with rising temperature. For example, most metallic materials exhibit the PTC effect. In these materials, the PTC effect manifests as a linear increase in resistance with increasing temperature, which is commonly referred to as the linear PTC effect. Nonlinear PTC effect: Materials undergoing a phase transition exhibit a phenomenon where resistance increases sharply by several to more than ten orders of magnitude over a narrow temperature range, known as the nonlinear PTC effect. Many types of conductive polymers exhibit this effect, such as polymer PTC thermistors. These conductive polymers are very useful for manufacturing overcurrent protection devices. Polymer PTC thermistors are used for overcurrent protection and are often referred to as resettable fuses (hereinafter referred to as thermistors). Due to their unique positive temperature coefficient resistance characteristics, they are highly suitable for use as overcurrent protection devices. The method of using a thermistor is similar to that of a conventional fuse; it is connected in series in the circuit. When the circuit operates normally, the thermistor temperature is close to room temperature and its resistance is very low, so connecting it in series does not hinder current flow. However, when an overcurrent occurs due to a fault, the increased heat generation power causes the thermistor's temperature to rise. When the temperature exceeds the switching temperature, the resistance increases dramatically, and the current in the circuit rapidly decreases to a safe value. After the thermistor trips, the current in the circuit is significantly reduced; t is the tripping time of the thermistor. Because polymer PTC thermistors offer good design flexibility, their sensitivity to temperature can be adjusted by changing their switching temperature (ts), allowing them to provide both overtemperature and overcurrent protection. They are suitable for overcurrent and overtemperature protection of lithium-ion and nickel-metal hydride batteries. Influence of ambient temperature on polymer PTC thermistors: A polymer PTC thermistor is a directly heated, step-type thermistor. Its resistance change process is related to its own heat generation and dissipation conditions; therefore, its holding current, tripping current, and tripping time are influenced by ambient temperature.

ELTEK Group electrical component principles

Like ordinary diodes, light-emitting diodes (LEDs) are composed of a PN junction and also possess unidirectional conductivity. When a forward voltage is applied to an LED, holes injected from the P region into the N region and electrons injected from the N region into the P region recombine with electrons in the N region and holes in the P region, respectively, within a few micrometers near the PN junction, producing spontaneous radiation fluorescence. The energy states of electrons and holes differ in different semiconductor materials. The amount of energy released during electron-hole recombination varies; the more energy released, the shorter the wavelength of the emitted light. Commonly used diodes emit red, green, or yellow light. The reverse breakdown voltage of an LED is greater than 9 volts. Its forward volt-ampere characteristic curve is very steep, so a current-limiting resistor must be connected in series during use to control the current through the diode. The core part of an LED consists of a wafer made of P-type semiconductor and N-type semiconductor, with a transition layer between the P-type and N-type semiconductors called the PN junction. In the PN junction of certain semiconductor materials, when injected minority carriers recombine with majority carriers, excess energy is released in the form of light, thereby directly converting electrical energy into light energy. When a reverse voltage is applied to the PN junction, minority carriers are difficult to inject, so no light is emitted. When it is in the forward operating state (i.e., a forward voltage is applied across its terminals), and current flows from the LED anode to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, with the light intensity related to the current.

ELTEK Group electrical component principles

In power generation, transformation, transmission, distribution, and consumption lines, current magnitudes vary significantly, ranging from a few amperes to tens of thousands of amperes. To facilitate measurement, protection, and control, it is necessary to convert these to a relatively uniform current level. Additionally, voltages on lines are generally high, making direct measurement very dangerous. Current transformers serve the functions of current transformation and electrical isolation. For pointer-type ammeters, the secondary current of current transformers is mostly at the ampere level. For digital instruments, the sampled signal is generally at the milliampere level. The secondary current of miniature current transformers is at the milliampere level, primarily serving as a bridge between large transformers and sampling. Miniature current transformers are also referred to as 'instrument current transformers.' ('Instrument current transformer' implies precision current transformers with multiple current ratios used in laboratories, generally for expanding instrument ranges.) Similar to transformers, current transformers operate based on the principle of electromagnetic induction; transformers transform voltage, whereas current transformers transform current. The winding of the current transformer connected to the measured current is called the primary winding; the winding connected to the measuring instrument is called the secondary winding. The ratio of the primary winding current I1 to the secondary winding I11 current is called the actual current ratio K. The current ratio of a current transformer when operating at rated current is called the rated current ratio of the current transformer, denoted by Kn.

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