Product name: Relay contact arc extinguishing composite thermistor, AC contactor arc extinguishing composite thermistor

　　Breakdown occurs between electrodes in absolute vacuum. The electrons that create the arc originate from the material of the contact itself. The temperature at which arcing occurs depends on the work function of the contact material. Considering work function issues, tungsten and molybdenum are often used as contact materials. Work function refers to the maximum insulating electrostatic field that a certain contact air gap can withstand. Note that during the switching of thermal environments, when the contact air gap shrinks to zero, the arc will be pulled out and the electrostatic field intensity increases. Therefore, as the contacts gradually close, the electrostatic field at some points will be very high enough to breakdown the gap.

　　Arc hazards

　　Common DC large-load DC motors, DC clutches, and self-flow solenoid valves. When these inductive load switches are turned off, there will be hundreds or even thousands of volts of back electromotive force, causing surges and arcs that will reduce the life of the contacts or even completely damage. If the current is small, such as around 1A, the back electromotive force will cause arc discharge. The discharge will cause metal oxides to contaminate the contacts, causing the contacts to fail, the contact resistance to increase, and sometimes the arc generated will even damage the relay contacts. The melting causes the contacts to stick together, causing the circuit that should be disconnected to fail, causing great harm to the equipment and even causing it to be scrapped. In response to the above problems, Huaju Electronics launched the composite PTC thermistor module WMZ13A-75E0610D431VT, which is used to solve the arc extinguishing of contact arcs, which effectively solves the problem of arc extinguishing of relay contacts.

　　1. Due to the influence of reverse electromotive force, the voltage applied to both ends of the relay or thyristor will reach 5-10 times the normal voltage at the moment the relay or thyristor contact is disconnected. This voltage will ionize the air at the moment the contact is disconnected to form HNO3, which will easily corrode the metal material or cause the thyristor to be broken down, directly affecting its service life. The use of this model of product has a better control effect on the arcing of relay contacts.

　　2. Composite PTC thermistor is currently the best way to extinguish arc when used in relay contacts. It can effectively reduce the micro-on current during charging and discharging of the resistor-capacitor circuit, and can also reduce the impact of a single varistor on the contact. point of residual voltage drop to achieve better protection effect. Nanjing Huaju Electronics grandly launches PTC composite thermistor with contact arc extinguishing. 3.Application circuit:

　

　　In many industrial circuit control sites or household appliance control circuits, small plastic relays or thyristors are generally used to switch on and off the relevant loads. For resistive or capacitive loads, as long as the contact capacity is large enough, the contact will generally not be damaged. Cause too much damage. But for inductive loads. Such as inductors, AC contactor coils, electromagnetic alarm single-phase motors, etc., due to the influence of reverse electromotive force. At the moment when the relay or thyristor contact is disconnected, the voltage applied to both ends will reach 5-5% of the normal voltage. 10 times. This voltage will ionize the air at the moment the contact is disconnected to form HN03, which will easily corrode the metal material or cause the thyristor to be broken down, directly affecting its service life.

　　At present, for inductive load relays, designers generally use two solutions: varistor or resistor-capacitor absorption to absorb the high voltage caused by the reverse electromotive force.

　　The first one: For the solution using varistor, due to well-known reasons, the varistor will gradually age under repeated overvoltage and continuous pressure, weakening its effective clamping effect, and even becoming a fault point itself. In order to reduce the probability of failure of the varistor itself, many designers have to select a relatively high varistor voltage when using a varistor for arc extinguishing control. Due to the high protection voltage, there is less chance of overvoltage of the varistor. In actual use, the effect is not ideal. If the time is longer, the relay contacts or the thyristor will be damaged.

　　Second type: Regarding the RC resistance-capacitance absorption scheme, there are three disadvantages in choosing this scheme:

　　l. When the series resistance is large, the charging and discharging time of the capacitor will become longer, the overvoltage absorption effect will be longer, and the arc extinguishing effect will not be good.

　　2. When the series resistance is small, the energy consumption of the resistor itself is less, the repeated charging and discharging process becomes longer, there will be a longer overvoltage time, the resistor itself is easier to be damaged, and the thyristor will withstand overvoltage for a longer time. long.

　　3. When the capacitance is large, the load will be charged due to the micro-conduction state of the capacitor, and the shutdown effect will not be obvious, and the long-term existence of leakage current is not conducive to energy saving and consumption reduction of the product.

　　In summary, the two current methods of voltage suppression and arc extinguishing both have certain shortcomings.

　　2. New usage scenarios

　　Based on the application principle of composite PTC thermistor for switching power supply, our company adopts the method of thermal coupling of thermistor and varistor in series. When the external high voltage is transient, the energy absorbed by the varistor transiently is used to make the thermal The rising resistance of the resistor shares most of the voltage to protect the varistor. Without worrying about damage to the varistor, we designed the varistor's varistor voltage within the range of DC400V ±10%, which not only ensures that the varistor responds to low voltage, but also ensures a faster response speed. It has a better control effect on the arcing of relay contacts.

　　Related models: WMZ13B-75E0610D431VT for 220Vac AC contactor or relay

　　WMZ13B-75E0610D821VT, WMZ13B-75E0814D821VT is used for AC contactors or relays below 380Vac

　　Based on the mechanism and phenomenon of arc generation, Huaju Electronics creatively proposed the use of composite resistors to solve the arc extinguishing problem, preventing the impact and harm of arcs on production and equipment. Huaju Electronics' composite resistance arc extinguishing device replaces the ordinary resistance-capacitance arc extinguishing circuit and has the characteristics of simple circuit, high reliability and low cost.

　　The relevant circuit diagram is as follows:

　　In the current domestic electric energy meter industry. Since built-in relays have been widely promoted in smart meters, the reliability of built-in relays and energy meters with built-in relays has become very important. Whether it is industrial and commercial sites or civil sites, sites with inductive loads always account for the majority. How to ensure that the built-in relay is effective and reliable, the design of relay contact arc extinguishing is very important.