What is the function of a capacitor connected in parallel on a relay coil

This is generally the case for DC relay circuits.

One of the characteristics of DC relays is that the working current of the coil only depends on the DC resistance and working voltage of the coil (AC relays also depend on the state of the armature).

When the armature of the DC relay is not engaged, a large enough current needs to be passed into the coil to be engaged, but once the armature is engaged, the magnetic circuit of the relay coil core is closed, and only a small magnetic force is required to maintain the armature in the engaged state (that is, only the coil needs to provide a small operating current). Therefore, in order to save energy, resistive capacitors are used in series in series on the circuit. When the relay power supply instant, due to the effect of capacitor charging, the relay coil can get a larger working current to complete the engagement action, after the capacitor is fully charged, the resistance limits the current, and the relay works in a smaller current state to keep the relay, which is the relay coil needs 12V working voltage to engage, but as long as the 5V working voltage can maintain the principle of engagement.

When the switch is disconnected, the primary coil will generate an induced electromotive force, and this instantaneous high voltage may break down the coil.

Therefore, the resistor in parallel in the primary coil is used as a discharge circuit for energy to suppress the self-inductance voltage and ensure the safety of the equipment.

The nature of the capacitor is that the voltage does not change abruptly, and the shunt capacitor can also suppress the self-inductive voltage, but the capacitor does not consume energy, and if there is no shunt resistor, the capacitor is composed of a coil and a DC resistance of the coil.

The LCR oscillation circuit will form a damping oscillation, and the energy will not be released quickly.

It should be a resistor in parallel, or the resistor should be connected in parallel with a small capacitance.

1. The voltage at both ends of the capacitor can not be changed, and the reverse electromotive force of the coil can be delayed and reduced after the capacitor is applied, so as to reduce the interference and prolong the life of the contact.

2. A proper resistor in series on the capacitor can dampen the oscillation, reduce the time of overvoltage, and achieve a better effect, which is the resistor-capacitance absorber.

3. The larger the capacitance, the smaller the impedance, and the higher the passing frequency. However, in fact, most capacitors over 1 F are electrolytic capacitors, which have a large inductance component, so the impedance increases when the frequency is high.

4. The key is that there is parasitic inductance on the capacitor, and the capacitor discharge circuit will resonate at a certain frequency point. At the resonance point, the impedance of the capacitor is small. Therefore, the impedance of the discharge circuit is minimized, and the effect of replenishing energy is also the best.

For the same capacitance, the more small capacitors in parallel, the better. Withstand voltage value, temperature withstand value, capacitance value, ESR (equivalent resistance) and so on are several important parameters of capacitance, and the lower the ESR, the better.

The function of the shunt capacitor of the contactor coil is to improve the electrical performance of the contactor and reduce the arcing phenomenon of the contactor. When the contactor switches the circuit, due to the inductance, the current in the coil will not disappear immediately, but will produce a reverse electromotive force ground state, resulting in an instantaneous peak of the current at the moment of switching, which will cause the contactor to produce arc slag deficiency, thereby damaging the contactor. The shunt capacitor can form a resonant loop in the first circle, so that the current in the coil quickly disappears at the moment of switching, thereby reducing the arc phenomenon of volt-generating front.

In addition, the capacitance can also improve the anti-interference ability of the contactor and reduce the impact of external interference on the contactor.