رله‌ لوازم جانبی رله

Product Attributes

Introduction

When switching resistive loads, the current directly follows the phase of the voltage (Figure 1). When switching relay coils, the current and voltage waveforms differ due to the inductive nature of the coil (Figure 2). A brief explanation of this mechanism is as follows: when energizing the coil, the build-up of the magnetic field generates a back-EMF, which delays the rise of the coil current. When de-energized, the sudden interruption of coil current causes the magnetic field to collapse abruptly, inducing a high-voltage spike of reverse polarity across the coil terminals. This reverse-polarity voltage spike can typically reach up to 15 times the supply voltage, and may therefore interfere with or damage electronic equipment. To counteract this potentially destructive effect, relay coils can be suppressed using diodes, varistors (voltage-dependent resistors), or RC (resistor/capacitor) modules selected according to the operating voltage (descriptions of the various available modules are provided below). The above description is based on the operating principle of DC coils; the reverse-polarity voltage spike upon de-energization applies equally to AC coils. However, when energizing an AC coil, there is also an inrush current of 1.3 to 1.7 times the nominal coil current, depending on coil size. If the coils are powered via a transformer — particularly if multiple coils are energized simultaneously — this may need to be taken into account when calculating the transformer's VA rating.