230V Relay Switching Delay with RF Receiver and Industrial Gong Bell Load

The discussion addresses a relay switching delay and malfunction issue when controlling a 230V industrial gong bell load via an RF receiver. The relay operates correctly without load, but with the load connected, it switches on timely but fails to switch off at the correct time. Attempts to stabilize switching using various RC snubber circuits, including matching resistor values to the relay coil resistance, provided temporary improvement but led to malfunctions after extended operation. Suggested solutions include ensuring a clean and powerful relay drive circuit, measuring relay coil resistance and monitoring signals with a CRO, and using a two-stage relay arrangement where one relay activates another to handle the load. Additional recommendations for DC relay protection and noise suppression involve placing a transient voltage suppressor (TVS) diode (5V) before the transistor base resistor, adding 0.1µF capacitors across the base resistor, using an IN4007 diode in reverse bias across the relay coil to suppress back EMF, and a 47µF 100V capacitor across the relay coil to prevent chattering and improve holding current. A 0.22µF 400V capacitor from the transistor collector to ground is also advised. For power supply noise reduction, it is recommended to add 0.01µF capacitors across rectifier diodes, insert a 22Ω 3W resistor in series with the AC ground to chassis ground to prevent earth loop noise, and place 0.22µF 450V capacitors on the transformer primary and across the relay contact output (phase to neutral). These measures aim to reduce noise, transient spikes, and improve relay switching reliability in RF-controlled 230V applications with inductive loads like industrial gong bells.
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