We are facing issue with relay PCN-112D3MHZ. We are switching a FAN of 80 Watt at 220V AC with this relay. we are operating relay with transistor MPSA42. Micro controller is driving this transistor through 1K resistance at base. Coil voltage is 12V DC. Diode is also connected parallel to relay coil in reverse direction.
Some times relay get stuck at on position. when we send off signal from micro controller, transistor becomes off, but relay contacts are not released to make FAN off. when we switch off the complete supply(both AC & coil DC) for some time and switch it on again, relay still is in on position.
As per specification relay is of 3A. Any hints?
Best Answer
It is because the fan is an inductive load. The relay is rated for 3A resistive load. Sometimes you will be switching the relay off when the current through the fan motor is at a peak, and hence you will get a high voltage surge - causing the contacts to arc, this tends to weld the contacts together.
I suggest you use a solid state relay with zero crossing switching for this instead.