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?

 

Sounds like your initial fan surge could be exceeding 3A and welding the contacts inside the relay. Can you check the surge current in any way?

 

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?

The surge (in-rush) current can be 10x of your running current and it looks like you have accounted for they by going with a 3amp relay. However, the contact material is silver-nickel and may be suffering from the arc caused when the relay is opened. You may want either..
A) arc suppression circuit
b) a relay with more robust contact material
Or both.

Here is an Application Note from TE (the manufacturer of your relay)

http://www.te.com/commerce/Document...v&DocNm=13C3236_AppNote&DocType=CS&DocLang=EN

 

You could also look at a SSR type and this would also do away with the relay.
The Opto22 range such as G40AC5A is rated for 3a 240vac and 5v logic controlled, this has around the same foot print as your TE ver.
http://www.opto22.com/site/pr_details.aspx?cid=4&item=G4OAC5A
There are higher rated SSR's if needed.
Max.

 

With a highly inductive load, you are likely welding the relay contacts together when they open. Welding is caused by the arc that forms as the relay contacts break the highly inductive circuit.

Solution: relay better suited for the job. Arc suppression snubber across the contacts.

This is not an inrush problem; it is a break problem.

 

Thanks for the suggestions. Since, the ARC voltage may exceed several times in a day, do you think MOV would be a suitable option as it would degrade with each such instance?

 

Thanks for the suggestions. Since, the ARC voltage may exceed several times in a day, do you think MOV would be a suitable option as it would degrade with each such instance?

Check the datasheet of a MOV. I think they are intended to handle this event many thousands of times. For such a low-power device like a fan, I am leaning towards using the solid-state relay as suggested by @MaxHeadRoom

 

Check the datasheet of a MOV. I think they are intended to handle this event many thousands of times.

Thanks. Can you suggest some?

 

Thanks. Can you suggest some?

Look on Digikey.com - search Metal oxide varistor. They will help.

 

Or simple R/C snubber.
Max.

 

Also.
Max.