Latching Relay - Page 1
Forum section: electronics / projects

author: trent76
author_rank: Newbie
timestamp: December 23, 2013, 03:24:11 am
content: G'day every one I'm using a standed 12V DC relay to control a 230V AC pump and solenoid but when it the relay is switch off the contacts stay latched closed and I have to turn the main power off to releas them. So any one have a idea as to how to stop the contacts latching?

author: Kohanbash
author_rank: Regular Contributor
timestamp: December 23, 2013, 03:28:07 am
content: Have you checked that it is not a latching relay?The exact scenario is not clear so this might be an invalid point but have you tried placing a resistor across the relay coil?

author: calexanian
author_rank: Super Contributor
timestamp: December 23, 2013, 03:36:56 am
content: Couple of things come to mind. We implement that sort of thing regularly. First if you can let me know what brand and part number relay you are using. Also do you have any contact protection such as an MOV or other type? Also how are you driving the relay? Single or double coil. Also some relays are called latching but are actually impulse relays. They behave in a different manner.

author: nickm
author_rank: Regular Contributor
timestamp: December 23, 2013, 03:44:44 am
content: What exactly is going on? What is the wiring to this pump? Is it connected directly to the motor or is there other stuff in between the relay and your motor? So when you're not giving it 12V everything is off. Then after it has been turned on and things have been running removing the 12V doesn't turn everything off?Larger motors use contactors rather than relays because they can disconnect under load without frying the contacts.

author: calexanian
author_rank: Super Contributor
timestamp: December 23, 2013, 03:49:53 am
content: After reading this again I see you are not using a latching relay. Your standard relay is staying engaged. Thats just work trying to creep into my nice Sunday evening!

author: trent76
author_rank: Newbie
timestamp: December 23, 2013, 04:35:25 am
content: I'm using a 555 time too turn the relay on and off. The first thing I cheack was too see if there was power still running though the coil but there is nothing. Once it's turned on then off the conacts will not reopen they stay closed. You can even hear the relay turning off but the click is not as load. I've tried 3 different relays but had the same thing with all of them. I tried replacing the pump and solenoid with a light to see what happen and it works great. It's not welding the contacts togeter or the would not reopen when I turn the main power off. There is no sparks as the contact close. I have no protection on the contacts they coneted strate to the pump and solenoid the pump and solenoid are single phase 230v ac.

author: SeanB
author_rank: Super Contributor
timestamp: December 23, 2013, 05:10:00 am
content: You are welding the contacts. Use a different relay to drive the pump, probably a plug in relay or contactor rated for AC motor use and with a 230V coil and use the smaller relay to drive that relay.

author: trent76
author_rank: Newbie
timestamp: December 23, 2013, 05:25:34 am
content: Thank you I'll give that a go