2 yrs ago programmed arduino to read temperature and activate linear actuators through relay to open/close greenhouse wall. Worked fine until yesterday. Bottom of relay has copper link burnt through. Board still 'clicks' when arduino tells it to. Worn out board? Checked all wiring for shorts -couldn't find any.
thisisted:
Bottom of relay has copper link burnt through.
This is the obvious problem - get a new relay board and this time, properly protect it from the elements.
Relay board was inside greenhouse and further, it was inside a plywood box. Guess my concern was why the board burned out. ( Old age? # of cycles?, any other reason?) BTW, I should have mentioned, only one link was burned out, so I bridged the burn with strands of copper wire from lamp cord. As soon as the arduino told the relay to click, the second link immediately burned out. I've ordered another board, but don't want it to burn out too. Greenhouse wall works fine when I directly apply 12 v to the actuators, so assume that they aren't the problem. Any other ideas?
Do you have a schematic to show us exactly how the relays fit into your project? You say you checked for shorts, but the shorts are only occurring when the relays operate, so you did not find the short causing the problem.
What function do these two relays perform? Since the NO and NC traces did not overheat, they are not involved in the circuit with the short.
I see a pin hole burned through the board on the left relay on the bottom picture. Is there a trace that runs under the relay? Is there a similar pin hole under the other burned trace?
Paul
This was my first and so far only project. No schematics, I just taught myself to code and figured out what went where. Pinhole you see is just a mark on the board. No burn.
Attached photo is the electronic stuff. Arduino reads temperature every 10 minutes through wires on left of Arduino. Depending on temp, relay signals to open or close Two 12v linear actuators for 6 seconds. Wait 10 minutes, repeat. Worked fine for about 2 years. 12 v comes in through black wires that have orange wire nut. Goes out through red and black wires into the Brown covered wire and to actuators. Unconnected wires were in case I wanted to add to system. I was going to add an annenometer to override and close the windows if it got too windy, but 1. Didn't want to struggle with code, and 2. Wind wasn't a problem. Sorry if this isn't super helpful. Whether you can or can't help, thank you for your effort. I've got another relay board on order and will just put it into the system and see what happens.
Then it's time to do an dissection of the relays. I had similar relays fail with contacts shorted after several months operation and removed them from the circuit board, sawed the plastic case top off the thing and found the contacts welded together. There was never any over voltage/current. soldered replacement relay to board and ran for a year till end of experiment. The contacts are really cheap crap metal balls on copper strips.
No one can use their crystal ball to discern the problem. Only scientific discovery will do that for you. And what do you have to loose?
Paul
May be the problem is not in relay?
May be it's short circuit.
And if so, you have a mistake in your circuit: no fuse.
P.S.
Interested in greenhouse automation too.
Do you have sensors?
endswitch for example?
Paul; I LOVE dissecting electrical and mechanical things. 
Thank you very much for your comments. I guess I'm just surprised the whole thing worked, let alone for 2 years. Maybe I are smarterer than I thinked?
