I use a "Thermalarm" to detect too high or too low temperatures in the greenhouse environment. It uses reed switches (Hamlin/Littelfuse 59025) mounted on the high and low set temperature arms, activated by a small magnet which is mounted on the thermometer (current temp) arm. Works great. Reed switches are well suited to the greenhouse environment, which has high humidity and lots of bugs/spiders.
For years, we wired the Thermalarm through a relay to a siren to warn us of high/low temps, powering the circuit with a 12v automotive battery. This year, I realized we have 120V outlet at same location and that we could use a 120VAC to 12VDC transformer wall plug. I did so, but found a problem with the relay (spiders). Then I thought maybe the relay was unnecessary.
I ran a 30 watt load through the Thermalarm which is rated for a 10 watt maximum load. I ran this load for several seconds. The switch now seems to be stuck closed. Is this likely to be a permanent failure of the reed switch? Or, is it repairable?
I have considered mechanically tapping the switch, applying a current of the opposite polarity to the switch, or waving a magnet in the vicinity of the switch. Not sure whether any will work.... Any thoughts most welcome. Thanks.
Al