@mrehorstdmd said in safety relay for ssr heated bed.:

How are you going to protect the protection relay from some crud preventing its armature from moving, or from the contacts welding shut?

My relay is noisy so I hear it clicking on each time I turn the printer on. Kind of a self test.

"perfect is the enemy of good" . 😉

It not a perfect solution but it reduces the risk of fire due to a short in the duet's mosfet or the SSR.

@hamiltonprops From re- reading your OP, you say that the temperature drops 20 degrees within a second or two. That would indicate it's not a "real" drop in temperature but rather a drop in the indicated (measured) temperature - unless your hot end has an insanely low thermal mass. So, yes I go for some sort of cross talk or electrical "noise". Are you sure you haven't got a bad crimp on the thermistor wiring somewhere?