This week I swapped the two DC heated pads for the anticipated AC heated pads. As these cannot be connected directly to the ramps I’m using two solid state relays to switch the two heated pads but in a different than expected way. The two relays are wired in series so if any of the two is open there is no current flowing to the heated pads that are wired in parallel. The heated pads have also a thermistor each so I’ll use one thermistor to give temperature feedback to the ramps that will switch the first relay and the other thermistor to give temperature feedback to the safety device that will switch the second relay. This way the ramps will control the bed temperature as it would any other bed but in case something goes horribly wrong I’ll use the 0ther set of thermistor/relay to switch the bed off with a completely different controller that is separated from the ramps. Redundancy is a must when dealing with safety in 3D printing, so please be safe, please be safe.
I also installed the cable chain the wrong way around but that’s an easily solvable minor incident.
The end is near!!