Using PS_ON as "safety switch" on SSR controlled bed
OwenD last edited by
I am in the process of gathering the required hardware to convert my I3 clone from Marlin/MKS Gen L to RRF/Duet.
On my current system I run an ATX power supply and a 240v bed with an SSR.
As an added safety device in case the SSR fails in the open position, I run a mechanical relay powered by the ATX.
In the event of a thermal runaway, Marlin shuts down the PS_ON supply which in turn switches of the relay and in turn the 240 volt supply.
I also have a thermal fuse as I believe in redundant systems.
Part of my upgrade will include switching to a 24 volt power supply, so I have to rethink this a bit.
I have searched the forum and found discussion within the last 12 months on how to implement PS_ON shutdown after a fault, but can't find anything that says that it has in fact been implemented and how it can be used.
In my case I'm hoping to use the PS_ON to switch the relay itself.
Is this now possible in RRF?
Thanks in advance...
When a heater fault occurs, RRF turns the affected heater off, pauses the print, and waits a defined period of time to allow you to reset the fault. If you don't respond within that time, it shuts down and attempts to turn off power via PS_ON.
The amount of time that it waits is set by the S parameter of the M570 command. See https://duet3d.dozuki.com/Wiki/GCode#Section_M570_Configure_heater_fault_detection. So if you want to replicate the Marlin behaviour, use S0 or a very low value.
OwenD last edited by
Thanks for the reply.
That's exactly what I'm after.
So I should be able to power a 5v relay from Pin1 of the expansion and run the ground of the relay to PS_ON.
This will require me to find an alternate power source for my BLTouch.
If I convert the BLTouch to 3.3v logic, is there any issue powering it from the 3.3v pin on the Z probe connector?
BLTouch manual says current draw is 300mA peak
3.3V probably isn't enough voltage to power the solenoid on the BLTouch.
You can get 5V from the PanelDue connector if your system doesn't include a PanelDue.