Recently, I tested the Prusa power panic feature in my new 3D printer. The test was accidental, but that does not matter. It worked fine.
I was demonstrating my new Prusa MK3S for a few friends. We were half way through the print, when I accidentally bumped the power cord out of its socket. With my old printer, power loss meant the end of any chance of a successful print.
When we plugged the power back in, the control board rebooted and gave us the message” Blackout occurred. Recover print?” as shown above. I said yes, and a few moments later, we were back in business.
So, how does this Prusa power panic feature work?
Basically, it takes advantage of the fact that filter capacitors in a power supply store energy. When AC power is removed, these capacitors will discharge over time, which depends on the resistive load on the power supply. If you reduce the load on the power supply, discharge time is increased.
You will find that an unplugged power supply can keep providing its output voltage for a few seconds. And, that’s when the magic occurs.
Prusa Power Panic – How it Works
My control board has a separate sensor to monitor the status of the power supply directly. When power is lost, this sensor signals my controller that it’s time to enter power panic mode.
Here’s what happens. First, your extruder and bed heating is turned off. This gets rid of the biggest load on the power supply and prolongs capacitor discharge time. Second, the firmware saves its current status into the EEPROM memory. I think this information is probably just a power panic flag, as well as current temperatures and print head position. Finally, your print head is raised a few millimeters and moved aside. This prevents the hot end from damaging the print.
When the printer reboots, it reads the power panic flag and provides the opportunity to recover. As long as your printed plastic has not cooled down too much, Prusa power panic will heat things up and continue printing as if nothing happened.
If you are interested, here is a more detailed explanation .