A few months ago, I upgraded my printer with 2 cooling fans, one on either side of the extruder. Stock configuration had a single fan that got destroyed when an unobserved print went haywire and plastic went into the fan itself. The time was right to do the upgrade.
I can’t remember why, but I updated my firmware at the same time to Marlin 1.1.8, the latest release at the time. I’ve since updated to 1.1.9 but both had the same issues I’m about to talk about. That is thermal runaway protection. The reality is, I’d been affected by this since day one but hadn’t known. The stock fan configuration wasn’t particularly strong, and the software didn’t complain about it, but when my prints started, the fan started cooling the extruder. Close to the bed, at the start of the print, this was quite significant. So much so that the updated software complained that the heater wasn’t able to keep up once the fan turned on, and shut itself off. Every time.
The solution is to use a silicon sock to prevent this by insulating the heater block. I don’t have one. I’m still looking for one that fits.
The workaround is to scale the fans maximum speed back. Way back. It was worse with the new fan configuration, especially near the bed where the cooler air gets reflected back. Depending on the print it will also happen away from the bed. So I turned runaway detection off and babysat the fans so I could maximize print cooling without allowing the extruder temperatures to drop out of acceptable range. That’s a lot of time staring at temperature plots and entering GCode since OctoPrint has no fan control.
Enter Marlin 2.0. It’s not a release version yet although it has experienced significant development already. It will eventually include 32 bit support for a number of boards. But for me the key feature is it automatically scales back the fan speed as the extruder temperature drops. No more babysitting my prints!
How well does it work? Well, the two prints here are printed with 1.1.9 and babysitting in white, and 2.0 with automatic control in green. So yeah, I think I’m happy!
Automatic fan speed control in green, manual control in white