Detection of Fan plugged

carlosspr · 8 Mar 2018, 16:20

Is it possible to detect if a fan is connected to the pins (plugged/unplugged status)?.

The reason of this question is to prevent some issues and add some extra security layers. I have recently upgraded my printer to 24V. This included rewiring the nozzle to add a 24V heater and the installation of a 24/12V buck converter with output connected to the middle fan pin to be able to keep my legacy Noctua fan. In the rewiring process, one of the pins of the Molex connector fitted to the Noctua fan slipped and did not make a proper contact. Because the Noctua is so quiet, plus the fact that I have set up a temperature trigger, I did not notice that the pin was not properly connected inside the molex. I started the print of a calibration cube on PETG and after a few layers, the nozzle clogged. Just then I realized that the Noctua cooling fan was stopped and all the filament melted inside the E3D hotend. Had I been not following all the print, the temperature at 230 degrees could have melted all my X-carriage.

i was thinking to apply some extra security measurements to prevent this:

If the presence/absence of the fans could be detected, some security features could be added to shut down associated tools. Also auto-configuration of the web interfaces depending on number of fans detected would be good.
A second prevention mechanism that I thought of was to add an additional thermistor on the cooling structure and link it to a a trigger that would stop the heater if the temperature passes certain threshold. This will prevent clogging and potential meltdown of the whole nozzle.

Does anyone have had this experience or implemented a better mechanism? I am not particularly fan of adding more cables from the x-carriage to the control board, but for the shake of security probably it will be the best.

dc42 · 8 Mar 2018, 16:23

The presence/absence of a fan can't be detected by the fan driver circuit.

The thermistor to monitor the heatsink temperature is probably the best option. Another option would be to use a 4-wire PWM-controllable fan (which needs to be driven a different way from the usual fans) and monitor the tacho output.