How to avoid PWM fans spinning at 100% while loading firmware

juliann · 13 Sept 2021, 14:06

Hi everyone!

I have several high power PWM fans installed on my Duet 3 Mini+, and every time I start the machine, reboot or press E-Stop they spin at 100% until the firmware reloads.

So I am just wondering if there is a way (with Duet or any other additional hardware/ component), to control the PWM while the firmware is not loaded. Something like a secondary PWM control maybe.

Actually this exact behaviour happens on desktop PC's fans while you reload the OS.

Of course it is not a big problem but actually a bit annoying sometimes

Thanks in advance
Julián.

achrn · 13 Sept 2021, 15:00

The PWM protocol is designed so that if the PWM wire is disconnected (either due to fault, or when using the fan on a controller / PC / whatever that doesn't have PWM) the fan spins at full speed. So the power supply comes up, there's no PWM yet, so the fan spins full speed.

I guess you could use an output from the Duet to switch a relay (or FET or SSR) that is inserted in the power supply wires to the fan. At the end of config.g you could switch the output so the fans are energised only after the firmware is running.

Or there are time-delay relay module cards on ebay that have an adjustable 0-10S (or other values) delay to switching on so put one of those into the power supply wires to the fan? Search 'delay relay'.

juliann · 13 Sept 2021, 15:58

Thank you very much @achrn! :-). Very good ideas indeed!
As I already have an extra SSR I will try that option first. Honestly it is the first time I heard about time-delay-relay... so I need to read more to correctly understand how they work and how to wire them

oliof · 13 Sept 2021, 16:10

This is a safety feature and I'd recommend against disabling it. It may be a bit of a regular occurrence during setup and tuning, but during normal operations it should almost never happen.

juliann · 13 Sept 2021, 17:47

Thank you @oliof
Sorry I did not clarify that point. Actually I am not referring to the hotend fan, that one it will keep its safety behaviour, the noisy fans I have are the air filtering and layer fans.

juliann · 17 Sept 2021, 01:18

Hi @achrn

Good news!
Just to confirm you, I put the SSR + config.g line to activate an output and this way solved completely my issue.

No more fan noise during boot or when I reset/ emergency stop the printer.

Thanks again for your help.
Julián.