Jetson Nano 3-Pin Fans

I’m running into an issue with booting up. I’d like a recommendation on how to proceed.

The Jetson Nano is being powered by a PoE power converter that takes in a PoE line at 30W and outputs a ethernet data line and a barrel jack line. The power output of the converter into the Nano is 20W @ 4A, 5V. Here it is:
https://www.uctronics.com/uctronics-poe-splitter-5v-4a-active-poe-to-barrel-jack-ieee-802-3at-compliant-for-jetson-nano-poe-security-camera-and-more.html
I also have a 3-pin, 40mm x 10mm fan attached to the Jetson Nano. The 3 pins are connected to ground, power, and the tachometer fan pinouts.

When I plug into a PoE port on a Cisco switch, peculiar behavior occurs: the Jetson Nano boots up inconsistently (i.e., sometimes succeeds, sometimes fails - failure is determined by the power not turning on on the device) when the 3-pin fan is connected. It boots up consistently when the 3-pin fan is disconnected. If the fan is connected after the green LED on the Jetson has turned on, the device continues to run nominally.

My guess is that the boot sequence succeeds when enough power is being supplied, but that a large amount of power is drawn away from the device as the fan turns on. It seems like a race condition that might be ameliorated by using a 4-pin fan that connects to the PWM - I could imagine that the PWM starts the fan at low speed while the device initially boots up.

Can anyone on the Jetson team verify whether or not my hypothesis makes sense and provide a solution to it? I’m just about to run and get some 4-pin fans to see if that fixes the problem.

Nikhil

hello nikhilshinday,

it’s by default to spin fan during kernel initialization stage. there’s RPM table to indicate the fan rpm configurations.
you may refer to hw monitor about pwm_rpm_table, i.e. # cat /sys/class/hwmon/hwmon1/pwm_rpm_table,
please have customization; you may have a try to configure target_pwm to workaround your booting issue.
please also refer to Thermal Cooling session for the fan control of thermal management.
thanks