Power Management + Fan on SATA HAT

#1

I am planning to build a NAS with 4x 3.5" HDDs and an external case fan, I would like to make sure I understand the power management on the SATA HAT.

My plan is to use power option 2, 12V 5A directly onto the DC jack of the SATA HAT.

  1. Is the Raspberry Pi 4 powered via the 5V pins on the GPIO? If yes, what kind of converter is being used to step the 12V down to 5V? Is any protection given for the 5V rail of the Pi?

  2. If I connect my own fan to the 5V (pin 4) on the 10 pin connector of the HAT, how much current can I draw? I guess this depends on answer 1 and how the 12V is stepped down to 5V.

  3. In order to use the built in fan control, I would need a 5V PWM fan connected to 4, 8 and 7-9 of the 10 pin connector, is that correct? Or alternatively a regular 5V fan with my own transistor connected to pin 8 of the 10 pin section.

Thank you in advance, looking forward to using the product!

#2

Hello,

  1. Yes. Via Switching Voltage Regulators (5V, max 8A). Be protected.
  2. Depends on how much power is left in the power supply and the SVR.
  3. PWM: GND, pin33, 5V. Regular: GND, pin33.
#3

Thank you!

Glad to hear the SVR can handle 8A, this will be plenty to drive an extra fan.

Unfortunately it seems the Noctua PWM fan I plan to use has a 5V pullup inside so driving it directly off the 3.3V GPIO pin would probably be unwise. I will add a 2n2222 transistor in between and control it with the GPIO, allowing the fan to be safely controlled at 5V.