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I'm new on Raspberry world and bought this components:

Raspberry Pi 3 Model B

Power Adapter 5V 2.5A

HDD 2.5

My question is: Is this enough to connect the HDD to Raspberry Pi, or must I buy a HUB? I don't want to have problems with high temperatures.

Thanks in advance.

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    depends on the power requirements of the specific HDD you have bought. We can't possibly know how much it needs - though, at a guess, I'd say you'll be fine
    – Jaromanda X
    May 19, 2016 at 23:47

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This SHOULD be sufficient to run the HDD, provided it is designed to run from USB with the 500mA limit this imposes.

Unfortunately it may not be reliable, as it depends on the voltage. My Pi2 power supply, rated at 2A, drops below 4.8V when I tried running a HDD, and while this is in spec proved unreliable, so I use a powered hub. There are a number of items in the path, the polyfuse and the USB supply regulator which contribute to the drop.

You need to give it a try, and measure the actual voltages.

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  • Don't forget to factor in that the drive startup power may be enough to force the pi to reboot, so it would depend on if he was going to be disconnecting the drive and reconnecting it frequently or only before boot because mechanical hard drives often require a large spike of power to get the platter(s) to speed and very little power thereafter to maintain that speed due to kinetic energy.
    – Mohammad Ali
    May 20, 2016 at 4:30
  • @Milliways How can I best measure the mA that a HDD connected with USB pulls? Is there any way to do that from within the OS? Good approach?
    – Socrates
    May 28, 2016 at 4:49
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    @Socrates Firstly it is Current not "mA" or "amps". Unfortunately it is not simple. The Pi has no analog capability. There is no convenient measurement point. What you would have to do is use a custom USB cable (or breakout panel) which lets you insert a meter in series with the +5V line. Even this won't give you the answer you need, as the current varies - higher when the motor is running, with a surge when starting. You need highly specialised equipment to do this accurately. The only satisfactory answer is to refer to the manufacturer's data.
    – Milliways
    May 28, 2016 at 4:57
  • Virtually all modern USB HDD run on <500mA. Some older (very old - usually PATA devices) need more, and usually come with a Y cable (with 2 USB connectors).
    – Milliways
    May 28, 2016 at 4:58

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