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Tomorrow I will buy a RPi 2 B, which I would like to use with an external 2.5 HD (5v 1A) and a single 2A charger (connected to the microUSB port). Will I be able to run both of them by adding max_usb_current=1 in /boot/config.txt? Or I will need to buy a powered usb hub? Thanks in advance

  • what do you mean by use with an single 2A charger (connected to the microUSB port)? you mean as power source for raspberry? – Flash Thunder Feb 20 '16 at 18:50
  • I doubt your HDD needs 1A. If it did it wouldn't run on anything with complying USB ports. In fact no modern drive needs more than 500mA. Those old devices typically needed 600-700mA. – Milliways Feb 20 '16 at 21:51
  • it m8 be unstable... max current from one usb port is 700mA. – Flash Thunder Sep 7 '17 at 20:29
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If a power supply is 2A and the only device connected to USB port will be 2.5' HD that uses 1A, it should be just fine, as 1A is totally enough to run raspberry. Even 1/3 of that would be probably fine. Please note that cheap 5V 2A chargers don't really produce 2A.

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just adding to the answer of @flash, I am powering my own RPi2 from a USB port of laptop and i am utilizing all four usb ports of RPI2. Its working just fine (although its not a good practice). So a 2A power supply is enough.

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You don't have to buy a powered usb hub, but it is highly recommended especially if you are using an external hard drive. The external drive may need more than 1A at a given time, so setting max_usb_current=1 would be a bad idea. Also, USB cables that provide 2A rarely actually provide 2A, this has been discussed many times on this site before.

You can go ahead and not buy the powered hub, and plug in all your stuff, but if you see the red PWR light on the Pi shut off, or even blink, while it is plugged in, then you need a powered usb hub. (If the PWR light turns off/blinks it indicates that the voltage has dropped below 4.75v)

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