Tutorials

Power Hungry USB Devices and the Raspberry Pi

By: Edgar Pisani

Overview

If you want to connect power hungry USB devices, but don't want to use a USB hub or another power supply to feed the hungry device, there are some alternatives you can use. First just a bit of background information about USB power. 

According to USB specifications, USB 1.0 ports should provide 150 mA, USB 2.0 ports 500mA and USB 3.0 ports 900mA. The Raspberry Pi Model B has 2 USB 2.0 ports. The Raspberry Pi Model b+ has 4 USB 2.0 USB ports.

Some USB devices require more power than is permitted by the specifications for a single port. This is common for external hard and optical disc drives, some WiFi devices and generally for USB devices with motors or lamps.

If you need to power some of those devices you can use an external power supply but if you just want to connect everything to the Raspberry Pi, there are other options you can consider, providing the power adapter of the Raspberry Pi can supply enough current for all the devices attached to it.

For example: The Raspberry Pi B+ uses about 650mA, external USB 2.5" hard drives can use more than 1A, so you have to make sure that if you're going to use them together, your power supply should provide around 2A to be on the safe side.

The following 3 options can help you solve the problem of a single power supply:

  • Option 1: You can connect the device to a single USB port, providing you enter a software setting in the Raspberry Pi that will allow it to supply more power to USB devices than the amountof power required by the specification.
  • Option 2: You can use a dual-input Y-shaped USB cable, one input of which is used for power and data transfer, the other solely for power.
  • Option 3: You can use a dual-input Y-shaped USB cable with a USB Type A female connected to the GPIO ports of the Raspberry Pi, so you don't lose one of the USB ports of the Pi. You can even piggyback other Raspberry Pi this way.

Option 1

If you have a Raspberry Pi B+, you can connect your device to a single USB port, after you add a couple of settings in the file located in /boot/config.txt. It is a bit confusing as there seems to be a couple of parameters. The parameters you have to add at the bottom of the file config.txt are listed here:

safe_mode_gpio=4
max_usb_current=1

It seems to only work with images that have the latest firmware. If your image doesn't have the latest firmware you might be out of luck.

Some more information can be found in the following links:

Option 2

You can use a dual-input Y-shaped USB cable, one input of which is used for power and data transfer, the other solely for power.

The following image illustrates this process:

Extra Power dual-input Y-shaped USB 2.0 cable

The main disadvantage of this technique is that it uses an extra USB port. If you have a Raspberry Pi Model B, this would use all the available ports.

If you want to use this approach, you'll need a cable like this:

USB 2.0 Type A Female to Dual Type A Male For Extra Power Y Cable - 20cm

If you have a power hungry USB device that a single USB port can not feed this is the solution for you.

Connect your power hungry device (i.e. an external 2.5" hard drive) to the female USB Type A connector. Then connect the 2 USB Type A male connectors to 2 different USB ports.

The thick Type A male cable provides power and data from one USB port. The thin Type A male cable provides power only from another USB port.

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Option 3

You can use a dual-input Y-shaped USB cable like the one described in Option 2, but instead of connecting the power only USB cable (the thin one) to the USB port of your Pi, you can connect it to a USB Female to Raspberry Pi GPIO Power Cable.

This way you won't lose one of the USB ports of the Pi. You can even piggyback other Raspberry Pi this way.

The following cable can help you achieve this:

USB 2.0 Type A Female to 2.54mm Raspberry Pi GPIO Power Cable - 15cm

Feed other USB devices from the Raspb erry Pi GPIO header pins. Including other Raspberry Pi. If you want to use a single USB power adapter to feed the Raspberry Pi as well as other devices, this is a solution for you. Just connect the red cable to to pin 2 of the Raspberry Pi GPIO header (5Vdc) and the black cable to pin 6 of the GPIO header (GND).

BEWARE if you make the wrong connections you could cause a short circuit and you could end up damaging your Pi and other devices connected to it, including the power supply!

Look at the images in the product details that show how to make the connection properly.

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Just be very careful in connecting the right cables to the right GPIO header pins of the Pi.

Connect the red cable to to pin 2 of the Raspberry Pi GPIO header (5Vdc) and the black cable to pin 6 of the GPIO header (GND).

BEWARE f you make the wrong connections you could cause a short circuit and you could end up damaging your Pi and other devices connected to it, including the power supply!

We won't be held responsible if you make the wrong connections.

The following image illustrates how to connect this cable to the header of the Raspberry Pi:

USB Female to Raspberry Pi GPIO Power Cable

At the end, this is the way it would look. Please notice that the thin Type A male of the Y USB cable is the one connected to the female USB cable connected to the GPIO of the Pi. If you connect the thick USB male cable instead it won't cause a short circuit but the device won't work as the data section of the USB connection will be totally disconnected.

USB Ycable connected to Raspberry Pi GPIO header

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