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5V power rail

stoobee

March 03, 2015 14:11

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Hello,
In the GPIO usage guide, you say that the 3V power rail cannot supply much current, but that you can use the 5V power rail. I have two related questions:

1) What is the maximum current that can be drawn from the 5V power rail
2) I want to connect a small stepper motor to the 5V rail, its current rating is 92mA – will this be ok do you think?

Thanks!

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11 comments

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  HiFiBerry team March 03, 2015 15:59

  Hi, 100mA should be ok. The power supply of the Amp can supply between 700mA and 1A (depending on the input volume), the Raspberry Pi itself uses usually less than 400mA.
  
  Best regards
  Daniel
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  stoobee March 04, 2015 09:48

  Thanks, that's great!
  
  I have a couple of other related questions:
  1. If using GPIO pins as an output, is it ok to use more than a few mA of current?
  2. More general interest, but why is it ok to use the 5V power rail, but not the 3V rail?
  
  Thanks
  
  Stuart
  
• 0
  
  HiFiBerry team March 04, 2015 14:23

  The GPIOs can only drive a few mA. Check the specifications of the Raspberry Pi CPU.
  
  The 3V rail is internally generated by the Raspberry Pi and can only driver 50mA.
  
  Best regards
  Daniel
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  stoobee March 04, 2015 15:33

  Thanks for your help and speedy response!!
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  stoobee March 22, 2016 11:50

  Just revisiting this for a new project... I wanted to check, if I have a 12v 3A power supply going to the HiFi berry, will the Pi still only get between 700mA and 1A? ie does the input current affect the current supplied to the Pi?

  If the pi uses 400mA, is there any way I can get more than 300mA - 600mA?

   

  Thanks

  Stuart

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  HiFiBerry team March 22, 2016 11:52

  Yes, the Pi will get only 700-1000mA. While this is enough for the Raspberry Pi3 itself, you can't use another 300-600mA for additional devices. If you need more power, you will need an additional power supply.

  Best regards,
  Daniel

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  stoobee March 22, 2016 12:37

  Sorry, do you mean I can't use MORE than 300-600mA? I assumed 300-600 would be ok for additional devices (700mA  - 400mA and 1A - 400mA)?

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  HiFiBerry team March 22, 2016 13:11

  With the Raspberry Pi 3 you should not use ANY additional power from the power supply as its peak consumption is a lot higher than the RPI2 consumption. With an RPI2 you can use some power, but definitely not 600mA. I can't guarantee a specific maximal current for additional devices as the Raspberry Pi power consumption is highly dynamic.

  Best regards
  Daniel

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  stoobee March 22, 2016 15:17

  Thanks Daniel,

  I'm working with a RPi 2. Thinking the additional power would be 400mA. Still probably safe not to risk it....

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  HiFiBerry team March 22, 2016 15:19

  400mA is quite a lot. You can try it. If it doesn't work stable, you will need an additional power supply for the additional device. What do you plan to add?

  Best regards,
  Daniel

• 0
  
  stoobee March 22, 2016 15:50

  It was an adafruit trinket and an adafruit 24pixel neopixel ring (I think each pixel is ~18mA).

  If I got a 12v 4A or 5A power supply, could i just put split the power supply between the HiFiBerry/RPi and the Trinket/Neopixels (with some step-down convertor so the voltage isn't so high), so that they are in parallel? I apologise for my poor electronics knowledge if this sounds crazy!

  Just wondering if I can get around needing two power supplies...