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Raspberry Pi 2 "5 V Power Supply" Notes

Former Member

Some time ago, I ordered and received the RPi 2,.  ordered and imaged a new SD card and found the board not booting.

 

Having been using a RPi 1 with power supply, monitor, mouse and keyboard and never seen any problems starting,. I expected

the new board also to boot with the new SD card and the rest of the hardware.

 

After spending quite some time with changing to another RPi 2 board ( exchange )  different SD cards, I had the conclude that

my problem most likely had to do with the the power supply.

 

All the used SD cards and hardware  did work with The RPi 1.

 

Up to this point both boards did not work while the RP1 1 never failed to boot.

 

The power supply I was using provided about 5.4 V measured on the miniature USB connector on the board. Changing start sequence

had no effect, 110 Volt first, USB switching with Power Supply already powered up. No variations in the board voltage were noticed.

during the start-up.

 

The power supply ( Chinese switching ) had a relative thin output power cord ( by closer inspection )

 

Finally, by using an home built power supply with adjustable output voltage and the heavier gauge output power cord, I got both computer

board to work with all the SD cards I had required in the previous process.

 

Not having an oscilloscope available, I was not able to look for any non wanted effects at the time of switching on the RPi 2.

My final conclusion is that the RP1 2 is much more sensitive to possible voltage changes than the RPi 1 during start-up and booting

With the adjustable 5 V power, I experienced no problems running between 4.5 and 5.5 V input to the board.

 

Wished I had known this a little earlier....!

 

Rein Smit

Parents

  • You need to be very careful providing in excess of 4.25V to the PI or Any 5V rated logic device, this is exceeding the recommended max volts and could damage something

     

    With the right adapter at 5V or no more than about 5.2V with 2A Capacity or more and a quality USB cable you should be fine. The 2A is to allow for any additions you may plug into the PI.

     

    I have performed a review and analysis of many cables here should you be interested in learning more about it

     

    Raspberry PI:- USB power cables, crashing and other problems

     

    Regards

     

    Peter

  • in reply to Robert Peter Oakes

    Peter, any chip that allows "5V nominal" powersupply will implment that as "5V +/- 10%". Now, if a powersupply were specified to provide 5V +/- 10%, it could in some cases provide one of the extreme voltages of that range. Then things would be "tricky". So for most powersupplies the range they provide is the nominal voltage +/- 5%.
    Another consideration would be that there is a slight voltage droop across the cable from the powersupply to the load. Expensive powersupplies will measure the resulting voltage at the load, and automatically compensate for that. However, cheaper powersupplies (e.g. the ones you might use to power your 'pi) cannot afford the extra electronics/wires. So it could be useful to pre-compensate a bit for the voltage drop. So now you see powersupplies that provide 5.25 nominal. A voltage like 5.35 coming out of such a powersupply will still be well within range for all chips that nominally take 5V.

Reply
  • in reply to Robert Peter Oakes

    Peter, any chip that allows "5V nominal" powersupply will implment that as "5V +/- 10%". Now, if a powersupply were specified to provide 5V +/- 10%, it could in some cases provide one of the extreme voltages of that range. Then things would be "tricky". So for most powersupplies the range they provide is the nominal voltage +/- 5%.
    Another consideration would be that there is a slight voltage droop across the cable from the powersupply to the load. Expensive powersupplies will measure the resulting voltage at the load, and automatically compensate for that. However, cheaper powersupplies (e.g. the ones you might use to power your 'pi) cannot afford the extra electronics/wires. So it could be useful to pre-compensate a bit for the voltage drop. So now you see powersupplies that provide 5.25 nominal. A voltage like 5.35 coming out of such a powersupply will still be well within range for all chips that nominally take 5V.

Children
  • in reply to rew

    I would largely agree except you do see many that are 5v +- %5 which would take the PSU out of spec.. All depends on how much you invest in the paranoia!

     

    Probably OK but John probably doesn't feel lucky image

  • in reply to Problemchild

    I disagree with the word "many". I can't find any.

     

    Some "special" chips might have stricter requirements than 5V +/- 10%. However, those are exceptions. For example, a sensor normally built for 3.3V might "stretch" to "5V + a little bit".

  • in reply to Problemchild

    John Alexander wrote:

     

    I would largely agree except you do see many that are 5v +- %5 which would take the PSU out of spec.. All depends on how much you invest in the paranoia!

     

    Probably OK but John probably doesn't feel lucky

    It's not a matter of luck, but of due diligence -- part of good engineering.  There are probably enough components between RasPi 2's Micro USB power connector and USB and HDMI so that those meet the 5.25V max spec, and RasPi 2's voltage regulator inputs probably go up to 5.5V.  However, without RasPi 2 schematics there is no way to verify this. image