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Powering Pi Directly from PSU

Discussion in 'Power Supplies' started by Kitman, Sep 27, 2016.

  1. Kitman

    Kitman Full Time Elf

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    Since I am going to be having my whole show run from multiple Raspberry Pi's I need to have them in or near my control boxes.


    I have already sorted this out for my 12v control boxes by ways of a 12v to 5v DC converter which has the Micro USB on the 5v side that plugs into the Raspberry Pi, however for the 1 set of 5v lights I was thinking of having a 5v regulator connected to the power supply before the Micro USB cable just to make sure that the voltage going to the raspberry pi is as close to 5v as possible so as to make sure no damage is caused to the pi and also so that the pi doesn't go low voltage on me and turn off mid show.


    Unfortunately I am not knowledgeable enough with electronics to design a simple voltage regulator circuit to do this job, I think I will need 1 or 2 capacitors and an actual voltage regulator of some kind, however all of the stuff I look up refers to dropping the voltage from some higher voltage down to 5v but I am going from 5v to 5v, I just want to smooth out the voltage to make sure it's 5v.


    Hoping someone can provide me with a simple circuit that I can solder up with a few parts from Jaycar or the like.
     
  2. Fing

    Fing Full Time Elf Generous Elf

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    Hi Kitman


    very simply all voltage regulators require power to operate and as such most need say 2v ( very roughly) so 7v to 5v is easy but 5v to 5v isn't possible.... but you already have 5v available from the PS so why not use it? if it dips below 5v you will have bigger problems than the Pi stopping.
    With your limited knowledge of electronics it maybe be a lot easier to simply install a 240v to 5v PS plug pack only for the Pi ?


    other options would be to obtain a nominal 5v to say 12v PS then put a 12v to 5v after that to get a regulated 5v for the Pi? these creatures exist on ebay for a couple of $ and are often called buck or booster regulators etc


    hope this helps
    Fing
     
  3. scamper

    scamper Senior Elf

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    You can just do what I did, or something similar, and just buy a power pack that has a couple usb power outputs built into it.
    I use one for the Pi and the other for my network switch.
    Then i use the power outlets to switch the 3 power supplies in the box and the last one is for the fm transmitter.
    excuse the mess of the box at the moment as i am re arranging it this year, but have been using it for testing throughout winter.
    [attachimg=1]
     

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  4. tooms

    tooms Apprentice Elf

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    Do your controllers have a 5v output?


    My new falcon's do, so I've just cut up a USB cable and attached it to the 5v out from the board.
     
  5. i13

    i13 Senior Elf

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    My understanding is that switchmode power supplies are well regulated by design. You shouldn't have a problem unless you push them past their rated wattage or if you accidentally adjust the output voltage.
     
  6. ShimmerNZ

    ShimmerNZ New Elf

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  7. OP
    OP
    Kitman

    Kitman Full Time Elf

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    I was simply going to connect the raspberry pi directly up to the 5v power supply. however because the Raspberry Pi likes to be a bit touchy when it comes to voltage I just wanted to make sure that it had a constant stable 5v supply.


    My Sandevice does have a 5v output on it, however it only supplies around 1.5amps and I need to make sure the raspberry pi has I believe 2 or 2.5 amps to ensure it runs correctly so sadly can't rely on the 5v out from the Pixel controller.


    Didn't want to have another 240v lead running into the control box, since it's going to be on the roof want it as simple as possible without too much extra work of having to include a plug pack in the box.


    Will try coming off the 5v power supply and make sure I set the Power supply to 5.1v or close enough when under a bit of load so that it doesn't vary too much.


    Thanks all for the suggestions, I may even up convert to 12v and then drop it back to 5v as per Fings suggestion as I did find the 5v to 12v up converters and I already got some 12v to 5v bucks for my 12v boxes so will see how we go.
     
  8. smartalec

    smartalec Im a SmartAlec what can i say! Community Project Designer

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    O.k. Just to help you out here.. i did some research why its 2 & 2.5amps for the rasp pi's.. its based on if you use the rasp pi USB ports (there Max port power is around 450-500ma)- ohh an there's 4 of them..

    so using the HDMI output is 250ma draw, using full cpu usage is only around 600ma, 500ma usb stick.

    This is what i read by people realy going into power usage on the rasp pi.
    get one of them cheap usb power monitor's there like $5 (does amps an volts)

    but in the end they all agreed its better to cut a usb cable an feed 5v in that way.. or use a step-down for higher voltages

    I hope that helps
     

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