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Arduino 5V pin supply

Discussion in 'Microcontrollers, Programming and IoT' started by mach7, Jan 8, 2013.

  1. mach7

    mach7

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    Jan 8, 2013
    I power up my arduino with 4XAAA Ni-Mh batteries from the 5V pin.
    I know that's it is not recommended but it works ok. Have anyone else try this?
    Is there a possibility to fry something on the board if i use it for long time in this mode?
    Thanks.
     
  2. GreenGiant

    GreenGiant

    830
    6
    Feb 9, 2012
    what 5V pin?

    I try to power mine with 7-10V personally on either the Vin pin or through the power adapter plug.

    What is the voltage rating on those batteries, I know that some are only rated at 1.2V fully charged, be careful you can lead to things being damaged this way.

    Also most AAA battery packs you can get for Arduino use six batteries not 4
     
  3. mach7

    mach7

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    Jan 8, 2013
    Thanks for your answer.
    The 5v pin is the output of the voltage regulator.
    Yes, these batteries supply 4x1.2=4.8V
     
  4. GreenGiant

    GreenGiant

    830
    6
    Feb 9, 2012
    This is from the Uno but they are all basically the same

    also 4.8 is a little low, you should probably use higher voltage
     
  5. mach7

    mach7

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    Jan 8, 2013
    Voltage higher than 6 volt will fry the board (there is no regulator in this pin)
     
  6. GreenGiant

    GreenGiant

    830
    6
    Feb 9, 2012
    My info was pulled right from the Arduino site, what board do you have?
     
  7. mach7

    mach7

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    Jan 8, 2013
    Arduino UNO.
    http://arduino.cc/en/Main/arduinoBoardUno
     
  8. GreenGiant

    GreenGiant

    830
    6
    Feb 9, 2012
    Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it. Says right there, they do not recommend it, use the Vin pin with a higher voltage (7-12 as stated) and you eliminate the risk of damaging anything.
     
  9. mach7

    mach7

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    Jan 8, 2013
    That's why i am asking. If anyone had tried it for a long period because it seems that works with no problem.

    Thank you GG.
     
  10. cosser

    cosser

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    0
    Dec 29, 2012
    Toyota ecm

    HI, everyone, I know this is not a motor Vehicle Forum, my wifes Toyota car broke down,the local grease monkeys,towed it to their work shop,they plugged in the dianostic cable,they agreed that the crankshaft sensor had failed, two new sensors later no start, out comes the electronic control module, sent to england for diagnostics and repair, ten days later it is returned at a cost of £250 .unit installed, toyota runs 8 minutes then dies out. auto spark sent for, he checks out systems leading to the engine management system, all is perfect , another specialist was sent for, he checked out the ecm with very expensive diagnostic toyota software, result faulty brain ,
    the local technition who works in an amusement arcade said bring the brain to me, i did and 8 hours later my toyota is running perfect. any one no whats going on here, thought it strange that a man working in an amusement arcade could repair this module so easeily. and for £10.00.

    BRING. BACK THE STARTING HANDLE.
     
  11. CocaCola

    CocaCola

    3,635
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    Apr 7, 2012
    If you are skipping the onboard voltage regulator (on say the UNO) and trying to run the device off of batteries or another fixed voltage source direcly, you should consult the datasheets for whatever AVR chip is on board... Most AVRs will work down to about 1.8V or up to about 5.5V depending upon the clock frequency you are using...

    Running off 4XAAA Ni-Mh should be fine for most hobby applications...
     
  12. mach7

    mach7

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    Jan 8, 2013
    The chip is the Atmega328 and it's ok with this voltage. I have seen standalone applications which are powered by unregulated voltage.
    How about the voltage regulator which is on the board and have voltage only on it's output?
     
  13. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,267
    Nov 28, 2011
    mach7 you've probably figured out the main reason for the warning.

    Regulators are not designed to be back-fed. That is, you're not supposed to put voltage on the output of a regulator if its input is not powered. What happens depends on the regulator's design.

    A traditional approach is to put a diode backwards across the regulator, that is with its anode to the regulator output and cathode to the regulator input. This ensures that if the regulator is back-fed, it has voltage on its input, even if that voltage is not enough for the regulator to do anything useful.

    This protects the pass element inside the regulator and is recommended for 78xx regulators and the like. Primarily it's intended to protect the regulator if the output voltage is held up by output capacitors and the input voltage tries to fall quickly, but it will also protect the regulator from back-fed voltage. It may not be enough to protect the regulator that's used on that board though.

    Another probable reason why the company doesn't recommend feeding voltage directly onto VCC is that the regulator provides smoothing and decoupling of noise and surges, i.e. it cleans up the voltage. If you use an external supply directly onto VCC, this introduces a lot of possible issues which could cause malfunction or even damage to the logic ICs, which the company wants very much to avoid.
     
  14. mach7

    mach7

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    Jan 8, 2013
    Thanks a lot Kris, but when we plug in only the usb, there is no reverse current in the regulator?
    Do you know a solution for this? Sure I can regulate the external voltage but how can I protect the regulator?
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,217
    2,695
    Jan 21, 2010
    Often the issue with back-feeding voltage regulators is that it reverse biases the BE junction of the internal pass transistor.

    Whilst I know of no regulator that has this specified, it is unlikely that 5.5V is going to cause a breakdown of this junction. As to whether it will cause other problems is largely unknown.

    A diode across the regulator will prevent these problems as long as the input is not shorted to earth or something crazy. Again, that seems quite unlikely.

    The schematic for the Arduino Nano does not show a diode across the regulator.
     
  16. mach7

    mach7

    18
    0
    Jan 8, 2013
    This is the datasheet of the regulator of the UNO R3.
    http://www.onsemi.com/pub_link/Collateral/NCP1117-D.PDF

    At page 10, it says the same thing! A 1N4001 can prevent the problems!!
    That's good news! I could connect a diode across Vin and 5V.

    I am thinking of using a zener diode voltage regulator to have a regulated voltage also. What do you think, Steve?
     
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