Running a 12v fan off 5v USB?

Discussion in 'General Electronics Chat' started by jayuk20, Jul 5, 2013.

  1. jayuk20

    Thread Starter New Member

    Jul 5, 2013
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    0
    This is not to be plugged into a PC USB port but into a USB wall plug that you get with mobile phones.

    I've got 3 5v fans but they are so loud and when the 12v is running on 5v USB it generates enough airflow at the slower speed and is super quiet, perfect for my needs. The only question is.... is there likely to be any type of safety hazed?
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    If you aren't exceeding the current rating of the mobile phone charger then no.
     
  3. jayuk20

    Thread Starter New Member

    Jul 5, 2013
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    The fan I have now is an xbox 360 fan and says the following:

    DC12v
    0.40A
    -9F15

    The charger says

    Input: 100-240v ~ 0.3A (Max.) 50/60hz
    Output: 5.0V ---- 1.5A
     
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    0.4a will be on the 12V DC supply , so on the 5 v dc usb it will take less current and run slower.
     
  5. jayuk20

    Thread Starter New Member

    Jul 5, 2013
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    OK so am I correct in thinking that the mobile charger can take 1.5A meaning the fan will require less current than the charger is actually able to provide?
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
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    yes.. you have some room to work with there.. all good
     
  7. jayuk20

    Thread Starter New Member

    Jul 5, 2013
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    Thats great. Thanks for your replies. I'm just starting to learn about this stuff so I'm always over cautious to start. Many thanks.
     
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Yes indeed your supply can provide more current than the fan requires.

    Two things about this.

    Firstly this is true of pretty well all electrical sources - the source determines the voltage (5 in your case) and the load determines the current (probably 0.2 - 0.3 amps in your case).

    However an electric motor relies on its speed generating a 'back emf' to limit the current. This is why the stall current is so high.

    So you should make sure your fan is kept clean and obstruction free so it never stalls as the 5 volt supply can probably supply enough current to burn it out.

    go well
     
  9. jayuk20

    Thread Starter New Member

    Jul 5, 2013
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    Again thanks. I will get a 5v fan but I prefer to "play and learn"
     
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
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    I didn't say don't use your 12v fan I said, don't obstruct it.
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Putting a series resistor with the fan will only drop a few percent of the running voltage, but can greatly reduce the startup and stall currents. If stalling will be an issue.
     
  12. Shagas

    Active Member

    May 13, 2013
    802
    74
    Does anyone know if these new brushless DC fans have internal protection circuitry ?
    I have a few 12 volt Pc fans and from the gap I can see some components in it . I don't want to take them apart yet because they are new and >10 bucks each but my curiosity probably won't hold out much longer
     
  13. David Knight

    New Member

    Aug 4, 2015
    26
    5
    I would expect that a USB port or charger would have internal current limiting protection circuitry. Have people found this not to be the case?
     
  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,813
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    David, you have resurrected a 2-year old thread. The original poster (OP) has probably lost interest by now.
    Google "USB current limit".
     
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