12v fan + LED issue

Discussion in 'The Projects Forum' started by CircuitMonkey17, Jan 22, 2013.

  1. CircuitMonkey17

    Thread Starter New Member

    Jan 22, 2013
    3
    0
    Just getting into electronics, first time poster. Would appreciate any help from the community.

    I have 2 9v batteries(in series) powering a 12v fan, using a 12v fixed voltage regulator. ive made several of the circuits with a simple switch and all seems to work fine. i decided that i would like an LED to indicate when the device was switched on, however i have to use a resistor for the LED. Which in turn does not allow the circuit to supply the fan with enough power to operate.

    So, how can i run a circuit with enough "juice" to power my fan but not blow the LED indicator light.

    i have supplied two photos for better understanding of my problem
    the first image is of the circuit "as is" with only the LED working.
    the second image is of me bypassing the LED and having the fan running but no LED indicator light.

    any help would be greatly appreciated. thanks in advance.
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    Connect the LED/resistor in parallel with the fan.

    And although you didn't ask, your regulator is wasting a lot of power and your batteries won't last long.
     
    CircuitMonkey17 likes this.
  3. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    You can actually use 3W chip LEDs in series with a fan. They won't burn out, and they will reduce voltage a bit. This is useful for 12V fans which spin too fast. The LED will reduce it just a few volts.

    You don't need to cool them as the current is about 100mA.
     
    Metalmann and CircuitMonkey17 like this.
  4. CircuitMonkey17

    Thread Starter New Member

    Jan 22, 2013
    3
    0
    thanks for the reply, ill have to run them in parallel. How would you go about not wasting so much power? i have a limited amount of space for batteries so i wouldn't be able to use AA's.
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    Your fan will probably run on 1 9 volt battery and no regulator. I wouldn't be surprised if 1 9 volt without a regulator lasted longer than 2 9 volts and a 12 V regultor. Better yet would be 8 AAAs and no regulator. Best choice would be a 12 V wall wart. What are you cooling, and what is its power source?
     
  6. CircuitMonkey17

    Thread Starter New Member

    Jan 22, 2013
    3
    0
    im using the 40mm fan inside an altoids can as a mini fume extractor. The 2 9V batteries fit perfect inside the tin...ill take your advice and try a wall wart, makes more sence then havingto invest in batteries in the future.. also, the fan does run without the voltage regulator.. humms real nice on 18V's
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    9V batteries only have a capacity of 300-500mAH, AA Batteries have capacities over 2,000 mAH.

    Inside many 9V batteries are 6 AAAA ,very skinny AAA cells, in series, so they have very, very low capacity. The cheaper lower capacity non-alkaline 9V stack 6 rectangular flat cells in series.

    9V batteries are only for things that use a tiny amount of current at a higher voltage. Smoke detectors, for example.

    Google "LED Resistor Calculator" and you'll find the resistor size you need. Usually about 470Ω for 9V for a 20mA LED.
     
    CircuitMonkey17 likes this.
Loading...