Wiring for 5V fans with 9V or AA batteries?

Discussion in 'Replica Props' started by Marthony, May 1, 2015.

  1. Marthony

    Marthony Active Member

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    Hello,

    I'm planning to add cooling fans into my next costume build, a 9' G1 Transformers Devastator rig similar to this: http://i1276.photobucket.com/albums/y470/Martaxus/devastator-old_zps1tysoxul.jpg. I want to have a number of small cooling fans in the rig, 1 on each thigh and at least two in the torso.

    I've wired a lot of LED circuits with resistors & 9V batteries, but not fans. I understand the draw is much greater and would try to use the smallest units I can find, hence the 5V .15A hardware. I don't think the LED circuit designer tool at http://led.linear1.org/led.wiz is ideal for this, or is the 'diode forward voltage' 1500mA here?

    Could someone please point me to a reference/tutorial for this?

    Thanks!
     
  2. vidman

    vidman Well-Known Member

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    1500 is not the forward voltage for the diode , 5v is

    .15 amps is .150 ma not 1500 ma which is 1.5 amps..........

    you will need a 27 ohm 1 watt resister to each fan from the source voltage............

    the designer will work for any electrical circuit
     
    Last edited: May 1, 2015
  3. AndyJ

    AndyJ Active Member

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    Honestly for a fairly high load, you'd probably be happier just getting a small power supply. It wont heat up and you can put more stuff on easily.

    https://www.pololu.com/product/2851
     
  4. Marthony

    Marthony Active Member

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    Arg. I meant 'diode forward current', but I guess that was obvious. Thank you Vidman for also correcting my units of measure; had a brainfart and confused this with microamps vs. milliamps.

    Andyj, what heat do you expect from such circuits? I'm hoping to keep with the KISS principle by setting up individual circuits & batteries for each. On a side note, I also plan to add a switch to each circuit for easy control while suited up.

    Next up, how to best estimate the operating life of a 9V battery when not provided with its rated capacity?

    Thanks guys!
     
  5. vidman

    vidman Well-Known Member

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    For heat from the circuit will be from the resistor which is 1 watt, so not much heat if any ,,,,

    operating time depends on quality and type of 9v battery you are going to use , my experience is at least 1 hr to 1.5 hrs run time, but that again depends on the battery,, try setting up your circuit and see how long it will actually run, remember to make it a complete test setup,, i.e. wires, fan, batt connector, resistor ,switch a complete circuit and see how long it will run and also to check the flow rate of the particular size fans you will be using.

    Hope this helps out a little more ;)
     
    Last edited: May 2, 2015
  6. LrdSatyr8

    LrdSatyr8 Sr Member

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    Why not just get a fan that was made to run off a 12v source? I know I bought a fan that plugs into my vans cigarette lighter.
     
  7. Marthony

    Marthony Active Member

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    I'm trying to keep down on weight, so fewer batteries & size of them to match the fan's voltage the better.

    Thanks!
     
  8. Marthony

    Marthony Active Member

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    After more thought (+ discussion at cosplay.com) I've decided to go with 5V fans powered by either 3x AAA batteries or 4x 1.25V rechargeable AA or AAA batteries, almost certainly the former unless I run into an awesome deal on rechargeables. I'm to understand I don't need a resistor or other items in the circuit, just the batteries, battery holder, fan, wire, and tools to connect properly (I'd solder everything).

    I understand I could go with 12V fans powered by 8 AAA batteries, but would prefer to keep the weight down.

    Thanks for your help everyone!
     
    vidman likes this.

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