Simple Question - Simple Solution?

Discussion in 'General Electronics Chat' started by RCinnis, Sep 27, 2010.

  1. RCinnis

    Thread Starter New Member

    Sep 27, 2010
    2
    0
    Hello,

    I just spent the last month building a desktop paint chamber. I designed the chamber to use 4 120MM case fans as ventilation. Not being very knowledgable about computers, I "thought" I could just plug in a old computer power, plug in fans and be good. Nope, no cigar. Seems the power supply has to go through a board circuit to even run.

    So, the Fans are 12vDC, .15Amp, 1.8 Watts. Can I daisy chain 2 6 volt batteries to get what I need? How can I run these fans by using plain old batteries?

    Please help.
    Thank you
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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  3. RCinnis

    Thread Starter New Member

    Sep 27, 2010
    2
    0
    Thank you for the site, but I fear this conversion might be a little beyond my ability. I guess I can try it, but forsee house fuses blowing already (not to mention get shocked myself). I was hoping there would be a simplier solution.

    Thank you
     
  4. mbohuntr

    Active Member

    Apr 6, 2009
    413
    32
    You could wire up a 12v 1 amp wall wart... Protect it with a .5 amp inline fuse. I suggest you show the schematic to the pro's here as they have years of wisdom.
     
  5. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Yes, you can run the fans with two 6 volt batteries connected in series. That will provide 12 volts DC. Then, connect each of the four fans to the 12 VDC source. The fans will then be in parallel (all the fan positive leads connected to the positive side of the battery chain and all the negative fan leads connected to the negative side of the battery chain.) Or you could use one 12 volt battery.

    The problem is that the fans will drain the batteries and unless you have a way to recharge the batteries, they will have to be routinely replaced. As the batteries discharge, the fans will run slower and slower. Using a rechargeable battery is an option, but you still have to charge it.

    As someone else has suggested, a 12 VDC wall wart is a good option (instead of batteries.) You need one that has an output of 12 VDC at .6 amps (4 fans times .15 amps) or more. A fuse in the positive leg of the power line would be good, but the fuse should be greater than the current required by the four fans (.6 amps) and should not be greater than the capability of the wall wart. The wall wart must be DC, but does not have to be regulated.
     
    Last edited: Sep 28, 2010
  6. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    You must have gotten those fancy fans. You need something simple like the one in the attached photo. The brand does not matter. Note that wires of the fan are spliced into power connector, you could do the same on the connector coming out of the power supply.
     
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  7. majsyd2010

    Member

    Aug 29, 2010
    61
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    Very nice and useful information ShortBus ... I always was thinking to do so but really didn't got it to work. After looking your referrance, I made it work
     
  8. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    RCinnis, ignore everything said so far.
    Find the connector coming from the power supply that usually goes to the motherboard. There will be a green wire, and there should be only ONE single green wire. Insert a piece of wire to short that green wire to any available black wire and the power supply will turn on, that's it. Strip and wire those wires to a SPST switch and you're all set.. I've used jumper wire to turn ATX power supplies on many times. It seems unintuative to short a wire on a power supply, but that green wire is very special, it's actually an input to the control electronics of the power supply, it's internally pulled up via a resistor to the 5V side bus, when it's shorted to ground the control electroncics go "yes sir" and turn on the rest of the rails.

    When off there is a wire that always has the +5V side bus that I'm refering to always on, I think it's blue but just check wikipedia for the color of the wires to verify should you need that +5V standby bus.
     
  9. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
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    If you hadn't already thought of it, you may want to be careful with your painting chamber if you're using paints that have volatile materials in them -- a motor can be a source of sparks that can lead to ignition. It can be challenging to come up with an explosion-proof design.
     
  10. sceadwian

    New Member

    Jun 1, 2009
    499
    37
    someonesdad, it wouldn't have to be away from the fans. Brushless DC motors can't spark under normal circumstances, also the objective of the air flow in the first place is to prevent that very condition of fuel/air mixture by keeping the air flow higher than the possible fuel flow.
     
  11. mbohuntr

    Active Member

    Apr 6, 2009
    413
    32

    Good catch, I misread, I thought there were only two fans. (.3A)
     
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