CPU Fans in Parallel Problem

Discussion in 'General Electronics Chat' started by Lancelot, Oct 11, 2013.

  1. Lancelot

    Thread Starter New Member

    Oct 11, 2013
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    Hi guys , I am very new to electronics and basically have a little bit of knowledge and im starting to learn things the hard way. Long story short, I tried wiring 7 cpu fans ( 12v , .17 amp ) in parallel in order to help cool off a little project im working on. I choose parallel to save on wiring ( or so I thought ) and to make things a little safer in the event that one fan dies. Basically after wiring them up the fans 1 by one started to die. I hooked them up to a higher voltage input ( 16v , 1Amp) for a second to see if they'd turn on. The "main branches" were made of 18 gauge wire. The cpu fan wires that are connected to these branches are the very very tiny wires and I think this was the problem. My thinking was that because each fan requires .17 amps that having a 1amp input would be enough to run them since they were wired in parallel and the current would ADD due to this and the tiny cpu fans wires were not meant to handle this and burnt the cpu fan boards maybe?. Anyway , I might be very wrong in this and would love some help on if this sounds right and maybe a better way to do this before I waste anymore money. Thanks alot.




    Also , if I were to wire them in series instead would I need a input that is 12v * 7 or would there simply be more resistance if they were wired in series. Thanks again
     
  2. #12

    Expert

    Nov 30, 2010
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    First, 7 fans x .17 amps per fan = 1.19 amps, but this did not kill your fans. It might load down the power supply to the point that it overheats, but that did not kill your fans. Wiring them in parallel is the right thing to do. You just have a problem with bad fans.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    2,372
    Don't see any reason what would affect them in parallel, but I would use a decent gauge wire based on their current draw and place a large electrolytic at the end of the supply conductors, or where they branch off. But 170Ma is not a lot of current.
    Ensure your voltage supply is stable.
    Max.
     
  4. Lancelot

    Thread Starter New Member

    Oct 11, 2013
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    Thanks for the replies. So getting a wall wart thats 12V , 1.2 Amps would be sufficient or would you all recommend something else? Also, what do you mean by large electrolytic?
     
  5. #12

    Expert

    Nov 30, 2010
    16,294
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    Basic problems include the idea that motors require more current to start than they use while running. Buying a wall wart capable of double the current on the labels would not be too much. Second, a, "large electrolytic" means an aluminum electrolytic capacitor that can store enough energy to help provide the starting current. Just guessing, 470 uf at 16 volts up to possibly 2200 uf at 16 volts (less than $1 at www.mouser.com) would help smooth out the current supply for the fans.
     
  6. Lancelot

    Thread Starter New Member

    Oct 11, 2013
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    0
    That clears things up a great deal thanks a ton. So the capacitor does not need to be at the same voltage as the fans in the situation? Also , when I go to buy more fans to do this again , lets say that the new fans stats are at 12V and .3Amp. Choosing a wall wart at 12V at .3Amp * 7 so 2.1Amp and then doubling that to make 4.2 amp will not burn out these little .3Amp fans? Does this mean that the fans' wires will not have a steady 2.1 Amp current on them due to them being in parallel and 7 wired at the same time? Sorry for the additional questions.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The fans will only draw the current they require, as long as the current rating of your supply is greater than the total fan current it should be OK, the voltage rating of the cap should be equal or preferably greater than the supply voltage.
    Max.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    If they're the square fans from PC PSUs, they'll take 17V no problem.

    I had some very thin PSUs that I could zip-ty to the lamp flex and power a fan to chop any moths that flew into the lightbulb.

    5V didn't spin the fan fast enough and the 12V rail couldn't supply current without the +5V loaded - so I hung the fan between +5V and -12V,

    The fan went fast enough to chop wasps as well.
     
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    3,814
    Some newer power supplies are going into protection mode if you connect a positive rail to -12 rail instead of to ground.
     
  10. ian field

    Distinguished Member

    Oct 27, 2012
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    You seem to have failed to understand.

    The +5 rail wasn't enough - so I grounded the negative end of the fan to the -12 rail to get a total drop of 17V.

    If you still can't comprehend - don't worry about it - it worked and that's all that matters.
     
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