Circuits: trying to understand when to use parallel or series

Discussion in 'General Electronics Chat' started by vgamesx1, Apr 1, 2015.

  1. vgamesx1

    Thread Starter New Member

    Apr 1, 2015
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    Alright silly question... I'm planning on making a solar powered fan for a greenhouse, pretty simple right?
    Well since I already have several little cheap case fans thought I might as well use those, although one might not be enough, so if I were to add more, how should it be wired? or.. should I not even bother and look for a slightly more pre-done solution such as a fan splitter?
    I'm not very experienced so would appreciate some suggestions, also while I don't need help finding a solar panel, if you know of any you could recommend that might make searching easier for me, Thanks and here's a diagram of what I mean below.
     
  2. Reloadron

    Active Member

    Jan 15, 2015
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    Case fans as in PC case fans? You have made no mention of what voltage or current the fans will be? What solar panel did you have in mind for this? You need a panel capable of supplying the required current for your fans and you need to have a total number of fans with data sheets specifications.

    Ron
     
  3. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,778
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    Two points:

    1) Due to 'load lability' series connection of fans is not advisable...
    2) The viability of parallel connection is 'down to' PS parameters...

    Best regards
    HP
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How many fans you can run depends on your panel.

    Most of those PC fans run on 12Vdc. It would take a panel that has a direct-sun no-load output voltage of ~17V to properly run the fans.

    Do you have an adjustable DC power supply so that you can do some testing on your fans?
     
  5. vgamesx1

    Thread Starter New Member

    Apr 1, 2015
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    Yes PC fans, the usual 12v ones and they typically run off a mere 0.1-0.2 amps, so nearly any panel that supplies 12v should work. (times x fans of course..)
     
  6. vgamesx1

    Thread Starter New Member

    Apr 1, 2015
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    Its likely two or a max of four of them and I actually don't have a power supply but I do have one of those DC-DC buck step up/down converters, so I could possibly use that.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    Not quite. Solar panels are basically current devices. The more current they supply the lower the voltage. Fans are likely to want more current as the voltage drops so you have things working against you. The suggested 17V solar panels allow you some headroom to design a voltage regulator that will supply the fans with +12V until the solar panel reaches the dropout voltage of the regulator.
     
  8. vgamesx1

    Thread Starter New Member

    Apr 1, 2015
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    Right, I just meant the panel wouldn't be much of an issue, Thanks though I'll try to find something about 17v then.


    Also Thanks HP circuits are the main thing I have trouble understanding, I dunno why it just confuses me a lot.
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    Just remember two simple rules
    1. A series circuit has the same current flowing through each element. It is a constant current arrangement.
    2. A parallel circuit has the same voltage across each element. It is a constant voltage circuit.
     
  10. wayneh

    Expert

    Sep 9, 2010
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    I would add a third simple rule: Regardless of current and voltage match-up, the power needed by your fans cannot exceed the power capacity of the panel.

    Your fans need ~1.5W each. So for instance you can forget about using more than 3-4 of them on a 5W panel.
     
    Papabravo likes this.
  11. Papabravo

    Expert

    Feb 24, 2006
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    I would expand on that to stress that you cannot get more power out of a system than you put into it. This is especially true of Switched Mode Power Supplies (SMPS).
     
  12. wayneh

    Expert

    Sep 9, 2010
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    There are no degrees of "True". There is only truth. ;)
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    Which most people doggedly refuse to accept inspite of overwhelming evidence.
     
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