Solar panel + 12v fan

Discussion in 'The Projects Forum' started by QMD, May 3, 2013.

  1. QMD

    Thread Starter Member

    Jun 30, 2010
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    I have a small 12 volt fan that I want to power with a solar panel. The fan power usage is at most 10 watts.

    A friend told me it would be ill advised to use a solar panel directly wired to the fan and that I should have an charge regulator + AGM battery in between. I was planning to have a solar charge regulator in between, but do I really need the battery? For what it's worth, the place of application is very sunny, and I will only need to run the fan during the day when it is very bright out.
     
    Last edited: May 5, 2013
  2. #12

    Expert

    Nov 30, 2010
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    That pretty much eliminates the battery. Just use a regulator to avoid over volting the fan and let 'er rip. If you find the drop out times annoying, when a cloud arrives, etc, add the battery.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Depending on solar panel, I see no need for battery or regulator. If V too high under load, add a low value resistor in series. One possible problem might be slow starting in morning when there is enough power to run but not enough to start; & there are solutions for that if needed.
     
  4. #12

    Expert

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    Here's an easy way to do this. Just use any fat NPN power transistor like a 2N3055 to dump the extra power.
     
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  5. QMD

    Thread Starter Member

    Jun 30, 2010
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    Assuming I went with a controller, many charge controllers output more than 12v (13, 14, etc) would this be an issue for the 12 volt fan?
     
  6. #12

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    Probably not. Fans are not designed to demand 12.00 volts and melt at 12.01 volts. Keep it reasonable and the fan will survive. That might require using a diode or resistor to waste some voltage, but I already gave you a circuit that will work.
     
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  7. QMD

    Thread Starter Member

    Jun 30, 2010
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    If I ised the NPN setup + zener diode, that will function as a simple 12 regulator. Any recommended zener diodes?
     
  8. QMD

    Thread Starter Member

    Jun 30, 2010
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    Thanks for the circuit. I need to brush up on my power electronics material.

    Of course I will make sure I get a high wattage resistor
     
  9. #12

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  10. QMD

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    Jun 30, 2010
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    If the panel output is less than 12v, will this be problematic?
     
  11. #12

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    Read the posts in this thread. You have already been given the answer.
     
  12. QMD

    Thread Starter Member

    Jun 30, 2010
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    Thanks, sorry I missed that.
     
  13. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    And now for a contrary opinion.

    A fan has a high start-up current, and if not properly supplied with current they may stall and just draw LOTS of current instead of turning or doing any useful work.

    If the fan is connected to the solar panel trouble may well result. It's not limiting the current or the voltage that's the problem, it is getting enough of both.

    As the sun comes up the panel will only be able to supply a small current... which just goes into the (stalled) fan motor. As the sun rises this current goes up but the motor is stalled, keeps drawing current that limits the voltage low... The motor may not turn even in full sun as there's nothing to provide a starting burst of extra energy with a direct connection.

    I've seen some schemes for introducing a capacitor into the setup to source a bit of current to get the motor to turn. Googling "solar pump" will give some other source materials, but be careful, there's lots of snake oil out there.
     
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  14. #12

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    I guess it depends a lot on the size of the solar panel. If this was some ginormous whopper of 32 square feet, it would not only start the motor, it would smoke the regulator. If it's about half a square foot, it might not start the motor under the best of conditions.

    I just got the OP started, based on no information about the solar panel except my guess that it is probably "about sufficient". If it isn't, he will soon be back asking why it's too small. I doubt that it's big enough to smoke a 2N3055, but if it is, he just lost over a dollar worth of parts...and a fan...which most hobbyists have a box full of.

    Sometimes you just do the best you can with what you have to work with.
     
  15. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Personally I have no experience running motors directly from solar cells. I've just caught some web pages where they describe problems they have had (especially with water pumps) and solutions that seem... "technically challenged."
     
  16. tindel

    Active Member

    Sep 16, 2012
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  17. QMD

    Thread Starter Member

    Jun 30, 2010
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    The solar panels I am looking at are either 12 or 15 watts, 12 volt nominally

    What I have considered for the start up issue is using two lantern batteries for a momentary start up, and then switching to the panel

    Alternatively, I could do a capacitor start setup
     
  18. #12

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    If the solar panels put out a maximum of 12 volts, you don't need a shunt regulator. Measure it.

    Here's an idea about a fan controller. It's kind of related to an SCR circuit.
    ps, that battery symbol is really a solar panel, but I don't have a symbol for a solar panel.
     
    Last edited: May 4, 2013
  19. Ramussons

    Active Member

    May 3, 2013
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    I would'nt use the circuit given by #12 which is a Shunt Regulator. If the Panel o/p voltage exceeds 12, the transistor will Sink enough current from the panel to reduce the o/p voltage and maintain it at 12. This current can exceed the limits and burn out the fine links in the panel.

    What I would suggest is a Series Regulator, even if there would be a small voltage drop across it when the input is < 12 Volts.

    Ramesh
     
  20. #12

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    Interesting. I would not have suspected that a solar panel manufacturer would build their panels in such a way that the wiring will not survive the current that the panel can produce.
     
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