Solar powered fan

Discussion in 'Power Electronics' started by Dustin Smith, Dec 6, 2017.

  1. Dustin Smith

    Dustin Smith

    Joined:
    Jun 27, 2012
    Messages:
    50
    Likes Received:
    0
    I'm building a box to collect solar heat. It will have two small fans 12vdc using 1.25w each. Each will be powered by a 1.5w 12vdc solar panel. So I will build two identical circuits to run independently. I want to delay the start up of the fan, but I will have to be able to calculate what values to change based on my delay needed. Maybe 5min, may 10 min. Not sure. Also, I will need a filter for the current because it may have some pulses in it as the solar panel is a battery tender type. I can use capacitor for filter, can I also use one for a delay? How do I calculate the values for filter and delay? Or should I use a different way for the delay?
     
    Dustin Smith, Dec 6, 2017
    #1
    1. Advertisements

  2. Dustin Smith

    Dustin Smith

    Joined:
    Jun 27, 2012
    Messages:
    50
    Likes Received:
    0
    Oh yea, and I will probably insert a voltage regulator cause it will put out from 12 to 15v from the solar panel.
     
    Dustin Smith, Dec 6, 2017
    #2
    1. Advertisements

  3. Dustin Smith

    kellys_eye

    Joined:
    Jun 25, 2010
    Messages:
    2,442
    Likes Received:
    630
    Location:
    West Coast, Scotland
    A 1.5W solar panel will only output the stated power in full, direct, sunlight perpendicular to the panel surface and, even then, only if it is from a recommended manufacturer or supplier.

    No smoothing necessary - the output is pure DC.

    A motor (fan) will likely be enough load to prevent over voltage situations so no regulation required either.

    Not sure of your timing needs - not very well explained.
     
    kellys_eye, Dec 6, 2017
    #3
  4. Dustin Smith

    Bluejets

    Joined:
    Oct 5, 2014
    Messages:
    2,240
    Likes Received:
    446
    I'm intrigued just what solar heat collection in a box is all about.
     
    Bluejets, Dec 6, 2017
    #4
  5. Dustin Smith

    Dustin Smith

    Joined:
    Jun 27, 2012
    Messages:
    50
    Likes Received:
    0
    The output of the panel has been measured at over 2w in full sun. I don't want the fan on full if the sun is not full on my heat box, I don't want to blow cooler air. I found a m9nostable circuit using a 555 timer that I think I can use to operate a mossfet which controls the fan delay. I will try to delay it about 8 min and see how much heat I gain in that time. A heat box as I've called it, is simply a box with metal inside that collects the heat from the sun, and while it can operate passively, they work more efficiently with some added air flow.
     
    Dustin Smith, Dec 6, 2017
    #5
  6. Dustin Smith

    Audioguru

    Joined:
    Sep 24, 2016
    Messages:
    1,807
    Likes Received:
    416
    The datasheet for the LM555 shows a graph with a monostable delay of 100 seconds maximum but you might get 3 or 4 minutes with a larger capacitor than the 100uF shown. A digital timer circuit would have much longer more reliable times.
     
    Audioguru, Dec 7, 2017
    #6
  7. Dustin Smith

    duke37

    Joined:
    Jan 9, 2011
    Messages:
    4,771
    Likes Received:
    591
    Location:
    Derbyshire. UK
    I do not know what you are trying to achieve. If it is to control temperature, then do this directly using a thermistor and a comparator.
     
    duke37, Dec 7, 2017
    #7
  8. Dustin Smith

    Alec_t

    Joined:
    Jul 7, 2015
    Messages:
    2,203
    Likes Received:
    569
    Location:
    Wales
    I can't see a timed delay being useful, given the variability of sunlight. Duke's suggestion to control the fans on a temperature basis seems a better bet.
    What are you going to do with the heat you collect?
     
    Alec_t, Dec 7, 2017
    #8
  9. Dustin Smith

    Audioguru

    Joined:
    Sep 24, 2016
    Messages:
    1,807
    Likes Received:
    416
    I think he want to control the temperature by having the solar powered fan to blow away the sun. Then when it gets too cool the sun comes back. Oh, instead blow away the clouds?
     
    Audioguru, Dec 7, 2017
    #9
    Alec_t likes this.
  10. Dustin Smith

    Fish4Fun So long, and Thanks for all the Fish!

    Joined:
    Aug 27, 2013
    Messages:
    422
    Likes Received:
    96
    Location:
    Holden Beach, NC
    Hey Dustin!

    You are **WAY** over-thinking this :) Firstly direct sunlight has ~1kW per square meter in energy readily transformed to low grade heat. Calculating heat gain, temperature rise etc, etc requires all kinds of assumptions and still leads to some mind-numbing math, but is fairly easily measured ;-) Here is the short version: The Maximum Efficiency will occur when the difference between the "Inlet" temperature and "Outlet" temperature approaches 0. I know, you think if the inside of the box is really hot and the air coming out of the "Outlet" is really hot that you will get "more heat" ... for a fixed energy input that simply isn't the case. Using solar power for your fans can help maximize efficiency, but you don't need to worry about "delays" and sensors .... HOWEVER you may well need to increase the size of your fans, LoL (and solar panels) to get the most out of your passive solar heater.

    As the temperature inside your solar collector rises above the outside ambient temperature the thermal losses increase exponentially. With a 1m^2 collection area in Direct Sun the temperature inside the box will rise until the thermal losses are in equilibrium with the input energy. You want enough air flow to keep the ambient temperature inside your collector as close to the ambient indoor temperature as possible. I know ... sounds crazy, but that is the way it works.

    Fish
     
    Fish4Fun, Dec 7, 2017
    #10
  11. Dustin Smith

    Bluejets

    Joined:
    Oct 5, 2014
    Messages:
    2,240
    Likes Received:
    446
    mmmmmmm....my suspicions were correct.:rolleyes:
     
    Bluejets, Dec 7, 2017
    #11
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.