Solar charger for weather station

Discussion in 'The Projects Forum' started by Kif, Aug 10, 2012.

  1. Kif

    Thread Starter New Member

    Aug 9, 2012
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    0
    Hi

    I have for some time been working on a weather station I can connect to my web-server, and are now at a point where I am almost ready to install the sensor assembly.

    I have hacked into a commercially available weather station, with wireless sensor assembly, without too many problems, but to get reliable readings it has to be placed high and very inaccessibly.

    So, to make it as maintenances free as possible, I would like to power it by solar cells, something like this :

    [​IMG]
    I have been (and still are) reading up on solar cell power supplies here and elsewhere on the net, but until now I'm just getting confused, and would like your input, how best to implement the charge controller, and which batteries to use.

    PS. I may end up with the load requiring a 5V supply.

    Thanks

    Kim
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Start at the load and work backwards. Think about how long it needs to run each day and how hard you need to avoid it going dead after a series of cloudy winter days. In other words, how much stored charge MUST you have. Watt-hours or amp-hours at the required voltage.

    Then, multiply by two for the fact that the battery charge/discharge process is about 50% efficient. Now you know how much solar energy you need to capture to get you through the dark times.

    Then you have to estimate how many hours of full-sun-equivalent exposure you can expect. For a big installation you would study solar data for your location, but for a small, not critical installation, you can make a conservative guess of maybe 5hrs for good days.

    Put it all together; energy required divided by the time you have to collect it tells you the power rating of the panel in watts. It's usually a lot more than folks expect.
     
    bug13 likes this.
  3. John P

    AAC Fanatic!

    Oct 14, 2008
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    I would suggest that the DC-DC converter will be a power drain that shouldn't be on the output side of the battery. I'd try to set things up so the battery and "load" can operate with no other components involved. Just use the converter when you have power from the solar cells.
     
  4. Kif

    Thread Starter New Member

    Aug 9, 2012
    3
    0
    Thanks for your input.

    How about charging ?

    Should I use trickle, bulk or pulse charger, or something entirely different ?

    What kind of battery should I use, as I understand it NiMH isn't optimal for long time low load ?

    Kim
     
  5. wayneh

    Expert

    Sep 9, 2010
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    One end of the spectrum is to not worry about it. All of those solar lights you see, for instance, rarely employ charge control. They get away with that because the PV panel is small enough relative to the battery, that the battery can tolerate any overcharge current the panel supplies. This strategy works better with Ni-cad and even sealed-lead-acid (SLA) batteries. NiMH batteries are more sensitive.

    The other end of the spectrum is a dedicated charge control IC for your particular battery chemistry. These might offer a bulk charge, gradual charge, trickle charge strategy. Very nice.

    In between there are various methods to dump excess current away from the battery. These can be fairly simple, but get more challenging when the "excess" gets large, ie. more than an amp or so.
     
  6. Kif

    Thread Starter New Member

    Aug 9, 2012
    3
    0
    Thanks you have been a great help.

    Kim
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,120
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    Post back how things are going for you. I'm sure others may benefit from your experience.
     
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