Solar Panel Project

Discussion in 'The Projects Forum' started by Codorr, Feb 10, 2011.

  1. Codorr

    Thread Starter New Member

    Jan 27, 2011
    1
    0
    Hello,
    I am working on a project in which I am attempting to run a micro controller with a solar panel during the day and run off a battery back up at night.I am having trouble coming up with a circuit design






    Panel : http://www.sparkfun.com/products/9759

    • Peak Power: 10W
    • Max voltage: 9.1V
    • Max current: 1.2A
    • Open-circuit voltage: 10.8V
    • Open-circuit current: 1.3A
    Batteries: http://www.sparkfun.com/products/335

    • 4 batteries (NiMH)
    • 2500mAH
    • wired in series
    Thanks
    Codorr
     
  2. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    How much experience do you have working with rechargeable batteries?

    It's not as simple as saying, "Voltage source, meet battery." You need to match the voltages and currents, and in fact if you want to use NiMH batteries, you have to know the right program to go through (or buy a chip that knows it) to get them to charge properly. Plain old lead acid batteries are the easiest ones to live with, and you can still get them.
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,123
    3,048
    1) You'll need a blocking diode to prevent current flowing backwards into the panel in low/no light.

    2) You may need a voltage regulator to avoid over-voltage at your micro. Don't rely on the batteries to "pull down" the voltage, since a slight disconnection would cause full panel voltage to be seen at the micro.

    3) The problem already mentioned is the risk of overcharging - and thus ruining - your batteries. Most projects here start with a panel that is far too small and overcharging isn't such a concern, but your panel is big enough to raise an eyebrow. You may need a circuit to protect your batteries.

    4) You didn't mention how much power you need on a continuous basis. This info helps.
     
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