Clarification of solar power controller.

Discussion in 'The Projects Forum' started by tekgen, Jul 2, 2012.

  1. tekgen

    Thread Starter New Member

    May 24, 2012
    Hey all,

    I have a 5V 200mA project and am using solar with a small SLA battery to power it. My problem is that I'm uncertain as to what I need to build for a solar charge controller, or if I should just buy one.

    Battery: 12V 7AH SLA
    (Standby , 13.5V-13.8V , Current:No limit )
    (Cycle Use , 14.4V-15.0V , Current: 0.3 Capacity)

    Solar Panels: 2 x 20 W Panels
    (17.2V Max 1.17A Max )
    ( Open Circuit 21.6V (I measured at ~19V) , Short Circuit Current 1.28A)

    So I have 4 questions here:
    1. Are my panels and battery sufficient for my project?
    2. I want to try building a charge controller , but would it be just easier to buy a morningstar ss-6 for 50$?
    3. Contingent on 2, am I right in thinking that I can use an atmega chip to PWM a voltage regulator from the panels based on the voltage level of the battery? Or something easier? I don't mind losing some power for a simpler circuit.
    4. How do you properly run a load and charge a battery at the same time? I can't just put everything in parallel... can I? I thought I read somewhere it causes problems with the battery.

    Thanks for your time all, and if anyone knows of a controller circuit diagram that fits my question more or less please share !
  2. wayneh


    Sep 9, 2010
    Yes! This is rarely true for posters here but I think you may actually have overkill. Your load is 1W (constant, intermittent?) and your panels provide a nominal 20W. Unless your load is constant and you're in a dark place, I think you'll be fine.
  3. wayneh


    Sep 9, 2010
    You already know the answer. But if you enjoy building stuff you could take this on. It's doable. Questionable you'll save any money, though, even if you price your time at zero. The commercial device will have built-in current and heat protections, connectors, a warranty, etc. A nice enclosure. By the time you order parts, pay shipping, maybe buy tools, you're likely to go over $50.
  4. afternath

    New Member

    May 7, 2012
    It depends if you have time/patience/learning desire or you just want to buy the stuff (if it exists) to make your project work.
    You can search on for solar controllers, china products are very cheap and pretty well built (IMO).
    Update us if you find sth interesting.