Solar panel to power LED interface

Discussion in 'The Projects Forum' started by Ben.Kleen, Feb 19, 2008.

  1. Ben.Kleen

    Thread Starter New Member

    Feb 19, 2008
    7
    0
    I'm working on a project that will use a photovoltaic panel as the primary source to drive a power LED array for interior lighting. My idea is to incorporate a storage battery to provide a stable power supply for the load (i.e. maintain a steady supply when clouds roll by) and to allow the load to be driven after the sun goes down. I'd also like to be able to drive the LED array directly once the battery is fully charged, but setting it up so that the battery is in series with the load seems like it will simplify the design of the voltage regulation circuitry, as well as eliminating the need to switch the direction of power flow from the solar panel. Anybody have any suggestions for me? Thanks a bunch.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    It would be helpful to know what voltage and current is involved.
     
  3. Ben.Kleen

    Thread Starter New Member

    Feb 19, 2008
    7
    0
    In preliminary tests the panel put out about 8.4 A short circuit current around noontime. The LED array I'm considering would be 4 parallel strings of 6 series connected LEDs, each with a typical forward voltage of 3.72 V (min 3.03 V, max 4.95). Hope this helps. Next time I get some sun I'll be getting some data on how the panel handles resistive loads.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    I was also looking for the voltage out of the solar panels. If it's high enough to push charge into a lead-acid battery, then this circuit - http://www.aaroncake.net/circuits/charger1.asp - might make a good charger.

    As far as the LED's go, you will want to get the most life out of the battery. So using a resistor to limit current could be wasteful, unless you can arrange the LED's in series strings where the limiting resistor was a minimal size (resistively). Otherwise, you could think about even more elaboration and look into PWM drive for them.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Beenthere's suggestion of PWM control is really good. You might also consider buck/boost (aka dc-dc converters). You can get better than 90% efficiency from them.

    12v Lead-acid batteries start to sulfate when they reach 12.4v, which shortens their life considerably. The more efficient your scheme of regulating the current to your LEDs, the longer they will stay lit.

    Each string of LEDs will need it's own current regulator. Trying to run strings in parallel from the same current regulator is an invitation to disaster; as LED's don't have identical voltage drops.
     
  6. Ben.Kleen

    Thread Starter New Member

    Feb 19, 2008
    7
    0
    To answer beenthere's question: the panel nameplate specifies Vdc = 21.6 V and Vpmax = 17.03 V, so it looks like the required voltage is available at a slightly less than optimal power point. The charger schematic looks good, too, though I'm wondering if it could be modified by using a different regulator to send more than 3 A to the battery. Any thoughts?

    Thanks, beenthere and SgtWookie, your comments have been very helpful!:)
     
Loading...