12v Solar circuit

Discussion in 'General Electronics Chat' started by Theodorez, May 8, 2012.

  1. Theodorez

    Thread Starter New Member

    May 8, 2012
    Hello everybody.

    I 'm not familiar with electronics and I would like to get some help.

    I have a solar panel 5W which sits and gets dust.
    I would like to use it as a battery charger to light up some leds for my balcony.

    My problem is where to find the proper circuit and if somehow can I find it already made.

    The only things I know is the panel specifications and also some infos that other people gave me. That I have to use a switching voltage regulator to step down the 21.6V of the panel, to 12.

    So please if anyone can help me with some clear and simple advises I would be really glad.

    Solar Panel Specifications:

    Max Power (Pm): 5W
    Open Circuit Voltage (Voc): 21.6V
    Short Circuit Current (Isc): 0,306A
    Max Power Voltage (Vmp): 17,6V
    Maximum Power Current (lmp): 0,278A
    Working Temperature: -45C to +85c
    Tolerance: +_5%
    Size: 100x600x28mm

    Thank you in advance!

  2. evilclem

    Active Member

    Dec 20, 2011
  3. dataman19


    Dec 26, 2009
    Solar panels will provide a full voltage float if not controlled. they can also over charge the battery as a result of their tendency to rise to "Max Power Voltage". A Flooded Cell Battery will begin gassing at about 14.2VDC (well below the Solar Panels Vmp), but the battery will tend to try and pull the solar panels output voltage down, and as a result will act as a heater and heat up (also causing even more electrolyte gassing).
    A simple regulator with a series transistor current regulator would do the trick. Then you just set the current trigger to interact with the 13.8VDC (the Float/charge voltage of a 12V Flooded cell).
    Solar Cell Charge Controllers are essentially just this. The regulate the voltage to keep it below a trigger voltage, when the trigger voltage is reached, they limit the current (but have a window where they will provide additional charge capacity - by increasing the voltage and maintaining current for a specific period. They sense charge capacity by monitoring the minute voltage changes when the current demand drops as the battery become closer to full charge). At rest a 12V battery will indicate around 12.8V-13.2V at rest.
    Granted, I am talking about Lead acid Batteries (ie: Flooded cell). There are some Nickle Cadmium batteries available, but you probably won't want to spend the bucks.
    There are also many so called "Solar Batteries" that have varying degrees of improvements in electrolyte, mats vs plates, etc...
    But a simple current regulator will work with a solar panel. This means a simple one or two transistor regulator (heck you could even use an LM317 with a bypass current transistor).
    My favorite trick to keep a low budget WEB Host up and running through stormy weather and unplanned blackouts was to set up two Deep Cycle Batteries buy a couple of cheap inverters and a battery charger. Run the computer off the battery (using the inverter to keep the batteries topped of using the household AC power) by keeping the battery charged hooked up and running - So essentially the "Computer(s)" ran off of the battery and the incoming 120VAC kept the battery charged using the battery charger. Should the Incoming AC power drop, the inverters didn't see anything and kept going, so essentially the computers never lost power. Another positive to this arrangement is that this cheapie home-made UPS also acting like a voltage/transient sponge. So Computer Hard drive life was extended (because more computer hard drives are "damaged" by voltage drops that voltage spikes - which cause the hard drives to develop sector errors).
    I did the same thing using solar panels at one location. For the initial charge regulator I just built a simple charge controller using a couple of transistors and components, nothing fancy.
    But you do need to provide some control of the solar panel power, otherwise the big bad solar demon will bite you in the #$$.