solar panal phone charger question.

Discussion in 'The Projects Forum' started by darklighterz, Jul 7, 2014.

  1. darklighterz

    Thread Starter New Member

    Jun 17, 2013
    Hi, i was thinking about making this for when im out camping


    But i was thinking,

    1) would this not need any capacitors??

    2) would it be ok to also daisy chain an additional battery in this circuit to make it store more, i.e. 12v??

    3) how to stop battery from overcharging?

    4) And finally is there an easy way to put a charge tester in this circuit so i know when the battery/s are full

    Last edited: Jul 7, 2014
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
    A lot depends on how much your solar panel puts out and the type of 9 volt battery you use. Putting another battery in series wouldn't help as the regulator wastes the power dropping the voltage back down to 5 volts. Please also note the diodes are shown backwards in the picture. If your going to use a little solar panel that is easy to take with you there might be an easier idea using a lipo 9 volt battery. (more capacity)
  3. NorthGuy

    Active Member

    Jun 28, 2014
    You do not need a diode between battery and regulator. You also do not need 9V battery, 6V battery will do just as well if your LDO is good, and will require lesser panel.

    1) no
    2) no. You need to keep the volatge, so connect in parallel.
    3) You need a charge controller (which may use some capacitors if you wish :))
    4) You can show battery voltage or light leds depending on the voltage. Not very effective, but simple.
  4. wayneh


    Sep 9, 2010
    There are all-in-one ICs that can do the functions you need, voltage regulation for the load plus battery tending. This would use a buck-boost voltage converter and would be more efficient than the 7805 regulator and the diode (both of which drop voltage and waste power).

    If you want to proceed with the circuit shown, the diodes are oriented backwards and, as noted, you can eliminate the one feeding the regulator. The 7805 needs a small capacitor on the input and output to avoid oscillation (see the data sheet). Depending on what you connect to the USB, you may want to put a diode from the 7805 output to input. The regulator may be damage by a voltage on its output that exceeds the input voltage.

    If your battery is big enough compared to the solar panel and is Nicad or lead acid, you may not need a charge controller.