Solar Powered Beacon with Supercapacitor

Discussion in 'General Electronics Chat' started by ywang627, Mar 31, 2016.

  1. ywang627

    Thread Starter New Member

    Jun 5, 2013
    Hello all,
    I am working on a project with the low power bluetooth module HM-11, and want to power the device with solar panel and super capacitor.
    I have attached a schematic. It is just a simple voltage regulator with a Schottky diode to prevent the current going from the supercap to the solar panel, a small 10 ohm resistor in series with the Schottky to limit current, and a Zener diode to regulate the voltage to 2.7V to protect the supercap.

    I am having a problem here. When the supercapacitor and HM-11 are connected to the circuit, and the solar panel is not providing a lot of power, the supercapacitor is discharging rapidly -- much more rapid than the calculated discharging time according to the equation It = CV.
    I then tried powering the HM-11 only with a fully charged supercap, and it is able to discharge at a much slower rate, and matches the calculated value.
    When I connect the super cap to the circuitry with HM-11 disconnected, and the solar panel is providing almost no power, the supercap starts to discharge rapidly, and based on the It = CV equation, it is drawing about 9mA current. (The average current draw from the HM-11 is less than 1mA).

    I am quite confused about what is exactly consuming power here. The Schottky diode would have some leakage current, but it should be very small, in the microAmps range, and shouldn't have that large of an effect. The capacitor voltage is under 2.7V, so I would think the Zener isn't consuming power either... Would it be the resistor then?
    It isn't making sense to me, because if the capacitor voltage is higher than the solar supply voltage, putting the Schottky diode in reverse biased mode, making it almost like an open circuit, what exactly in the circuitry is drawing power?

    Please let me know if you have any ideas, or need more explanation!

    Thank you so much!
  2. Roderick Young


    Feb 22, 2015
    Try this. Charge up your supercap to 2.7 volts, or whatever operating voltage you use. Then try it in the circuit, without the zener, and without the solar panel. Keep disconnecting things until you find what is consuming all the current. Looks like there's not much else except other capacitors to remove. Is the processor driving any I/O? That will consume power.
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    What is the purpose of the two 10uF caps?
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    I first read "Solar Powered BACON" and got all excited.. Darn.. :(
    ywang627 and wayneh like this.
  5. ywang627

    Thread Starter New Member

    Jun 5, 2013
    ok, thanks, will try! do you see anything wrong with the circuit?
  6. ywang627

    Thread Starter New Member

    Jun 5, 2013
    They were in the schematics, just to have some sort of protection, but when doing the testing, they aren't actually included.