rechargeable battery problem

Discussion in 'The Projects Forum' started by xeroshady, Oct 13, 2012.

  1. xeroshady

    Thread Starter New Member

    Aug 1, 2012
    hey guys, I'm designing a circuit that requires a rechargeable battery, but I have a problem.

    Please see attached image.

    When I disconnect the rechargeable battery, the LED glows. But when I connect the battery, the LED switches off, possibly because the rechargeable battery shorts the circuit. I want the LED to glow and the rechargeable battery to get recharged at the same time. I think the solar panel can provide enough juice for that. So, what am I doing wrong?
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Obviously the battery cannot turn the LED on. It's voltage is too low.

    The way you have the diode makes the panel voltage higher then the battery voltage: you could try the LED back there.

    You may need to add several diodes in series to boost this voltage back closer to it's 5V open circuit value
  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    You could put the led in series like this, then it will light when its charging.

    (B1 is the solar Cell, V1 is the Battery)
  4. Audioguru


    Dec 20, 2007
    You must tell us the details:
    1) What type of battery? Lead-acid, Ni-Cad, Ni-MH or Lithium?
    2) How many cells in series is the battery?
    3) Is the battery very old or is it dead?
  5. NFA Fabrication

    Active Member

    Aug 12, 2012
    I was just gonna say, the battery has to have a voltage lower than what will run the LED. And when the battery is connected, it is pulling the circuit voltage lower because it will obviously over power the solar cell.
  6. xeroshady

    Thread Starter New Member

    Aug 1, 2012
    2 Ni-MH rechargeable batteries in series. It's brand new, but I don't know if it's dead because it might just need recharging, and that isn't working out either.

    NFA Fabrication:
    So, how do I overcome that problem? Use less powerful batteries?

    Thanks, I'll check if it works and get back to you
  7. Audioguru


    Dec 20, 2007
    Two charged Ni-MH cells in series are about 1.25V each which is a total of 2.5V.
    A fairly dim old green LED needs about 2.2V so it might light but a very bright modern green LED (usually in a clear case) needs about 3.3V so it will never light from that low voltage battery. Yes, the battery reduces the voltage from the solar panel.