Circuit for charging 3 x 1.2 batteries through USB

Discussion in 'The Projects Forum' started by kuera, Sep 24, 2014.

  1. kuera

    Thread Starter New Member

    Aug 17, 2012
    Okay short story, I'm more of a machinist who likes to TRY mess around with electronics so I need a little help with a project.
    I've got a little paraffin lamp I've converted to a USB light using a 3w super bright LED. Basic set up is the light, switch and a 3x 1.2v 2700 mAh batteries. I want to be able to wire up a USB cable to charge the little thing so I can plug it into a cells charger plug(the USB connection ones) or computer/laptop USB.
    Anyone got a diagram they could help out with please. Another thought is considering the little switch I have has a no/nc and com should I use that to limit the system to only charge while the light it Off?

    Thanks much in advance.
  2. wayneh


    Sep 9, 2010
    That LED is drawing nearly an amp, and adding the charge current to that would take you well over 1A. That's too much for a USB port. It might be OK, but I wouldn't plug it into MY laptop!

    You didn't mention the battery chemistry. NiCad?
  3. kuera

    Thread Starter New Member

    Aug 17, 2012
    oh yeah sorry, skipped my mind. Ni-MH.
    thats why I mentioned about the switch. Having it only charge when the light is off so that it cant draw from the USB when its on.