Smaller Battery + Bigger Battery + Resistor.

Discussion in 'General Electronics Chat' started by cjdelphi, Jul 8, 2009.

  1. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    I got a powerful LED which can draw up to 1 amp at 4.2volts.

    The Regulator I have runs off of 12volts knocking it down to 4.2volts which works but the linear regulator (LM317) gets very very hot doing this So anyway would this work?...

    1 Lithium Cell (4.2v) I wire this to the 12Volts Cell with a 5watt resistor and limit the current from the 12volts battery to around 1000ma Stick a Diode on the end of that to force 1 amp into the 4.2volt cell

    now the - + terminals of the 4.2cell I connect that up to the LED and I'm thinking if it draws the same amount of current as the 12v is supplying via the Resistor, would that not eliminate the heat from using a Regulator?...

    (I'm thinking the Current has to match the current being consumed by the LED or i'd risk OC or Venting the Lithium?....)

    Would this work? believe me I'm not going to try it if my reasoning is out :)
  2. cjdelphi

    Thread Starter New Member

    Mar 26, 2009
    ah forget it, i just realized i was being very very dumb lol, I could just use the Resistor directly to the LED supplying 1000mah.

    But could i use this method to run something else like a small radio using this method?..... would it supply the 4.2volts or 12volts when i charge a small cell it always reads around the smaller cell's voltage....
  3. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    See there's where you are wrong, you were able to find your self to use the resistor to drop the extra voltage as the LED draws a constant current.

    Tell me a whether a radio draws a constant current at any time?