BD135 battery charger for 8.4V/150mAh battery

Discussion in 'General Electronics Chat' started by vrfood, Feb 5, 2016.

  1. vrfood

    Thread Starter New Member

    Feb 5, 2016
    3
    0
    Hey guys. Long story short, i built THIS schematic, using a BD135 transistor, to charge a 8.4V 150 mAh battery with. I am trying to figure out the exact value resistor (R2) I need to use, in order to get a 15mA current (to be in the 1/10 rule).

    p.s. i figured somewhere around 220-240, but i am not sure. For some reason my DMM won't measure it correctly

    Cheers
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,995
    745
    78ohms 1/2W is 15mA charge.
     
  3. vrfood

    Thread Starter New Member

    Feb 5, 2016
    3
    0
    Thanks. What about a 1/4 W? Is it the same value?
     
  4. Terrypin

    New Member

    Feb 5, 2016
    1
    0
    Yes.
     
  5. vrfood

    Thread Starter New Member

    Feb 5, 2016
    3
    0
    Since i could not find a 78 ohm resistor anywhere locally, i used 3 x 27 ohm 1% 1/4W resistors, soldered in series, to get a close enough value. Measured it at 80.8 ohms. I suppose that should work.
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,995
    745
    Try 75 ohms, will give you 15.6mA.
     
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