Genereal Electronic Question ----7.2 volt LiPo to 3.7 volt

Discussion in 'General Electronics Chat' started by RadioControlEnthusiast, Feb 13, 2016.

  1. RadioControlEnthusiast

    Thread Starter New Member

    Feb 13, 2016
    1
    0
    Please help. What resister precisely do I use to reduce a 7.2 volt lipo battery to a 3.7 lipo battery
     
  2. WBahn

    Moderator

    Mar 31, 2012
    17,768
    4,804
    You don't.

    Depending on your application, the best thing to do is probably use a DC-to-DC converter. If you are talking about low enough power, then using a linear regulator would be an option.

    A resistor is only a reasonable option if all of the following apply:

    1) The current draw from the battery is always the same.
    2) The current draw from the batter is continuous.
    3) You don't care too much about significant variations away from 3.7 V.
    4) You don't care about wasting nearly half your power in the resistor.
    5) You can vent the heat that is dissipated in the resistor.
     
  3. SLK001

    Well-Known Member

    Nov 29, 2011
    821
    229
    Here's the answer you asked for:

    7.2V -/\/\/\----3.7V----/\/\/\----- GND
    ----------R1-------------------R2--

    R1=3.5/3.7 R2

    Select R2=10k and R1=9.46k.

    This isn't what you want to do, but you weren't specific in your question, so I only answered your question. You have to select your prefered value of R2.

    The diagram above shows two resistors, the midpoint where the 3.7V is obtained and ground.
     
  4. hp1729

    Well-Known Member

    Nov 23, 2015
    1,964
    219
    How much current are you dealing with?
    7.2 V minus 3.7 Volts is 3.5 Volts. Volts divided by current gives you resistance. If current will vary you may want to use a voltage regulator. For < 100 mA use the T0-92 case version. For up to 1 Amp use the TO-220 version. Same resistor values.
    This works but it wastes about as much power as it delivers.
     
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