Voltage Divider

Discussion in 'The Projects Forum' started by jons, Feb 17, 2012.

  1. jons

    Thread Starter New Member

    Feb 17, 2012
    2
    0
    Hi,

    I need to monitor a DC charging voltage and have a 4-20ma and a 0-10V input available on my PLC. The charging voltage will flucuate but I'm mainly interested in between 20 and 30 Vdc.

    My question is would a simple voltage divider with a pair of resistors to drop the max 30v down to max 10v (I calculated 10K and 5K would take me there abouts) or would these resistors just sit and get excessivly hot?

    Any other suggestions?

    Cheers

    Jon
     
  2. chandrashekhar

    New Member

    Feb 17, 2012
    1
    0
    you can also use op-amp as comparator.
     
  3. Brownout

    Well-Known Member

    Jan 10, 2012
    2,375
    998
    P=V^2/R = 30^2/15,000 = 60mW. That's not much power. You only need to make sure that the pin your reading from has much higher resistance. A typical input pin should by > 1M ohm, so usually that's not a problem either.
     
  4. luvv

    Member

    May 26, 2011
    186
    31
    Love using this http://www.falstad.com/circuit/ as a litmus test for simple circuits.

    It is no pro simulator...but what it lacks in accuracy it makes up in simplicity.

    Just hover the mouse over the resistor it will show you all the info including power dissipated.


    -luvv-
     
  5. jons

    Thread Starter New Member

    Feb 17, 2012
    2
    0
    Many thanks for the replys.
    That simulator is a great tool - thanks

    Jon
     
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