calculating power budget for electronics

Discussion in 'General Electronics Chat' started by donut, Dec 3, 2012.

  1. donut

    Thread Starter Member

    May 23, 2012
    51
    0
    Im trying to determine how much power a electronics pcb consumes.

    So far I know the total current used by measuring it from a current sensor on the pcb. 2.25Amps

    The way the pcb is made there is 18V AC rms coming into the board transformer primary side where it is then stepped down to other voltages (1.9V,3.3V,5V). Then the signals are rectified, filter to provide DC where needed to the various IC's.

    So knowing the total current consumption how should I go by obtaining total power used on the pcb? Do i need to find out the voltage required for each IC via data sheet and then add then all up together?
     
  2. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    Not sure I understand what you are trying to accomplish. If you know the board runs from 18VRMS and draws 2.25A, the power draw by the board is P = (18V)(2.25A)=40.5W.

    Is this what you're looking for? Or is some of that power actually used elsewhere (off the PCB) and you're trying to figure out how much is used on the PCB itself?
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    That's not Watts, it's Volt-Amps which is apparent power. The 18VRMS is an AC voltage.

    BTW, he did not say where he measured the 2.25A (?).
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Measure the DC current flowing from each of the DC sources feeding the various voltage regulators. Multiply times the voltage and that gives you Watts.
     
  5. donut

    Thread Starter Member

    May 23, 2012
    51
    0

    I measured the 2.85V from U8 pin 7 which is a ACS714ELCTR-05B-T current sensor. 2.85V corresponds to 2 Amps

    The current sensor is on a different board than the transformer. The board with the transformer is powered by the board that has the sensor on it.

    I attached the the sensor board part.
     
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