LED array layout verification, and questions

Discussion in 'The Projects Forum' started by tp724, Jul 27, 2015.

  1. tp724

    Thread Starter New Member

    Jul 27, 2015
    4
    0
    Hi Folks,

    I'm new to electronics and electronic projects. Below is a crude schematic I made in Excel. I used Excel so I could check the math easily.

    Q1: Are my calcs correct?
    Q2: How much power does the 75 Ohm resistor consume? 0.02 Amps?
    Q3: What is the total power consumer per series (3 LEDs and one resistor)?
    Q4: What is the total power consumed for the entire LED array?

    If you could show me the math, then I could learn a little something in the process.

    Thanks All.

    led-layout-calcs.jpg
     
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,809
    834
    Current is constant in a series circuit, like exists in each branch of the parallel circuits. In an LED circuit, an LED is a current limiting circuit, and your calculations are correct (Q1).

    (Q2) Power is not expressed in Amps; power is expressed in Watts. To calculate power, use the equation P=VI. Per your calculations, there are 1.5 volts across the resistor, carrying 0.02 amps of current.
    Watts = 1.5 V * 0.02 amps = 0.03 W​

    (Q3) Per series, we have 12 volts at 0.02 amps.
    Watts = 12 V * 0.02 A = 0.24 W​

    (Q4) You have four identical series. Each series draws 0.24 Watts. Multiply that by 4 and you get...?
     
  3. tp724

    Thread Starter New Member

    Jul 27, 2015
    4
    0
     
  4. tp724

    Thread Starter New Member

    Jul 27, 2015
    4
    0
    Fantastic. Thank you for the review and explanation. I'm picking things up a little at a time. Your reply helped a lot.
     
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