# 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.

2. ### djsfantasi AAC Fanatic!

Apr 11, 2010
3,486
1,245
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...?

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.