# 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.

File size:
92.5 KB
Views:
18
File size:
132 KB
Views:
18
File size:
123 KB
Views:
16