Physics Forums (http://www.physicsforums.com/index.php)
-   Electrical Engineering (http://www.physicsforums.com/forumdisplay.php?f=102)
-   -   power in dc circuits...supplying or consuming? (http://www.physicsforums.com/showthread.php?t=293283)

 spazzy32 Feb18-09 02:06 AM

power in dc circuits...supplying or consuming?

hi guys! i've been having some trouble thinking about power in DC circuits. i've been guessing my way through my problems and have been correct most of the time, but i just wanted to know the following...

so if i have a dc circuit with a capacitor, resistor, inductor, and multiple voltage or current sources, how can i tell when each of the individual branches is supplying or consuming power? i know resistors always consume power, but i'm a little iffy on the inductors, capacitors, and sources. by default when i label my circuits, i use passive sign convention on the RLC (current goes from + voltage to - voltage) and i use active sign on the sources (i draw current from - voltage to + voltage).

 MATLABdude Feb18-09 03:55 AM

Re: power in dc circuits...supplying or consuming?

Quote:
 Quote by spazzy32 (Post 2081218) hi guys! i've been having some trouble thinking about power in DC circuits. i've been guessing my way through my problems and have been correct most of the time, but i just wanted to know the following... so if i have a dc circuit with a capacitor, resistor, inductor, and multiple voltage or current sources, how can i tell when each of the individual branches is supplying or consuming power? i know resistors always consume power, but i'm a little iffy on the inductors, capacitors, and sources. by default when i label my circuits, i use passive sign convention on the RLC (current goes from + voltage to - voltage) and i use active sign on the sources (i draw current from - voltage to + voltage). thank you in advance!
Well, once you've completed your analysis with your given ASSUMPTIONS above, you look at the directions of the currents at each of the sources. If the current goes into the positive and exits the negative of a voltage supply, this means that the supply is sinking current and is consuming power. If, for a current supply / ammeter, the current that you calculated is going in the opposite direction of that given in the question... well, it probably means that you did your analysis incorrectly.

 All times are GMT -5. The time now is 07:49 PM.