# multiple power sources (DC circuits)

Discussion in 'General Electronics Chat' started by LukeDXB, May 26, 2008.

1. ### LukeDXB Thread Starter New Member

May 25, 2008
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Hi Everyone,

I have a general question.

I can calculate series and parallel circuits ok, with one power source, such as a battery but how do I work out resistance values when there are two power sources (in a DC circuit)?

For example, two 9v batterys wired in series, with 1 X 5 ohm and 1 X 10 ohm resistor and a 12v lamp - all in series.

Regards,

Luke

May 7, 2007
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3. ### John Luciani Active Member

Apr 3, 2007
477
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The general method would be to use superposition. You determine the effect due to each
power source individually, by disabling all but one source, and add the effects.

To disable a voltage source replace it with a short circuit. To disable a current source
replace it with an open circuit.

For two equal voltage sources in series disabling one source gives you a current V/R.
Disabling the second source also gives you a current V/R. Adding the two currents
together gives you 2V/R.

(* jcl *)