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Electronics/Current Direction - Nodal Analysis

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Question
circuit problem
circuit problem  
Hi,

I want to use Nodal analysis to find the current, Ix in the circuit.

Iíve worked out the problem mostly ok, and I realize that I probably have an error (compared to the book) with the direction the 3A current source is going in my first KCL equation, at nodal voltage v1.  I have the 1st equation equal to -6, but in the book itís 6.  And that seems to make the difference.

However, I thought KCL was just the sum of all currents leaving a node must sum to zero.  I didnít think the direction of the currents actually mattered and that the direction would get resolved later.

So why was I supposed to put the 3A current source on the right side of the 1st equation, and not keep it as I have written it?  Apparently I get the correct magnitude of Ix (0.8A), but the direction is just wrong.

Thanks!

Answer
Yes you are right about summing currents into a node but you must keep the same direction for all the currents.

Since you got the same answer but different direction maybe you used backward current flow in your equations.

Your diagram was so light I could not read it on my small smartphone.  

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Electronics questions about AC, DC and digital theory.

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Graduate electrical engineer with over 40 years in electronic design, manufacturing, project organization and patent review. Experience in fields of industrial and consumer electronics (audio, video, acoustics, etc.)

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IEEE (Institute of Electrical and Electronics Engineers); Senior Life member AES (Audio Engineering Society), Fellow Life member

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BSEE University of North Dakota

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