RL Circuit Refresher

  • #1
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Hi, I have just been refreshing my theory and was going over a parallel RL circuit, like this one.

vFu2isf.png


The site I was reading had this for the total current

wSOg5fX.png


I tried some values as a test but it doesn't give me the correct answer, for total current. eg if I set
V=10V
R=2.5ohm
jXl=5ohm

Then IR=10/2.5 =4A

IL=10/5=2A

IT=√42 +22 =4.47A

However when I try the formula from the second answer I get 10/(2.5-2j) which following the maths gives me 2.44+1.95j=3.12A

Am I going wrong somewhere or is it the formula?


Thanks
 

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  • #2
jim hardy
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However when I try the formula from the second answer I get 10/(2.5-2j) which following the maths gives me 2.44+1.95j=3.12A
Admittances in parallel add. That should be your approach.

upload_2018-8-8_21-15-30.png

A 'Site', you said ? If it's on the internet it must be right, eh ? See my signature..............

see if that works any better.

old jim
 

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  • #3
jim hardy
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Oops ----- make that it equals Vin X ( 1/R -j1/ωL )

i put my j in wrong place . :cry:
 
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  • #4
Delta2
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Oops ----- make that it equals Vin X ( 1/R -j1/ωL )

i put my j in wrong place . :cry:
Seems we cant even trust Old Jim when he posts at the internet with a computer, cause we can never trust a computer with anything important :-p

Ok seriously speaking that was a minor mistake, I didn't notice it either, I just noticed the huge mistake in the algebra in the OP.
 
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jim hardy
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i do that all the time. I'm just clumsy.

Thanks @Delta2
 
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i do that all the time. I'm just clumsy.

Thanks @Delta2
Thanks Jim for clearing that up
 
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