AC RL circuit walkthrough




An inductor and a resistor walk into a bar.

We know that when we have a circuit of pure resistance, the current and the voltage are in phase.

pic c 1

We also know that in a circuit of pure inductance the current lags the voltage by 90 degrees.

pic c2

So what do we do when we have an inductor in series with a resistor?

Give up and join the plumbing trade?  No!!!!  Nothing is that drastic.  Calm down and pay attention.

Breathe in, Breathe out and remember your triangles.

baby buddha

First you need to convert the inductance of the coil into it’s inductive reactance.  (XL = 2πfL).

After that you are free to add up the resistance and the inductive reactance but don’t forget that you can’t do this arithmatically.  It has to be added vectorally as they are 90 degrees out of phase with one another.  Use pythagoras and you’re laughing.

Once you add the resistance and the reactance you have your impedance.  Impedance is the overall opposition to current flow in the circuit.

Once you have the impedance you have unlocked the whole series circuit.

OHHHH That doesn’t seem so bad.

Nope, just take your time and slowly work out your triangles.  Once current is calculated you have everything you need for calculating power and voltages.

What about Power factor and Q factor?  I go over those in more detail in the video.

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