RL Transient analysis

ericgibbs

Joined Jan 29, 2010
13,585
hi ZM,
Is IL(t=0) really 0Amps.?
There is a steady current thru the 40R and 20R||20R resistances, what do you calculate that to be.?
E

Another point: why have you chosen 400mSec for 'T'


Update:
Ref the Rth value.
Consider when the switch is Closed, the 80V is applied across the middle 20 ohm resistor, so how can Rth be 20||20.?
 
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ericgibbs

Joined Jan 29, 2010
13,585
hi ZM,
The questions asks for the current thru the 4H inductor.
ESP_ 173.png

What is the Inductor current before the switch is Closed.??
[Note this moves the Base line of the current Up above 0Amps before the switch is Closed.]


When the switch is Closed what will be the Time Constant and the Transient time value of the series R L circuit.?

E
 

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MrAl

Joined Jun 17, 2014
8,473
It looks like your answer is 2.3 amps but there is another character between the '3' and the 'A' for amps that i cant quite make out. But 2.3 amps is correct rounded to two significant figures, although we usually strive for a few more digits or at least one more. The more exact result is slightly less than 2.3 amps.
 

ericgibbs

Joined Jan 29, 2010
13,585
hi ZM,
Your result looks OK.
Look at this simpler method.
E

I would solve the initial <t0 IL current this way IL= [80V*(10R/50R)]/20R = 0.8Amps
also IL max = 80R/20R = 4Amps

then @t125m+

IL = 4A +( 0 - (4A-0.8A)*e^ -tc) ; where tc = 0.125 * 5 = 0.625
So
IL = 4A + ( -3.2*e^-0.625)
IL =4A + ( -3.2 *0.5352)
IL = 4A - 1.7126A = 2.28A
 
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