Why Does Inductive Kickback Voltage Vary in a Solenoid?

[arul005]

please help me with the theoretical calculation of inductive kick back voltage for a solenoid(supply voltage is 12V,L=8mH and current passing through is 1A)

i tried experimenting i got surges around 80-200V. why is it varying from time to time. please tell me a method to predict the exact surge without experimentation.

 

[Dickfore]

The formula for the inductive emf is:

$$\mathcal{E} = -L \, \frac{d I}{d t}$$

As you can see, it depend on the rate of change of the current in the circuit. Your data is insufficient to solve the problem.

 

[arul005]

current changes from 1A to 0A(in 1 ms) when i switch off the supply of 12 V


so according to the formula:


e=-(8*.001)*(1/.001)
=-8V

but the actual surge voltage is greater than 80V every time.

 

[Dickfore]

That's cause you estimated the rate with the average rate. The instantaneous rate of change might be 10 times higher at the instant when you read the voltage. Your instrument might be in a mode where it measures the peak signal.