Kickback confusion......

[boylesg]

https://www.allaboutcircuits.com/vol_3/chpt_3/9.html

I am confused here.

The current is defined as flowing from high (+) potential to low (-) potential isn't it?

So why is the diagram in the above webpage showing current flowing from the negative battery terminal to the positive when the switch is closed?

The kick back current makes sense because the current is flowing from the positive end of the inductor to the negative end after the polarity has flipped.

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According to this simulation, without a snubber, the current through the inductor immediately reverses when the switch is turned off and the inductor reverses polarity.
https://www.falstad.com/circuit/e-inductkick.html

Then the polarity flips again and the current again reverses...................until the kick back voltage is dissipated through the inductor and wires etc.

Looking at the example circuit simulation, where an RC snubber has been added to the above, the capacitor provides an alternative low potential for the reversed inductor to voltage to flow to rather than back through the inductor. So in this case there is a current surge in the same direction through the inductor as when the swtich was closed but back through the RC snubber to the other side of the inductor instead. Again it oscillates until the energy is dissipated.

Which leads me to the conclusion that the details in the above website about kickback are not correct.

 

[BradtheRad]

https://www.allaboutcircuits.com/vol_3/chpt_3/9.html

I am confused here.

The current is defined as flowing from high (+) potential to low (-) potential isn't it?

So why is the diagram in the above webpage showing current flowing from the negative battery terminal to the positive when the switch is closed?

You are correct.

Diagram 'b': The arrow is wrong. It should be pointing in a clockwise direction. This applies to both the first and second series of diagrams.

Diagram 'c', first series: The arrow is wrong. It should point clockwise. It would be more correct to show arcing across the switch contacts.

Diagram 'c', second series (showing how the diode carries inductive kickback). The arrow is wrong. It should point counter-clockwise.

I wouldn't be surprised if the author asked an artist to draw the diagrams, and the artist could not be sure which polarity markings meant what. So he or she guessed.

The website does say the articles need to be proofread.

- - - Updated - - -

According to this simulation, without a snubber, the current through the inductor immediately reverses when the switch is turned off and the inductor reverses polarity.
https://www.falstad.com/circuit/e-inductkick.html

Then the polarity flips again and the current again reverses...................until the kick back voltage is dissipated through the inductor and wires etc.

Looking at the example circuit simulation, where an RC snubber has been added to the above, the capacitor provides an alternative low potential for the reversed inductor to voltage to flow to rather than back through the inductor. So in this case there is a current surge in the same direction through the inductor as when the swtich was closed but back through the RC snubber to the other side of the inductor instead. Again it oscillates until the energy is dissipated.

Which leads me to the conclusion that the details in the above website about kickback are not correct.

You are observant. I have never noticed this. It appears to be an error in Falstad's simulator, showing up when the coil must suddenly generate current through a high impedance, and when the iteration speed is set to Fast.

Coil current is supposed to continue in the same direction after opening the switch. It does this most of the time in Falstad's.

However the schematic called 'inductive kickback' shows current reversing direction immediately on opening the switch. This is not right. The definition of an inductor is that it resists a change in current. Yet the scope depicts the current jumping suddenly from negative to positive as soon as you open the switch.

I'm disconcerted at seeing this since I have been playing up Falstad's simulator here.

Notice it acts correctly in the schematic called 'Blocking inductive kickback.' Watch the scope traces.

And I find that if you increase the capacitor value, the coil does not generate so great a spike, and current behaves correctly.

In fact I am now seeing correct behavior when I reload the 'Inductive kickback' circuit. As though the simulation had to be forced into correct mode at least once, and now it remembers.

Or else you have to slow down the iteratation speed, so each iteration can have more time to come out right.

One thing that is not an error... It is possible to close the switch while the coil is generating current in one direction, and it seems to take forever for the current to slow down and change direction so that it agrees with the battery polarity. This is consistent with coil behavior, especially large henry values.

 

[BradtheRad]

I have been trying to reproduce the same error as before in Falstad's. Now I find the 'inductive kickback' is working okay. Both at the website and running it on my computer. On opening the switch, it shows current slowing down and then reversing direction, correctly.

I restarted my computer since yesterday.

This doesn't make sense. All I can reckon is that the coil kickback is severe (a kilo-volt or two), and so taxes the ability of the simulator. It could have trouble converging on a satisfactory solution, especially when the simulation speed is set fast. I wouldn't be surprised if the simulator skips a frame or two, with the result that we don't see a fluid change, but an erroneous sudden reversal.

I slowed down the simulation speed, so I can spot what the scope trace does. While it may help, I'm not sure how.

It seems for one day Falstad's misbehaved with this particular circuit. It has its quirks, but this one will be hard to nail down.