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I though that an inductor, when it doesn't have current flowing through it anymore, would quickly discharge in the opposite polarity. More precisely, I was expecting one quick peak in a negative voltage, and then the voltage going back to its previous value once the inductor is discharged.

The kickback, however, seems to behave more like a slowly fading sine wave on my oscilloscope, going in multiple times in high ranges of negative / positive values before fading away. (see picture)

  1. Why are there are multiple peaks?
  2. Why are there are peaks of positive voltage as well?

Am I missing something?

Oscilloscope readings of a 5 volts circuit being opened Oscilloscope readings of a 5 volts circuit being opened

EDIT:
Picture of a 1.5 volts circuit using battery (without breadboard) enter image description here

Oscilloscope readings when the 1.5 volts circuit is closed enter image description here

Oscilloscope readings when the same 1.5 volts circuit is opened at probe 1x enter image description here

Edit : Oscilloscope readings when the same 1.5 volts circuit is opened at probe 10x enter image description here

Oscilloscope readings when the same 1.5 volts circuit is opened at probe 1x but with longer wires enter image description here

Edit : Oscilloscope readings of a circuit composed of a 3 volts battery , 2 short wires to the battery (~ 1 inch each), and the 1x probe connected directly to each of these wires

enter image description here

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  • \$\begingroup\$ How to you "open" the circuit? By doing manually, there is something called "bouncing". The connection between cable and battery is lost and reformed for a number of times in high frequency until it is finally broken. \$\endgroup\$ Jan 6, 2023 at 3:33
  • \$\begingroup\$ Your scope should/could have a 1kHz test-Output. Use this signal to drive the inductor instead of the battery for a quick test. \$\endgroup\$ Jan 6, 2023 at 3:35

1 Answer 1

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Capacitance somewhere in your system has made a resonant LC circuit. The current through your inductor charges a capacitor, which then discharges through the inductor, creating a current through your inductor, which charges the capacitor...

For a more detailed explanation, see this answer from Andy aka.

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    \$\begingroup\$ Breadboard? They're famous for having stray capacitances and inductances... electronics.stackexchange.com/questions/302850/… \$\endgroup\$
    – Matt S
    Dec 27, 2022 at 22:20
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    \$\begingroup\$ @Charles-UgoBrouillard All pairs of conductors are capacitors. Two adjacent rows in a breadboard are a really small capacitor (something like a picofarad, I dunno), but they're a capacitor all the same. \$\endgroup\$ Dec 28, 2022 at 20:18
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    \$\begingroup\$ @Charles-UgoBrouillard Inductors also have self capacitance which can be significant. Inductor data sheets usually report the resonant frequency of the inductor which is due to the inductance and self capacitance. Oscilloscope probes also have capacitance, around 13pF for a 10x probe and generally higher than 50pF for a 1x probe. \$\endgroup\$
    – qrk
    Jan 6, 2023 at 1:24
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    \$\begingroup\$ I can see all the effects mentioned in your post. But i would like to append another possible cause for the ringing. Assuming the connection battery -> wire -> DUT is broken manually, there can be much more severe effects due to bouncing. \$\endgroup\$ Jan 6, 2023 at 3:36
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    \$\begingroup\$ @Charles-UgoBrouillard Note that a 1x probe itself has quite a lot of capacitance. A 10x probe has much less (this is the main reason no one ever uses 1x probes), but still a fair few pF, enough to ring like that. \$\endgroup\$
    – Hearth
    Jan 6, 2023 at 13:42

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