Inductor Tester

In this video i show how to build a circuit that can measure the value of an inductor in conjunction with an oscilloscope. This is meant to be a replacement for my $10 LCR meter, which isn't very accurate, and has very poor resolution below ~1mH of inductance.

The circuit works by sending a single pulse through an inductor, which has a known capacitance in parallel with it. When current through the inductor is shut off, the L-C pair "rings" at its resonant frequency, determined by f = 1/[2pi*sqrt(LC)]. Since frequency "F" and capacitance "C" are known, the inductance can be determined.

Current through the inductor under test is limited by current limiting resistor(s), which are manually configured by toggle switches. By default, a 680 ohm resistor is connected in series with the inductor, but 220, 100, and 10 ohm resistors can be toggled as well to allow more current for the test pulse. This is because smaller inductor values need to be pulsed with a larger current to generate a readable "ringing" signal, due to their lower energy storage for a given current.

In addition to multiple resistor options, there are two capacitance values that can be tested against. By default, a 1 nF capacitor is connected in parallel with the inductor under test, but a 47 nF can be added in parallel by toggling a switch.

If you don't have an oscilloscope, it may also be possible to measure frequency using a high impedance AC coupling to a schmitt trigger which would send square wave pulses to an arduino or similar microcontroller to be measured.

This is a valuable addition to any power electronics toolkit, because inductors/chokes and transformers are used so often, and knowing the exact component values is crucial for design optimization.

However, if you're only looking for something to give you a rough approximation of inductance / capacitance, the cheap amazon/ebay LCR meters will still get the job done, and I've used this one for several years:

https://www.amazon.com/AITRIP-Transis...


Automatic coil winder video:
   • Automatic Coil Winding Machine  


Music Used:
Lakey Inspired - Chill Day
Lukrembo - This is for you
Kevin MacLeod - Lobby Time