Power Inductor Measurement Without LRC Meter

This method is suitable for measuring high power, low bandwidth inductors, not suitable for small signal inductors.

This method involve the use of dangerous voltage, so please be CAREFUL of electrical safety.

Explanation

This method make use of household power line to provide a AC source of the circuit. By compare a circuit's impedance with and without the inductor-under-test, you can find the extra reactance generated by the inductor, therefore calculate its inductance.

Procedure

1.Gather information

1-1 Measure power line frequency by digital multimeter with frequency measure function

If your multimeter don't have this function, assume it is 50.0/60.0Hz (depends on region you live), doing so will create some error but are generally within acceptable range

1-2 Measure internal resistance of the inductor-under-test

Gathered information will affect the test result

2.Prepare material

3.Wire up the test circuit

4.Taking data: switch the circuit on, then measure AC voltage and current in the secondary winding of transformer

Do this quick(e.g. <=10 sec),or the heating of the resistor will create error to the measurement

5.Calculate inductance

with equations shown in above picture

Step 1: Instruments and Materials Required

Instrument:
1.Digital Multimeter

2.Clamp meter

3.Paper and pen

4.Scientific calculator(real one or online)

Material:
1.AC power cord with fused plug(0.5-3A recommended for 220v)

2.A AC switch

3.wiring terminal >=6(more the better)

4.some 400v rated wire

5.220v(or 110v)-12v transformer, power >=12 VA to provide enough current

6.27ohm 10W cement wire-wound resistor x1

Step 2: Example

Step 3: Afterwords

It is my first instructable, I apologize for any inaccuracy of content within.

This method is useful when there are no LRC meter available in your hands(they are too expensive, while you may not have a lot of opportunity working with inductor coils).

Using better multimeter and clamp meter can certainly improve accuracy of this test, the clamp meter I use here is just a cheap Chinese product.

Comments

[carlos66ba]

Not at all a good idea to use mains, especially if they are 220 V. Maybe get hold of a transformer and lower the voltage to 12 V...

[rafununu]

A Wheatstone bridge is safer I think !

[andrewty]

Very approximate.

Your answer depends on the difference between two very similar values

The inductive impedance is too low for this method to work well.

You need to use a much higher frequency and/or a much higher inductance.

I suggest the voltage loss across the inductor be similar to the voltage loss across the reference resistor.

That would give you some chance of being nearly accurate to two significant figures.

As is, your inductor measured value is not even accurate to 1 significant figure.

[SimonLithedreamer]

I admit it is not that accurate.

[SimonLithedreamer]

Also with the minimum inductance range too.

It is practical to raise the source frequency and lower

the value of reference resistor(You reminded me to give it a right name)

But with a price of more complex signal generating circuitry.

IMHO, If you want to fast estimate the value of inductor,this method has its

worth.

Simplicity and precision are two things that always in contrary.

[DIY Hacks and How Tos]

Great first Instructable. Very well written.

[andrewty]

his arithmetic is riddled with mistakes. Can't you see that?

[AMbros Custom]

very good tip. I like your idea...