# Measuring Henry?

Discussion in 'General Electronics Chat' started by ctwistedpair, Apr 26, 2013.

1. ### ctwistedpair Thread Starter New Member

Jan 14, 2013
25
2
Hi, I just received an assortment pack of coils and inductors (toroids and others), but there are no markings on any of the coils. How can I measure the Henry of these coils? Is there a way or do I just wing it and see if anything explodes?

Thanx

2. ### #12 Expert

Nov 30, 2010
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3. ### TheComet Member

Mar 11, 2013
88
12
If you have access to a signal generator, you can get a pretty accurate estimation by connecting the coil in series with a capacitor and resistor (check attached image). You then measure the effective voltage over the resistor, and sweep through the frequency spectrum (sinus wave) until you find the maximum voltage. When capacitor and coil are in resonance, their voltage drop combined will equal 0V, and therefore the voltage over the resistor will be at maximum.

You can then use the following formula to calculate the inductance.

Note that you could potentially generate lethal amounts of voltage with this technique, as the power oscillating between capacitor and coil can be a multiple of the input voltage. Make sure to use a capacitor with a high enough voltage rating.

Also note that using larger capacitors yield more accurate results, because the resonant frequency will be lower.

TheComet

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Last edited: Apr 26, 2013
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