My Circuit

This is the coil I want to find L for

I am a newbie at electronics and was hoping I could find some help. I have a coil with a removable iron core, photo for which is given above. I tried to find L1 or the inductance of the coil. I was using the circuit shown in the diagram and a cheap multimeter. I tried applying AC and DC voltage to it. I was wanting to find the voltage drop in R1 so I can use it to find XL or the Inductive reactance, which I would use to find L1. But I am not getting any voltage drop in the resistor across points AB (my multimeter might not be good enough to measure a really . Both in AC and DC. Is it because the coil I am using will have such a high L value that all the voltage is dropping across the coil? Is there anyway of doing this without an oscilloscope, function generator and such tools?

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    \$\begingroup\$ I think you are making a measurement error. The inductance will be about 1 henry and 1 henry at 50 Hz is about 314 ohms. Try again and confirm there is no wire broken by measuring the coil's dc resistance. \$\endgroup\$
    – Andy aka
    Dec 14, 2015 at 10:24
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    \$\begingroup\$ Assuming the inductance is that high, it would only be 0.3V drop.. and the DC resistance of the coil is going to cause significant error! \$\endgroup\$
    – Daniel
    Dec 14, 2015 at 10:35
  • \$\begingroup\$ Thanks so much for your prompt reply Andy. The coil might be broken. I don't get any resistance value for the coil when I check it with the my mutlimeter. \$\endgroup\$ Dec 14, 2015 at 10:55
  • \$\begingroup\$ Thanks Daniel. I checked the voltages by passing an AC current. Voltage AD was 10.3 and voltage CD is 10.1V . Are these the values I can expect?Can I assume that the voltage drop across AB is 0.2 V (in my mind I cant simply subtract the input voltage and the voltage across the inducting coil because they will not be in phase)? Also can I assume the Voltage reading across CD 10.1 is the actual voltage drop across the coil? \$\endgroup\$ Dec 14, 2015 at 10:59
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    \$\begingroup\$ "I don't get any resistance value for the coil when I check it with the my multimeter" If you measure infinite DC resistance with a multimeter then the coil is broken. You should ALWAYS be able to measure the DC resistance and it must be much lower than 1 M ohm. BTW, also check that your meter is OK (short the pins, it must read around 0 ohms). \$\endgroup\$ Dec 14, 2015 at 11:25

1 Answer 1


The easiest way to determine an inductance is by using an RLC measuring bridge. Since this isn't a very cheap solution, most of the time the step response of an RL circuit is used in combination with an oscilloscope.

For more details have a look a this site:

How to Measure Inductance?


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