Measurement of DC choke inductance

Hi,

I have a 10H 100mA Iron cored choke I wish to measure the inductance of.

If I place a 10K pot in series, and apply a 50Hz sine wave (from 6.3V transfromer), I can measure the reactance of the choke, and work out the inductance, approx 6K Ohms, so this is indeed 10H.

So now I use an NPN transistor constant current souce, to give me 100mA constant DC current, in addition to the 6.3V rms from the transformer.

Now I measure about 2.3H.

I thought that the choke would be 10H at 100mA?

I need some help in understanding the results please.

John

 

Assuming that you have wired everything up correctly, one possibility is core saturation, as the current increases in an inductor, its inductance drops as the core nears saturation.
Your initial test was with AC at a low level, the second was with the fully rated DC current. I suggest you start with a few mAmps DC current and increase it in 20mA steps and see what happens,
cheers,
Richard