I have five small brushless DC motors from KDE, model# KDE2315XF-2050. The specs for this motor state that the winding resistance is 0.034 Ohms, and having conversed with KDE, they state the winding inductance is ~3.6uH as measured with a scope at 150kHz.
I want to verify these values, and according to KDE they use the method outlined in Tektronix's document "Capacitance and Inductance Measurements Using an Oscilloscope and a Function Generator", document ID 75W-28152-1.
KDE modified some of the variables in their example video on YouTube such that the voltage amplitude is 2.5V, and the test frequency is 150kHz.
I performed this test myself using a value of R reference being measured at 995.9 Ohms (using a calibrated Fluke 289 multimeter), freq generator set at 2.5V amplitude and 150kHz. I then measured the windings of 5 motors. The following are the average results for all five motors:
Average Inductance = 3.46uH
Average Resistance = 0.5972 Ohms
When I measure the DC resistance of all five motors using the Lo Ohms setting of the Fluke 289 I get an average resistance reading of:
0.031 Ohms.
Using the scope and the I-V method the inductance jives with the specs, but not the resistance. I trust my multimeter to provide an accurate DC resistance measurement.
If I adjust the voltage amplitude and frequency to 5V and 50kHz I get:
R = 0.08584 Ohms
L = 3.814uH
So my question is this, why is there such a difference in the winding resistance between the two methods of measurement (scope vs. multimeter)?
As an FYI I do not have a high end scope of function generator, so I do expect a difference but not so much. Also note it has been 20+ years since I have worked with electronics at this level. If I am missing something please forgive me.
