RDR-291 33mH Inductor Heat Issue

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I am working on RDR-291 150W circuit.

After one day testing I found that input inductor 33mH is getting too much hot.

I have developed the inductor in house with wire gauge SWG 36.

With LCR meter it shows near by 33mH.

May I doing wrong with measurement of Inductance or I am using wrong SWG wire.

Inductor core is UU 10.5  bobbin is also UU 10.5 Size.

Can you explain how to wind inductor or mesurement technique for the Inductor.


Did you check if the polarity of each leg of the common mode choke is the same? If you did not wind it in the same direction, then it will act as a differential choke and the core will saturate.

Secondly, please ensure that you use the right material for CMC which is high permeability.

Lastly, the gauge looks small for the power you are operating so you need to use a larger gauge. Please note the DCR of the CMC used in the DER is only 800mohm. Measure the DCR of the windings and if it's much higher, then it means your wire size is too small.


I have checked the polarity it is correct. I have measured the following results in exixting swg 36 Common Mode Choke

@100KHz,  L=35mH,     DCR=14.2KOhm

@50Hz,     L=12.26mH,  DCR=2.48Ohm

I have also wind the other common mode choke using SWG26 gauge folloing are the results:

@100KHz,  L=6.32mH,     DCR=2.28KOhm

@50Hz,     L=5.16mH,  DCR=0.32Ohm


Now Question is at which frequency common mode choke needs to be tested?

Please guide me to solve out this heat issue.

How can I achieve 800mohm DCR.

The inductance should be specified based on its operating frequency which in your is the line frequency. Standard off-the-shelf CMC specifies at 1 kHz. So please use this frequency since the 800mohm was reference to this parameter.

Nevertheless, gauge 36 looks really small based on the measured DCR at 50 Hz. If you can fit gauge 26 the better, or choose whatever can fit in the bobbin. Use high perm core to reduce the number of turns, or reduce the inductance value since you still need to check EMI later on.