AC resistance of an inductor?

Thread Starter

Manjesh Gowda

Joined Oct 19, 2020
83
I measured the AC resistance of my customized inductor with network analyzer of core E70. I got 23mohms AC resistance and 2.3mohm DCR for 14uH inductor with 8 number of turns using litz wire(1400) of 4.3mm diameter. I also got 30mohm AC resistance and 11mohm DCR for 54uH inductor with 16 number of turns using different litz wire(1050) of 2.8mm diameter. Both measured at same frequency. I am confused now, on which factor AC resistance depend upon. I thought I should have gotten more AC resistance for 54uH inductor. Is it depend on the type of litz wire we use? or number of small wire? How can I reduce the AC resistance? Please let me know. Thank you
 

BobTPH

Joined Jun 5, 2013
3,304
How did you measure “AC resistance.” On second thought, how do you define it? Inductors do have resistance, which applies to both AC and DC. They also have reactance, which applies only to AC and is dependent on frequency. What is it you are trying to measure, and at what frequency?

Bob
 

BobaMosfet

Joined Jul 1, 2009
1,767
Inductors have small resistance- the conductor itself, and then they can have large inductive _reactance_ when AC potential is dropped across them- which is field effect, not thermal. Make sure you undertand the difference.
 

Thread Starter

Manjesh Gowda

Joined Oct 19, 2020
83
How did you measure “AC resistance.” On second thought, how do you define it? Inductors do have resistance, which applies to both AC and DC. They also have reactance, which applies only to AC and is dependent on frequency. What is it you are trying to measure, and at what frequency?

Bob
The inductor which I am going to use it in AC application so I measured AC resistance using network analyzer with frequency of 85KHZ
 

DickCappels

Joined Aug 21, 2008
7,418
Is it depend on the type of litz wire we use? or number of small wire? How can I reduce the AC resistance? Please let me know. Thank you
The broad answer is "yes". Sorry for this digression: Inductors primarily have inductance but they also have DC resistance and losses having to to with the AC current flowing through the inductor -these are mostly eddy current and skin effect losses. Using Litz wire reduces skin effect losses and eddy current losses in many cases.

Skin effect is the effect on average less than 100% of the conductor's diameter can be considered as carrying the current, which is forced to flow along the surface of the inductor at high frequencies while eddy current losses are largely because of interaction of the wire's magnetic field interacting with and inducing currents in magnetic material outside the conductor, this happens a lot in magnetic cores containing AC currents.

If you are still awake, there regular DC resistance that adds into the other losses and can be masured at DC.

To minimize AC losses use Litz wire or multiple twisted small diameter strands where practical and avoid low resistance magnetic cores - this is why ferrites are so useful.

Additional information:
Eddy Current
Skin Effect
Litz Wire
 

Thread Starter

Manjesh Gowda

Joined Oct 19, 2020
83
The broad answer is "yes". Sorry for this digression: Inductors primarily have inductance but they also have DC resistance and losses having to to with the AC current flowing through the inductor -these are mostly eddy current and skin effect losses. Using Litz wire reduces skin effect losses and eddy current losses in many cases.

Skin effect is the effect on average less than 100% of the conductor's diameter can be considered as carrying the current, which is forced to flow along the surface of the inductor at high frequencies while eddy current losses are largely because of interaction of the wire's magnetic field interacting with and inducing currents in magnetic material outside the conductor, this happens a lot in magnetic cores containing AC currents.

If you are still awake, there regular DC resistance that adds into the other losses and can be masured at DC.

To minimize AC losses use Litz wire or multiple twisted small diameter strands where practical and avoid low resistance magnetic cores - this is why ferrites are so useful.

Additional information:
Eddy Current
Skin Effect
Litz Wire
Thank you for the detailed answer. I have measured it with the core on, I think I did not measured the true ac resistance which gives copper loss. I should have measured without core, I mean just the windings. I attach the picture of the network analyzer, Please let me know what are all the resistance is measured and what I can calculate or have a idea about the losses using this. 1.PNG
 

DickCappels

Joined Aug 21, 2008
7,418
I have not used a network analyzer. If anybody can come along and tell us how to read these charts and help answer the Thread Starter's questions, we will appreciate it.
 

MaxHeadRoom

Joined Jul 18, 2013
23,084
Also.
The inductance and resistance essentially appear in series, the ratio of one to another is known as the 'Q' value and is calculated from the ratio of reactance to ohmic resistance.
Max.
 
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