Calculator KB-51
Skin Effect Calculator
At high frequencies, current is pushed toward the surface, so a thick wire behaves like a thin one.
Result
In brief: Calculate skin effect: current penetration depth in copper and aluminum at a specified frequency, recommended conductor diameter, and increase in resistance at high frequency. Example: Skin depth: 0.209 mm.
Calculation example
| Frequency | 100 kHz |
|---|---|
| Material | Copper |
| Wire diameter | 1 mm |
| Skin depth | 0.209 mm |
|---|---|
| Strand diameter up to | 0.417 mm |
| Resistance increase | 1.45 × |
| Effective cross-section | 66 % |
How it is calculated
Copper: δ ≈ 66 / √f mm
Alternating current creates a field that pushes it out of the conductor's center. Skin depth decreases as frequency rises. In copper, it's about 9 mm at 50 Hz, but only 0.2 mm at 100 kHz. The estimated increase in resistance does not account for adjacent turns in a winding.
What to look for
- In multilayer windings, the proximity effect adds losses on top of the skin effect. That's why strands are often made even thinner.
- Instead of one thick wire, use several thin strands, or litz wire at high frequencies.
Frequently asked questions
What is the skin depth in copper at 100 kHz?
About 0.21 mm: δ ≈ 66 / √f mm. At 50 Hz, it's about 9 mm.
What wire should I use for a 100 kHz winding?
Use wire with a strand diameter no greater than twice the skin depth, i.e. up to 0.42 mm. If you need more copper, use several strands in parallel or litz wire.
Why is litz wire better than thick wire?
The insulated strands are twisted together, so each carries current through almost its full cross-section, and the current is distributed evenly. This is especially noticeable in multilayer windings, where the proximity effect also comes into play.
