Flat Spiral Coil Resistance Guide
Overview
A flat spiral coil uses one continuous conductor. It turns outward on one plane. This shape appears in heaters, sensors, wireless pads, NFC coils, and printed boards. Resistance matters because it controls heat, voltage drop, current limit, and power loss. A small error can change performance.
Why Coil Resistance Matters
Every conductor has resistance. Long spirals have more length than they first appear. Tight spacing also increases the number of turns, so total length grows fast. The calculator estimates length from the inner size, outer size, and number of turns. It then applies material resistivity and temperature correction. The result helps you judge safe current, expected voltage drop, and power dissipation.
Key Inputs Explained
Choose round wire when using copper, aluminum, silver, nichrome, or custom wire. Enter the diameter and lead length. Choose rectangular trace when working with copper foil, etched boards, or flat strip. Enter width and thickness. The temperature field adjusts resistivity from the standard reference point. Copper resistance rises as temperature increases. Nichrome changes less, so heater designs can behave differently.
Design Tips
Keep units consistent. Measure the inner and outer dimensions across the coil path. Use the conductor centerline when possible. Add lead length because terminals can contribute meaningful resistance in low-ohm coils. Increase the safety margin for handmade coils, solder joints, bends, and hot spots. For high current designs, compare the power loss with the cooling method. Heat can raise resistance again, which changes the final operating point.
Practical Use
This tool is useful during early electrical design. It cannot replace lab measurement. Real coils may have coatings, bends, pressure contacts, surface roughness, and temperature gradients. These details create small differences. Still, the estimate is valuable. It shows whether a design is close to the target before material is cut or a board is ordered.
Better Decisions
Use the example table to test common cases. Export the result for records. Compare materials and dimensions. Adjust turns or conductor size until resistance, current, voltage drop, and power loss are acceptable. When accuracy is important, build one first sample. Measure resistance after the coil reaches working temperature. Compare the reading with the estimate. Then update the safety factor for future production batches.