How much does motor winding resistance increase with temperature?

Motor winding resistance increases linearly with temperature, with copper windings typically showing a 30-40% resistance increase over a 100°C temperature rise. For example, a motor with 50Ω resistance at 25°C will have 68.65Ω at 120°C, representing a 37.3% increase.

What is the temperature coefficient of resistance for copper motor windings?

The temperature coefficient of resistance (α) for copper motor windings is typically 0.00393 Ω/Ω/°C. This value is used in the formula R_T = R_25 [1 + α(T - 25)] to calculate resistance at different temperatures.

How do you calculate motor winding resistance at operating temperature?

Use the formula R_T = R_25 [1 + α(T - 25)], where R_T is the resistance at temperature T, R_25 is the reference resistance at 25°C, and α is the temperature coefficient (0.00393 for copper). Always use datasheet-specific temperature coefficients for accurate results.

Why does motor resistance change affect efficiency and thermal management?

Higher winding resistance at elevated temperatures causes increased copper losses and power dissipation, directly reducing motor efficiency. This additional heat generation can lead to thermal runaway risks if not properly managed through adequate thermal design.

Motor ControlApril 25, 202612 min read

Motor Winding Resistance vs Temperature Calculations

Learn how temperature impacts motor winding resistance and why accurate thermal modeling matters for electrical design and performance.

Contents

Understanding Motor Winding Resistance Variations
Why Temperature Matters
The Physics Behind Resistance Change
Practical Example: BLDC Motor Winding Analysis
Common Pitfalls and Gotchas
Thermal Design Implications
When to Use This Calculator
Try It Out

Understanding Motor Winding Resistance Variations

Motor designers and electrical engineers know that resistance isn't a static property. Temperature dramatically changes how conductors behave, and for motor windings, this isn't just academic — it's critical performance engineering.

Why Temperature Matters

Copper wire resistance increases linearly with temperature. A 100°C jump can mean 30-40% more resistance, which directly impacts motor performance, efficiency, and thermal management. Most engineers underestimate this effect.

The Physics Behind Resistance Change

The fundamental relationship is described by the equation:

R_T = R_{25} [1 + \alpha(T - 25)]

Where:

$R_T$ is resistance at temperature $T$
$R_{25}$ is resistance at 25°C reference
$\alpha$ is the temperature coefficient of resistance

Practical Example: BLDC Motor Winding Analysis

Let's break down a real scenario. Consider a small BLDC motor with these characteristics:

Base resistance at 25°C: 50 Ω
Temperature coefficient: 0.00393 Ω/Ω/°C
Operating temperature: 120°C

Plugging these into our Winding Resistance vs Temperature calculator, we get:

Resistance at 120°C: 68.65 Ω
Resistance increase: 18.65 Ω
Percentage change: 37.3%

This isn't trivial. That 37% resistance bump means:

Higher copper losses
Reduced motor efficiency
Potential thermal runaway risks

Common Pitfalls and Gotchas

Most engineers make three classic mistakes:

Using room temperature resistance for all calculations
Ignoring temperature coefficient variations
Assuming linear behavior across extreme ranges

Pro tip: Always use datasheet-specific temperature coefficients. Generic values can introduce significant errors.

Thermal Design Implications

Higher resistance means more power dissipation. For our example motor, that 18.65 Ω increase translates to substantial additional heat generation. Thermal management isn't optional — it's mandatory.

When to Use This Calculator

Use the Winding Resistance vs Temperature tool when:

Designing motor drive circuits
Calculating thermal losses
Predicting performance across temperature ranges
Selecting appropriate wire gauges and insulation

Try It Out

Open the Winding Resistance vs Temperature calculator and plug in your specific motor parameters. Understanding these dynamics could save your next design.