How do you calculate copper losses in a BLDC motor?

Copper losses in BLDC motors are calculated using the formula I²R, where I is the operating current and R is the phase resistance. For example, a motor with 0.085Ω phase resistance running at 35A generates approximately 42W of copper loss.

What is typical BLDC motor efficiency for drone applications?

A typical 5-inch drone motor operating at 35A with 14.8V supply achieves approximately 89% efficiency, with total losses around 62W distributed between copper losses (~42W), iron losses (~12W), and mechanical losses (~8W).

What causes iron losses in BLDC motors?

Iron losses in BLDC motors result from magnetic core material hysteresis and eddy currents. These losses depend on operating frequency and magnetic flux density, and are estimated from the motor's no-load current.

What are common mistakes when calculating BLDC motor efficiency?

The three most common mistakes are ignoring no-load current's impact on iron losses, assuming losses scale linearly with current, and not accounting for temperature effects on winding resistance. These errors can significantly underestimate actual power losses.

Motor ControlApril 25, 202612 min read

BLDC Motor Efficiency: Real-World Performance

Master BLDC motor efficiency calculation with our comprehensive analyzer — learn how to optimize power, minimize losses, and improve motor design.

Contents

Understanding BLDC Motor Efficiency: More Than Just Numbers
Why Efficiency Matters
Dissecting Motor Losses
Copper Losses: The Resistive Culprit
Iron Losses: The Hidden Energy Sink
Worked Example: Drone Motor Analysis
Common Pitfalls
When to Use the Efficiency Analyzer
Try It Yourself

Understanding BLDC Motor Efficiency: More Than Just Numbers

Every electrical engineer knows motors aren't 100% efficient — but quantifying those losses? That's where things get interesting. The BLDC Efficiency Analyzer lets you break down exactly where your motor's energy is disappearing.

Why Efficiency Matters

In drone design, electric vehicles, or industrial robotics, every percentage point of efficiency translates directly into performance and battery life. A motor losing 20% of its input energy as heat isn't just wasting power — it's generating unnecessary thermal stress.

Dissecting Motor Losses

Real BLDC motor efficiency isn't a single number — it's a complex interaction between copper, iron, and mechanical losses. Our calculator helps you model these precisely.

Copper Losses: The Resistive Culprit

Copper losses occur in the motor windings. They're proportional to $I^2R$ — current squared multiplied by phase resistance. A 50KV motor with 0.08 Ω phase resistance running at 30A will generate significant heat.

Iron Losses: The Hidden Energy Sink

Iron losses come from magnetic core material hysteresis and eddy currents. These aren't as straightforward as copper losses and depend critically on operating frequency and magnetic flux density.

Worked Example: Drone Motor Analysis

Let's analyze a typical 5inch drone motor:

Kv Rating: 2300 RPM/V
Phase Resistance: 0.085 Ω
No-Load Current: 3.5A
Supply Voltage: 14.8V (4S LiPo)
Operating Current: 35A
Pole Pairs: 7

Plugging these into our BLDC Efficiency Analyzer reveals fascinating insights:

Copper Loss: ~42W
Iron Loss: ~12W
Mechanical Loss: ~8W
Total Loss: ~62W
Output Power: ~520W
Efficiency: ~89%

Common Pitfalls

Most engineers make three critical mistakes when analyzing motor efficiency:

Ignoring no-load current's impact on iron losses
Assuming linear loss scaling
Not accounting for temperature effects on resistance

Our calculator helps sidestep these traps by providing a holistic view.

When to Use the Efficiency Analyzer

Reach for this tool when:

Designing battery-powered systems
Optimizing motor selection
Performing thermal management calculations
Comparing motor performance across different configurations

Try It Yourself

Want to understand your motor's true performance? Open the BLDC Efficiency Analyzer and start exploring. Real engineering insights are just a few clicks away.