BLDC Motor Power Calculator

What Is a BLDC Motor Power Calculator?

A BLDC Motor Power Calculator is a tool that helps you estimate how a brushless DC motor performs under load. It converts basic electrical inputs into useful real-world results like:

• Mechanical output power
• Electrical input power
• Motor efficiency
• Torque
• Heat loss
• Voltage sag
• Loaded RPM

Instead of guessing or relying only on motor datasheets, this calculator shows what actually happens when current flows through the motor.

This is useful for electric vehicles, drones, e-bikes, robotics, RC systems, and industrial drives.

Why Power Calculation Matters in BLDC Motors

BLDC motors are efficient, but they are not magic. Every motor turns some electrical energy into useful work and the rest into heat.

If you do not calculate power correctly, you risk:

• Overheating the motor
• Burning windings
• Wasting battery energy
• Choosing the wrong motor or battery
• Poor performance under load

A power calculator gives you clarity before problems show up in hardware.

What This BLDC Motor Power Calculator Does

This calculator is designed around real motor physics, not marketing numbers. It estimates performance using voltage, current, motor constants, and internal losses.

Here is what it calculates:

1. Electrical Input Power

This is the power drawn from the battery.

Formula:
Input Power = Voltage × Current

Example:
22.2 V × 50 A = 1110 W

2. Mechanical Output Power

This is the usable power delivered at the shaft.

The calculator subtracts losses from the input power to estimate real output.

Formula:
Mechanical Power = Input Power − Total Losses

Losses include copper loss and iron loss.

3. Copper Loss (Winding Loss)

Copper loss happens because motor windings have resistance.

Formula:
Copper Loss = Current² × Motor Resistance

This loss rises fast as current increases.

4. Iron and No-Load Loss

Even with no load, a BLDC motor consumes power due to magnetic and mechanical effects.

Formula (approximation):
Iron Loss = Voltage × No-Load Current

This calculator uses no-load current measured at 10 V as a reference.

5. Motor Efficiency

Efficiency tells you how much input power turns into useful output.

Formula:
Efficiency (%) = (Mechanical Power ÷ Electrical Power) × 100

• Above 75% is good
• 60–75% needs attention
• Below 60% is risky

The calculator highlights this clearly.

6. Loaded RPM

Motor speed drops under load due to internal resistance.

Formula:
Loaded RPM = (Voltage − IR Drop) × KV

This gives a more realistic speed than no-load RPM.

7. Torque Output

Torque shows how much turning force the motor produces.

The calculator uses the standard BLDC approximation:

Torque Constant:
Kt ≈ 9.55 ÷ KV

Torque Formula:
Torque = Kt × (Load Current − No-Load Current)

This helps you see whether the motor can actually move your load.

8. Voltage Sag (IR Drop)

Internal resistance causes voltage loss inside the motor.

Formula:
Voltage Drop = Current × Resistance

High voltage sag means wasted power and heat.

Inputs Explained in Simple Terms

Battery Series (S) and Voltage

You can select a battery pack (like 6S) or enter voltage manually.

• 1S ≈ 3.7 V
• 6S ≈ 22.2 V
• 12S ≈ 44.4 V

Voltage affects speed, power, and losses.

Motor KV

KV means RPM per volt.

• High KV = high speed, lower torque
• Low KV = lower speed, higher torque

The calculator uses KV to estimate speed and torque.

Load Current

This is the current the motor draws at throttle.

It directly affects:

• Power
• Heat
• Torque
• Efficiency

Higher current always means higher thermal stress.

Motor Resistance

This is internal winding resistance.

Small values matter. Even 0.04 Ω can cause large losses at high current.

No-Load Current

This is the current drawn when the motor spins freely.

It represents friction, bearing loss, and magnetic drag.

Visual Output: Why It Helps

The calculator includes a power bar that shows:

• Green section: useful mechanical work
• Red section: heat loss

This makes efficiency easy to understand at a glance, even for non-engineers.

Motor Health Advice System

Based on efficiency and voltage sag, the calculator gives clear feedback:

• Optimal range: Safe and efficient operation
• Inefficient zone: High heat, cooling needed
• Critical overheat risk: Motor likely overloaded or stalled

This turns raw numbers into practical guidance.

Who Should Use This Calculator?

This tool is helpful if you are:

• Designing an electric vehicle
• Selecting a motor for a project
• Tuning an ESC and battery setup
• Comparing motors realistically
• Checking thermal safety
• Learning how BLDC motors behave under load

It works for beginners and experienced builders alike.

Important Limitations to Know

This is an estimation tool, not a lab instrument.

It does not model:

• ESC switching losses
• Advanced magnetic saturation
• Temperature-dependent resistance
• Mechanical drivetrain losses

Still, it is accurate enough for design decisions and safety checks.