1. What is DC Motor Resistance?

The DC motor resistance (R) is the internal resistance of the motor windings, calculated using stall voltage and current. It's a key parameter for understanding motor performance and power dissipation.

2. How Does the Calculator Work?

The calculator uses Ohm's Law under stall conditions:

Where:

• \( R \) — Motor resistance in ohms (Ω)
• \( V_{stall} \) — Voltage applied during stall condition (V)
• \( I_{stall} \) — Current drawn during stall condition (A)

Explanation: At stall condition (motor shaft prevented from rotating), the back EMF is zero, so the only opposition to current is the winding resistance.

3. Importance of Motor Resistance

Details: Knowing motor resistance helps in:

• Calculating power losses (I²R losses)
• Determining starting current
• Designing appropriate motor drivers
• Predicting thermal performance

4. Using the Calculator

Tips:

• Measure stall voltage and current accurately
• Apply voltage briefly to avoid overheating
• Ensure motor is properly stalled during measurement
• Values must be positive numbers

5. Frequently Asked Questions (FAQ)

Q1: Why measure at stall condition?
A: At stall, there's no back EMF, so the full voltage appears across the resistance, making measurement straightforward.

Q2: How does temperature affect resistance?
A: Resistance increases with temperature (positive temperature coefficient). Measure at operating temperature for accurate results.

Q3: What's a typical DC motor resistance range?
A: Small hobby motors: 1-10Ω, Larger motors: 0.1-1Ω, varies greatly with motor size and design.

Q4: Can I measure resistance with a multimeter?
A: Yes, but stall method often gives more accurate results as multimeters may not provide enough current.

Q5: How does resistance relate to motor performance?
A: Lower resistance generally means higher efficiency but may require more robust current handling.