1. What is the DC Series Motor Speed Equation?

Definition: This equation calculates the rotational speed (RPM) of a DC series motor based on electrical and magnetic parameters.

Purpose: It helps engineers and technicians predict and control motor speed for various applications.

2. How Does the Equation Work?

The equation is:

Where:

• \( RPM \) — Rotational speed (revolutions per minute)
• \( V \) — Applied voltage (volts)
• \( I \) — Armature current (amps)
• \( R_m \) — Total resistance (armature + field, ohms)
• \( K_v \) — Motor velocity constant (RPM/volt)
• \( \Phi \) — Magnetic flux (webers)

Explanation: The numerator represents effective voltage after IR drop, while the denominator relates to motor's torque-producing capability.

3. Importance of Speed Calculation

Details: Accurate speed prediction is crucial for motor selection, performance analysis, and control system design.

4. Using the Calculator

Tips: Enter all parameters with correct units. Typical values:

• K_v: 100-1000 RPM/V for small motors
• Φ: 0.001-0.1 Wb depending on motor size
• R_m: 0.1-10 ohms

5. Frequently Asked Questions (FAQ)

Q1: Why does speed decrease with load?
A: Increased current causes larger IR drop (I×R_m), reducing effective voltage and thus speed.

Q2: How does flux affect speed?
A: Higher flux decreases speed (inverse relationship). In series motors, flux increases with current.

Q3: Where can I find K_v?
A: It's typically specified in motor datasheets or can be measured experimentally.

Q4: What if I don't know the flux?
A: For series motors, flux is approximately proportional to current (Φ ≈ k×I).

Q5: Why is speed at no-load very high?
A: With I≈0, the equation becomes RPM ≈ V/(K_v×Φ), which can be very high since Φ is small at low current.