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Bemf explanation
Brushed DC motors are common in various applications due to their simplicity, reliability, and ease of control. One important aspect of these motors is the Back Electromotive Force (BEMF). Here’s an explanation of what BEMF is and its role in the operation of brushed DC motors:
Back Electromotive Force (BEMF), also known as counter-electromotive force (CEMF), is a voltage that is generated by the spinning motor and opposes the applied voltage driving the motor. It is a fundamental characteristic of all electric motors and plays a crucial role in their operation.
In a brushed DC motor, when current flows through the windings in the armature (the rotating part of the motor), a magnetic field is created. This magnetic field interacts with the permanent magnets in the motor, producing torque that causes the armature to spin. As the armature spins, the windings cut through the magnetic field, inducing a voltage according to Faraday's Law of Electromagnetic Induction. This induced voltage is the BEMF.
- Direction: BEMF is always in the opposite direction to the applied voltage (hence "back" or "counter").
- Magnitude: The magnitude of BEMF is proportional to the speed of the motor. The faster the motor spins, the higher the BEMF.
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Impact on Motor Operation:
- Startup: At startup, the motor speed is zero, so BEMF is also zero. The applied voltage fully determines the current flowing through the motor windings.
- Running Condition: As the motor speeds up, BEMF increases, reducing the net voltage across the motor windings and consequently reducing the current.
- Steady State: The motor reaches a steady speed when the driving torque (resulting from the current and applied voltage) balances the load torque and the opposing BEMF.
The relationship between the applied voltage ( V ), BEMF ( E ), armature current ( I ), and armature resistance ( R ) can be expressed as: [ V = E + I * R ]
Where:
- ( V ) is the applied voltage.
- ( E ) is the BEMF.
- ( I ) is the current flowing through the motor.
- ( R ) is the resistance of the armature windings.