Electrician Red Seal · Question
A 24 V DC permanent magnet motor used in an automated gate opener starts to run inconsistently and sometimes fails to respond to commands. You check the supply voltage, and it is stable at 24 V. What is the most likely cause within the motor itself?
Inconsistent operation, sometimes failing to respond while the supply voltage is stable, is a classic symptom of poor contact between the brushes and the commut
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Question: A 24 V DC permanent magnet motor used in an automated gate opener starts to run inconsistently and sometimes fails to respond to commands. You check the supply voltage, and it is stable at 24 V. What is the most likely cause within the motor itself?
Answer options: ✅ Worn or dirty commutator and brushes.
- A short circuit in the permanent magnets.
- An open circuit in the field windings.
- Overheating due to excessive load.
Correct answer: Worn or dirty commutator and brushes.
Explanation: Inconsistent operation, sometimes failing to respond while the supply voltage is stable, is a classic symptom of poor contact between the brushes and the commutator in a DC motor. Worn brushes, a dirty commutator, or insufficient brush tension can lead to intermittent electrical connection, causing the motor to run erratically or not at all. Permanent magnet motors do not have field windings. Permanent magnets cannot 'short circuit'. While overheating can cause issues, the intermittent nature points more directly to brush/commutator issues.
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