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Talking about Speed, Torque, Current Characteristics of DC Series Motor

By shaquila | Published on Sep 16,2015

1. DC motor Torque versus Speed Curve:

Seeing from the following figure, we can easily get the result that the motor speed varies with its load amount when the input voltage is fixed. The motor rotates at the no-load speed, the fastest possible speed, when theres no load on the shaft. The speed would reach zero when the It is fully loaded and the motor is producing its stall torque (ST), the maximum possible torque. At that moment, motors could only works for a short time to save on batteries.

2. Self excited motor torque versus speed:

A. Compound motor speed versus armature current

The compound motors speed is changed with the applied voltage amount. The below chart shows: the higher the armature current is, the higher the compound motors speed is. As for the extra current contributes to the weakness of the magnetic field, the increasing of the speed happens. That can be translated into this sentence: the magnetic field is weakened with the speed of the motor.

B. Shunt wound motor speed versus armature current:

The shunt motors armature torque is proportionally increased with the speed of the motor increasing for the proportional relationship between the torque and the armature current.

When the motor is starting: Low speed, little torque

When the motor reaches full rpm: Fullest torque

When the motor is at full rpm, shunt field current is reduced slightly:

The rpm slightly increases, the motor's torque will also increase slightly.

C. Series wound motor torque versus speed:

When under no-load, the motor will eventually reach some high speed.

Notes: some series motors can be damaged by excessive speed.

3. Separately excited DC motor speed versus torque:

4. Permanent magnetic DC motor torque versus speed:


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