Torque produced by a DC motor is proportional to the field flux x armature current x k (a constant). When a customer desires more HP, approximately a 15 percent increase in torque can be accomplished by increasing the field current by the desired increase. In other words, a 10 percent increase in field current should result in 10 percent more torque without increasing the armature current. Field temperature should be monitored when this is done.
Armature current can also be increased, as long as the additional heat can be dissipated. Increasing the blower size is one way to accomplish this.