![]() ![]() The problem here is that this short uselessly consumes power without producing any motion (nor even any coil current.) In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful. Note that this problem is independent of the non-starting problem above even if there were a high current in the coil at this position, there would still be zero torque. The power leads are shorted together through the commutator plates, and the coil is also short-circuited through both brushes (the coil is shorted twice, once through each brush independently). At the zero-torque position, both commutator brushes are touching (bridging) both commutator plates, resulting in a short circuit. ![]() There is a second problem with this simple pole design. However, once it was started, it would continue to rotate through this position by momentum. The motor would not be able to start in this position. In the pictures above, this occurs when the core of the coil is horizontal-the position it is just about to reach in the second-to-last picture on the right. when the rotor poles are 90 degrees from the stator poles-the torque is zero. ![]() To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle (in a two-pole motor) thus causing the motor to continue to rotate in the same direction.Ī problem with the motor shown above is that when the plane of the coil is parallel to the magnetic field-i.e. ![]() According to Fleming's left hand rule, the forces cause a turning effect on the coil, making it rotate. When a current passes through the coil wound around a soft iron core situated inside an external magnetic field, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. ![]()
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