Specifically for a single phase AC induction motor...I'm having trouble wrapping my head around the concept of an overloaded motor drawing more current. Since current draw increases when electrical resistance decreases, then how does a motor with bad bearings increase current draw? I realize the motor needs to do a lot more work, but how does the extra mechanical resistance caused by bad bearings translate into a decrease in electrical resistance, which causes higher current draw? Is there a power equation factor here that I'm not taking into consideration?
Hello Sanchez, When electrical energy is given to any motor, the mechanical output is always less than desired. This is because there are always some windage and frictional losses. You will understand from the following description: Motor input in stator can be divided into Stator Copper Iron losses and Rotor input. The rotor input can be further divided into Rotor Copper loss and Mechanical Power developed or Gross Rotor output. This Gross rotor output can be divided into Windage and friction loss and Rotor output or motor output. So in your case, even though the motor electrical resistance is not varying, but due to bad bearings, the windage and friction loss increases tremendously, leading to heating of motor. Since induction motor rotates at high speed, these losses will be very high, will lead to burning of motor, if the bearings are not replaced quickly.
