Rotor dynamic balancing is a crucial step in the motor manufacturing process. Whether it's a cast aluminum rotor or a wound rotor, balancing is achieved by adding weight. However, some clever people always come up with some "good" methods that, while physically balancing the rotor, lead to other problems that are truly laughable.
A foreign businessman sent a message saying that they inspected a motor supplied by a Chinese factory and found that the motor vibration was slightly excessive. Because it was to be supplied to a relatively demanding end customer, they disassembled the motor to perform rotor dynamic balancing. After the balancing was completed, they tested the motor and found that the stall current was seriously uneven. The purpose of the message was to find out the cause.
I really admire the generosity of these foreigners; they sent over all the disassembly pictures. One picture of a balanced rotor almost made Ms. Can almost choke with laughter—to achieve rotor balance, they actually cut off a large piece of the rotor end ring, which naturally resulted in uneven rotor current. Below, I'll show you that picture. If you see this picture, I suggest you buy a lottery ticket; you're sure to win!
Regarding motor stall and stall current
Motor stall is a situation where a motor continues to output torque even when its speed is zero. It is generally caused by mechanical or human factors, such as excessive motor load, mechanical failure of the driven motor, bearing damage, rotor rubbing, etc., which prevent the motor from starting or cause it to stop rotating.
When a motor is stalled, its power factor is extremely low, and the current during stall can reach 5-12 times the rated current. If this continues for a while, the motor will burn out.
If the motor stalls, there is no back EMF. The motor becomes like an inductive element connected to the power supply, with only its own resistance and inductance, and the current will naturally increase greatly.
When a motor is running, it generates back electromotive force, which is the main component that consumes voltage. When the motor is stalled, the back electromotive force is zero, and all the voltage is applied to the windings, resulting in a large current.
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