what is an inertial load?

[usernam]

what are the characteristics of an inertial load for motors? Is the inertia very high. and at steady state what is the load torque on the motor?

what are some examples of inertial loads?

Thnx

 

[flatulent]

I suspect that this is a load whose rotational moment of inertial is much larger than the motor's. One example would be a street car. Loads that are resistive would be a saw for cutting logs.

 

[House_Cat]

A classic example of an inertial load is a flywheel. The inertia of the flywheel presents a large load to the motor as it is being accelerated to the motor speed. As the flywheel accelerates, the amount of energy required from the motor decreases. Once the motor shaft speed is reached, the load on the motor is only the torque necessary to overcome the frictional losses.

A classic example of a resistive load is a paddlewheel. The paddlewheel moves fluid by pushing against it, so the work done by the driving motor is relatively constant while the paddlewheel is in motion in the fluid.

To expand on Flatulent's description - a power saw motor sees mostly inertial loading getting the blade up to speed. When the running saw is applied to a piece of wood, the load becomes mostly resistive as the saw moves through the material.

 

[usernam]

thnx for the answers.
so a dc series motor wud be ideal for such a load?

 

[House_Cat]

so a dc series motor wud be ideal for such a load?

A series DC motor has the high starting torque required to get a heavy load moving. Realize that nothing comes without a price - the series DC motor will draw high starting current as it accelerates the load. The ability of a series wound DC motor to move big loads from a standing start is exactly why they are used as automobile starter motors ( the load in that case is both inertial and resistive).

You must also realize that a large series DC motor cannot be operated without a load. It will accelerate to self-destruct speeds. Additionally, the speed of the series wound motor will vary with load. If you need a safe constant speed motor, you will have to look to a compound motor.

A compound wound DC motor has both the high starting torque of a series motor, and the constant speed characteristic of a shunt wound motor. In most applications, it is a safer motor than a series wound motor. If the load on a compound motor is lost, it doesn't run away in speed.