What is full load speed? What is the difference between full load speed and maximum speed? 1 website defines full load speed as the speed a dc motor develops under full torque conditions. I don't know what full torque conditions are. Are full torque conditions the full load torque or maximum torque?

 

Every motor/load configuration will have a speed-torque characteristic relationship. In general, you get high torque at low speed and low torque at high speed. With no load on a motor, you have only the rotor inertia to worry about. This is the condition at which maximum speed is possible. Things like "full load speed" would be defined for a load with a given moment of inertia. Full torque conditions might be derived form a given configuration of voltage and current, although torque is usually just a function of current.

 

Every motor/load configuration will have a speed-torque characteristic relationship. In general, you get high torque at low speed and low torque at high speed. With no load on a motor, you have only the rotor inertia to worry about. This is the condition at which maximum speed is possible. Things like "full load speed" would be defined for a load with a given moment of inertia. Full torque conditions might be derived form a given configuration of voltage and current, although torque is usually just a function of current.

You said things like full load speed would be defined for a load with a given moment of inertia. What load does the designer pick?

 

You said things like full load speed would be defined for a load with a given moment of inertia. What load does the designer pick?

This is more of a mechanical thing than an electronic thing. It depends on the motor frame, mounting, and bearings. You specify these things so that the motor does not get hot on startup and can accelerate to the desired speed in a reasonable amount of time. For example, consider the rotor inertia and say that empirical evidence suggests that a load of 7 times the rotor inertia yields a 10 second startup time. This will either be acceptable or not, and you go from there.

 

You need to have a proper performance-graph showing RPM / Torque vs Current.

If You can't obtain such a graph, You may be able to "guesstimate" the performance by
comparing a similar Motor which does have a performance-graph available.

Motor-Weight is sometimes a reasonable metric to compare Motors with,
although there are no guarantees that this will be reliable or accurate.

If You have a critical application, forget about buying from China.

You can sometimes just simply employ plenty of over-kill in your Motor selection,
this usually has the bonus of increased Motor longevity and
increased power available for unforeseen circumstances, and possible over-loads.
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If inertia was the only limit on motor speed, it would continue increasing in speed forever.

I don’t know how the manufacturers define full load speed but logically it would be when the motor is delivering its rated power to the load.

You have to be careful about generalizations here because there are different types of motors. For example, a 60Hz synchronous motor would always run at the same speed until the load was too large for it to handle.

 

This is more of a mechanical thing than an electronic thing. It depends on the motor frame, mounting, and bearings. You specify these things so that the motor does not get hot on startup and can accelerate to the desired speed in a reasonable amount of time. For example, consider the rotor inertia and say that empirical evidence suggests that a load of 7 times the rotor inertia yields a 10 second startup time. This will either be acceptable or not, and you go from there.

So the designer picks the maximum load at which the motor will not overheat?

 

So the designer picks the maximum load at which the motor will not overheat?

It would me more correct to say the designer determines the maximum load at which ...
in the absence of information from the manufacturer.

 

So the designer determines the maximum load at which the motor will not overheat?

 

So the designer determines the maximum load at which the motor will not overheat?

Unless the manufacturer is kind enough to provide it. Not all of them will do that. The best you could hope for is a representative test, which may or may not correspond to your actual situation.

 

So the designer determines the maximum load at which the motor will not overheat?

Both DC and BLDC motor manuf. etc generally supply torque curves for their products, The chart usually shows the max continuous torque, throughout the range from from 0 RPM to max rated RPM.
Above this is the peak torque rating, where the motor can only be used for just a very short period at a time.
Max torque at zero speed would be common for these motors.

 

Unless the manufacturer is kind enough to provide it. Not all of them will do that. The best you could hope for is a representative test, which may or may not correspond to your actual situation.

So if the manufacturer does not provide the desired maximum load at which the motor will not overheat, the designer determines the maximum load at which the motor will not overheat, and the full load speed is the speed at the maximum load at which the motor will not overheat?