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Dol Starting Current Correction/clarification


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First of all I would like to say that your website is quite informative. I have found the descriptions of induction motor starters to be accurate and in-depth.


I am just writing to nitpick the following statement in your description of DOL starting current:


The actual starting current curve is a function of the motor design, and the terminal voltage, and is totally independent of the motor load. The motor load will affect the time taken for the motor to accelerate to full speed and therefore the duration of the high starting current, but not the magnitude of the starting current.


I feel it is misleading to state that the current curve is independent of the motor load, especially since this is repudiated in the very next sentence. It would be more accurate to state that the maximum starting current is independent of the motor load, though I still do not believe this to be entirely true. Regardless, since the duration of the starting current is dependent on motor load, the starting current curve is obviously also dependent on motor load and the first sentence is misleading.


I hope you take this comment as constructive criticism of your informative and useful site.



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Hi Ben


Welcome to the forum


The curve of start current against rotor speed is totally independent of motor shaft load, but the start current curve against time is affected by the load. At any speed during acceleration, the current draw is independent of the load on the motor.

The start current curve is usually quoted and drawn as start current against speed, not time, as the time is dependent on the load torque against speed and the load inertia.


Best regards,


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Hi Ben.

Motors start with rotors at stand still. There current's at its maximal (it equals actually LRA), no matter is there 1 N or 100 000 000 N force on shaft to overcome. Motor size + voltage applied only matter with the current.

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