Motor start times to its lifetime

It is a fact that starting is by far the most stress on a motor; so minimize number of starts; but a motor in your ink-jet printer could start once every couple of seconds, a motor must perform the job it is designed for. This is where the concept of short time rating, variable frequency drive, soft start all becomes important and handy tools.

Let us also think of short time duty motors used in Rockets (missiles. launchers) where the motors in a stage , is allowed to burn out after, say a few seconds, once its job is over. Therefore, as suggested above, size, rating and application. What API states are applicable to only those ratings that are within the scope of laid down specifications. There are no laid down tests for the extreme duties, where the experience counts.

One of my teachers from Purdue had designed a single run motor for a rocket, that was to burn out when the motor was tested at the equivalent rating the temperature was found to be 2 degree celcius higher than the design value. Time available up to launch was just 2 days, was not enough to make and test a new machine. He thought over it over the night and came up with a solution from the fundamentals of science - dipped the motor in black paint. I forgot, the motor was of size that could fit your Palm.

There are no standards on startup of electric motor. You may be able to estimate what happens to the motor components during individual and successive starts, but it cannot be linked to the life. I understand that various consultants have specified total number of starts to a motor, in its life time, but it is cosmetic and everybody agrees to it without thought, unless it is a special application.