Estimating power usage of idle motor
I would assume "power usage of idle motor" would be if it were running full-speed, no-load. Motors generally consume a large current for a short time to spin up. Since most larger AC motors are typically 85-92% efficient at converting electricity into mechanical work, 8-10% loss seems reasonable, including bearing friction and windage. Start-up speed depends on load and motor type (AC induction, capacitor-start, synchronous, DC, etc.) While they do generally start faster with no load, synchronous AC motors feature very fast start-up time (but generally lower efficiencies.) High-inertia loads can be problematic for some motors, as they use a special "start-winding" which is designed to work for only a split second.