Disadvantages of Synchronous Motors

1. These motors cannot be used for variable speed jobs as there is no possibility of speed adjustment
2. It requires external source for supplying dc excitation
3. It cannot be started under load, the starting torque being zero
4. It has a tendency to hunt.
5. It may fall out of synchronism and stop when over-loaded.
6. Collector rings and brushes are required.
7. For some applications these motors are not desirable as for driving shafts in small work-shops having no power available for starting and in cases where frequent starting or strong starting torque is required.