"Here is what I do know about this issue from researching a couple of electrical engineering sites. Lowering the motor input voltage by 50 % does several things.
1) The motor will run slower.
2) The torque developed will drop to about 25% of its full voltage rating.
3) This decrease in torque can make the motor stall when trying to start under a heavy load.
4) There may be drastic speed fluctuations due to load variations.
5) The motor current will double if the load remains constant."