Speed controls provide several functions: (a) converting input AC voltage to DC for the motor; (b) a potentiometer enables the user to select the motor operating speed; (c) "automatic" circuitry regulates the motor speed; (d) other functions, such as braking/reversing, temperature and line voltage compensation, can be provided at additional cost.

The design of the electronic speed control has a dramatic effect on motor speed performance and life. SCR speed controls can be: (a) 1/2 wave of full-wave; (b) filtered or unfiltered. Most industrial controls are full-wave. We will assume full-wave rectification and discuss difference between filtered and unfiltered.

Form Factor for a DC voltage electronic control is a measure of the amount of current (ampere) filtering (smoothing) provided by the control to a motor. Form Factor cannot be determined until a motor and control combination are driving a load. However, most control manufacturers catalog their controls with a FF rating. Most small motor and control combinations exhibit FF=1.0 to 1.05 with a filtered control and FF=1.6 to 1.8 with an unfiltered control at rated torque.

Most Bodine permanent magnet DC motors are rated for continuous duty on 130 VDC, FF-1.05 current as supplied by Bodine type FPM and WPM controls. These motors and gearmotors can be successfully operated from unfiltered controls at FF=approximately 1.6, at speed not less than 1700 rpm. For intermittent duty operation, full nameplate torque may be available. The designers should test for each individual application.