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How It Works : Adjustable Speed Motor




The DynaMotor™ is an integrated adjustable speed motor and drive unit that produces high torque at low speeds, while virtually eliminating Radio Frequency Interference (RFI) or Ground Fault Circuit Interrupter (GFCI) signals.

  How an Adjustable Speed Motor works

Basic Adjustable Motor Description


How a Variable Speed Motor works

The DynaMotor looks like an ordinary AC or DC motor. It is the same shape and size and is made from the same mechanical parts; laminations, windings, shaft, end-bell, bearings and housing. The difference is that the DynaMotor uses optically controlled solid-state switches embedded in its rotor windings to control speed and torque. Opening and closing these switches controls the current, and thus the torque, right where it is being produced. The result is enhanced

Slotted Armature from our Custom Motor Design
Slotted Armature

performance in a package that is much more than a motor—a self-contained variable-speed motor and drive unit.


The DynaMotor is constructed somewhat like a universal motor with a pair of opposed salient poles whose copper windings are connected directly to the two legs of a single-phase or three-phase line.


The rotor is similar to universal motors, consisting of slotted steel laminations stacked on a shaft.


Copper wire is wound in opposite slots and the two ends of each coil are connected by a solid-state switch, such as a transistor. In contrast, universal and DC motors have each coil connected to copper bars in a commutator that receives external power through carbon brushes. The DynaMotor is brushless.

When the stator poles are connected to an AC line, a resultant magnetic field varies with the line current and the flux passes directly through the rotor inducing a voltage in each rotor coil. When the solid-state switch is closed, current flows through the coil, producing flux, torque and rotation.


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                <td align=  Adjustable Speed Motor with Coil Closed with Rotation
Switch Open
Coil Closed with Rotation

Torque and Speed Adjustment


When the switch is open, current cannot flow and no torque or rotation is produced by the coil. Closing the switch for a longer period produces more torque and increases the speed. Thus, the motor's torque and speed can be adjusted as desired by controlling how long (over what rotational angle) the switches are open.


High Torque Motor   Adjustable Speed Motor
Time/angle switches closed vs. speed

Each switch is actuated by a photo-detector as it rotates past a stationary illuminated infrared light-emitting diode (LED). An array of LED’s mounted on the motor end-bell can be turned on for varying amounts of time to adjust the motor’s speed.


photo detectors on adjustable speed motor

As shown above, the stationary and rotating switches and associated electronic components can be installed outside the main motor compartment to protect them from heat and dirt and to permit easy replacement. This is accomplished by bringing leads from the rotor coils out through the bearing via slots in the motor shaft.


Since there are multiple coils on the rotor that can be energized simultaneously and controlled individually, continuous smooth torque can be produced.

Self-Contained Closed-Loop Drive


A simple internal optical speed sensor provides speed feedback thus making the DynaMotor a self-contained, closed-loop drive system. The speed can be controlled manually with a potentiometer or keypad or automatically by transducer or serial link, etc.

No Separate Control Box Required


Since the DynaMotor's control and power electronics are an intrinsic part of the motor itself there is no need for a box on the wall at any horsepower level. Eliminating this unnecessary control box creates a substantial saving in cost and space required.


The DynaMotor is connected directly to the AC supply line. This eliminates the power wires from the controller cabinet to the motor as well as the connectors at both ends and the installation labor. It also cuts power losses by reducing extra wiring distance.


Since the speed feedback loop is part of the rotating electronics, there is generally no need for feedback signal wiring. This reduces wiring errors, loose connections and stray signal pick-up, thereby increasing motor drive reliability.


NOTE: Some smaller inverters and DC drives are available attached to the back or top of the motor but are not embedded like the DynaMotor.



No Reversing Electronics or Contactors Required


The direction of rotation can be reversed easily without contactors or an additional set of power electronics by merely turning on LED's on the opposite side of each stator pole.


LED Quadrant vs. Direction



DynaMotors' unique use of optically controlled non-contact solid-state switches eliminates traditional motor-drive pulse width modulation, which typically generates significant amounts of RFI and ground currents that prevent operation on GFCI protected circuits.


GFCI Operation


The DynaMotor is the only AC variable speed motor technology able to operate on GFCI protected circuits. Conventional technologies utilizing Pulse Width Modulation have high ground currents due to capacitive coupling to ground as well as bearing current. The DynaMotor produces less than 1 mA ground current. The graph below illustrates DynaMotor's ground current compared to three typical manufacturers of conventional single phase drives relative to the Class A GFCI limit



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