Two-position (on-off) HVAC actuators are typically controlled by directly applying power to a drive motor. The actuators commonly use soldered leads, printed circuit boards, conductor stampings, or a combination to make connection between the motor terminals and the output connector.
The polarity of the applied power determines the direction of actuator rotation. The necessary electrical connection requires two conductive paths, connecting the two connector pins to two motor terminals. The actuator housing also typically forms the shroud for the connector around the connector pins.
The electrical connection is usually achieved via one of the following designs approaches:
1. Printed circuit board (PCB): a PCB is used to mount a pair of connector pins. Copper traces are screened onto the board, leading to two copper pads where motor terminals are attached (soldered). The motor is then electrically connected to these two terminals via lead wires, or directly. PA1 2. Conductor stampings: two stampings are formed into the shape of a connector pin on one end, and motor terminal on the other end. These stampings are mechanically secured into the plastic actuator housing. PA1 3. Flying leads: insulated lead wires are soldered onto the motor, and terminated with a connector. Lead wires are captured by the two halves of the actuator housing.
In FIG. 1, an example of a lower housing section 10 of an actuator housing is shown. A connector shroud 12 is integral with the housing section 10 and leads into the interior 14 of the housing actuator. A printed circuit board 16 is shown which fits into the lower housing section 10 such that two connector pins 18a, 18b project into the connector shroud 12.
A free end of the connector pins forms the electrical connection between a controller or a power supply inserted into the shroud 12. The opposite ends of the connector pins are welded to the underside of the PCB 16.
The connector pins are electrically connected to two trifurcated terminals 20a, 20b by copper connectors screened to the underside of the PCB. The terminals 20a, 20b are also welded at a free end on the underside of the PCB.
Optionally a capacitor can be secured to the underside of the PCB and be electrically connected between the terminals and the connector pins. The capacitor is commonly employed to reduce electromagnetic interference (EMI).
Interior 14 of the lower housing section 10 is exposed through the connector shroud 12. This communication may allow entry of fluid to the actuator housing, and thereby potentially adversely affect the workings of the housing actuator.
The PCB and the other design approaches are expensive and exhibit weaknesses, ranging from allowing fluid ingress to the difficulty in adding additional components, such as a capacitor across the motor terminals.