HVAC actuator with line voltage input

1. An actuator in a building HVAC system, the actuator comprising:

a housing;

a mechanical transducer;

an input connection configured to receive a voltage signal having a power supply line voltage; and

a voltage divider circuit comprising:

a first capacitor disposed in series between the input connection and the mechanical transducer, the first capacitor having a capacitance value based on an electrical impedance of the mechanical transducer;

a second capacitor arranged in parallel with the first capacitor between the input connection and the mechanical transducer; and

a switch operable to connect and disconnect at least one of the first capacitor and the second capacitor from the voltage divider circuit, wherein operating the switch adjusts a capacitance between the input connection and the mechanical transducer;

wherein the voltage divider circuit is configured to receive the power supply line voltage from the input connection, to use the first capacitor to reduce the power supply line voltage to a reduced voltage, and to provide the reduced voltage to the mechanical transducer,

wherein the input connection comprises:

a first input connection configured to receive a voltage signal for driving the mechanical transducer in a first direction; and

a second input connection configured to receive a voltage signal for driving the mechanical transducer in a second direction opposite the first direction.

2. The actuator of claim 1 , wherein the voltage divider circuit is located within the housing of the actuator or within an adaptor configured to attach to the housing of the actuator.

3. The actuator of claim 1 , wherein the capacitance value is based on an electrical inductance of the mechanical transducer.

4. The actuator of claim 1 , wherein the capacitance value is based on a voltage value of the power supply line voltage.

5. The actuator of claim 1 , wherein the voltage divider circuit comprises:

the first capacitor and the second capacitor disposed in parallel with each other and in series between the first input connection and the mechanical transducer; and

a third capacitor disposed in series between the second input connection and the mechanical transducer.

6. The actuator of claim 1 , further comprising:

a user-operable switch attached to the housing and configured to switch between multiple different values for the capacitance.

7. The actuator of claim 1 , wherein the voltage divider circuit is configured to measure the power supply line voltage and to adjust an impedance between the input connection and the mechanical transducer based on the measured line voltage.

8. The actuator of claim 7 , wherein adjusting the impedance between the input connection and the mechanical transducer comprises at least one of connecting and disconnecting the first capacitor from the voltage divider circuit.

9. The actuator of claim 7 , wherein adjusting the impedance between the input connection and the mechanical transducer comprises:

determining an impedance of the mechanical transducer;

using the impedance of the mechanical transducer and the measured power supply line voltage to calculate an impedance required to reduce the power supply line voltage to the reduced voltage; and

adjusting the impedance between the input connection and the mechanical transducer to achieve the reduced voltage.

10. A method for operating an actuator in a HVAC system using a power line voltage, the method comprising:

providing an actuator comprising a housing, a mechanical transducer, and an input connection configured to receive a voltage signal having a power supply line voltage;

arranging a voltage divider circuit in series between the input connection and the mechanical transducer, the voltage divider circuit comprising multiple capacitors arranged in parallel with each other, a first capacitor of the multiple capacitors having a capacitance value based on an electrical impedance of the mechanical transducer;

receiving the power supply line voltage at the voltage divider circuit via the input connection;

using the first capacitor to reduce the power supply line voltage to a reduced voltage;

providing the reduced voltage from the voltage divider circuit to the mechanical transducer; and

operating a switch arranged in series with at least one of the multiple capacitors to electrically connect or disconnect at least one of the multiple capacitors from the voltage divider circuit, wherein operating the switch adjusts a capacitance between the input connection and the mechanical transducer,

wherein the input connection comprises:

a first input connection configured to receive a voltage signal for driving the mechanical transducer in a first direction; and

a second input connection configured to receive a voltage signal for driving the mechanical transducer in a second direction opposite the first direction.

11. The method of claim 10 , further comprising:

locating the voltage divider circuit either within the housing of the actuator or within an adaptor configured to attach to the housing of the actuator.

12. The method of claim 10 , further comprising:

using at least one of an electrical inductance of the mechanical transducer and a voltage value of the power supply line voltage to calculate the capacitance value; and

selecting the first capacitor from a set of multiple different capacitors based on the calculated capacitance value.

13. The method of claim 10 , further comprising:

using a user-operable switch attached to the housing to switch between multiple different values for the capacitance.

14. The method of claim 10 , further comprising:

measuring the power supply line voltage; and

adjusting an impedance between the input connection and the mechanical transducer based on the measured power supply line voltage;

wherein adjusting the impedance between the input connection and the mechanical transducer comprises at least one of connecting and disconnecting the first capacitor from the voltage divider circuit.

15. The method of claim 10 , further comprising:

measuring the power supply line voltage;

determining an impedance of the mechanical transducer;

using the impedance of the mechanical transducer and the measured power supply line voltage to calculate an impedance required to reduce the power supply line voltage to the reduced voltage; and

adjusting the impedance between the input connection and the mechanical transducer to achieve the reduced voltage.

16. An actuator in a building HVAC system, the actuator comprising:

a housing;

a mechanical transducer;

an input connection configured to receive a voltage signal having a power supply line voltage;

a voltage divider circuit comprising a capacitor disposed in series between the input connection and the mechanical transducer, the capacitor having a capacitance value based on an electrical impedance of the mechanical transducer; and

a time out circuit;

wherein the voltage divider circuit is configured to receive the power supply line voltage from the input connection, to use the capacitor to reduce the power supply line voltage to a first reduced voltage, and to provide the first reduced voltage to the mechanical transducer;

wherein the voltage divider circuit is configured to provide a second reduced voltage, different from the first reduced voltage, to the time out circuit.

17. The actuator of claim 16 , wherein the voltage divider circuit is located within the housing of the actuator or within an adaptor configured to attach to the housing of the actuator.

18. The actuator of claim 16 , wherein the input connection comprises:

a first input connection configured to receive a voltage signal for driving the mechanical transducer in a first direction; and

a second input connection configured to receive a voltage signal for driving the mechanical transducer in a second direction opposite the first direction.

19. The actuator of claim 18 , wherein the voltage divider circuit comprises:

a first capacitor disposed in series between the first input connection and the mechanical transducer; and

a second capacitor disposed in series between the second input connection and the mechanical transducer.