Patent Application
20090180220
This invention relates generally to compressor fault status indication and more particularly to a method and apparatus to determine the state of protection contacts in a sealed compressor.
A compressor is an important component of a heating, ventilation, and air conditioning (HVAC) system. In most residential HVAC installations, the compressor is the highest cost component. When an HVAC system fails to operate properly, a service technician is generally called to diagnose and repair the system. When the service technician finds an inoperative compressor, the technician must determine whether the problem is in the compressor, or elsewhere in the HVAC system, including whether the compressor has overheated and simply needs time to cool and reset itself because of some other system fault. Under pressure to make a quick diagnosis and repair, technicians finding an inoperative compressor often replace the compressor with a known “good” compressor, most typically a new one. Historically up to 40% of returned compressors turn out to be good, with no defect found. These incorrect diagnoses translate directly to increased HVAC down time, wasted repair time, labor, and unnecessary labor and parts costs.
Most hermetically sealed compressors include internal protection switch contacts that open the internal compressor motor electrical circuit following a overheat condition as can be caused by a high mechanical load, an anomalously high line voltage, or by excessive compressor cycling. Once the abnormal condition that caused the overheat condition is cleared, most systems recover automatically after the compressor cools to a sufficiently low temperature where the protection contacts close.
Unfortunately, there is no immediate way for a servicing technician to determine if the internal protection contacts of the compressor are closed or momentarily open due to a non-catastrophic overload. The problem is that there is no convenient and more “fool-proof” method for a service technician to determine the state of the protection contacts inside of a sealed compressor at the external compressor electrical circuit terminals. Therefore, what is needed is a non-intrusive electronic control to inform the technician of the open or closed state of the protection contacts.
An electronic apparatus externally detects open protector contacts inside of a compressor. The compressor includes a compressor motor having a run winding and a start winding. The run winding and the start winding each have a first and a second winding connection. The first connection of both the start winding and the run winding are electrically connected together and to a common terminal (“C”). The second connection of the start winding is electrically connected to a start winding terminal (“S”) and the second connection of the run winding is electrically connected to a run winding terminal (“R”). The compressor motor also includes internal protector contacts that open the electrical circuit to the “C” terminal in a protection condition. A contactor switches power to the compressor motor, the contactor electrically connected to a source of power and to the compressor motor. A capacitor is electrically connected between the source of power and the start winding or the run winding of the compressor motor. And, a compressor running indicator circuit is electrically connected between the “S” and the “R” terminals to indicate a compressor running condition. Also, a protection indicator circuit is electrically connected between the “C” and the “S” terminals to indicate a voltage present across the “C” and the “S” terminals. The protection indicator circuit is also coupled to the compressor running indicator circuit such that the protection indicator circuit is disabled when the compressor is running normally and the protection indicator is enabled and indicates when protector contacts open inside of the compressor.
For a further understanding of these and objects of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, where:
A preferred embodiment of a non-intrusive electronic control according to the invention to indicate the state of the protection contacts (open or closed) of a HVAC compressor is shown in
We now turn to
The non-invasive (external) protector contact indication operates as follows. An indicator lamp based on half wave rectified current illumination of an LED indictor light can show when there is an AC voltage present between the compressor motor 206 “S” and “C” terminals. This voltage is present whether the compressor is running normally or the internal protection contacts are open due to a fault condition. It was realized, however, that by disabling the indicator based on the “S” “C” terminal potential (voltage) when there is an “R” “S” potential caused by normal compressor motor 206 operation, the result is an advantageous indication of the state of the otherwise inaccessible internal compressor motor protection contacts 201.
Note that the protector open LED indicator is dependant on the electrical windings in the compressor being intact. This is because when the internal compressor motor protection contacts 201 are open, the motor protection open indication circuit with its rectifier diodes, completes the indicator circuit through start winding 204 and run winding 203 to the L2 line connection. Therefore, if either start winding 204 or run winding 203 is failed “open”, the protector open LED indicator will not illuminate. Thus, where all other indications and wiring infer that a compressor should be running, but the compressor fails to operate, and the protector open LED indicator is not illuminated, the technician can further diagnose a failed compressor winding.
The operation of the non-invasive protector contact control indication is now explained in more detail. It is understood that both system line voltage is present (as optionally indicated by the “Line Voltage Indication” LED 131) and that line voltage has been applied to the compressor motor 206, such as by a compressor contactor 202, as optionally indicated by the “Contactor Closed Indication” LED 141. Compressor 206 typically comprises a start winding 203, and run winding 204, and protection contacts 201. In normal operation, protection contacts 201 are closed, applying power (line current caused by the line voltage between L1 and L2) to compressor motor 206 run winding 203 and start winding 204 via series capacitor 205a. It will be understood by those skilled in the art, that compressor motor 206 can be a motor of a type where shaft rotation is cause by the phase difference in the voltage appearing across the run winding 203 and start winding 204 caused by a capacitor such as capacitor 205a connected in series with one of the windings, most typically the start winding, as shown in
Returning to
Before proceeding to the “Hermetic Compressor Motor Protection Open Indication” section of the circuit 100, note that the connection and opto-coupler functions as described are symbolically represented on the schematic diagram of
Returning to the “Hermetic Compressor Motor Protection Open Indication” (protection indicator) section 100 of the schematic diagram of
As has been noted, the disable function in the exemplary circuit can be provided by an opto-coupler OC1, such as part number 4N27, a 6-pin package phototransistor output opto-coupler, manufactured by the Fairchild Semiconductor Corporation of South Portland, Me. Other suitable opto-couplers can be used as well. Any suitable coupler technology can also be used. While somewhat less desirable, a relay can also be used to provide the disable function.
It should also be noted that resistors have maximum voltage ratings, beyond which there can be an arc-over due to excessive voltage across them. Also, as is well known, resistors are rated for power dissipation. It can therefore be desirable for these or other reasons, to use series combinations of resistors to achieve a desired circuit resistance value. This is the case, for example, for the series combination of resistors R111 and R112. It is noted however, that a suitable valued resistor in ohms, watts, and voltage can be substituted for the series combination with no change in circuit performance. Such a substitution is unimportant to the invention.
Similarly, it is noted that the values of the components given in
Also, it should be noted that since the connections to the compressor motor are all external to the compressor, all of the circuitry of
A preferred embodiment was tested using the exemplary control board of
The following exemplary component values were used in the circuit of
R132, R133, R135, R136, R142, R143, R145, R146, R101, R105: 15 kilo ohms
R134, R144, R103, R116, R115: 1 kilo ohms
R111, R112, R114, R113: 10 kilo ohms
All diodes: 1N4007, 1A, 1,000 V, as manufactured by the On Semiconductor Corporation of Phoenix, Az.
LED: general purpose light emitting diodes
It should be emphasized that the above parts values are merely the values of parts used in a preferred embodiment of the inventive circuit and that it is not necessary to use these values to practice the invention. Moreover, one skilled in the art will note that variations of the circuit, such as using one suitably rated resistor to replace two series resistors is not important to the operation of the inventive circuit.
The internal motor protection contacts of the compressor were tripped open by short cycling the compressor. Short cycling can be done by operating the compressor motor for a period of time sufficient to build up a normal operating refrigerant pressure differential between the suction and discharge of the compressor. The compressor unit is then turned off for a short period of time so that only minimal pressure equalization occurs. Because of the short off period, when the compressor attempts to re-start, it can not start against the pressure differential, thus the internal protector contacts open due to the relatively high compressor motor load current. During this testing, before the trip condition the following indicator lamps (LEDs) were “ON”: the optional “Line Voltage Indication”, the optional “Contactor Closed Indication”, and the “Compressor Running Indication”; the “Hermetic Compressor Motor Protection Open Indication” indicator lamp was observed to be “OFF”. Following the trip of the compressor internal motor protection contacts as intentionally caused by short cycling the compressor, the following indicator lamps (LEDs) were “ON”: the optional “Line Voltage Indication”, the optional “Contactor Closed Indication”, and the “Hermetic Compressor Motor Protection Open Indication”; the “Compressor Running Indication” indicator lamp was observed to be “OFF”. This test demonstrated external detection of open protector switch contacts in a hermetically sealed compressor by use of the exemplary non-intrusive electronic control circuit shown in
While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US06/18557 | 5/15/2006 | WO | 00 | 11/5/2008 |
