Note: Descriptions are shown in the official language in which they were submitted.
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A Compressor Motor ~nit and A Method of
Troubleshooting Power Supply Circuits Therefor
This invention generally relates to compreæsor motor units,
particularly hermetically or semi-hermetically sealed motors, and
more specifically to a method of troubleshooting power supply
circuits therefor.
The utilization of electrically driven motor-compressor units
which are enclosed within hermetically or semi-hermetically sealed
shells has become increasingly prevalent in recent years,
particularly in refrigeration applications wherein the motor-
compressor unit is employed to compress a refrigerant vapor. Inmany of these motor-compressor units, the electric power supply
circuit for the-motor includes a switch responsive-to motor
conditions such as temperature or current. This switch, generally
referred to as an internal line break switch, is positioned within
the sealed shell and is typically directly secured to the motor.
The internal line break switch is electrically located between the
motor nnd an electric current source, and the switch is normally
closed for conducting current from the source to the motor.
However, if the switch senses the development of an undesirable
condition such as excessive motor temperature, the switch opens,
disconnecting the motor from the electric current source and
thereby terminating operation of the motor. When the undesirable
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condition is alleviated, the internal line break switch recloses,
allowing the motor to restart.
Because the internal line break switch is located within the
hermetically or semi-hermetically sealed shell, it may be
difficult to determine whether the switch is open or closed.
Under certain circumstances, this may make it difficult for a
mechanic or serviceman to determine why a motor is not operating.
For example, if the motor is not operating while external factors
appear to indicate it should be operating, the internal line break
switch may be closed and the motor inoperative because it is
defective. Alternately, the motor may not be operating only
because the internal line break switch is open. In the vast
majority of cases, most servicemen and mechanics are quickly able
to correctly determine why a motor is not operating. However,
occasionally mistakes are made. For example, a mechanic may
conclude that a motor is not operating because it is defective
when in fact the motor is not defective but is not operating only
because the internal line break switch is properly, temporarily
terminating operation thereof. On the basis of this mistaken
conclusion, the mechanic may return the motor to the manufacturer
for repair or replacement, causing an unnecessary inconvenience to
all parties involved and a waste of time, money, and other
resources.
In accordance with teachings of the present invention, these and
other prior art difficulties may be overcome with a compressor
motor unit comprising an electric motor, a shell enclosing the
motor, and an electric power supply circuit. The power supply
circuit includes electrically conductive conduit means for
connecting the motor to a source of electric current, a switch
positioned within the shell and electrically located in the
conduit means, the switch changing from a closed, current
conductive state to an open, current non-conductive state to
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selectively terminate operation of the motor, and a bypass circuit
for conducting current around the switch and through the motor.
This invention will now be described, by way of example, with
reference to the accompanying drawing which is a schematic
representation of a compressor motor unit employing teachings of
the present invention.
Referring to the drawing, there is depicted a schematic
representation of electric power supply circuit 10. Circuit 10
connects electric compressor motor 12 to a source of electrical
energy, represented in the drawing by lines L1 and L2. As will
become apparent to those skilled in the art, the present invention
may be employed with numerous types of electric motors. In the
preferred embodiment illustrated in the drawing, though, motor 12
is a single phase induction motor including main or run winding 14
and auxiliary or start winding 16, with the windings 14 and 16
electrically located in parallel with respect to each other.
Also, as will be obvious to those skilled in the art, circuit 10
and motor 12 may be used with numerous types of electric energy
sources. One suitable type, for example, provides an alternating
current of approximately 230 volts with a frequency of about 60
Hert~.
Circuit 10 includes lines ~3, L4, L5, and L6, with start switch 18
located in line L3, capacitor 20 positioned in line L4, resistor
22 located in line L5, and normally closed internal line break
switch 24 positioned in line L6. Preferably, supply circuit 10
includes a plurality of additional devices not shown in the
drawing. For example, circuit 10 may include thermostatic
switches, indicator lights, and safety switches such as a low oil
pressure cutout switch. Such devices are well known in the art,
and they have been omitted from the drawing for the sake of
clarity.
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Referring back to the illustration of the drawing, run winding 14
is connected to electrical energy source Ll, L2 via lines L3 and
L6, and start winding 16 is connected to the electrical energy
source via lines L3, L4, and L6. With this arrangement, closure
of start switch 18 connects motor 12, specifically windings 14 and
16 thereof, across lines L1 and L2, thereby starting the motor.
As is well known in the art, capacitor 20 produces a phase
difference between the currents passing through run and start
windings 14 and 16, increasing the torque produced thereby. Motor
12 is enclosed within shell 26, and preferably the motor is
hermetically or semi-hermetically sealed within the shell.
Internal line break switch 24 is also located within shell 26.
Preferably, switch 24 is physically directly secured to motor 12
and senses one or more parameters thereof such as current or
temperature. As mentioned above, internal line break switch 24 is
normally closed, however, if the switch senses the development of
an unsatisfactory condition, for example excessive motor
temperature, the switch opens.
As explained earlier, with prior art compressor motor units of the
general type described above, when the internal line break switch
opens, the compressor motor is disconnected from the electric
current source and operation of the motor is temporarily
terminated. Also, as previously discussed, with this typical
prior art arrangement a serviceman or mechanic may occasionally
have some difficulty learning why a motor is not operating.
Specifically, it may be difficult to determine if the line break
switch is open. In light of this, circuit 10 of the present
invention includes a bypass circuit, specifically line L5 and
resistor 22, for conducting a current around switch 24 and through
motor 12. More particularly, resistor 22 is located in line IS
electrically in parallel with switch 24, and preferably the
resistance of resistor 22 is sufficiently great, for example
lO,000 or 15,000 ohms, so that the magnitude of the current flow
therethrough, while measurable, is less than the magnitude
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necessary to operate motor 12. With this arrangement, when only
switch 24 is open, motor 12 is temporarily rendered inoperative,
but circuit 10 is still complete and current passes therethrough.
This fact may be advantageously employed by a serviceman or
mechanic to facilitate troubleshooting circuit 10. More
specifically, if a cause located in circuit 10 prevents motor 12
from operating, a mechanic can test to determine if this cause is
an open internal line break switch 24. This troubleshooting test
is made by connecting circuit 10 to a current source, for example
source Ll, L2 may be used or a test current source having a much
lower voltage may be used. Then the mechanic measures the
magnitude of current passing through resistor 22. If this
magnitude is greater than zero, then circuit 10 is complete and
the probable cause for the inoperative motor 12 is only an open
switch 24. However, if the measured current magnitude is zero,
then circuit 10 is broken and it is highly probable that a cause
other than an open switch 24, for example a defective motor 12 or
a break in line L6, prevents the motor from operating.
It should be noted that electric lines (not shown) may extend from
each end of resistor 22 to the exterior of shell 26 to allow an
easy, direct measurement of the current passing through the
resistor. Preferably, however, this current is indirectly
measured by simply measuring the current through lines L3 and L6.
As will be appreciated by those skilled in the art, if a break in
circuit 10 or an open switch 24 prevents motor 12 from operating,
the magnitude of the current passing through lines L3 and L6 .
equals the magnitude of the current passing through resistor 22.
Moreover, in practice, it may be easier to measure the resistance
of circuit 10 instead of the current passing therethrough or
through resistor 22. As will be apparent to those skilled in the
art, if the sole cause for an inoperative motor 12 is an open line
break switch 24, the resistance of circuit 10 substantially equals
the resistance of resistor 22. In contrast, in the huge majority
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of other cases where a cause in circuit 10 prevents motor 12 from
operating, the resistance of the circuit is essentially infinite.
The above-described current and resistance tests are quick, highly
reliable, and simple to understand and apply. In many
circumstances the tests reduce the time needed by a mechanic to
locate the reason why a motor is not operating. This, in turn,
decreases the cost of troubleshooting a non-operating motor and
increases the productivity of the mechanic. Moreover, the present
invention improves the accuracy of the troubleshooting process.
Specifically, the present invention enables a mechanic to identify
with a high degree of reliability those situations where a motor
is not operating only because of an open line break switch. Thus,
the possibility is greatly reduced that a mechanic will mistakenly
believe a defect in the power supply circuit or motor prevents
operation thereof while the fact is only the internal line break
switch is open. Hence, the present invention may be effectively
employed to reduce the number of motors erroneously returned to
the manufacturer for repair or replacement. This eliminates, for
example, much of the heretofore wasted time, money, and effort of
the manufacturer devoted to checking properly functioning units
that are mistakenly alleged to be defective.
While it is apparent that the invention herein disclosed is well
calculated to fulfill the objects above stated, it will be
appreciated that numerous modifications and embodiments may be
devised by those skilled in the art, and it is intended that the
appended claims cover all such modifications and embodiments as
fall within the true spirit and scope of the present invention.
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