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BACKGROUND OF THE INVENTION
This application relates to the art of control circuits and, more
particularly, to control circuits for electric motors. The invention is
particularly applicable for use with a capacitor start two speed motor and
will be described with specific reference thereto. However, it will be
appreciated that certain features of the invention have broader aspects
and can be used in other applications.
A motor start winding is activated to start a motor and is deactivated once
the motor is up to speed. If the motor speed decreases to a predetermined
threshold point, the start winding is reactivated until the motor is back
up to the proper speed. In motors having centrifugal switches for
activating and deactivating the start winding, the reduced motor speed at
which the start winding is reactivated is the same regardless of whether
the motor is running on the low speed winding or the high speed winding.
It would be desirable to have a control arrangement for reactivating the
start winding at different reactivating speeds depending upon whether the
motor is running on its high speed run winding or on its low speed run
winding.
When a motor is running on its low speed run winding and the start winding
is reactivated, it is desirable to deactivate the low speed run winding
and activate the high speed run winding until the motor is again up to
speed. Many arrangements have used electro-mechanical relays to perform
these control functions. It would be desirable to have an electronic
control for performing all of the control functions of the type described.
SUMMARY OF THE INVENTION
The improved electronic switching arrangements of the present application
are used in a motor control circuit that monitors a reference value
correlated to motor power supply voltage and a sensed value correlated to
motor current. The two values are compared by a comparator that changes
states to activate and deactivate the motor start winding according to
whether the sensed value is higher or lower than the reference value.
A motor control circuit includes a low speed electronic switch in series
with a low speed run winding of a motor, a high speed electronic switch in
series with a high speed run winding of the motor and an electronic start
switch in series with the motor start winding.
In a preferred arrangement, the low speed run winding is activatable only
through the low speed electronic switch. The high speed run winding is
activatable either through the high speed electronic switch or directly
through a speed selector switch. When the low speed electronic switch is
biased on, the high speed electronic switch is biased off and the speed
selector switch is in a position for activating only the low speed run
winding.
When the start winding is reactivated while the motor is running on its low
speed run winding, the low speed electronic switch is biased off and the
high speed electronic switch is biased on. The high speed run winding is
then activated through the high speed electronic switch and the low speed
setting of the speed selector switch.
A detector is provided for detecting whether the motor is running on its
low speed run winding to provide different reactivating motor speeds for
the start winding depending upon whether the motor is running on its high
speed run winding or on its low speed run winding.
It is a principal object of the present invention to provide a control
circuit having electronic switches for activating and deactivating motor
windings.
It is another object of the invention to provide a control circuit having
electronic switches for reactivating a motor start winding at different
reduced motor speeds depending upon whether the motor is running on its
high speed run winding or on its low speed run winding.
It is a further object of the invention to provide a control circuit having
electronic switches for deactivating a low speed run winding and
activating a high speed run winding when the motor start winding is
reactivated while the motor is running on the low speed run winding.
BRIEF DESCRIPTION OF THE DRAWING
FIGS. 1A and 1B are a schematic illustration of a control circuit in
accordance with the present application;
FIG. 2 is a graph showing motor current versus motor speed; and
FIG. 3 is a graph showing resistance versus temperature for a sense
resistor used in the control circuit of the present application.
DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the drawing, wherein the showings are for purposes of
illustrating a preferred embodiment of the invention only and not for
purposes of limiting same, numerals 1-7 identify the circuit lines that
are interrupted at the right side of FIG. 1A to provide a reference for a
continuation of the same lines that are identified by the same numbers 1-7
at the left side of FIG. 1B.
FIGS. 1A and 1B show a motor M connected across lines L1 and L2 of an
alternating current power supply 10 through a main switch 12 and a speed
selector switch having a high speed position 14 and a low speed position
14a.
Motor M includes a high speed run winding 16 connected across lines 1 and
L2 by lines 17, 18. A low speed run winding 19 in series with a low speed
electronic switch A is connected across lines 2 and L2 through lines 4, 18
and 20.
A start winding 21 in series with an electronic start switch B is connected
across lines L1 and L2 by lines 18 and 22. A capacitor 23 in series with
start winding 21 provides a phase displacement of approximately 90.degree.
between the start and run winding currents.
A high speed electronic switch C is connected to low speed electronic
switch A by line 3. Lines 24 and 25 connect high speed electronic switch C
to lines 1 and 2.
When the output of comparator G on line 26 goes low, pnp transistor 27 in
series with a current limiting resistor 28 is turned on and supplies
current to a photo diode 29 of an opto-isolator 30. Pnp transistor 27
inverts the output of comparator G to achieve proper operation of the
circuit. Energization of photo diode 29 turns on triac portion 32 of
opto-isolator 30 which turns on triac 33. Low speed winding 19 is then
activated through triac 33 from line 2 to line 20, triac 33, line 4 and
line 18. A current limiting resistor 31 is connected with photo diode 29.
Resistors 34 and 35 limit the gate current into triac 33 and prevent false
triggering of triac 33.
Opto-isolator 30 is used as a voltage isolator and translator between
comparator G and triac 33 because the output of comparator G on line 26
and the input to triac 33 on line 36 are at incompatible electrical
potentials.
Low speed electronic switch A is connected by line 3 through a current
limiting resistor 37 to triac 38 of high speed electronic switch C. Triac
38 is connected through current limiting resistor 39 to high current triac
40. Current limiting resistors 41 and 42 cooperate with current limiting
resistors 37 and 39 for limiting current to triacs 38 and 40, and help to
prevent false triggering.
When low speed electronic switch A is on, the current through triac 33 to
triac 38 on line 3 forces triac 38 to its off state. Therefore, high speed
electronic switch C is always off when low speed electronic switch A is
on. When low speed electronic switch A is off, high speed electronic
switch C is always on.
With the speed selector switch in low speed position 14a, motor M is
running on low speed run winding 19 through electronic switch A and the
output of comparator G is low. If the motor slows down to a start winding
reactivation speed, the output of comparator G on line 26 goes high and
turns transistor 27 off to deactivate low speed electronic switch A which
in turn deactivates low speed run winding 19. At the same time, high speed
electronic switch C turns on because there is no longer a current on line
3 forcing triac 38 to its off state. Therefore, high speed winding 16 is
connected in series with high speed electronic switch C through low speed
switch setting 14a of the speed selector switch, line 2, line 25, triac
40, line 24, line 1 and line 17. Both start winding 21 and high speed run
winding 16 are then active for accelerating motor M back up to the proper
speed. Once the motor is back up to speed, the output of comparator G on
line 26 again goes low to turn on low speed electronic switch A, and turn
off electronic start switch B and high speed electronic switch C. The
motor then returns to running on low speed run winding 19.
Electronic start switch B includes current limiting resistors 43, 44 and 45
that also help prevent false triggering of logic triac 46 and high current
snubberless triac 47. Electronic start switch B is connected with output
line 26 of comparator G by lines 5 and 154. When the output of comparator
G on line 26 is low, electronic start switch B is off. When the output of
comparator G on line 26 goes high, logic triac 46 of electronic start
switch B turns on to also turn on high current snubberless triac 47. Start
winding 21 is then activated through line 22, triac 47 and line 18.
High speed electronic switch C is connected in series with high speed run
winding 16 only when the speed selector switch is in its low speed setting
14a. The circuit through high speed electronic switch C to high speed run
winding 16 is interrupted when the speed selector switch is in high speed
position 14 because line 2 is disconnected from line L1.
With the speed selector switch in its high speed position 14, high speed
run winding 16 is directly connected across lines 1 and L2 through lines
17 and 18. Thus, there are two alternative paths for activating high speed
run winding 16. Low speed run winding 19 and low speed electronic switch A
are always deactivated when electronic start switch B and start winding 21
are activated.
When the speed selector switch is in solid line high speed position 14
connecting line L1 to line 1 for operating motor M on high speed run
winding 16 through line 17, the control circuit turns electronic switch B
on and off to activate and deactivate start winding 42 for maintaining
proper motor speed. Electronic switch A is inoperative under these
circumstances because line 2 is open circuited with the speed selector
switch in high speed position 14. High speed electronic switch C is
likewise inoperative because of open line 2.
The control circuit of the present application reactivates start winding 21
at different reduced motor speeds depending upon whether the motor is
running on high speed run winding 16 through high speed position 14 of the
speed selector switch or on low speed run winding 19 through low speed
position 14a of the speed selector switch. This is accomplished in part by
providing a low speed run winding detector D for determining whether low
speed run winding 19 is active.
Low speed run winding detector D is connected by line 7 to line 4 between
low speed electronic switch A and low speed run winding 19. When low speed
electronic switch A is turned on and a voltage greater than 90 volts ac is
present at the connection of line 7 to line 4, the resulting dc voltage
provided by detector D at positive input 50 to comparator 52 exceeds the
voltage at negative input 54 to comparator 52, and the output of
comparator 52 goes high. This adjusts the circuit for reactivating the
start winding at a lower motor speed than when motor M is running on its
high speed run winding. This aspect of the control circuit will be
described in more detail as the description proceeds.
Low speed run winding detector D includes resistors 56, 58 that form a
voltage divider for reducing the magnitude of the line voltage to a
certain desired value. Diode 60 rectifies line voltage into a positive
pulsating dc voltage and is in series with a current limiting resistor 62.
A zener diode 64 clamps the desired dc voltage value. Capacitor 66 filters
the positive pulsating voltage into a steady dc voltage, and resistor 68
provides a controlled discharge path for filter capacitor 66. Diode 70 and
resistor 72 provide a path for rapid discharge of capacitor 66 when low
speed electronic switch A is turned off.
A sense resistor 80 is connected in series with motor M in line 18. In one
arrangement, the sense resistor is a short length of wire. A preferred
example that has been tested is a 15-inch length of 18 gauge copper wire,
with the wire gauge corresponding to American Wire Gauge Standards. The
current running through motor M correlates to the rotational speed of the
motor as shown in the graph of FIG. 2. The motor current also runs through
sense resistor 80, and measuring the voltage drop across sense resistor 80
is a way of measuring motor current or a value that is correlated to motor
current. Because the voltage drop correlates to motor current which in
turn correlates to motor speed, the voltage drop also correlates to motor
speed.
It will be recognized that the sense resistor could be of other metals,
gauges and lengths, and that other kinds of sense resistors could be used.
The sense resistor preferably is positioned inside the motor housing in
close proximity to the motor windings for exposure to approximately the
same temperature environment as the motor windings. However, it will be
recognized that the sense resistor can be positioned in other locations,
including outside of the motor housing, as long as the sense resistor is
in approximately the same temperature environment as the motor and motor
windings.
The motor current changes with variations in the temperature of the motor
windings. However, motor current changes that are due solely to
temperature variations do not appreciably affect motor speed. A control
circuit that is sensitive to such changes in motor current could interpret
them as motor speed changes and significantly contribute to inaccuracies
in the motor rpm trip points at which the start winding is activated and
deactivated.
The resistance of sense resistor 80 varies with temperature and is
positioned for exposure to substantially the same temperature environment
as the motor windings. This provides automatic compensation for current
changes that are due to temperature variations because the current
decreases with increasing resistance in accordance with Ohms law which
states that V=IR, where V is the voltage, I is the current and R is the
resistance. Therefore, the voltage drop across sense resistor 80 remains
substantially constant with changes in motor current that are caused
solely by temperature variations in the motor windings and that do not
appreciably affect motor speed.
A line 84 connected at point 86 on the opposite side of sense resistor 80
from motor M terminates in an arrowhead 88 to designate a reference
potential. All of the other arrowheads in the circuit of FIG. 1 are
referenced to the same potential as arrowhead 88.
Line 6 is connected at point 90 between motor M and sense resistor 80, and
to positive input 92 of operational amplifier 94 in amplifier E. The
voltage across sense resistor 80 is amplified by amplifier E for
conversion to a dc voltage. The input voltage at positive input 92 to
operational amplifier 94 is a sine wave in the millivolt range and the
output is a positive pulsating dc voltage in the single digit volt range.
Amplifier E includes an impedance matching resistor 96, and resistors 98,
100 that set the amount of voltage gain provided by the amplifier.
A peak detector F is connected by line 102 to the output of amplifier E and
converts the pulsating positive dc voltage from amplifier E to a steady dc
voltage. The magnitude of the steady dc voltage is close to the peak of
the pulsating dc voltage from amplifier E and correlates to the speed of
motor M. Peak detector F includes a capacitor 104 that filters the
positive pulsating dc voltage into a steady dc voltage, and a diode 106
prevents capacitor 104 from discharging back into amplifier E. Resistor
108 provides a controlled discharge path for capacitor 104, and zener
diode 110 clamps the desired dc voltage value. Input impedance matching
resistor 112 is in line 114 connecting the output of peak detector F to
the positive input of comparator G.
The negative input of comparator G is connected by line 120 with voltage
reference H that in turn is connected by line 122 to lines 1 and 2 through
diodes 124, 126. Voltage reference H includes resistors 130, 132 that form
a voltage divider for reducing the magnitude of line voltage to a
reference voltage value. The reference voltage provided by voltage
reference H to the negative input of comparator G varies in magnitude with
variations in the magnitude of line voltage so that the ratio of the
reference voltage to line voltage remains substantially constant.
Variations in the magnitude of line voltage also cause changes in motor
current and this in turn causes changes in the voltage drop across sense
resistor 80 that are substantially proportional to the changes in the
reference voltage. This provides the control circuit with automatic
compensation for changes in motor current caused by line voltage
variations because increases and decreases in the reference voltage are
substantially matched by corresponding increases and decreases in the
voltage drop across sense resistor 80. This improves the accuracy of the
motor rpm trip points at which the start winding is deactivated and
reactivated. The actual motor rpm trip points do not deviate by more than
around plus or minus 150 rpm from the optimum motor rpm trip points.
Voltage reference H includes a diode 134 that rectifies the sine wave into
a positive pulsating dc voltage. Capacitor 136 filters the positive
pulsating dc voltage into a steady dc voltage, and resistor 138 provides a
controlled discharge path for capacitor 136.
Adc power supply J connected to lines 1 and 2 converts ac line voltage to
adc power supply for circuit components requiring adc voltage. Adc voltage
140 provided by dc power supply J is connected to other circuit components
as indicated at 140a, 140b, 140c, 140d, 140e and 140f. Power supply J
includes a diode 144 that rectifies line voltage into a positive pulsating
dc voltage. Capacitor 146 filters the positive pulsating voltage into a
steady dc voltage at 140, while zener diode 148 clamps the desired dc
voltage value. A resistor 150 in series with diode 144 is a current
limiting and voltage dropping resistor.
An inverter K is provided to invert the output of comparator G by use of an
inverting comparator 152. Line 154 connects the output of comparator G to
the negative input 156 of inverting comparator 152 through an impedance
matching resistor 158.
Output line 160 from inverting comparator 152 is connected by line 162 to
negative input line 120 of comparator G. Positive input line 164 of
inverting comparator 152 includes a current limiting resistor 166 and an
impedance matching resistor 168. Zener diode 170 clamps the positive input
to a desired dc voltage value and sets the reference voltage for inverter
K.
When the output of comparator G goes low, the connection through line 154
to the negative input at 156 of inverting comparator 152 drops below the
regulated reference positive input at 164 and causes the output of
inverting comparator 152 to go high. Capacitor 172 in line 162 provides
hysteresis and pulls the negative input to comparator G higher when the
output of inverter K goes high. This helps to prevent chattering of
comparator G during switching, i.e., when comparator G changes between its
high and low states. When the output of inverter K goes low, capacitor 172
pulls the negative input to comparator G lower and helps prevent
chattering of comparator G when it changes to its opposite state.
A start winding gain adjuster P is provided for adjusting the gain of
amplifier E when the start winding is inactive. When motor start winding
21 is active, there is a different correlation between motor current and
motor speed compared to when start winding 21 is inactive as shown in the
graph of FIG. 2. The purpose of gain adjuster P is to adjust the gain of
amplifier E for achieving proper motor rpm and motor current switching
points for activating and deactivating start winding 21.
When comparator G goes high to activate start winding 21, npn transistor
180 of gain adjuster P is off because the input voltage on line 154 to
negative input 156 of inverting comparator 152 is higher than the
reference voltage to positive input 164 and the output on line 160 goes
low. Under these conditions, gain adjuster P is inoperative while start
winding 21 is active so there is no adjustment in the gain of amplifier E.
The output of comparator G goes low to deactivate start winding 21, and the
reference voltage on line 154 to negative input 156 of inverting
comparator 152 is below the reference voltage at positive input 164. This
causes the output of inverting comparator 152 to go high and turns on
transistor 180 through current limiting resistor 184 connected with the
base of the transistor. Resistor 182 of gain adjuster P is then connected
in parallel with resistor 100 of amplifier E to provide a higher gain for
amplifier E due to the relationship between resistors 100 and 182. When
transistor 180 is off, resistor 182 has no effect on amplifier E.
A low speed run winding gain adjuster R is connected to the output of low
speed detector D and the negative input 190 of operational amplifier 94.
When electronic switch A is on for operating motor M on its low speed run
winding 19, the relationship between motor current and motor speed changes
as shown in FIG. 2. Gain adjuster R adjusts the gain of amplifier E when
low speed run winding 24 is active to obtain proper motor rpm and motor
current switching points. The switching points being the motor rotational
speeds and motor currents at which the start winding is reactivated and
deactivated.
When low speed electronic switch A is on with the speed selector switch in
low speed position 14a for running motor M on low speed run winding 19,
the voltage at positive input 50 of comparator 52 is larger than the
reference voltage at negative input 54. Therefore, the output of
comparator 52 on line 200 through current limiting resistor 202 goes high
and turns npn transistor 204 on. This connects resistor 206 in parallel
with resistor 100 in amplifier E to provide a higher voltage gain due to
the relationship between resistors 100, 206.
When the motor speed selector switch is in solid line high speed position
14, or when low speed electronic switch A is off, low speed detector D
detects a voltage less than 90 volts ac on the connection of line 7 to
line 4. Therefore, the voltage at positive input 50 of comparator 52 is
less than the reference voltage at negative input 54, and the output of
comparator 52 goes low so that transistor 204 remains off and gain
adjuster R has no effect on amplifier E when the low speed winding is
inactive.
The output of comparator G goes high when the control circuit calls for
activation of the start winding. Logic triac 46 of electronic start switch
B is then turned on through the connection between lines 5 and 154 to
comparator output line 26. When logic triac 46 turns on, this also turns
on high current snubberless triac 47 to activate start winding 21.
The sensed value provided by the voltage drop across sense resistor 80 is
constantly monitored, and amplifier E along with peak detector F provide a
sensed value input to the positive input of comparator G. A reference
value is provided to the negative input of comparator G from reference
voltage H that monitors line voltage. When the positive input sensed value
to comparator G from amplifier E and peak detector F is larger than the
negative input reference value to comparator G from voltage reference H,
the output of comparator G goes high and this turns on electronic start
switch B to activate start winding 21.
The magnitude of the output from peak detector F correlates to motor
current because the voltage drop across sense resistor 80 correlates to
motor current which in turn correlates to motor speed as shown in FIG. 2.
The magnitude of the reference voltage provided by voltage reference H to
the negative input of comparator G correlates to the magnitude of line
voltage. These relationships provide improved accuracy in the motor rpm
trip points at which start winding 21 is reactivated or deactivated when
changes in motor current are caused by line voltage variations.
When motor M is turned on with the motor speed selector switch in its solid
line high speed position 14, the current running through high speed run
winding 16 increases until the voltage drop across sense resistor 80 is
sufficient for amplifier E and peak detector F to provide a positive input
sensed value to comparator G that causes comparator G to go high.
Electronic switch A is inactive because it has no power supply through
line 2 when the motor speed selector switch is in its solid line high
speed position 14. Comparator G going high also turns on electronic switch
B to activate start winding 21. The motor then ramps up to speed with both
high speed run winding 16 and start winding 21 active.
When comparator G goes high to activate the start winding, the output of
inverter K goes low to turn gain adjuster P off so that the circuit
automatically compensates for the higher motor current due to both high
speed run winding 16 and start winding 21 being active. The current
through high speed run winding 16 and start winding 21 decreases as the
motor reaches its desired predetermined rotational speed. The sensed value
provided by the voltage drop across sense resistor 80 also decreases with
decreasing motor current until the positive input at 114 to comparator G
from amplifier E and peak detector F falls below the reference voltage to
negative input 120 of comparator G and causes the output of comparator G
to go low. This turns off electronic switch B and deactivates start
winding 21. This also causes the output of inverter K to go high and turns
on gain adjuster P.
If the rotational speed of the motor slows down, the motor will draw more
current and the voltage drop across sense resistor 80 will again increase
until the positive input to comparator G from amplifier E and peak
detector F is once more sufficient to turn on electronic start switch B
for reactivating start winding 21.
When motor M is turned on with the motor speed selector switch in its low
speed position 14a, the output of comparator G is low and electronic
switch A is on to activate low speed run winding 19. Low speed detector D
detects the voltage on line 4 through line 7 and the output of comparator
52 in detector D goes high to activate low speed gain adjuster R. At the
same time, current through low speed run winding 19 and sense resistor 80
increase until the voltage drop across sense resistor 80 provides an input
to comparator G from amplifier E and peak detector F to cause the output
of comparator G to go high. Gain adjuster R adjusts the gain of amplifier
E to account for different currents running through motor M depending upon
whether high speed run winding 16 or low speed run winding 19 is active.
Gain adjuster R is inactive when low speed run winding 19 is inactive.
With low speed run winding 19 active and the output of comparator G going
high to activate start winding 21 through switch B, electronic switch A is
turned off and high speed electronic switch C is on. This deactivates low
speed run winding 19 and activates high speed run winding 16. Both gain
adjusters P and R are turned off. The motor then ramps up to speed on high
speed run winding 16 and start winding 21. When motor M reaches its
desired predetermined rotational speed, the current running through the
motor decreases until the voltage drop across sense resistor 80 is low
enough to provide a positive input to comparator G from amplifier E and
peak detector F that is less than the negative input from the voltage
reference and causes the output of comparator G to go low. This turns on
electronic switch A which then biases high speed electronic switch C off
to reactivate low speed run winding 19 through switch A and deactivate
high speed run winding 16. The output of comparator G going low also opens
electronic switch B to deactivate start winding 42, and both gain
adjusters P and R are turned on. The motor will then run on low speed run
winding 19 alone unless the motor slows down sufficiently to provide a
current through low speed run winding 19 and sense resistor 80 resulting
in a voltage drop that drives the output of comparator G high.
The motor has three different operating conditions. The first condition is
when both high speed run winding 16 and start winding 21 are active. In
this condition, both gain adjusters P and R are inactive. This condition
corresponds to curve 250 of FIG. 2 when the motor current is highest and
the voltage drop across sense resistor 80 is largest. The second condition
is when only the low speed run winding is active. In this condition, both
gain adjusters P and R are active. This condition corresponds to curve 262
of FIG. 2 when the motor current is lowest and the voltage drop across
sense resistor 80 is smallest. Under this condition, amplifier E is
provided with the highest gain. The third condition is when only the high
speed run winding is active. In this condition, gain adjuster P is active
and gain adjuster R is inactive. Thus, amplifier E has less gain than in
the second motor run condition. This third condition corresponds to curve
260 in FIG. 2 when the motor current is intermediate the motor current in
the other two motor run conditions.
With reference to FIG. 2, when the motor is running on only the low speed
run winding as represented by curve 262, both the low speed gain adjuster
R and the start gain adjuster P are on to provide amplifier E with its
greatest gain. When the motor is running on only the high speed run
winding as represented by curve 260, low speed gain adjuster R is off and
start gain adjuster P is on so that amplifier E has an intermediate gain.
When the motor is running on both the start and high speed run windings as
represented by curve 250, both of gain adjusters P and R are off and
amplifier E has its lowest gain that is built into it with no boost from
either gain adjuster P or R.
When the output of comparator G goes high, both start winding 21 and high
speed run winding 16 are activated, low speed run winding 19 is
deactivated and gain adjusters P and R are turned off. When the output of
comparator G goes low, start winding 21 is deactivated, gain adjuster P is
turned on and the motor continues to run on either high speed run winding
16 or low speed run winding 19 depending on the position of speed selector
switch 14, 14a. Comparator G going low will turn on gain adjuster R if the
speed selector switch is in position 14a for the low speed run winding,
and will leave gain adjuster R off if the speed selector switch is in
position 14 for the high speed run winding.
The output of comparator G goes high in response to higher motor currents
running through sense resistor 80, and goes low in response to lower motor
currents running through sense resistor 80.
With reference to FIG. 2, curve 250 shows the correlation between motor
speed and motor current when both the start winding and the high speed run
winding are active. At a motor speed of around 1,250 rpm, the start
winding is deactivated and the motor current drops off as indicated by
horizontal arrow lines 252, 254. The motor continues to run on only the
high speed run winding represented by curve 260 or the low speed run
winding represented by curve 262.
When the start winding is deactivated at a speed of around 1,250 rpm and
the motor continues to run on only the high speed run winding, the motor
speed continues to ramp up to an operating speed of around 1,600-1,800
rpm.
When the start winding is deactivated at a motor speed of around 1,250 rpm
and the motor continues to run on only the low speed run winding, the
motor speed ramps down slightly to an operating speed of around
1,000-1,200 rpm.
With the motor running on only the hi | | |
