CA1178657A - Control circuit for reducing hum in split phase electric motors - Google Patents
Control circuit for reducing hum in split phase electric motorsInfo
- Publication number
- CA1178657A CA1178657A CA000373722A CA373722A CA1178657A CA 1178657 A CA1178657 A CA 1178657A CA 000373722 A CA000373722 A CA 000373722A CA 373722 A CA373722 A CA 373722A CA 1178657 A CA1178657 A CA 1178657A
- Authority
- CA
- Canada
- Prior art keywords
- transistor
- motor
- emitter
- collector
- control circuit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P1/00—Arrangements for starting electric motors or dynamo-electric converters
- H02P1/16—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters
- H02P1/42—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor
- H02P1/44—Arrangements for starting electric motors or dynamo-electric converters for starting dynamo-electric motors or dynamo-electric converters for starting an individual single-phase induction motor by phase-splitting with a capacitor
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
- H02P25/04—Single phase motors, e.g. capacitor motors
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Ac Motors In General (AREA)
- Control Of Motors That Do Not Use Commutators (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
The annoying, audible hum which is usually encountered during low speed operation of a permanent split capacitor motor is substantially eliminated by a control circuit which is connected in series with one of the motor's windings. In the illustrated embodiment the circuit comprises an NPN transistor having its emitter-collector circuit connected in series with the motor capacitor, and auxiliary winding.
The transistor collector terminal is connected, during motor operation, to one side of an AC power supply and through a fixed resistor to the transistor and through a potentiometer and a fixed resistance to the emitter.
By adjusting the potentiometer to vary the resistance in the emitter-base circuit the current flow in the emitter-collector circuit can be controlled to vary the speed of the motor,
The annoying, audible hum which is usually encountered during low speed operation of a permanent split capacitor motor is substantially eliminated by a control circuit which is connected in series with one of the motor's windings. In the illustrated embodiment the circuit comprises an NPN transistor having its emitter-collector circuit connected in series with the motor capacitor, and auxiliary winding.
The transistor collector terminal is connected, during motor operation, to one side of an AC power supply and through a fixed resistor to the transistor and through a potentiometer and a fixed resistance to the emitter.
By adjusting the potentiometer to vary the resistance in the emitter-base circuit the current flow in the emitter-collector circuit can be controlled to vary the speed of the motor,
Description
CONTROL CIRCUIT FOR REDUCING AC HUI!~ IN SPLIT
PH~SE ELECTRIC MOTORS
This invention relates to an improved control circuit for con-trolling the speed of split phase electric motors, and more particularly to a circuit which permits operation of permanent split phase capacitor motors at low speeds without any objectionable AC hum.
There are numerous appliances in the modern-day household which are operated by small, split phase electric motors of the fractional horsepower variety. Many such items (for example, refrigerators, exhaust fans, ceiling fans, etc.) are within earshot of the members of the household, when in use, and it is therefore most desirable that their associated motors operate - as quietly as possible.
One of the principal problems heretofore encountered in connection with electric motors of the type described is that, when used with electronic speed controls~ and particularly at lower speeds, they tend to develop an objectionable hum, which can be very distressing to any one within hearing distance of the motorn Efforts have been made in the past to minimi~e signal distor-tion inherent in electronic speed controls and consequent undesirable humming during low speed operation of motors of the type described, but such efforts have not proved to be successful.
It is an object of this invention, therefore, to provide an improved motor control circuit which substantially eliminates any objectionable hum heretofore encountered during low speed operation of split phase motors of the type described.
Another object of this invention is to provide for motors of the type described an improved, adjustable control circuit which/relatively simple and inexpensive to manufacture, and which is capable of operating fractional (and larger) horsepower motors at variable speeds, and with a minimum of signal distortion and substantially no undesirable hum.
: "
`^"`` 3~:17iS~7 A more speci~ic .objec~ of this invention is to provi.de for a permanent split phase c~pacitor motox an improved speed control circuit wh.ich permits ope~ation of the motor a~ variable speeds, but without an~ undesirable signal distortion or humO
Accordingly, the present invention provides a control circuit for a variable speed, permanent split phase capacitor mo-tor of the type having a main stator winding, an aux;.liary stator winding, and a capacitor connected in series with said auxiliary winding, means for substantially eliminating signal distortion and consequent audible hum from the motor during low speed opera-tion thereof, comprising, a transistor with a base and main elec-trodes consisting of a collector and emitter, having its emitter=
collector circuit connected in series with said auxiliary winding for supplying power thereto from an ~C power supply, means for connecting one of the main electrodes of said transistor to one side of the AC power supply~ and to the base of said transistor, and a ~irst variable resistor connected between the base and the other main electrode of said transistor, and adjustable to control the r~rrent flow through the emitter-collector circuit of said transistor during operation of said motor and thereby the current flow through said auxiliary winding.
Other objects of the invention will be apparent herein-after from the specification and from the recital o~ the appended claims, particularly when read in conjunction with the accompany-ing drawing.
In the drawing;
Fig. 1 is a wiring diagram illustratiny the windings of a conventional permanent split phase capacitor motor, together with a control circuit made according to one embodiment of this invention, and shown connected in series with the auxiliary wind-ing of the motor to permit operation .thereof at ~Jariable low speeds; and -~\
'7 Fig. 2 is a wiring diagram illustrating this control in greater detail.
Referrin~ now *o the drawing by numerals of reference, and first to Fig. 1, Wl and W2 represent the main and auxiliary windings, respectively, of a conventional permanent split capa-citor motor, which is of the type that is frequently employed to drive household ceiling fans, exhaust fans, etc. Opposite ends of the main winding Wl are connected by lines Ll and L2 to one side of a conventional On-Off switch Sl, the opposite side of which is connected to an AC power supply, which may be of the usual 120 Volt, 60 Hertz household variety.
The auxiliary winding W2 is connected between lines Ll and L2 in parallel with the main winding Wl, and in series with a capacitor Cl and a control circuit 10, by means of a line L3 which connects one end of winding W2 to line L2, by a line L4 - 2a ~P7B65~ , which connects the opposite end of winding W2 to one side of the capacitor Cl, by a line L5 connecting -the opposite side of the capacitor Cl to the control circuit 10, and by a Iine L6 which connects circuit 10 to L1. As a consequence, when switch Sl is closed, the control circuit 10, the capacitor Cl and auxiliary winding W2 are connected in series across the AC
power supply. Also at this time, of course, the winding Wl will also be connected directly across the power supply.
Referring now to Fig. 2, the control circuit 10 comprises an NPN power transistor 21, which has its emitter connected directly to line L5, it collector connected directly to line L6, and its base connected by a line 22 to the movable contact P of a 100 ohm potentiometer (pot) having a variable resistance R1. The fixed or æero end of the pot resistance Rl is connected by a line L8 to one end of a fixed resistor R2, the opposite end of which is connected to line L5, thereby placing resistor R2 in the emitter-base circuit of the transistor 21. Line 22 is also connected through another fixed resistor R3 and a line L9 to line L6~ so that resistor R3 is in the collector-base circuit of the transistor. By way of e~ample, ~he resistor R2, may have a valueof approximately twenty-seven ohms, while resistor R3 has a much larger value, for example, in the vicinity of fifteen thousand ohms.
In operation, and assuming that -the switch Sl is closed, the pot contact P can be adjusted manually to control the value of Rl, and consequently the forward biasing voltage that is developed across the emitter-base circuit of -the transistor 21. In turn, this permits manual control of the current flow through the emitter-collector circuit. For example, assuming that the adjustable pot contact P is moved toward the left in Fig. 2 to reduce the value of the resistance Rl placed in the circuit, then the forward biasing voltage between the base and ~ 6S'7 the emitter will be reduced, thereby reducing the current flow through the emitter-collector circuit. At this stage the transistor 21 functions as a high resiStance in parallel with R2 and R3 between lines L5 and ~6. This, in turn, reduces current flow through winding W2.
On the other hand, as the movable pot contact P
is moved toward the right Fig. 2, so as to increase the value of resistance Rl, the voltage drop between the base and the emitter will increase, and thereby effectively will increase the current flow in the emitter-collector circuit. This permits the transistor 21 to function more nearly as a short circuit and allows most of the current flow to take place through the emitter-collector circuit of the transistor, rather than through the hi~h resistance circuit represented by R3, Rl, and R2.
At intermediate settings oE the pot contact P the transistor 21 acts as a variable resistance between ~he emitter and collector, either lncreasing or decreasing the fcrward biasing voltage between the emitter and the base, depending upon the position of the movable contact P of the pot. The feedback resistor R3 and the biasing resistor R2 tend to stabilize the operation of the control circuit.
In practice it has been found that this control circuit provides relatively simple and inexpensive means for controlling the intermediate speed ranges of the motor repre-sented by the windings Wl and W2. For low speed operation of the associated motor, the pot is adjusted $o that the resistance Rl is almost negligible, thus switching the transi9tor 21 almost to its blocking mode. This causes a decrease in current through W2 which causes a decrease in motor tor~ue. On the other hand, as the pot is adjusted to increase the resistance of Rl, thereby causing a corresponding increase in the current flow in the emitter-collector circuit of the transistor 21, the current flow through the au~ialiary winding W2 increases which ~ s~i causes an increase in motor tor~ue and thereby causirlg a pro-gressive speeding up of the motor. In all such operations, however, the control circuit 10 tends to minimize, if not substantially to eliminate signal distortion and the consequent audible hum which heretofore tended to accompany the intermediate and low speed operations of permanent split capacitor motors of the type des-cribed.
The transistor 21 may be of the type sold, for example, by Sylvania GTE as type ECG-280, while the adjustable poten-tiometer can be of the wire wound variety rated at one hundredohms, 2 to 4 watt, and sold for example by Clarostat under the catalog No. A43-100. Moreover, while in the embodiment disclosed above it has been suggested that an NPN power transistor be em-ployed, it will be apparent to one skilled in the art that an equi-valent solid state element, or the compliment of the solid state element could be utilized in its place. Likewise, although speci-fic values have been given for resistors R2 and R3, it will be appreciated that these values also can be modified within reason without departing from this invention. Furthermore, while this invention has been illustrated and described in detail in con-nection with only one embodiment thereof, it will be apparent that it is capable of still further modification, and that this appli-cation is intended to cover any such modifications as may fall within the scope of one skilled in the art or the appended claims.
PH~SE ELECTRIC MOTORS
This invention relates to an improved control circuit for con-trolling the speed of split phase electric motors, and more particularly to a circuit which permits operation of permanent split phase capacitor motors at low speeds without any objectionable AC hum.
There are numerous appliances in the modern-day household which are operated by small, split phase electric motors of the fractional horsepower variety. Many such items (for example, refrigerators, exhaust fans, ceiling fans, etc.) are within earshot of the members of the household, when in use, and it is therefore most desirable that their associated motors operate - as quietly as possible.
One of the principal problems heretofore encountered in connection with electric motors of the type described is that, when used with electronic speed controls~ and particularly at lower speeds, they tend to develop an objectionable hum, which can be very distressing to any one within hearing distance of the motorn Efforts have been made in the past to minimi~e signal distor-tion inherent in electronic speed controls and consequent undesirable humming during low speed operation of motors of the type described, but such efforts have not proved to be successful.
It is an object of this invention, therefore, to provide an improved motor control circuit which substantially eliminates any objectionable hum heretofore encountered during low speed operation of split phase motors of the type described.
Another object of this invention is to provide for motors of the type described an improved, adjustable control circuit which/relatively simple and inexpensive to manufacture, and which is capable of operating fractional (and larger) horsepower motors at variable speeds, and with a minimum of signal distortion and substantially no undesirable hum.
: "
`^"`` 3~:17iS~7 A more speci~ic .objec~ of this invention is to provi.de for a permanent split phase c~pacitor motox an improved speed control circuit wh.ich permits ope~ation of the motor a~ variable speeds, but without an~ undesirable signal distortion or humO
Accordingly, the present invention provides a control circuit for a variable speed, permanent split phase capacitor mo-tor of the type having a main stator winding, an aux;.liary stator winding, and a capacitor connected in series with said auxiliary winding, means for substantially eliminating signal distortion and consequent audible hum from the motor during low speed opera-tion thereof, comprising, a transistor with a base and main elec-trodes consisting of a collector and emitter, having its emitter=
collector circuit connected in series with said auxiliary winding for supplying power thereto from an ~C power supply, means for connecting one of the main electrodes of said transistor to one side of the AC power supply~ and to the base of said transistor, and a ~irst variable resistor connected between the base and the other main electrode of said transistor, and adjustable to control the r~rrent flow through the emitter-collector circuit of said transistor during operation of said motor and thereby the current flow through said auxiliary winding.
Other objects of the invention will be apparent herein-after from the specification and from the recital o~ the appended claims, particularly when read in conjunction with the accompany-ing drawing.
In the drawing;
Fig. 1 is a wiring diagram illustratiny the windings of a conventional permanent split phase capacitor motor, together with a control circuit made according to one embodiment of this invention, and shown connected in series with the auxiliary wind-ing of the motor to permit operation .thereof at ~Jariable low speeds; and -~\
'7 Fig. 2 is a wiring diagram illustrating this control in greater detail.
Referrin~ now *o the drawing by numerals of reference, and first to Fig. 1, Wl and W2 represent the main and auxiliary windings, respectively, of a conventional permanent split capa-citor motor, which is of the type that is frequently employed to drive household ceiling fans, exhaust fans, etc. Opposite ends of the main winding Wl are connected by lines Ll and L2 to one side of a conventional On-Off switch Sl, the opposite side of which is connected to an AC power supply, which may be of the usual 120 Volt, 60 Hertz household variety.
The auxiliary winding W2 is connected between lines Ll and L2 in parallel with the main winding Wl, and in series with a capacitor Cl and a control circuit 10, by means of a line L3 which connects one end of winding W2 to line L2, by a line L4 - 2a ~P7B65~ , which connects the opposite end of winding W2 to one side of the capacitor Cl, by a line L5 connecting -the opposite side of the capacitor Cl to the control circuit 10, and by a Iine L6 which connects circuit 10 to L1. As a consequence, when switch Sl is closed, the control circuit 10, the capacitor Cl and auxiliary winding W2 are connected in series across the AC
power supply. Also at this time, of course, the winding Wl will also be connected directly across the power supply.
Referring now to Fig. 2, the control circuit 10 comprises an NPN power transistor 21, which has its emitter connected directly to line L5, it collector connected directly to line L6, and its base connected by a line 22 to the movable contact P of a 100 ohm potentiometer (pot) having a variable resistance R1. The fixed or æero end of the pot resistance Rl is connected by a line L8 to one end of a fixed resistor R2, the opposite end of which is connected to line L5, thereby placing resistor R2 in the emitter-base circuit of the transistor 21. Line 22 is also connected through another fixed resistor R3 and a line L9 to line L6~ so that resistor R3 is in the collector-base circuit of the transistor. By way of e~ample, ~he resistor R2, may have a valueof approximately twenty-seven ohms, while resistor R3 has a much larger value, for example, in the vicinity of fifteen thousand ohms.
In operation, and assuming that -the switch Sl is closed, the pot contact P can be adjusted manually to control the value of Rl, and consequently the forward biasing voltage that is developed across the emitter-base circuit of -the transistor 21. In turn, this permits manual control of the current flow through the emitter-collector circuit. For example, assuming that the adjustable pot contact P is moved toward the left in Fig. 2 to reduce the value of the resistance Rl placed in the circuit, then the forward biasing voltage between the base and ~ 6S'7 the emitter will be reduced, thereby reducing the current flow through the emitter-collector circuit. At this stage the transistor 21 functions as a high resiStance in parallel with R2 and R3 between lines L5 and ~6. This, in turn, reduces current flow through winding W2.
On the other hand, as the movable pot contact P
is moved toward the right Fig. 2, so as to increase the value of resistance Rl, the voltage drop between the base and the emitter will increase, and thereby effectively will increase the current flow in the emitter-collector circuit. This permits the transistor 21 to function more nearly as a short circuit and allows most of the current flow to take place through the emitter-collector circuit of the transistor, rather than through the hi~h resistance circuit represented by R3, Rl, and R2.
At intermediate settings oE the pot contact P the transistor 21 acts as a variable resistance between ~he emitter and collector, either lncreasing or decreasing the fcrward biasing voltage between the emitter and the base, depending upon the position of the movable contact P of the pot. The feedback resistor R3 and the biasing resistor R2 tend to stabilize the operation of the control circuit.
In practice it has been found that this control circuit provides relatively simple and inexpensive means for controlling the intermediate speed ranges of the motor repre-sented by the windings Wl and W2. For low speed operation of the associated motor, the pot is adjusted $o that the resistance Rl is almost negligible, thus switching the transi9tor 21 almost to its blocking mode. This causes a decrease in current through W2 which causes a decrease in motor tor~ue. On the other hand, as the pot is adjusted to increase the resistance of Rl, thereby causing a corresponding increase in the current flow in the emitter-collector circuit of the transistor 21, the current flow through the au~ialiary winding W2 increases which ~ s~i causes an increase in motor tor~ue and thereby causirlg a pro-gressive speeding up of the motor. In all such operations, however, the control circuit 10 tends to minimize, if not substantially to eliminate signal distortion and the consequent audible hum which heretofore tended to accompany the intermediate and low speed operations of permanent split capacitor motors of the type des-cribed.
The transistor 21 may be of the type sold, for example, by Sylvania GTE as type ECG-280, while the adjustable poten-tiometer can be of the wire wound variety rated at one hundredohms, 2 to 4 watt, and sold for example by Clarostat under the catalog No. A43-100. Moreover, while in the embodiment disclosed above it has been suggested that an NPN power transistor be em-ployed, it will be apparent to one skilled in the art that an equi-valent solid state element, or the compliment of the solid state element could be utilized in its place. Likewise, although speci-fic values have been given for resistors R2 and R3, it will be appreciated that these values also can be modified within reason without departing from this invention. Furthermore, while this invention has been illustrated and described in detail in con-nection with only one embodiment thereof, it will be apparent that it is capable of still further modification, and that this appli-cation is intended to cover any such modifications as may fall within the scope of one skilled in the art or the appended claims.
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a control circuit for a varible speed, permanent split phase capacitor motor of the type having a main stator winding, an auxiliary stator winding, and a capacitor connected in series with said auxiliary winding, means for substantially eliminating signal distortion and consequent audible hum from the motor during low speed operation thereof, comprising, a transis-tor with a base and main electrodes consisting of a collector and emitter, having its emitter-collector circuit connected in ser-ies with said auxiliary winding for supplying power thereto from an AC power supply, means for connecting one of the main electrod-es of said transistor to one side of the AC power supply, and to the base of said transistor, and a first variable resistor con-nected between the base and the other main electrode of said transistor, and adjustable to control the current flow through the emitter-collector circuit of said transistor during operation of said motor and thereby the current flow through said auxiliary winding.
2. A control circuit as defined in claim 1, wherein said connecting means includes a second resistor connected at one end to the collector of said transistor, and at its opposite end to the base of the transistor.
3. A control circuit as defined in claim 2, including a third, fixed resistor connected in series with said first resis-tor between the emitter and base of said transistor.
4. A control circuit as defined in claim 3, wherein the ohmic value of said second resistor is substantially greater than that of said third resistor.
5. A control circuit as defined in claim 4, wherein said transistor is an NPN power transistor and said resistors are connected in series across the emitter and collector of said tran-sistor.
6. In a control circuit for a permanent split phase capacitor motor, a speed control device connected in series with a capacitor and the auxiliary stator winding of said motor, and operative substantially to eliminate signal distortion and con-sequent audible hum during low speed operation of the motor, said device comprising a transistor connected to one side of said ca-pacitor to be interposed between the capacitor and one side of an AC power supply for the motor, and with its emitter-collector circuit connected in series with said auxiliary winding, a plur-ality of resistors connected in a series circuit with each other and in parallel with said transistor, one of said resistors being variable, means connecting said variable resistor to said tran-sistor and operative when said motor is energized to increase the current flow through said transistor as the ohmic value of said variable resistance decreases, a second one of said resistors be-ing connected between the collector and base of said transistor, a third one of said resistors being connected between the emitter and base of said transistor in series with said variable resistor, and said second resistor having an ohmic value substantially grea-ter than either of said third resistor and said variable resistor.
7. A permanent split phase capacitor motor as defined in claim 6, wherein said transistor is selected from the group consisting of an NPN transistor and its complimentary equivalent.
8. A permanent split phase capacitor motor as defined in claim 1, wherein said one main electrode is the collector.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16654080A | 1980-07-07 | 1980-07-07 | |
| US06/166,540 | 1980-07-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1178657A true CA1178657A (en) | 1984-11-27 |
Family
ID=22603743
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000373722A Expired CA1178657A (en) | 1980-07-07 | 1981-03-24 | Control circuit for reducing hum in split phase electric motors |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1178657A (en) |
| GB (1) | GB2080056A (en) |
-
1981
- 1981-03-18 GB GB8108542A patent/GB2080056A/en not_active Withdrawn
- 1981-03-24 CA CA000373722A patent/CA1178657A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2080056A (en) | 1982-01-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |