GB2296112A - Speed controller for a single phase AC motor in a water heating system - Google Patents
Speed controller for a single phase AC motor in a water heating system Download PDFInfo
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- GB2296112A GB2296112A GB9422813A GB9422813A GB2296112A GB 2296112 A GB2296112 A GB 2296112A GB 9422813 A GB9422813 A GB 9422813A GB 9422813 A GB9422813 A GB 9422813A GB 2296112 A GB2296112 A GB 2296112A
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 33
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24D—DOMESTIC- OR SPACE-HEATING SYSTEMS, e.g. CENTRAL HEATING SYSTEMS; DOMESTIC HOT-WATER SUPPLY SYSTEMS; ELEMENTS OR COMPONENTS THEREFOR
- F24D19/00—Details
- F24D19/10—Arrangement or mounting of control or safety devices
- F24D19/1006—Arrangement or mounting of control or safety devices for water heating systems
- F24D19/1009—Arrangement or mounting of control or safety devices for water heating systems for central heating
- F24D19/1012—Arrangement or mounting of control or safety devices for water heating systems for central heating by regulating the speed of a pump
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
- Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Control Of Ac Motors In General (AREA)
Abstract
A water heating system comprising a pump driven by an ac motor includes a coil switching device which automatically switches between high, low and intermediate speeds, according to the output of a temperature sensor attached to the return feed to the boiler. Changes of temperature are detected using a "staircase" window comparator. When the voltage across the sensor enters each window in turn a transistor operates a relay and simulates the operation of the original manual switch, altering stator coil connections so that different speeds can be produced. The invention includes a manual override switch so that the speeds can be controlled manually as well as when switched to "Auto".
Description
SPEED CONTROLLER
FOR A
SINGLE PHASE AC MOTOR SECTION 1 INTRODUCTION AND OBJECTIVE 1.1 Introduction
This feasibility study addresses specific problems imposed by the inherent
limitations of small and medium sized, pumped central heating systems. The
distribution of heat by water circulation is poorly regulated, and consequently
inefficient. The boiler, is unable to regulate its power output except by repeatedly
switching ON and OFF.
The "engine" runs either at full power or tickover. Temperature controls on the
boiler and system are imposed by ON/OFF thermostats. Consequently repeated
cycling on and off eventually results in a system running at the required
temperature.
Boiler design is very advanced and no attempt is made here to review their design
or operation. If the water feed rate were itself regulated, in order to maintain
preferential conditions for maximum heat transfer across the boiler heat exchanger,
then improved system operation should be expected. In particular this would apply
to any average sized household making use of thermostatic radiator valves (TRV's), or similarly equipped larger office premises. In these systems the capacity of the
system effectively changes as room temperatures achieve their intended levels. A
cold system may be supplying typically between ten and twenty radiators, but as
TRV's regulate and then isolate, the overall capacity will reduce until only two three
radiators may be in use.A single speed, off the shelf circulating pump may be well
matched for a nominal sized system, but may have a speed inappropriate for the
changing demands of the system.
1.2 Objective
The objective of this project is to devise a means of optimising the circulating
efficiency of a hot water system by automatically varying the pump speed, according
to the changing thermal load on the heat exchanger.
The final design will result in reduced boiler cycling (extending boiler life and
reducing maintenance), increasing economy (lower running costs) and reduced
hydrodynamic noise. The prototype materials will cost approximately 50 to build,
subsequent models will cost progressively less, until a production build cost of less
than 25 is achieved, thereby allowing the manufacturer's mark up to be confined
within the limit of a reasonable sales value. This device will then be available as an
accessory that can be fitted with DIY levels of expertise, to virtually all small to
medium sized pumped central heating systems.
1.3 The completed device will be known as the " P-TEC ", an abbreviation of Pdmp speed Thermo Electronic Controller. During development the prototype build
standards will be defined by a suffix as follows.
eg: 1st prototype (design only) P-TEC.01(d)
2nd prototype (design only) P-TEC.02(d) 3rd prototype (build) P-TEC.03
The production model will be launched with the name WIZARD.
SECTION 2 JUSTIFICATION 2.1 The majority of domestic water heating systems all follow the general principles
illustrated in Figure 1, page 5. Configurations do vary, but in almost every case the
installer selects a coarse range circulating pump according to the approximate
capacity of the final system. The wide range of possibilities is reduced by having
a standard range of circulators, each of which can be preset to one of two, three or
even four speeds. Generally the choice is very simple. Installers of domestic two or
three bedroom house circuits favour a particular model or size, and usually preset
the fastest pump speed, with little regard to the merits of slower speeds. By using
the fastest speed the assumption is made that the system will waste no time in raising
room temperatures.
2.2 The motors themselves are small ac single phase induction motors, based on a
squirrel cage design. Speed adjustment is effected by manually selecting the number
of stator pole pairs driving the rotor, or by changing the interconnection circuit
between windings. Starting is ensured by the use of a starting capacitor in series
with a seperate stator coil, together wired across the supply and in parallel with the
main coil(s).
The motor/pump manufacturer enjoys a virtual monopoly and can boast that they
are a "household name". An automatic speed control system has just recently
become commercially available, but by employing a variable frequency inverter is
expensive and only available for large capacity (office and industry), applications.
2.3 Measurements were made of temperatures around an eleven radiator domestic
heating system, using twenty thermocouples. Some of these results are tabulated in
Tables 1 to 4. The survey exposed shortcomings in the way the system was designed
and installed. The tables compare measurements of heating applied to the hot water
circuit and to the central heating circuit, both at two pump speeds. The results
illustrated are not in themselves conclusive, other than to show a marginal reduction
in the time the central heating water is raised 37 deg C (55 minutes) using pump
speed 1, as compared to the 35 deg C rise (59 minutes), using pump speed 3. Added
to this observation is the fact that pump speed 1 consumed less electrical power,
170 mA 40 Watts, than pump speed 3, 420 mA 105 Watt. The heat exchanger
differential temperature is more advantageous.Boiler flame outs, if monitored,
would be expected to be more frequent on the higher pump speed.
Further studies requiring controlled load conditions are considered essential.
After ten minutes into the water heating cycle, water leaving the heat exchanger has only increased 2 deg C in temperature. Eventually as the recirculating water increases in temperature so this differential increases to approximately 5 to 7 deg C, and useful work is now being done. The water should now circulate at the fastest speed consistent with the pump performance curve. All radiators will come up to heat rapidly. The faster speed will also generate a certain amount of noise, both from the pump and from the pipe system itself.
The temperature trial was repeated for different pump speeds and system configurations. It was found that system performance improved when the slowest speeds were used for cold starts, and progressively higher speeds were used once the entire circulation had achieved a certain level of heating. Eventually the action of
TRV's will reduce the capacity of the system and a lower pump speed should be employed.
WATER CIRCUIT ONLY PUMP SPEED #1
ELAPSED COLD HOT DIFF.
TIME RETURN SUPPLY TEMP. Notes (MINUTES) oo 16 19 3 low start temp.
39 42 3 10 51 58 7 12 65 70 5 15 71 78 7 16 74 81 7 18 76 81 5 flame out Temperature change of 25 deg C in Average diff. 5.3 10 minutes WATER CIRCUIT ONLY PUMP SPEED #3
ELAPSED COLD HOT DIFF.
TIME RETURN SUPPLY TEMP. Notes (MINUTES) oo . 33 33 0 start temp.
4 52 52 0 8 70 73 3 10 79 81 2 12 | 84 86 2 flame out Temperature change Average diff. 1.4 of 32 deg C in 8 minutes TABLE 1 (top) Survey, Pump Speed #1 (1150 rpm)
TABLE 2 (bottom) Survey, Pump Speed #3 (2250 rpm)
CENTRAL HEATING ONLY PUMP SPEED #1
ELAPSED COLD HOT DIFF.
TIME RETURN SUPPLY TEMP. Notes (MINUTES) 5 25 33 8 start temp.
20 42 51 9 45 59 68 9 60 62 72 10 Temperature change Average diff. 9 of 37 deg C in 55 minutes CENTRAL HEATING ONLY PUMP SPEED #3
ELAPSED COLD HOT DIFF.
TIME RETURN SUPPLY TEMP. Notes (MINUTES) 6 26 31 5 start temp.
20 41 45 4 50 57 62 5 65 61 63 2 Temperature change Average diff. 4 of 35 deg C in 59 minutes TABLE 3 (top) Survey, Pump Speed #1 (1150 rpm)
TABLE 4 (bottom) Survey, Pump Speed (2250 rpm)
SECTION 3
APPLICATION AND DESIGN OPTIONS 3.1 Application
The requirement is to adjust motor speed to suit the system loading, determined by
the effectiveness of the boiler heat exchanger and the changing capacity of the
system. The speed will be selected according to the temperature of recirculated water
returning to the boiler. Cold water will be passed through the heat exchanger
slower than hot water, in order to pick up more heat.
Substitution of the standard ac induction motor with a dc or universal (commutator)
motor would be uneconomic, impractical and not at all likely to gain acceptance by
the industry or consumer. The existing single phase induction motor remains in use,
consequently a number of options are available as a means of changing speed. Such
a motor can only change speed as follows:
a) by varying the supply frequency
b) by selecting a different configuration of pole pairs
Method a) requires the use of a variable frequency inverter. Method b) requires that
the motor is equipped with multiple poles. Standard pump motors change speed by
changing the number of pole pairs, so adaption of this design should be possible.
An alternative method in common use, often incorrectly described as speed control,
is voltage regulation.
Design options are available in terms of speed control and temperature sensing, these
are considered briefly in the remainder of this section.
3.2 DESIGN OPTIONS - SPEED CONTROL 3.2.1 Frequency Adjustment (Variable Frequency Inverter)
This method would allow smooth adjustment of motor speed between the designed
maximum and minimum speed limits.
The speed of rotation of an induction motor possessing a fixed number of poles, is
determined by the angular speed of the rotating magnetic flux generated by the
stator windings. There is an element of slip between the stator flux and rotor, so
the rotor does not quite achieve synchronous speed. If the supply frequency were
increased so would the speed of rotation of the magnetic flux, according to the
following equation....
n = f /p where: n is in revolutions per second
f is supply frequency in Hertz
p is the number of pole pairs
By adjusting the supply frequency to the motor, so its speed will alter accordingly.
Inverters are generally circuits which have a dc source, and by switching of
rectifying devices, enable an alternating voltage to be synthesised for supply to an
ac load. Various circuits are in common use , such as the single phase centre tapped
inverter, see Figure 2, and the dc chopper regulator in Figure 3. Analysis of the
circuits is complex and the difficulties associated with efficient commutation of the
SCR's render such systems impractical and uneconomic for small scale systems, and
are primarily of use in large 3-phase loads.
To maintain optimum magnetic flux conditions in the induction motor, the ratio of
voltage to frequency must be kept constant. This is because in any magnetic circuit
the induced voltage is proportional to the flux level and the frequency, (v=d/dt).
If the ratio is not kept constant then the torque characteristic becomes less efficient.
Again, this demands a complex circuit, see Figure 4, and cannot be justified for such
a simple application as P-TEC.
3.2.2 Voltage Regulation
It is possible to obtain some measure of speed adjustment by simply reducing the
supply voltage, with consequential increase in slip.
Thyristors, diacs and triacs are usually used and the simplest circuit is identical to
that employed for lamp dimmers. A typical circuit for a motor speed controller is
illustrated in Figure 5.
Apart from the obvious handicap of reduced efficiency with incresed slip there are
other disadvantages associated with this method. The increased rotor losses with
falling speed means that the load torque has to be restricted so as to avoid excessive
rotor heating. Consequently this form of speed control is only practicable for lightly
loaded systems, such as ventilation fans. At particular firing angles large harmonic
components can be set up, producing reverse torque effects. Additionally problems
of interference and a need for suppression, due to the repetitive action of the SCR's
would be a further disadvantage.
3.2.3 Pole Pair Configuration
This method represents the simplest solution to the problem and is the cheapest and
easiest to implement. Two or three speeds can be obtained by having the stator
poles interconnected in two or three different ways.
Because the motors are already designed to change speed manually then the motor
requires no modification. P-TEC will be transferable between any multi-pole single
phase motor, with only minor modifications or adjustment required for different
speed ranges, or higher rated motors.
Torque is produced when the rotating magnetic flux links with the rotor conductor bars, and induces an emf in the bars. This emf drives a current in the rotor and creates a magnetic field around the rotor. The rotor and stator magnetic fields interfere to produce a torque reaction. In a two pole motor the rotor and flux rotate with with the same cyclic period as the supply frequency, and rotational speed can be shown to depend on the number of poles in the stator windings and the ac frequency.
As stated above in 3.2 n = f/p
Due to the relationship between the torque reaction, induced emf, rotor current, friction and windage losses, an element of "slip" is introduced and the rotor runs at slightly less than synchronous speed. For a 4-pole winding at 50 Hz the rotor turns at lower than 25 rev/sec, typically 1200-1400 rpm.
Two and three phase motors are self starting, from switch on they immediately generate a cyclic rising and falling magnetic flux that rotates around the stator. A single phase motor will only start by an external influence or by artificially simulating the magnetic effect of a 2-phase motor. This is achieved by providing a second set of windings at 90 degrees to the main windings, and supplied through a capacitor. The currents in the two windings differ in phase by 90 degrees and set up a rotating magnetic field for the rotor to follow.
A suitable control circuit for switching between windings is a window comparator.
A cascade or "staircase" of comparators, provides a series of windows, each one capable of activating an output device specific to that stage. Each window can be adjustable and referenced to a different temperature range, so that changing inputs will operate relays to engage different winding circuits. Monolithic IC chips are available that could simplify the construction process, but would build in some redundancy and would be prohibitively expensive. A relatively simple circuit, using comparator IC's or Op Amps, resistors and diodes etc, provides the cheapest development and production solution. See Figure 6 for typical single window circuit.
3.3 DESIGN OPTIONS - TEMPERATURE SENSOR 3.3.1 The three temperature sensors considered were the thermocouple, platinum
resistance temperature detector (PRT) and thermistor.
Each method is well proven and documented for practical applications. Final
selection can easily be made based on criteria such as cost, desired accuracy,
reliability and simplicity of circuit.
The principle advantages and disadvantages of each type, are listed below.
TEMPERATURE
ELECTRICAL 110
TYPE CHARACTERISTICS COMMENTS
Thermocouples Low source impedance, typ- Low voltage output requires
ically 10#. Voltage-output low-drift signal conditioning.
devices. Output shift is 10's Small size and wide tempers
of microvolts/ C. Outputs ture range are advantages. Re
typically in the millivolts at quires reference to a known
room temperature. temperature. Nonlinear
response.
Platinum and Resistance changes with Highly repeatable. Good lin
other RTD's temperature. Positive tem- earity over wide ranges.
perature coefficient. Typical Requires bridge or other
impedance (0 C) 20# to 2k#. network for typical interface.
Typical sensitivities 0.1%/ C
to 0.66%/ C, depending on
material.
Thermistors Resistance changes with tem- Highest sensitivity among
perature. Negative tempera- common temperature trans ture coefficient. Typical im- ducers. Inherently nonlinear
pedances (25 C) of 50# to (exponential function) but 1MQ available. Sensitivity at accurate linearized networks
250C is about 4%PC. Lin. available.
earized networks available with
with 0.4%/ C sensitivity.
Any of the devices above is suitable and can be inter-changeable within P-TEC, with only
minor modification or adjustment required for temperature calibration.
Typical sensor circuits are illustrated in Figures 7, 8 and 9 (next page).
SECnON 4
DESIGN SOLUTION 4.1 The design solution was approached by considering practical circuits to satisfy the
components of the block diagram, illustrated as Figure 10 below. A detailed circuit
diagram is illustrated in Figure 11, pagel8.
4.2 Temperature Sensor
After consideration of the three methods described in 3.4.3, the thermistor was
selected as the preferred sensor, on the basis of its low cost, reliability and simple
circuit. The sensor shall be sited as close to the boiler feed water inlet as possible,
but subject to individual heating system assessment, may also be sited further
upstream provided the system temperature remains closely aligned to that entering
the boiler. Consequently it should be possible to locate the sensor circuit within the
same enclosure as the control circuit.
It is intended the P-TEC will be installed as a single unit, mounted in close
proximity to the motor and with easy access to the existing power supply point. The
thermistor is supplied with a constant current from the + ve voltage supply rail and
forms one part of a potential divider. Voltage sensed across the thermistor is fed to
the inverting input of an Op Amp employing negative feedback. The feedback is
adjustable so that an appropriate gain can be provided.
4.3 Control Circuit
The control circuit is required to be a staircase window comparator. The
temperature sensor will provide an output which will be identified within the
threshold limits determined by adjustable voltage references.
The single window circuit of Figure 6, has been replicated to provide the required
number of stages (windows). See Figure 11 page 18 for a detailed circuit diagram.
The output of IC1 is applied to the non-inverting input of IC2 and the inverting
input of 1C3. The amplifiers have no feedback and hence operate with full gain.
For all practical considerations the outputs will be at either the + ve or -ve supplies,
depending on the comparison of IC 1 output with the upper and lower limits of each
window. When the output of IC1 is between the limits of one window both outputs
will be + ve, and that window transistor will be switched ON. The associated relay
will be energised and the contacts will close. When each window threshold is
crossed by a rising sensor voltage, the Upper Limit comparator output (ULl), changes from "high" to "low", ie + ve to -ve, providing a current sink to the
redundant transistor circuit. Consequently the transistor switches OFF and its
associated relay is de energised. Meanwhile UL1 is also the Low Limit (LL2) for the
next incremental window.Its low limit comparator output changes from "low" to
"high", ie -ve to +ve. The upper limit (UL2), has not been exceeded and
consequently its output is also high. The window transistor switches ON and its
associated relay is energised.
As the sensor registers higher temperatures, so the output from IC1 is detected in
progressively higher windows. Three windows correspond to the motor speeds. The
final 4th window, is only activated when boiler return (feed) water is near to
maximum working temperature. This would indicate reducing heat transfer to the
system being heated, due to rooms at temperature and/or TRV's isolating, and a
lower motor speed can be utilised. Consequently the final window re-energises
either pump speed 1 or 2, depending on which link is shorted, Link 1 or Link 2.
An LED across each transistor load will provide energised indication for each relay
for diagnostic purposes.
4.4 Motor Interface
This unit marries the control circuit output to the stator winding terminals. A
command switch is incorporated so that automatic (thermo-electronic) operation
can be over-riden and manual control selected if required. The switch is a two pole
4-way switch which facilitates isolation of an ac/dc transformer rectifier circuit when
the automatic operation is de-selected.
Also contained within this unit is a starting capacitor, and the relays operated by
the control circuit. The relays are not required to switch regularly or at high speed,
they are required only to be reliable and cheap. Consequently solid state relays are
not justified and standard electro-magnetic relays will be employed.
4.5 Power Supply
A single rail power supply is favoured for low cost and simplicity. A dual power
supply has been included in the design plan as an option.
Note: Present research suggests that ready made regulated ac/dc power supplies
can be obtained cheaper than the cost of manufacturing a single
demonstration prototype. Consequently the dc power for this project will
be derived from bench sources, the purpose of this project being to prove
the design of a control circuit.
SECTION 5
SPECIFICATION 5.1 The specification for the P-TEC prototype is as follows: 5.2 Demonstration System P-TEC.01(d)
AC Power Supply 240 V 50 Hz DC Power Supply 12 V Motor Type single phase 16-pole induction motor Motor Speeds (nominal) 800 rpm 1200 rpm 1900 rpm Load Current 160 mA 250 mA 380 mA Load Power 40 watt 70 watt 105 watt Temperature Sensor Range 0 to 100 degrees C Temperature References RV2 0 to 55 ( #5) deg C * RV3 55 to 65 ( #5) deg C * RV4 65 to 75 ( #5) deg C * RV5 75 to 90 ( #5) deg C * * These values arbitrarily set as required by individual heating systems, see 4.3
The values above are considered suitable for the thermodynamic response
of the system examined and referred to in Section 2.3. When the water
only circuit is required a very small pipework system is in use. The hot
water reservoir thermostat is set to 550C, consequently the motor has been
confined to the lowest speed for this duty cycle.
SECTION 6
COSTS 6.1 The following table lists all components and includes a circuit reference
for Figure 11, supplier, unit and batch costs. Batch costs can be further
substantially reduced, when bulk purchases for manufacturing purposes
are placed.
Prices stated are those advertised in the October 1994 issues of the
Maplin and RS Components catalogues.
6.2 TEMPERATURE SENSOR CIRCUIT
DESCRIPTION IDENTITY SPECIFICATION SUPPLIER PRICE (#) pu/batch Thermistor TH1 50k# at 25 C RS/856 DO-35 NTC -55 to 250 C 19 & 55 0.95/0.88 Op Amp 741 IC1 UA741CP RS/644 Vimax=#30V 305-311 0.51/0.25 Resistors +5% RS/563 carbon film 0.25w R1 120k2 131-508 0.03/0.02 R2 100kQ 131-491 0.03/0.02 Variable Resistor RS/571 3/8 in sq. Top RV1 500k# #10% 186-794 0.44/0.35 RV2 100k# +10% 186-772 0.44/0.35 6.3 CONTROL CIRCUIT
DESCRIPTION IDENTITY SPECIFICATION SUPPLIER PRICE (#) pu/batch Op Amp 741 IC2 IC3 UA741CP RS/644 IC4 IC5 Vimax=#30V 305-311 0.51/0.25 IC6 IC7 IC8 IC9 Variable Resistors RS/571 3/8 in sq. Top #10% RV3 50k# 186-766 RV4 RV5 10k# 186-744 0.44/0.35 RV6 20k# 186-750 Resistors #5% RS/563 carbon film 0.25w R3 R4 R5 2.2k# 131-299 0.03/0.02 R6 R7 R8 R9 R10 R11 R12 10k# 131-378 0.03/0.02 R13 R14 1% metal film 0.125w R15 R16 5.1k# RS/560 R17 164-362 0.05/0.04 Diodes D1 D2 D3 OA202 RS/579 D4 D5 D6 150 V 80mA D7 D8 D9 D10 D11 109-258 0.23/0.16 D12 D13 D14 D15 Transistors TR1 TR2 BC108 30m W RS/583 TR3 TR4 L@max 100 mA 293-533 0.22/0.19 Relays RL1 RL2 12V/5A 400# MAP/807 RL3 JM18U 1.29/ LED low current D16 D17 2-7mA 24m W RS/425 D18 Green 589-014 0.27/0.21 CONTROL CIRCUIT (continued)
Strip Board SRBP/Cu RS/513 0.1 in. 433-826 4.78/4.36 95 X 292 X 1.6 Capacitors input stability C1 C2 0.1yF ceramic RS/92 C3 C4 50V 124-178 0.26/0.21 CS C6 C7 C8 power supply by-pass C9 C10 1F tantalum RS/81 0.4/0.23 C11 C12 128-007 C13 C14 16V 6.4 MOTOR INTERFACE MODULE
DESCRIPTION IDENTITY SPECIFICATION SUPPLIER PRICE (#) pu/batch Rotary Switch SW1/2 2 Pole 4-Way MAP/794 0.99/ 300 Vac 5A continuous 150mA Box, Polypropylene RF Shielded RS/1171 120 X 65 X 40 501-569 2.97/2.72 Edge Strip Connector ESC 1 H Type RS/154 (nearest equivelant) 15-Way blade 481-960 5.31/4.78 Capacitor C17 2 F 400V RS/83 107-713 2.58/2.36 6.5 POWER SUPPLIES (Single Rail)
DESCRIPTION IDENTITY SPECIFICATION SUPPLIER PRICE (#) pu/batch Transformer T1 12V RS/966 207-649 4.75/4.28 Heatsink 4 C per W RS/816 401-497 2.44/1.9 Rectifier Bridge D18 D19 Diode lN4002 D20 D21 X 4 RS/578 VRRM 100V 261-154 0.05/0.03 Regulator, Fixed Reg MC7812CT RS/614 Voltage 641-623 1.01/0.3 Capacitors RS/76 C17 2200 F Electro 106-192 2.55/2.26 RS/80 C18 470nF disc 101-765 0.15/0.13 RS/70 C19 10 F Electro 107-397 0.07/0.05 Modular Power See Section Regulated MAP/43 Supply 4.5 page 17 Fixed Voltage 240/12V BZ83A 8.99/ 500mA 6.6 MATERIAL COSTS
From the foregoing tables, a maximum costing for the P-TEC.01 prototype
can be estimated.
()
Temperature Sensor Circuit 1.64
Control Circuit 2.23
Motor Interface Unit 11.17
Power Supplies 11.17
Total 46.21
Batch Price 33.70
6.7 The following should be noted: - All prices can be reduced by batch purchase, and further reduced by bulk
purchase.
- The power circuit will not be constructed, a ready made modular unit will
make a significant reduction in cost.
For this project bench supplies will be used.
- Capacitor C17 is part of the redundant manual control unit and will be
re-used.
- the required edge strip connector is not a standard pattern and will either
need to be manufactured or a modification kit provided.
For this project the original connector will be modified.
6.8 The revised material cost, based on the changes listed in 6.7 above, is as
follows:
()
One P-TEC.01 prototype 27.15
Batch price (no psu) 18.32
SECTION 7
TOOLS AND TEST REQUIREMENTS 7.1 Only standard range test instruments and tools are required.
7.2 Tools Availability
Soldering Iron home/work Sidecutters/pliers/screwdrivers home/work
PCB Drill home/work
PCB Etching Equipment home/work
Labelling Equipment home/work 7.3 List of Instruments Availability M ultimeters home/work
Thermometer home/work
Power Supplies work
Tachometer work/college
Oscilloscope work/college 7.4 Test Requirements
The test procedure involves the testing of the individual "modules" of the
system as defined by the block diagram, Figure 10. The temperature and
control circuits will require only a 12 V power supply.
Final testing of the P-TEC system will require the use of 240 V ac, but only as
connected within a standardised and proprietary connector to drive the load.
The stages of testing are defined within the critical path analysis, see
Appendix I.
7.5 Areas of Uncertainty
Calculations for component values are not yet finalised and are likely to require alteration during the test phases.
The final adjustment of voltage references RV2, RV3, RV4 and RV5 (temperature thresholds), will very much depend on the characteristics of individual heating systems. For the prototype the temperatures will be arbitrarily set, but will attempt to achieve those listed in 5.2.
The operation of each comparator stage is mutually exclusive, so only one relay at a time will be energised. Consequently there is no perceived need for
hysteresis, however capacitors will be inserted across the power supply to each
comparator Op Amp and the inputs, in order to eliminate any transients that might result in chatter, and to provide additional stability. An additional method of improving stability, is to latch the comparator output with a schmidt trigger. This will be an option reserved for the design review.
Similarly screening of the sensor cable and installation of the circuits within a metal box may be necessary to protect against radiated interference.
Claims (7)
1) An electronic device that automatically switches
between motor windings on a multi-pole single phase ac
motor.
2) An electronic device as claimed in 1), that drives a
pump and circulates water around a water heating
system, adjusting the flow rate of the driven pump
according to the heat dissipation from the system.
3) An electronic device as claimed in 1) and 2) above,
that detects heat dissipation by using a temperature
sensor positioned on the water return line to the
water heater/boiler.
4) An electronic device as claimed in 1), 2) and 3) that
changes motor speed according to any increase or
decrease in capacity of the water heating system.
5) An electronic device as claimed in 2), that in a dis
proportionate two (or more) circuit system, eg hot
water and central heating, always selects the lowest
pump speed for the smallest circuit.
6) An electronic device as claimed in 4) and 5), that
ensures that the lowest electrical power is used for
circulation, at all load conditions.
7) An electronic device as claimed above that controls a pump
which circulates water around a water heating system,
adjusting the flow rate of the pump according to the heat
dissipation from the system. No e::isting components of the
system or its central programmer/controller (e::cept the
plug), require alteration or replacement. The existing
thermostatic and other controls of the system remain
unaffected.
7) An electronic device as claimed above that can be
fitted as an accessory to any single phase ac motor
that employs pole switching as a means of changing
speed.
Amendments to the claims have been filed as follows 1) An electronic device, that automatically switches between
motor windings on a multi pole single phase ac motor and
pump on a central heating system, in order to select
alternative fi::ed motor speeds and change pump output to
match the load on the system.
2) An electronic device as claimed in 1), that detects heat
transfer in a hot water heating system by using a single
temperature sensor, positioned on the return line before
the water heater/boiler.
The detected temperature is identified within one of
several "windows" and the motor speed changeover initiated
by the progressive transition between windows.
3) An electronic device, as claimed in 1) and 2) above that
changes motor speed according to any increase or decrease
in the volumetric capacity of the water heating system. A
reduction in capacity leading to a reduction in motor speed
and pumping rate.
4) An electronic device as claimed in 2), that in a
disproportionate two (or more) circuit system employing a
diverting valve, eg hot water and/or central heating,
always selects the slowest pump speed for the smallest
circuit.
5) An electronic device according to the preceding claims, in
which the lowest electrical power is used for water
circulation under predetermined load conditions.
6) An electronic device according to the preceding claims that
can be fitted as an accessory to any single phase ac motor
that employs pole switching as a means of changing speed,
and connects directly onto the existing terminals with a
substitute plug.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9422813A GB2296112A (en) | 1994-11-11 | 1994-11-11 | Speed controller for a single phase AC motor in a water heating system |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9422813A GB2296112A (en) | 1994-11-11 | 1994-11-11 | Speed controller for a single phase AC motor in a water heating system |
Publications (2)
Publication Number | Publication Date |
---|---|
GB9422813D0 GB9422813D0 (en) | 1995-01-04 |
GB2296112A true GB2296112A (en) | 1996-06-19 |
Family
ID=10764262
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB9422813A Withdrawn GB2296112A (en) | 1994-11-11 | 1994-11-11 | Speed controller for a single phase AC motor in a water heating system |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2296112A (en) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1271094A (en) * | 1968-04-13 | 1972-04-19 | Mini Ind Constructillor | Single phase ferroresonant servomotor |
GB1555511A (en) * | 1975-04-18 | 1979-11-14 | Matsushita Electric Ind Co Ltd | Compressor control system |
GB2113427A (en) * | 1981-12-10 | 1983-08-03 | Stock Electronics Limited | Central heating systems |
-
1994
- 1994-11-11 GB GB9422813A patent/GB2296112A/en not_active Withdrawn
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB1271094A (en) * | 1968-04-13 | 1972-04-19 | Mini Ind Constructillor | Single phase ferroresonant servomotor |
GB1555511A (en) * | 1975-04-18 | 1979-11-14 | Matsushita Electric Ind Co Ltd | Compressor control system |
GB2113427A (en) * | 1981-12-10 | 1983-08-03 | Stock Electronics Limited | Central heating systems |
Non-Patent Citations (1)
Title |
---|
WPI Acc No 87-257610/37 and DE3607162 * |
Also Published As
Publication number | Publication date |
---|---|
GB9422813D0 (en) | 1995-01-04 |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |