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305C Series
Vishay Cera-Mite
PTCR Motor Start Packages PSC Single Phase Motor Start Assist
* ECONOMICAL SOLID STATE TORQUE ASSIST FOR HEAT PUMPS, ROOM AIR, COMMERCIAL AND RESIDENTIAL AIR CONDITIONING AND REFRIGERATION SYSTEMS
Positive Temperature Coefficient Resistors have been used for many years in millions of HVAC applications to provide starting torque assistance to Permanent Split Capacitor (PSC) single phase compressor motors. Sizes are available to cover the full range of 120/240 volt PSC compressor motors. Three methods have historically been employed to generate starting torque for PSC motors. All are well-proven technologies and may be compared relative to one another based upon categories shown below. Table 1
MECHANICAL ELECTRICAL FINANCIAL
Safety Agency Recognition Vishay Cera-Mite motor start PTCRs are recognized by Underwriter Laboratories file E97640 in accordance with Standard for Thermistor Type Devices UL 1434; and Canadian Standards C22.2 No. 0-1991.
RELATIVE COMPARISON OF VARIOUS MOTOR STARTING METHODS
The importance of each category is dependent upon the motor application and industry sector. In general, if the PTCR starter produces sufficient starting torque, it is considered the simplest and most economical choice.
STARTING METHOD PTCR Starter Start Cap with PTCR Acting as A Current Relay Start Cap used With Potential or Current Relay
EASE OF WIRING Simple 2 Wire Moderate 2 or 3 Wire Difficult 4 or 5 Wire
PANEL SENSITIVE TO ACCELERATION ACCELERATION RESET INVENTORY SPACE MOUNTING TORQUE (SWITCH) TIME EMI/RFI MIX PURCHASED REQUIRED DIRECTION PRODUCED TIME REQUIRED GENERATED TECHNOLOGY REQUIRED RELIABILITY COST Lowest No Lowest Fixed 3-5 No Solid State Lowest Highest Lowest Minutes Medium Yes Medium Fixed 2-5 No Solid State Medium Medium Medium Minutes Highest Yes Highest Variable Based on Motor Speed None Yes Electro Mechanical Highest Lowest Highest
SIMPLIFIED PTCR STARTING DIAGRAM
Start Sequence. When starting the compressor, contactor (M) closes; the PTCR, which is at low resistance, provides starting current to the motor's auxiliary winding. After time delay (t), the current passing through the PTCR causes it to heat and "switch" to a very high resistance. At this point the motor is up to speed and the run capacitor (C R ) determines the current in the auxiliary winding. The PTCR remains hot and at high resistance as long as voltage remains on the circuit. When contactor (M) opens, shutting off voltage to the compressor, the PTCR cools to its initial low resistance and is again ready to provide torque assist on the next startup. Fig T-2
L1 M THERM TR AC Line 120 or 240 VOLTS AC M
Protective Device
Restart. It is important to provide time between motor starts to allow the PTCR to cool to near its initial temperature. This time is usually 3 to 5 minutes and is determined by the thermostat (THERM) or separate time-delay relay (TR). Attempts to restart in less time may be successful depending on compressor equalization, line voltage, temperature, and other conditions. If the motor were to stall in a locked-rotor state, overload device (PD or TS) would open the line and a further time delay would occur until the motor overload is reset. Motor start PTCRs are applied to compressors having means to equalize pressure during shutdown.
TYPICAL PTCR CHARACTERISTICS AS A MOTOR START DEVICE
Fig T-3
10,000 PTCR Resistance (ohms)
CURRENT
20.0
1,000
PTCR Current (Amperes)
100
Switch Time (t) RESISTANCE
10
0.02 150 50 100 PTCR Temperature C
20.0
PD
Protective Device
TS
Internal Motor Winding Overtemp. Switch
PSC MOTOR MAIN
M
Optional OFF Time Delay TR Relay
CR
AUX.
M
PTCR
Low Voltage Control Transformers Not Shown
L2
Document Number: 23086 Revision 14-May-02
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305C Series
Vishay Cera-Mite
PTCR Motor Start Packages
START AND ACCELERATION TORQUES SINGLE PHASE PSC HIGH EFFICIENCY COMPRESSORS
The use of a PTCR start assist insures sufficient acceleration torque to overcome not only breakaway friction, but also parasitic asynchronous torques associated with the 5th and 7th motor harmonics or lamination slot harmonics. ACCELERATION TIME CONSIDERATIONS RPM x WK2 (lb ft 2 ) Avg. Torque (lb ft) x 308
Percent Rated Speed
Fig T-4
100
A1 A2
75
Full Load Operating Point
max. Torque
The time to accelerate a rotating machine is: Accelerating Time (Seconds) =
50
B1
(Avg. Torque = Curve B - Curve A)
B2
1. If (Curve B - Curve A) is zero or less, the motor may stall. 2. In calculating torque available from Curve B, allowance should be made for cusps in the torque curve due to harmonics. The time needed to accelerate from rest to 1/2 speed is critical, as the average torque available in this region is limited. Select a PTCR with sufficient switching time (t) to accelerate the compressor. 3. Scroll and rotary compressors may have less breakaway torque than shown. 4. A compressor with no equalization may require over 100% starting torqe and time as long as several seconds. PTCR starters not recommended.
25
5th 7th Slot
Possible Region of Harmonic Torques
100 200
0
Cold Breakaway Torque
Percent Rated Torque
CURVE A1 Torque req'd to accelerate unloaded compressor
CURVE A2 Torque req'd to accelerate compressor at partial differential pressure
CURVE B1 Motor speed versus torque with run cap only
CURVE B2 Motor speed versus torque with run cap and PTCR
CONSIDERATIONS FOR CURRENT IN PTCR APPROXIMATE EQUIVALENT CIRCUIT PSC MOTOR AT ZERO SPEED
Fig T-5
HP x 746
Line Voltage VM
IL (run) = VM x pf x eff For running conditions:
IL (start) 6 x IL run
L1
L2
IL Iaux
IM Ic
RM *
XM *
IL If Vaux = VM, then IM and Iaux = If Vaux VM, then Iaux = IL x 2 Vaux VM and Zaux = Iaux 2 VM
C
PTCR
Raux Vaux
Xaux
IR
For the greatest starting torque, PTCR should be chosen to make: VM x IM = Vaux x Iaux. In many cases the auxiliary VoltAmperes are limited to about 50% of the main winding Volt-Amperes to get 50% - 70% rated torque. Then at start, with PTCR in series: Z'aux = R PTCR + Zaux VM I R start through PTCR = Z'aux IC start through Run Cap = Iaux start = IR start + IC start
If Zaux is low impedance, less than 10% of RPTCR then it can be ignored and IPTCR at start = V M RPTCR This closely approximates the condition for motors over 1/2 HP. www.vishay.com 4
*R and X are total of stator and rotor
Fig T-6 Simplified Voltage Diagram of the PSC Motor at Operating Speed *IA (auxiliary current) leads IM (main current) by 80 to 90 when C (run capacitor) is chosen for balanced operation at 3/4 to full load. Line Power Factor = sine 2

=V
C
1 VM ; Xc = ohms Xc 2 f C
=I
A
VM Applied Voltage
C
V
CR PT
IA
IM
VA
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Document Number: 23086 Revision 14-May-02
305C Series
PTCR Motor Start Packages
EFFECT OF PTC RESISTANCE ON STARTING TORQUE OF PSC MOTORS
Table 2
LOCKED ROTOR STARTING TORQUE WITH RUN CAP TORQUE WITH RUN AND PTCR (% RATED TORQUE) (SEE B) MOTOR HP CAP ONLY RESISTANCE (Rdyn) (TABLE 4) % RATED TORQUE (NOTE 7) (SEE A) 50 ohm 25 ohm 20 ohm 12.5 ohm 10 ohm 0.5 1 2 3.5 5 6.5 25% to 35% 70 - 100% 80 - 100% 25% to 35% 20% to 30% 20% to 30% 15% to 25% 15% to 25% 50 - 70% 70 - 100% NA NA NA NA NA NA NA NA NA
Vishay Cera-Mite
A. Rated torque is the torque at full speed rated load. It is calculated as: HP x 5250 Torque (lb - ft) = RPM The range shown includes both normal slip and high efficiency low slip motors. Starting torque varies as: (Line Voltage) 2 . B. Figure T-4 shows effect of using PTCR to increase starting torque. For reciprocating compressors, it is advised to choose a resistance value that gives at least 50% rated torque at locked rotor. Scroll and rotary compressors may require less torque.
40 - 60% 60 - 90% 70 - 100% 70 - 100% 80 - 100% 40 - 60% 50 - 85% 60 - 90% 70 - 100% NA NA 40 - 60% 50 - 75% 60 - 90% NA 40 - 70% 50 - 80%
TYPICAL PTCR CURRENT VS. TIME SHOWING DEFINITION OF RDYN AND SWITCH TIME (T)
Fig T-7 Time (t) KM (130C - T0)
Peak Current
RDYN V 2 PTCR
OSCILLOSCOPE
SHUNT
I PTCR Amperes (RMS) (Normalized)
M = PTCR mass T0 = PTCR temp at time 0 K = 0.75 J/g/ C
R DYN =
Applied Voltage (ERMS)
I PTCR at .05 Sec
ERMS
IPTCR
PTCR
20% Peak Current
Switch Time (t)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Motor Contactor Closes
PTCR Switchout
Time to Switch (Seconds)
START CAPACITOR REPLACEMENT
Capacitor Starting Comparison Some PSC motors have historically been started with a capacitor and relay. To deliver the same starting current as a start capacitor, a PTCR resistance is available for approximately equal ohms. Table 3 can be used for conversion. Even though the start current may be the same, the start torques may differ depending on the motor design. The PTCR has a fixed time built in. The start capacitor will stay in the circuit until a relay switches it out. The longer time provided by the capacitor and relay may be needed on applications where equalization is not present or adequate reset time is not available.
STARTING CURRENT APPROXIMATION BASED ON
Xc = 1 2fC Table 3
START CAPACITOR 50 microfarads 75 microfarads 100 microfarads 125 microfarads 200 microfarads 250 microfarads PTCR VALUE 50 ohms 37.5 ohms 25 ohms 20 ohms 12.5 ohms 10 ohms
Document Number: 23086 Revision 14-May-02
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305C Series
Vishay Cera-Mite
PTCR SELECTION
* Choosing the best PTCR for an application is a simple matter. See Table 4 and Table 2. Vishay Cera-Mite PTCRs are available in three case sizes (A, B, and C). * Table 4 indicates the correct case size for the application. Table 2 shows how to choose the correct resistance value. Table 4 * Using a device too small or resistance too high will give inadequate starting performance. An oversize device will not harm the motor, but may not be optimum with regards to acceleration dynamics, or power dissipation. * The PTCR is generally self protecting when applied within the voltage and current ratings.
PTCR Motor Start Packages
PTCR MOTOR START SELECTION CHART
VISHAY CERA-MITE PART CASE NUMBER STYLE 305C20* 305C21 305C22* 305C19* 305C12* 305C2 305C9* 305C11 305C1* C C C B B B A A A RESISTANCE (OHMS) RDYN R0 20% 30% 25 35 50 20 25 50 10 12.5 25 35 50 75 30 40 85 15 20 42.5 Note 2 SWITCH TIME (T) SECONDS @ 230V 0.25 0.35 0.50 0.50 0.60 1.00 0.50 0.60 1.00 Note 3 CURRENT RATING AMPERES 10 8 6 18 15 12 36 30 24 Note 4 MAX. VOLTAGE RATING VOLTS, RMS 410 410 410 500 500 500 500 500 500 Note 5 AVG. POWER DISSIPATION WATTS 3.5 3.5 3.5 7 7 7 9 9 9 Note 6 COMPRESSOR RANGE BTU (000) HP 10 - 28 8 - 18 5 - 12 20 - 50 18 - 42 10 - 25 28 - 68 28 - 62 14 - 36 0.75 - 2.0 0.5 - 1.5 0 ..25 - 1.0 1.5 - 4.0 1.5 - 3.5 1.0 - 2.5 3.0 - 7.0 3.0 - 6.0 1.5 - 3.5 Note 7
Note 1 * Preferred Values
Note 1 Part number is stamped on the device for UL recognition. The customer part number will also include 1 or 3 character alpha-numeric suffix to designate mounting bracket, customer marking, wire jumper, or other accessory furnished. The suffix is not marked on the part. Certified outline drawing and complete part number will be furnished on request for specific applications. (Example: 305C19K01.) Mounting brackets and other accessories are shipped in separate boxes to simplify installation in end use equipment. Note 2 RDYN is nominal resistance equal to E/I when 230 volts, 60 Hz is applied (See Fig T-7). This resistance determines current and starting torque at the moment of application of voltage to the motor and can be measured with an oscilloscope. For receiving inspection or routine trouble shooting, the D.C. resistance (Ro) as measured with an ohmmeter is approximately 50% greater. For example: 305C20 measured with an ohm meter would be 35 ohms 30% tolerance.
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Note 3 Resistance values are duplicated in several case sizes (ie: 305C20, C12, and C1) to provide longer switch time (t) and higher current ratings (See Fig T-7). Larger parts may be needed for more difficult starting conditions (voltage or temperature) or may be used for accelerating fans against back pressure. Note 4 Maximum current in the PTCR is determined by Max Line Voltage Min RDYN Motor auxiliary winding impedance is usually small compared to PTCR resistance, and does not materially affect PTCR current. Current in PTCR is a percentage of the full motor inrush (locked rotor) current; usually 30% to 50% (See Fig T-5). Note 5 In application, the maximum voltage is the voltage that appears across the
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run capacitor at rated speed, high line, light load. This is not the applied line voltage (See Fig T-6). THESE DEVICES ARE INTENDED FOR APPLICATION ON 240 VOLT LINES OR SYSTEMS WITH MAXIMUM LINE VOLTAGE UP TO 264 VOLTS. The 305C20, 21 and 22 are also used on 120 volt systems where the motor is designed to use same run capacitor and PTCR as equivalent 230 volt compressor. Note 6 This is the power used to keep the PTCR switched off under full load running conditions at typical ambient temperature. Note 7 BTU and horsepower ranges are for reference only. PTCR may be applied outside those ranges as long as maximum voltage and maximum current are not exceeded. Scroll and rotary compressors may require less starting assistance allowing use of smaller devices.
Document Number: 23086 Revision 14-May-02
305C Series
PTCR Motor Start Packages
Vishay Cera-Mite
DIMENSIONS FOR PTCR MOTOR START DEVICES - IN INCHES * PACKAGED MOTOR START PTCRs ARE OFFERED IN THREE DIFFERENT CASE SIZES TO ACCOMMODATE THE RANGE OF PSC COMPRESSOR MOTORS SERVED. CASE STYLE C
Case Style C is a 2-terminal single pellet device with current carrying capacity up to 10 amperes. It is furnished with a round mounting bracket. Fig T-8
1.780 max Weld Projection (2) .050 HT. TYP. .175 WD. TYP. .298 .328 .920 .980 .609 .641
CASE C 305C20 -- Black 305C21 -- Black 305C22 -- Black
.975 1.025 .135 DIA. .140 .329 .358
MOUNTING BRACKET 36-520M -- Round
Round Bracket -- Spring Steel Phosphate & Oil Finish. Accepts #6 Sheet Metal Screw
.579 .609
.810 .880
.200 max
CASE STYLE B
Case Style B is a 2-terminal single pellet unit with current carrying capacity up to 18 amperes. Depending upon the model, either a U-shaped or round bracket is furnished. Fig T-9
Weld Projection (3) .050 HT. TYP. .175 WD. TYP. 2.37 max .15 OD x .055 HT 4 places .990 1.010 1.430 1.530 1.50 max .213 .223 DIA. .650 max .20 TYP. .110 Nail Pierce .120 REF. 1.490 1.510 1.05 1.44 max .579 .609 .550 .580
CASE B 305C2 -- Black 305C12 -- Black or Blue 305C19 -- Blue
MOUNTING BRACKET 7-36-5C -- U-Shaped 36-520H -- Round
1.475 1.525 .135 DIA. .140 .298 .328
.25 max. 2 places
1.344 1.406
U-Bracket -- Spring Steel Zinc Dichromate Finish. Accepts #8 Sheet Metal Screw
Round Bracket -- Spring Steel Phosphate & Oil Finish. Accepts #6 Sheet Metal Screw
CASE STYLE A
Case Style A is a 3-terminal device that incorporates two pellets in parallel, resulting in lower resistance values and current carrying capacity up to 36 amperes. A jumper wire to complete the parallel connection with the two internal pellets is required. Fig T-10
5.25 max 2.75 max (To End of Q.C.)
.20 TYP. .15 OD X .055 HT 4 Places
CASE A 305C1 -- Blue 305C9 -- Tan 305C11 -- Tan
.185 .190 DIA. .990 1.010 1.590 1.690
MOUNTING BRACKET 7-36-4C -- U-Shaped 36-520H -- Round
.550 .580
WIRE JUMPER 50-1278 -- 9.75" Long 105C Wire
1.475 1.525 .135 DIA. .140 .298 .328
.110 Nail Pierce .120 REF. 1.490 1.510
1.05 1.44 max .579 .609
.650 max
.25 max 3 Places
1.716 1.781
Weld Projection (2) .050 HT. TYP. .175 WD. TYP.
1.50 max
U-Bracket -- Spring Steel Zinc Dichromate Finish. Accepts #8 Sheet Metal Screw
Round Bracket -- Spring Steel Phosphate & Oil Finish. Accepts #6 Sheet Metal Screw
OPERATING TEMPERATURE
Under normal operation, the ceramic pellet inside the case reaches a temperature of 150C. The plastic case material has been recognized by UL for operation up to this temperature. The actual temperature on the outside of the case will be approximately 100C while the motor is running. An appropriate mounting location and 105C, 600 volt wiring are recommended.
Document Number: 23086 Revision 14-May-02
CONNECTION DIAGRAMS
PTCR Motor Start units are connected directly across the PSC motor's "run" capacitor. Case style A is a 3-terminal device and uses an external jumper wire to connect the two internal pellets in parallel. A special "piggyback" terminal on the jumper wire provides for two connections on one side of the A-style case. Fig T-11
Motor Run Cap
Fig T-12
Motor Run Cap
A Style 3-Terminal Case
B & C Style 2-Terminal Case
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305C Series
Vishay Cera-Mite
PTCR Motor Start Packages
VISHAY CERA-MITE MOTOR START FEATURES ADVANCED CERAMIC ENGINEERING FOR HVAC
Vishay Cera-Mite's capability in large diameter ceramic pellets, unique formulations tailored to motor starting, and heavy duty electrode systems, have been developed and proven with the cooperation of HVAC industry experts over a period of 20 years.
INHERENT PERFORMANCE
Large diameter pellets make possible low resistance start devices needed to match torque requirements of high efficiency compressor motors. Various package sizes offer selection of timing intervals, providing optimum switching time without dependence on sensing speed, counter EMF, or current.
RUGGED MECHANICAL CONSTRUCTION
Vishay Cera-Mite PTCR cases are molded from a UL94V0 high temperature, engineered plastic/glass composite. Heavy duty aluminum contact plates and stainless steel force springs are scaled to the pellet sizes and current ratings to insure no internal arcing and to enhance quick reset time. Unbreakable metal mounting brackets attach securely with a single screw. The NEW "U" - brackets developed by Vishay Cera-Mite feature lower power consumption and greater reliability by maximizing case to ground thermal impedance.
SIMPLE AND ECONOMICAL
A solid state device requiring only 2 quick connect wires and one bracket screw to install. Compared to the alternative start capacitor and relay, PTCR start devices save several wires, occupy less panel space, mount more easily, and cost less.
OUTSTANDING RELIABILITY
Over a fifteen year period, with an installed base of millions of Vishay Cera-Mite PTCR start devices, experience has demonstrated reliability at 1.0 FITS or less. Users have benefited from very low warranty expense. Fig T-13
100 CASE STYLE C Cold Start 75 75 100
RESTART CONSIDERATIONS
A properly sized PTCR will provide adequate starting current and starting time with a cool down time of 3 to 5 minutes, coordinating perfectly with standard "off delay" equalization timers Restart characteristics of the three case sizes are shown.
Fig T-14
CASE STYLE B Cold Start 100
Fig T-15
CASE STYLE A Cold Start 75 5 Min. Cooling
% Initial 50 Current 3 Min. Cooling 5 Min. Cooling
50 3 Min. Cooling 25 5 Min. Cooling
50
3 Min. Cooling
25
25
0
0
.2 .4 .6 Time In Seconds
.8
0 0
.2
.4 .6 .8 Time In Seconds
1.0
0 0
.2
.4 .6 .8 Time In Seconds
1.0
1.2
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Document Number: 23086 Revision 14-May-02

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