ptc thermistors motor start packages www.vishay.com for technical questions, contact: ceramitesupport@vishay.com document number: 23086 74 revision: 20-may-10 ptc305c series vishay cera-mite features ? large diameter ceramic pellets for high starting current ? various package sizes for optimum inrush current and switching time ? rugged mechanical construction for reliable long life operation ? ul approved packages ? plastic case mold ul 94 v-0 approved ? adapted accessories for easy mounting ? compliant to rohs directive 2002/95/ec applications ? single phase motorstart assist in - refrigerator systems - airconditioning systems - heat-pumps - small compressors quick reference data parameter value unit resistance value at 25 c 15 to 75 tolerance on resistance value 30 % current ratings 6 to 36 a rms switching times (typical) 0.25 to 1.0 s maximum voltage rating 410, 500 v rms operating temperature range - 10 to + 80 c storage temperature range - 25 to + 105 c ptc motor start selection chart vishay cera-mite part number case style r dyn ( ) 20 % r 25 ( ) 30 % switch time t (s) at 230 v current rating (a rms ) max. voltage rating (v rms ) compressor range (btu 000) compressor range (hp) ptc305c20 c 25 35 0.25 10 410 10 to 28 0.75 to 2.0 ptc305c21 c 35 50 0.35 8 410 8 to 18 0.5 to 1.5 ptc305c22 c 50 75 0.50 6 410 5 to 12 0.25 to 1.0 ptc305c19 b 20 30 0.50 18 500 20 to 50 1.5 to 4.0 ptc305c12 b 25 40 0.60 15 500 18 to 42 1.5 to 3.5 ptc305c2 b 50 85 1.00 12 500 10 to 25 1.0 to 2.5 ptc305c9 a 10 15 0.50 36 500 28 to 68 3.0 to 7.0 ptc305c11 a 12.5 20 0.60 30 500 28 to 62 3.0 to 6.0 ptc305c1 a 25 42.5 1.00 24 500 14 to 36 1.5 to 3.5
document number: 23086 for technical questions, contact: ceramitesupport@vishay.com www.vishay.com revision: 20-may-10 75 ptc305c series ptc thermistors mo tor start packages vishay cera-mite economical solid state torque assist for heat pumps, room air, commercial and residential air conditioning and refrigeration systems positive temperature coefficient themistors (ptc) 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 v/240 v psc compressor motors. safety agency recognition vishay cera-mite motor st art ptc thermistors 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. all packages and accessories are rohs compliant. relative comparison of various motor starting methods 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. the importance of each cat egory is dependent upon the motor application and industry sector. in general, if the ptc starter produces sufficient starting torque, it is considered the simplest and most economical choice. table 1 simplified ptc starting diagram start sequence. when starting the compressor, contactor (m) closes; the ptc, which is at low resistance, provides starting current to the motor?s auxiliary winding. after time delay (t), the current passing through the ptc 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 ptc 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 ptc cools to it s initial low resistance and is again ready to provide torque assist on the next startup. restart. it is important to provide time between motor starts to allow the ptc to cool to near its initial temperature. this time is usually 3 min to 5 min and is determined by the thermostat (therm) or separa te 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 ptcs are applied to compressors having means to equalize pressure during shutdown. typical ptc characteristics as a motor start device starting method mechanical electrical financial ease of wiring panel space required sensitive to mounting direction acceleration torque produced acceleration (switch) time reset time required emi/rfi generated technology inventory mix required reliability purchased cost ptc starter simple 2 wire lowest no lowest fixed 3 min to 5 min no solid state lowest highest lowest start cap with ptc acting as a current relay moderate 2 wire or 3 wire medium yes medium fixed 2 min to 5 min no solid state medium medium medium start cap used with potential or current relay difficult 4 wire or 5 wire highest yes highest variable based on motor speed none yes electro mechanical highest lowest highest fig t-2 m low voltage control transformers not shown protective device optional off time delay relay protective device ac line 120 or 240 volts ac t herm internal motor winding overtemp switch main psc motor aux. ptc ts tr tr pd m m m l 1 l 2 c r fig t-3 resistance current switch time (t) ptc current (a rms ) 0.01 50 100 150 1000 10 000 10 100 ptc resistance ( ) ptc temperature c 0.1 1.0 10.0
www.vishay.com for technical questions, contact: ceramitesupport@vishay.com document number: 23086 76 revision: 20-may-10 ptc305c series vishay cera-mite ptc thermistors mo tor start packages start and acceleration torques single phase psc high efficiency compressors the use of a ptc 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 the time to accelerate a rotating machine is: accelerating time (s) = (avg. torque = curve b - curve a) 1. if (curve b - curve a) is ze ro 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 a ccelerate from rest to 1/2 speed is critical, as the average torque available in this region is limited. select a ptc with sufficient switching time (t) to accelerate the compressor. 3. scroll and rotary compre ssors may have less breakaway torque than shown. 4. a compressor with no equalization may require over 100 % starting torque and time as long as several seconds. ptc starters not recommended. considerations for current in ptc approximate equivalent circuit psc motor at zero speed for running conditions: for the greatest starting torque , ptc should be chosen to make: v m x i m = v aux x i aux . in many cases the auxiliary volt-amperes are limited to about 50 % of the main winding volt-amperes to get 50 % to 70 % rated torque. then at start, with ptc in series : z' aux = r ptc + z aux i aux star t = i r start + i c start if z aux is low impedance, less than 10 % of r ptc then it can be ignored and i ptc at start = this closely approximates the c ondition for motors over 1/2 hp. fig t-5 fig t-6 simplified voltage diagram of the psc motor at operating speed. note (1) i a (auxiliary current) leads i m (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 rpm wk 2 lb ft 2 () avg. torque lb ft () 308 ---------------------------------------------------------------- 100 75 50 25 0 5th 7th slot percent rated speed 100 200 a 2 a 1 b 1 b 2 curve b2 motor speed versus torque with run cap and ptcr curve b1 motor speed versus torque with run cap only curve a2 torque req?d to accelerate compressor at partial differential pressure curve a1 torque req?d to accelerate unloaded compressor cold breakaway torque percent rated torque full load operating point possible region of harmonic torques max. torque i l run () hp 746 v m pf eff --------------------------------- i l start () i l run = if v aux v m then i m and i aux i l 2 ------- = = if v aux v m () then i aux i l 2 ------- v m v aux ----------- - and z aux v m i aux --------- = = i rstart through ptc v m z aux ----------- = i cstart through run cap v m x c ------- x c 1 2 fc ------------- - = ; = v m r ptcr ----------------- fig t-5 line voltage v m i aux i m i c r m (1) x m (1) l 2 c ptc x aux r aux *r and x are total of stator and rotor v aux l 1 i l i r v m applied voltage v a i a i m 7 7 v ptc = v c = i ac
document number: 23086 for technical questions, contact: ceramitesupport@vishay.com www.vishay.com revision: 20-may-10 77 ptc305c series ptc thermistors mo tor start packages vishay cera-mite effect of ptc resistance on starting torque of psc motors table 2 a. rated torque is the torque at full speed rated load. it is calculated as: 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 ptc to increase starting torque. for reciprocating compressors, it is advised to choose a resistance value that gives at least 50 % rated torque at locked roto r. scroll and rotary compressors may require less torque. typical ptc current vs. time showing definition of r dyn and switch time (t) 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 ptc 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 ptc 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 table 3 motor hp (table 4) (note 7) locked rotor torque with run cap only % rated torque (see a) starting torque with run cap and ptc (% rated torque) (see b) resistance (r dyn ) 50 25 20 12.5 10 0.5 1 2 3.5 5 6.5 25 % to 35 % 25 % to 35 % 20 % to 30 % 20 % to 30 % 15 % to 25 % 15 % to 25 % 70 % to 100 % 50 % to 70 % 40 % to 60 % na na na 80 % to 100 % 70 % to 100 % 60 % to 90 % 40 % to 60 % na na na na 70 % to 100 % 50 % to 85 % 40 % to 60 % na na na 70 % to 100 % 60 % to 90 % 50 % to 75 % 40 % to 70 % na na 80 % to 100 % 70 % to 100 % 60 % to 90 % 50 % to 80 % torque ib ft ? () hp 5250 rpm --------------------------- - = fig t-7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 230 v rms i ptc max. r dyn = peak current 20 % peak current i ptc (a rms ) (normalized) time to switch (s) motor contactor closes ptc switchout switch time (t) oscilloscope shunt i ptc e rms ptc m = ptc mass (g) t 0 = ptc temp at time 0 k = 0.75 j/g/c time (t) km (130 c - t 0 ) r dyn v 2 ptc start capacitor ptc value 50 f 50 75 f 37.5 100 f 25 125 f 20 200 f 12.5 250 f 10 x c 1 2 fc ------------- - =
www.vishay.com for technical questions, contact: ceramitesupport@vishay.com document number: 23086 78 revision: 20-may-10 ptc305c series vishay cera-mite ptc thermistors mo tor start packages ptc selection ? choosing the best ptc for an application is a simple matter. see table 4 and tabl e 2. vishay cera-mite ptcs 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 ? using a device too small or resistance too high will give inadequate starting performance. an oversize device will not harm the motor, but may no t be optimum with regards to acceleration dynamics, or power dissipation ? the ptc is generally self protecting when applied within the voltage and current ratings ? all ptc305c series starters and accessories are rohs compliant table 4 notes (1) preferred values. (2) part number is stamped on the device for ul recognition. the customer part number can also include 1 or 3 character alpha-numer ic suffix to designate specific customer marking and acce ssory furnished. the suffix is not marked on the part. certified outline drawing an d complete part number will be furnished on request fo r specific applications.(example: ptc305c 19k01.) mounting brackets and other accesso ries can be ordered separately. (3) r dyn is nominal resistance equal to u/i when 230 v, 50 hz/60 hz is applied (see fig t-7). this resistance determines current and m aximum starting torque at the moment of application of volt age to the motor and can be m easured with an oscilloscope. for receiving inspection or r outine trouble shooting, the dc resistance at 25 c (r 25 ) as measured with an ohmmeter is approximately 50 % greater. for example: ptc305c20 measured with an ohmmeter would be 35 30 % tolerance. (4) resistance values are duplicated in several case sizes (i.e.: pt c305c20, c12, and c1) to provide longer switch time (t) and hig her current ratings (see fig. t-7). larger parts may be needed for more difficult starting conditions (voltage or temperature) or may be us ed for accelerating fans agai nst back pressure. (5) maximum current in the ptc is determined by motor auxiliary winding impedance is usually small compared to ptc resistance, and does not materially affect ptc current. current in ptc is a percentage of the full motor inrush (locked rotor) current; usually 30 % to 50 % (see fig t-5). (6) in application, the maximum voltage is the voltage that appears across the run capacit or 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 265 v. the ptc305c20, 21 and 22 are also used on 120 v systems wher e the motor is designed to us e same run capacitor and ptc as equivalent 230 v compressor. (7) this is the power used to keep the ptc switched in a high imped ance state under full load runni ng conditions at typical ambie nt temperature. (8) btu and horsepower ranges are for reference only. ptc may be app lied outside those ranges as long as maximum voltage and maxim um current are not exceeded. scroll and rotary compressors may requi re less starting assistance al lowing use of smaller devices. ptc motor start selection chart vishay cera-mite part number (2) case style (2) resistance ( ) (3) switch time (4) (t) s at 230 v current rating (5) (a rms ) max. voltage rating (6) (v rms ) avg. power dissipation (7) (w) compressor range (8) r dyn 20 % r 25 30 % btu (000) hp ptc305c20 (1) ptc305c21 ptc305c22 (1) c c c 25 35 50 35 50 75 0.25 0.35 0.50 10 8 6 410 410 410 3.5 3.5 3.5 10 to 28 8 to 18 5 to 12 0.75 to 2.0 0.5 to 1.5 0.25 to 1.0 ptc305c19 (1) ptc305c12 (1) ptc305c2 b b b 20 25 50 30 40 85 0.50 0.60 1.00 18 15 12 500 500 500 7 7 7 20 to 50 18 to 42 10 to 25 1.5 to 4.0 1.5 to 3.5 1.0 to 2.5 ptc305c9 (1) ptc305c11 ptc305c1 (1) a a a 10 12.5 25 15 20 42.5 0.50 0.60 1.00 36 30 24 500 500 500 9 9 9 28 to 68 28 to 62 14 to 36 3.0 to 7.0 3.0 to 6.0 1.5 to 3.5 ul file e97640 maximum line voltage minimum r dyn ---------------------------------------------------------------------
document number: 23086 for technical questions, contact: ceramitesupport@vishay.com www.vishay.com revision: 20-may-10 79 ptc305c series ptc thermistors mo tor start packages vishay cera-mite dimensions for ptc motor start devices - in inches (millimeters) ? packaged motor start ptcs are offere d 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 a. it is furnished with a round mounting bracket. case style b case style b is a 2-terminal single pellet unit with current carrying capacity up to 18 a. depending upon the model, either a u-shaped or round bracket is furnished. 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 a. a jumper wire to complete the parallel connection with the two internal pellets is required. operating temperature under normal operation, the ceramic pellet inside the case reaches a temperature of 150 c. 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 100 c while the motor is running. an appropriate mounting location and 105 c, 600 v wiring are recommended. connection diagrams ptc thermistors 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. case c mounting bracket ptc305c20 - black ptc305c21 - black ptc305c22 - black ptcaux36-520m - round round bracket - spring steel phosphate & oil finish. accepts #6 sheet metal screw fig t-8 1.780 (45.2) max. 0.810 (20.6) 0.880 (22.4) 0.200 (5.1) max. weld projection (2) 0.050 (1.25) ht. typ. 0.175 (4.45) wd. typ. 0.920 (23.35) 0.980 (24.90) 0.609 (15.45) 0.641 (16.30) 0.329 (8.35) 0.358 (9.10) 0.579 (14.7) 0.609 (15.5) 0.135 0.140 (3.50 0.07) dia. 0.298 (7.55) 0.328 (8.35) 0.975 (24.75) 1.025 (26.05) 0.25 (6.35) typ. case b mounting bracket ptc305c2 - black ptc305c12 - black or blue ptc305c19 - blue ptcaux7-36-5c - u-shaped ptcaux36-520h - round round bracket - spring steel phosphate & oil finish. acce p ts #6 sheet metal screw steel u-bracket - accepts #8 sheet metal screw fig t-9 2.37 (60.2) max. 0.20 (5.1) typ. 0.25 (6.35) max. 2 places weld projection (3) 0.050 (1.27) ht. typ. 0.175 (4.45) wd. typ. 1.50 (38.1) max. 0.650 (16.5) max. 0.15 (3.81) od x 0.055 (1.4) ht 4 places 1.344 (34.1) 1.406 (35.9) 1.430 (36.3) 1.530 (38.9) 0.990 (25.1) 1.010 (25.7) 0.213 0.223 (5.54 0.13) 0.110 (2.8) nail pierce 0.120 (3.05) ref. 0.550 (13.95) 0.580 (14.75) 1.490 (37.8) 1.510 (38.4) 1.05 (26.7) 1.44 (26.7) max. dia. 1.475 (37.45) 1.525 (38.75) 0.579 (14.7) 0.609 (15.5) 0.135 0.140 (3.50 0.07) dia. 0.298 (7.55) 0.328 (8.35) 0.25 (6.35) typ. case a mounting bracket wire jumper ptc305c1 - blue ptc305c9 - tan ptc305c11 - tan ptcaux7-36-4c - u-shaped ptcaux36-520h - round ptcaux50-1278 9.75" long 105 c wire fig t-10 1.50 (38.1) max. 0.650 (16.5) max. 2.75 (69.9) max. (to end of q.c.) 5.25 (133.5) max. 1.716 (43.6) 1.781 (45.4) 0.25 (6.35) max. 3 places weld projection (2) 0.050 (1.27) ht. typ. 0.175 (4.45) wd. typ. 0.20 (5.1) typ. 0.15 (3.8) od x 0.055 (1.4) ht 4 places 1.590* (40.4) 1.690 (43.0) 0.990 (25.1) 1.010 (25.7) 0.185 0.190 (4.75 0.08) 0.110 (2.8) nail pierce 0.120 (3.05) ref. 0.550 (13.95) 0.580 (14.75) 1.490 (37.85) 1.510 (38.35) 1.05 (26.7) 1.44 (36.6) max. dia. * installed dimension steel u-bracket - accepts #8 sheet metal screw round bracket - spring steel phosphate & oil finish. accepts #6 sheet metal screw 1.475 (37.45) 1.525 (37.75) 0.579 (14.7) 0.609 (15.5) 0.135 0.140 (3.50 0.07) dia. 0.298 (7.55) 0.328 (8.35) 0.25 (6.35) typ. fig t-11 fig t-12 motor run cap a style 3-terminal case motor run cap b & c style 2-terminal case
www.vishay.com for technical questions, contact: ceramitesupport@vishay.com document number: 23086 80 revision: 20-may-10 ptc305c series vishay cera-mite ptc thermistors mo tor 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 25 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 switchi ng time without dependence on sensing speed, counter emf, or current. rugged mechanical construction vishay cera-mite ptc 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 ?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, ptc start devices save several wires, occupy less panel space, mount more easily, and cost less. outstanding reliability over a twenty year period, with an installed base of millions of vishay cera-mite ptc start devices, experience has demonstrated reliability at 1.0 fit or less. users have benefited from very low warranty expense. restart considerations a properly sized ptc will provide adequate star ting current and starting time with a cool down time of 3 min to 5 min, coordina ting perfectly with standard ?off delay? equaliz ation timers restart characteristics of the three case sizes are shown. fig t-13 fig t-14 fig t-15 25 % initial current 50 75 100 0 0 0.2 0.4 0.6 0.8 5 min coolin g 3 min cooling cold start 0 0.2 0.4 0.6 0.8 1.0 5 min cooling 3 min cooling cold start 25 50 75 100 0 0 0.2 0.4 0.6 0.8 1.0 25 50 75 100 0 1.2 cold start 3 min cooling 5 min cooling time (s) time (s) time (s) case style c case style b case style a
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