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305C Series
Vishay Cera-Mite
ceramite.support@vishay.comDocument Number: 23086
Revision 14-May-02
ECONOMICAL SOLID STATE TORQUE ASSIST FOR HEAT PUMPS, ROOM AIR, COMMERCIAL
AND RESIDENTIAL AIR CONDITIONING AND REFRIGERATION SYSTEMS
RELATIVE COMPARISON OF VARIOUS MOTOR STARTING METHODS
Table 1
Fig T-2
TYPICAL PTCR CHARACTERISTICS
AS A MOTOR START DEVICE
Fig T-3
MECHANICAL ELECTRICAL FINANCIAL

PANEL SENSITIVE TO ACCELERATION ACCELERATION RESET INVENTORY
STARTING EASE OF SPACE MOUNTING TORQUE (SWITCH) TIME EMI/RFI MIX PURCHASED
METHOD WIRING REQUIRED DIRECTION PRODUCED TIME REQUIRED GENERATED TECHNOLOGY REQUIRED RELIABILITY COST
PTCR Starter Simple Lowest No Lowest Fixed 3 - 5 No Solid State
Lowest Highest Lowest

2 Wire Minutes
Start Cap with Moderate Medium Yes Medium Fixed 2 - 5 No Solid State
Medium Medium Medium
PTCR Acting as 2 or 3 Minutes
A Current Relay Wire
Start Cap used Difficult Highest Yes Highest Variable None Yes Electro
Highest Lowest Highest
With Potential or 4 or 5 Based on Mechanical
Current Relay Wire Motor Speed
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.
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.
Three methods have historically been employed to generate
starting torque for PSC motors. All are well-proven technolo-
gies and may be compared relative to one another based
upon categories shown below.
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.
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.
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 equaliza-
tion, 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.
PTCR Motor Start Packages
PSC Single Phase Motor Start Assist
20.0
PD
C
R
MAIN
PTCR
PSC
MOTOR
AUX.
TS
Internal
Motor
Winding
Overtemp.
Switch
Protective
Device
Optional OFF
Time Delay
Relay
TR
M
Protective
Device
L
2
M
M
AC Line
120 or 240
VOLTS AC
THERM
TR
L
1
Low Voltage Control Transformers Not Shown
M
PTCR Temperature °C
RESISTANCE
CURRENT
Switch Time (t)
PTCR
Current
(Amperes)
20.0
0.02
50 100 150
1,000
10,000
10
100
PTCR Resistance (ohms)