305C Series
Vishay Cera-Mite
PTCR Motor Start Packages
PSC Single Phase Motor Start Assist
鈥?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 technolo-
gies 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鈥檚
auxiliary winding. After time delay (t),
the current passing through the PTCR
causes it to heat and 鈥渟witch鈥?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
L
1
M
T
HERM
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 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.
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 擄C
20.0
PD
Protective
Device
TS
Internal
Motor
Winding
Overtemp.
Switch
PSC
MOTOR
MAIN
M
Optional OFF
Time Delay
TR
Relay
C
R
AUX.
M
PTCR
Low Voltage Control Transformers Not Shown
L
2
Document Number: 23086
Revision 14-May-02
ceramite.support@vishay.com
www.vishay.com
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