305C21 Datasheet, PDF (1/6 Pages) Vishay Siliconix – PTCR Motor Start Packages PSC Single Phase Motor Start Assist

305C Series
PTCR Motor Start Packages
Vishay Cera-Mite
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.
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
Three methods have historically been employed to generate
The importance of each category is dependent upon the
starting torque for PSC motors. All are well-proven technolo-
motor application and industry sector.
gies and may be compared relative to one another based
upon categories shown below.
In general, if the PTCR starter produces sufficient starting
torque, it is considered the simplest and most economical
choice.
Table 1
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
2 Wire
Lowest
Fixed
3-5
Minutes
No
Solid State _{Lowest Highest Lowest}
Start Cap with Moderate Medium Yes
PTCR Acting as 2 or 3
Medium
Fixed
2-5
No Solid State
Minutes
Medium Medium Medium
A Current Relay Wire
Start Cap used Difficult Highest Yes
With Potential or 4 or 5
Highest
Variable None
Based on
Yes
Electro
Mechanical
Highest
Lowest
Highest
Current Relay Wire
Motor Speed
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 (CR)
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.
Fig T-2
L₁
THERM
TR
AC Line
120 or 240
VOLTS AC
M
PD
M _Protective
Device
TS
Internal
Motor
M
Winding
Overtemp.
Switch
Optional OFF
Time Delay TR
Relay
MAIN
PSC
MOTOR
C_R
AUX.
Protective
Device
L₂
M
PTCR
Low Voltage Control Transformers Not Shown
TYPICAL PTCR CHARACTERISTICS
AS A MOTOR START DEVICE
Fig T-3
10,000 ^CURRENT
20.0
1,000
100
10
PTCR
Current
(Amperes)
Switch Time (t)
RESISTANCE
0.02
50
100
150
PTCR Temperature °C
20.0
Document Number: 23086
Revision 14-May-02
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