www.vishay.com

3

305C Series

Vishay Cera-Mite

ceramite.support@vishay.com

Document 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

used for many years in millions of HVAC applications to

provide starting torque assistance to Permanent Split

Capacitor (PSC) single phase compressor motors.

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

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.

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

MAIN

PTCR

PSC

MOTOR

AUX.

TS

Internal

Motor

Winding

Overtemp.

Switch

Protective

Device

Optional OFF

Time Delay

Relay

TR

M

Protective

Device

M

M

AC Line

120 or 240

VOLTS AC

TR

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