Psc Motor Starting - Tecumseh AH5540E Service Handbook

potential relay removes the start ca-
pacitor from the circuit after the mo-
tor is up to speed. This motor may
use either:
• an external thermal protector, or
• an internal thermal protector.
Permanent Split Capacitor
(PSC)
Here a run capacitor is in series with
the start winding. Both run capacitor
and start winding remain in the circuit
during start and after motor is up to
speed (see Figure 3-5). This normal
starting torque motor is sufficient for
capillary and other self-equalizing
system. No start capacitor or relay
is necessary. For additional starting
torque, a proper start assist kit may
be added (see Figure 3-6). Some
start assist kits may include:
• a wired-in Positive Temperature
Coefficient (PTC) relay, or
• a module Positive Temperature
Coefficient (PTC) relay.
This motor may use either:
• an external thermal protector, or
• an internal thermal protector.
PSC motors are basically air condi-
tioning compressor motors and are
very common up through 5 HP .

PSC Motor Starting

Tecumseh Products Company pioneered the
development of Permanent Split Capacitor
compressor motors. This type of motor elim-
inates the need for potentially troublesome
and costly extra electrical components, e.g.,
start capacitors and potential motor starting
relays (see Figure 3-5).
To fully realize the capabilities of this simplified
type of compressor motor, it is necessary
to understand its starting and operating
characteristics and the field conditions that
can affect it.
The following conditions affect PSC motor
starting:
• Low voltage: Reduces motor start-
ing and running torque. A 10%
voltage drop reduces a motor's
starting ability by 19%. Low volt-
age can cause no start, hard start,
light flicker, and TV screen flip flop.
Control
Line 1
Relay -
Potential
Line 2
Ground
Compressor -
Unit Ground
FIGURE 3-4:
CSR motor diagram
Control
Line 1
Line 2
(115 Volt Only - Neutral)
Ground
Compressor -
Unit Ground
Run Capacitor
Control
Line 1
Line 2
FIGURE 3-5:
PSC motor diagram
(115 Volt Only - Neutral)
Ground
Compressor -
Thermal Protector
Unit Ground
Line 1
Run Capacitor
C
Plug-In
Run Capacitor
C
2
C
1
Line 2
Thermal Protector
N
Line 1
(115 Volt Only - Neutral)
C
Ground
Plug-In
PTC Starting and
Run Capacitor
Protector Pa ckage
Compressor -
Unit Ground
C
2
C
1
Line 2
N
(115 Volt Only - Neutral)
Ground
PTC Starting and
Protector Pa ckage
Compressor -
Unit Ground
Control
FIGURE 3-6: PSC motor diagram with start
Line 1
Relay -
assist kit that includes a module
Potential
Line 2
PTC relay
Ground
Compressor -
Unit Ground
Control
Line 1
Relay -
Potential
Line 2
External or Internal
Thermal Protector
C
S
R
External or Internal
Thermal Protector
C
S
External or Internal
R
Thermal Protector
C
S
R
C
S
PTC
Relay
R
C
S
PTC
Relay
R
External or Internal
Thermal Protector
C
External or Internal
Thermal Protector
S
R
C
17