APPLICATION GUIDELINES
18
FRCC.PC.007.B5.02
ELECTRICAL DATA, CONNECTIONS AND WIRING
Winding resistance is the resistance between
phases at 25°C (resistance value +/- 7%).
Winding resistance is generally low and it requires
adapted tools for precise measurement. Use a dig-
ital ohm-meter, a "4 wires" method and measure
under stabilised ambient temperature. Winding
resistance varies strongly with winding tempera-
ture ; if the compressor is stabilised at a diff erent
value than 25°C, the measured resistance must be
corrected with following formula:
a + t
amb
R
tamb
= R
25°C
_______
a + t
25°C
t
25°C
: reference temperature = 25°C
t
amb
: temperature during measurement (°C)
R
25°C
: winding resistance at 25°C
R
amb
: winding resistance at t
amb
Coeffi cient a = 234.5
The max. operating current is the current when
the compressors operates at maximum load con-
ditions and 10% below nominal voltage (+15°C
evaporating temperature and +68°C condensing
temperature).
Max Oper. A can be used to select cables and
contactors.
In normal operation, the compressor current
consumption is always less than the Max Oper. A.
value.
The MCC is the current at which the motor pro-
tection trips under maximum load and low volt-
age conditions. This MCC value is the maximum
at which the compressor can be operated in tran-
sient conditions and out of the application enve-
lope. Above this value, the internal motor protec-
tion or external electronic module will cut-out the
compressor to protect the motor.
Locked Rotor Amp value is the higher average
current as measured on mechanically blocked
compressor tested under nominal voltage. The
LRA value can be used as rough estimation for the
starting current. However in most cases, the real
starting current will be lower. A soft starter can be
applied to reduce starting current.
Winding resistance
Max. operating Current
MCC (Maximum Continuous
Current)
LRA (Locked Rotor Amp)
The inrush current for the Performer® SH scroll
compressors with motor code 4 (400V /3ph /
50Hz or 460V / 3ph / 60Hz) can be reduced using
the Danfoss digitally-controlled MCI compressor
soft starter. MCI soft starters are designed to re-
duce the starting current of 3-phase AC motors;
they can reduce the inrush current by up to 40%,
thereby eliminating the detrimental eff ects of
high starting torque surges and costly demand
charges from the resultant current spike. Upon
starting, the controller gradually increases the
voltage supplied to the motor until full-line volt-
age has been reached. All settings, such as ramp-
up time (less than 0.5 sec) and initial torque, are
preset and do not require modifi cation.
Danfoss MCI
soft-start controller
Compressor model
Soft start reference
Ambient max. 40°C
Soft start reference
Ambient max. 55°C
SH090 MCI15C MCI15C
SH105 MCI25C MCI25C
SH120 MCI25C MCI25C
SH140 MCI25C MCI25C *
SH161 MCI25C MCI25C *
SH184 MCI25C MCI25C *
SH180 MCI50CM MCI50CM
SH240 MCI50CM MCI50CM *
SH300 MCI50CM * MCI50CM *
SH380 MCI50CM * MCI50CM *
* by pass contactor K1 is required
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