t
25°C
t
amb
R
25°C (77°F)
R
amb
a
Three phase electrical characteristics
Table 9: Motor voltage code 4
Compressor model
LRA
MCC
Max. operating current
Winding resistance
A
A
A
Ω
CH290
260
62
56
0.52
CH485
389
106
91
0.28
LRA (Locked Rotor Amp)
Locked Rotor Amp value is the higher average current as measured on mechanically blocked compressors tested
under nominal voltage. The LRA value can be used as a rough estimation for the starting current. However, in most
cases, the real starting current will be lower.
MCC (Maximum Continuous Current)
The MCC is the current at which the motor protection trips under maximum load and low voltage conditions. This
MCC value is the maximum at which the compressor can be operated in transient conditions and out of the
application envelope. Above this value, the internal motor protection or external electronic module will cut-out the
compressor to protect the motor.
MOC (Maximum Operating Current)
The max operating current is the amperage the compressor will draw when it operates at maximum load of
operating envelope within the voltages printed on the nameplate.
MOC can be used as a basis for contactors selection.
Winding resistance
Winding resistance is the resistance between phases at 25°C (77°F) (resistance value +/- 7%). Winding resistance is
generally low and it requires adapted tools for precise measurement. Use a digital ohm-meter, a “4 wires” method
and measure under stabilised ambient temperature. Winding resistance varies strongly with winding temperature. If
the compressor is stabilised at a different value than 25°C (77°F), the measured resistance must be corrected using
the following formula:
R
tamb
= R
25°C (77°F)
a + t
amb
a + t
25°C (77°F)
reference temperature = 25°C (77°F)
temperature during measurement °C (°F)
winding resistance at 25°C (77°F)
winding resistance at tamb
Coefficient a = 234.5
Motor protection
CH Compressor models are delivered with a pre-installed motor protection module inside the terminal box. This
device provides for efficient and reliable protection against overheating and overloading as well as phase loss/
reversal.
The motor protector comprises a control module and PTC sensors embedded in the motor winding. The close
contact between thermistors and windings ensures a very low level of thermal inertia.
The motor temperature is being constantly measured by a PTC thermistor loop connected on S1-S2. If any
thermistor exceeds its response temperature, its resistance increases above the trip level (4,500 Ω) and the output
relay then trips – i.e. contacts M1-M2 are open. After cooling to below the response temperature (resistance < 2,750
© Danfoss | Climate Solutions | 2022.09
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Scroll compressors, CH290 and CH485 | Electrical connections