Danfoss DSH090 Application Manual page 42

Scroll compressors, DSH090 to DSH600 | Electrical connections
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:
a + t
R = R
tamb 25°C (77°F)
a + t
25°C (77°F)
t reference temperature = 25°C (77°F)
25°C
t temperature during measurement °C (°F)
amb
R winding resistance at 25°C (77°F)
25°C (77°F)
R winding resistance at tamb
amb
a Coefficient a = 234.5
Motor protection
DSH090 to DSH184
Compressor models DSH 090 to 184 are provided with internal overload motor protection to prevent against
excessive current and temperature caused by overloading, low refrigerant flow or phase loss.
The protector is located in star point of motor and, should it be activated, will cut out all three phases. It will be reset
automatically.
While not compulsory, an additional thermal magnetic motor circuit breaker is still advisable for either alarm or
manual reset.
Then it must be set at the Max Operating Current value (MOC):
• When the motor temperature is too high, then the internal protector will trip.
• When the current is too high the thermal magnetic motor circuit breaker will trip before the internal protection
therefore offering possibility of manual reset.
DSH240 to DSH600
Compressor models DSH240-295-381-485-600 are delivered with a pre-installed motor protection module inside
the terminal box. This device provides 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 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
Ω), a 5-minute time delay is activated.
After this delay has elapsed, the relay is once again pulled in – i.e. contacts M1-M2 are closed. The time delay may be
cancelled by means of resetting the mains (L-N -disconnect) for approximately 5 sec.
A red/green twin LED is visible on the module. A solid green LED denotes a fault free condition. A blinking red LED
indicates an identifiable fault condition:
© Danfoss | Climate Solutions | 2022.10
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AB288965961751en-001402 | 42