SN-25 DC Motor Protector

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The SN-25 Series is a high current DC motor protector, which delivers the benefit of complete protection in locked rotor and overload conditions in a robust integrated package. The SN-25 Series has been designed to offer protection for a wide range of voltage from 12-48 VDC. It is suitable for both intermittent and continuous rated motors. The SN-25 is physically small and has unique snap action bimetal disc, ensuring a positive make and break switching action for enhanced contact life.

SN-25 provides complete protection in,
Overload Condition: Gradual increase in winding temperature due to overload is sensed by the SN-25, causing it to switch open and protect the motor from overloading.

Lock Rotor Condition: High current due to Locked Rotor Condition generates high internal heat in the SN-25, causing it to switch open within 3 to 10 seconds.

Short Circuit Condition: Very high short circuit current generates instantaneous internal heat inside SN-25, causing it to switch open in a fraction of second and protect the motor.

SN-25 DC Motor Protector is excellent for use in DC motors. It is available in 20 to 125 Amps trip current rating for 12 to 48 VDC (10,000 cycles).

Features

- Copper plated steel base and tab.
- Current and Temperature Sensitive.
- Designed to trip time or temperature specifications.
- Multiple bimetallic resistivities available.
- Wide range of trip current.
- Precise range of trip time.
- Compact Design.
- Quick and Accurate Action.

Applications

Examples of applications :

- Over current and temperature protection in DC Motors
- Motors used in automobiles
- Refrigerator Compressors
- DC blowers
- Engine Cooling fan motors
- Pump Motors

Switching Action

SN-25 is available in single poles, single throw (SPST) switching action. It is built to open its contacts on temperature rise. The temperature rise takes place due to rise in external temperature and internal heat generated due to I²R loss of Bimetal Disc.

Temperature, Differentials and Tolerances

SN-25 DC Motor Protector has a snap action opening and closing of contacts, which ensures no sparking or chattering.

SN-25 DC Motor Protector is supplied to customer specified open and close temperature set points with a tolerance on both set points. Temperature difference between cut-off and cut-in temperature is called differential temperature.

- Cut-off Temperature range: 50 to 170°C
- Cut off Temperature Tolerance: ± 10%
- Differential Temperature: 10 to 70°C

Specifications

Model	SN-25 DC Motor Protector
Nominal Operating Voltage	12 to 48 VDC
Operating trip current Range	20 to 125 Amps
Life Cycle	10000 Cycles
Trip time	4 sec to 10 sec

Dimensions

Current Vs Trip Time Graph

The Current Vs Trip Time Graph shows that whenever there is a locked rotor condition and the current exceeds 2.5 times the rated current the circuit is opened by SN-25 within 4-7 sec without harming the motor.

Selection Code

To make ordering hassle free we have created a standardized selection code.

Example:

Explanation
Model	SN-25 DC Motor Protector
Trip Current Rating:	65 Amps
Cut-off temperature & Tolerance	170 ± 8°C
Cut-in Temperature & Tolerance	80 ± 10°C

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