Compressor Starting Relays and Capacitors) Solid State Potential Relays

 

Characteristics and Use

• Replace most field potential relays.
• Intended as temporary replacements for OEM (Original Equipment Manufacturer) relays.
• Less accurate due to use of a timer instead of measuring pickup voltage.
• Useful for getting units up and running quickly.

Installation and Function

• Simple wiring, similar to regular potential relays.
• Active terminals: 1, 2, and 5.
• Uses a timer to open contacts between terminals 1 and 2 after about a second.
• Breaks power to start winding and start capacitor.
• Run capacitor wired across terminal 4 (dummy terminal) and terminal 2 for better running efficiency.
• Example: Capacitor start-capacitor run motor.

Limitations

• Timer-based operation lacks the accuracy of voltage-responsive OEM parts.
• OEM relays match specific pickup and dropout voltages:
  • Pickup Voltage: Voltage needed to energize the relay coil and open contacts.
  • Dropout Voltage: Minimum back EMF to keep coils energized and contacts open.
• Solid state relays can be less precise.

Adjustable Solid State Potential Relays

• Some solid state relays have adjustable pickup voltage dials.
• Adjustable to match manufacturer specifications or default settings:
  • Default Settings:
    • 10 pickup voltage for 120V equipment.
    • 310 pickup voltage for 240V equipment.
• Manufacturer: Subko, leading in these devices.

Examples and Recommendations

• Copland specification sheets show pickup and dropout voltages for various compressors.
• Solid state relays should be used only temporarily if proper relays are not available on service trucks.
• Adjustable solid state relays provide more accurate matching to specifications.