Compressor Starting Relays and Capacitors) Current Relays

 

Current Relays

• Designed to plug onto the triangular terminal configuration of most hermetic compressors.
• Can be mounted with a bracket, must be positioned upright due to gravity-dependent contacts.

Positional Mounting

• Arrow or decal indicates proper mounting position.
• Ensures contacts drop out by gravity once relay coil is energized.
• Important when mounted within the control box using a bracket.

Specifications

• Used on small compressors (under 1/2 horsepower).
• Normally open contacts in series with start winding.
• Relay coil in series with run winding.

Operation

• At startup: high locked rotor amperage energizes the relay coil, closing the contacts.
• Contacts apply power to the start winding.
• Contacts open as amperage drops when motor reaches ~80% speed, de-energizing the start winding.

Diagram and Graph

• High amperage at startup closes contacts.
• As motor speeds up, amperage drops, contacts open, start winding de-energized.

Application

• Limited starting torque, used in fixed metering device systems.
• Repulsion start induction run motors equalize pressure when off, easier starting.

Terminal Designations

• Standard designations:
  • L (or 1): line voltage.
  • M: main winding (run winding).
  • S: start winding.
• Current relay terminals: L, M, S (contacts between L and S, coil between L and M).

Relay Diagram

• Power applied to run winding, drawing locked rotor amperage.
• Contacts close, power flows to start winding, engaging it.
• Motor reaches ~80% speed, contacts open, start winding de-energized.

Cutaway View

• Terminal configurations: S and M plug into run and start terminals.
• Terminals 1 and 2 can be used for a start capacitor.
• Coil: low resistance (typically <1 ohm).
• Jumper wire and terminal configurations visible.

Coil Operation

• Power applied to coil increases locked rotor amperage.
• Electromagnetism pulls plunger, closing contacts.
• Power flows to start winding.