Amperometric Relay in Single-Phase Refrigeration Systems

The amperometric relay plays a crucial role in starting single-phase compressor motors by quickly connecting and disconnecting the compressor’s start winding. This process is essential to ensure an efficient start-up and to avoid damage to the refrigeration system.

Here is a step-by-step explanation of how this device works:

How the Amperometric Relay Works

1. The start winding is essential for turning on the equipment. However, once the compressor is running, it must be quickly disconnected to prevent overloads.
2. The amperometric relay consists of an internal coil and a movable plunger connected to internal contacts that regulate the flow of current.
3. When the equipment is powered on, the initial current is significantly high because additional effort is required to start the compressor motor’s rotation.
4. This high starting current passes through the relay’s coil, generating a magnetic field strong enough to attract the plunger.
5. The plunger closes the relay’s internal contacts, allowing the current to flow to the compressor’s start winding.
6. The start winding helps overcome inertia and initiate the compressor’s movement.
7. Once the compressor motor starts turning, the current decreases significantly, as less energy is needed to keep it running.
8. This decrease in current causes the relay’s magnetic field to weaken, which releases the plunger and opens the internal contacts.
9. When the internal contacts open, the current to the start winding is cut off, leaving the compressor running only on the run winding.

Using a Start Capacitor

Some compressors require an additional start capacitor to facilitate starting under more demanding conditions. In these cases, a modification to the amperometric relay connection is necessary.

10. The internal bridge of the relay is replaced with a connection to the start capacitor. This allows the current to pass through the capacitor first before reaching the start winding.
11. During startup, the current passes through the start capacitor, providing an extra boost to overcome the motor’s initial resistance.

Connecting the Amperometric Relay with a Start Capacitor

Here is how to connect the amperometric relay with a start capacitor:

• Connect the relay’s common terminal to the start capacitor.
• The relay’s start terminal is connected to the compressor’s start winding.
• The start capacitor is connected in parallel with the start winding, providing the necessary initial boost.

This configuration allows the compressor to start effectively and safely, preventing overloads and protecting the system’s internal components.

Benefits of the Amperometric Relay

• Protects the compressor motor from overloads.
• Facilitates quick and efficient startup.
• Extends the compressor’s lifespan.
• Prevents overheating and potential electrical damage.

The correct implementation of an amperometric relay, with or without a start capacitor, is essential to ensure the proper operation of a single-phase refrigeration system. This device not only optimizes the startup process but also enhances the overall safety and efficiency of the system.