Starting refrigeration compressor outside the standard housing is a task faced not only by diagnosticians, but also by home craftsmen who create compressors for painting or aeration. Modern models often use a c starting capacitorcircuit, which distinguishes them from older systems with a start relay. Proper connection of the electrical circuit is critical to prevent the windings from burning out.
In this article we will analyze the physics of the process, determine the purpose of the terminals and draw up a safe connection diagram. Errors in connecting a capacitor can lead to instantaneous failure of expensive equipment or even a wiring fire. Therefore, each step requires care and understanding of the principles of operation single-phase motor.
To get started, you will need a minimum set of tools and basic knowledge in electrical engineering. We will consider both the theoretical part and the practical nuances of assembling a temporary or permanent system. It is important to understand that working with mains voltage is always fraught with risk, so compliance with safety precautions is priority number one.
The principle of operation of a single-phase motor and the role of a capacitor
A single-phase asynchronous motor installed in household refrigerators is not capable of independently creating a rotating magnetic field. To start the rotor, it requires a phase shift, which is provided by an additional winding. This is where the starting capacitor (or capacitor starting device) comes into play, creating the necessary phase shift of the current.
Unlike motors with a starting relay, where the contacts open after a set of revolutions, in circuits with a capacitor, current continues to flow through the starting winding for a certain time or constantly, depending on the design. This allows the engine to develop more torque on the shaft at start, which is especially important for piston compressors experiencing high refrigerant back pressure.
The capacitor accumulates an electrical charge and releases it at the right moment, providing a powerful impulse for start. If the container is selected incorrectly, the engine will hum, overheat, or simply be unable to crank the crankshaft. Understanding this process helps to avoid common mistakes when selecting replacement elements.
Why does the engine hum, but does not start?
If you hear a hum, but the shaft stands still, it means that voltage is supplied to the engine, but the starting torque is insufficient. Most often, this indicates a malfunction of the starting capacitor (loss of capacitance) or an open circuit in the starting winding. Also, the cause may be jamming of the mechanical part of the compressor.
Identification of compressor terminals and search for contacts
The first stage of connection is to accurately determine the purpose of the contacts on the terminal block of the unit. There are usually three of them, and they are arranged in a triangle. On many modern models, such as Secop or Danfoss, markings can be applied directly to the case or present on the accompanying tag, but you often have to act by elimination.
For identification, you will need a multimeter switched to resistance measurement mode (Ohm). By measuring the resistance between pairs of contacts, you will find two windings: starting and working. The resistance of the working winding is always lower than the starting winding, since it is wound with a thicker wire and is designed for constant operation.
The total resistance between the two extreme contacts (starting + working windings) will be equal to the sum of the resistances measured separately. The point common to these two dimensions is common contact (Common). It is to this that one of the power wires is supplied, and the other two go to the starting circuit.
☑️ Algorithm for finding contacts with a multimeter
Selection and calculation of starting capacitor parameters
The key element of the circuit is the capacitor, the parameters of which must strictly correspond to the engine power. Using a part with too small a capacity will result in the compressor not starting under load. Exceeding the rating will cause overheating of the windings and may damage the insulation.
For low- and medium-power refrigeration compressors, capacitors with a capacity of 4 to 30 μF are usually used. The operating voltage must be at least 450 Volts, and it is better to take it with a margin of 500 V or higher to prevent breakdown during voltage surges in the network.
| Compressor power | Recommended capacity (uF) | Minimum voltage (V) | Capacitor type |
|---|---|---|---|
| up to 150 W | 4 - 8 µF | 450 V | Starting (CBB60/CBB61) |
| 150 - 250 W | 10 - 16 µF | 450 V | Starting (CBB60/CBB61) |
| 250 - 400 W | 20 - 30 µF | 500 V | Starting (CBB60/CBB61) |
| more than 400 W | 35 - 50 μF | 500 V | Starting (CBB60/CBB61) |
When choosing, pay attention to the type of dielectric. For motor starting circuits, polypropylene capacitors of the CBB60 or CBB61series are best suited. They have self-healing properties and are designed to work in alternating current circuits. The use of DC electrolytic capacitors in such circuits is strictly prohibited.
Assembling an electrical connection circuit
The assembly process requires a serial connection of all elements. First make sure the compressor is unplugged. Connect the phase wire of the network to one of the terminals of the capacitor. Connect the second terminal of the capacitor to the contact of the starting winding on the compressor.
The contact of the working winding on the compressor is connected directly to the phase wire of the network (parallel to the capacitor) or through a thermal relay, if provided for in the design. The neutral wire of the network is connected to the common contact (Common) of the compressor. This circuit ensures that voltage is supplied to both windings with the necessary phase shift.
For ease of control and safety, it is recommended to install a circuit breaker and a grounded socket. All connections inside the housing must be made using terminal blocks or high-quality soldering with heat shrink insulation. Sagging wires are unacceptable, since vibration of the compressor can lead to their separation.
Test launch and diagnostics of system operation
Before the first start-up, assemble the structure in a safe place, away from flammable objects. When power is applied, a working compressor should start within 1-2 seconds with a characteristic hum, turning into a smooth hum of a running motor.
If only a hum is heard, but the engine does not rotate, immediately turn off the power. This may indicate a mechanical jam or a faulty capacitor. If startup is successful, run the compressor for a few minutes while monitoring the housing temperature. It should heat up, but not reach temperatures at which it is impossible to hold your hand.
Check the strength of the air being blown or the pressure created if a receiver is connected. Sudden voltage drops can affect the stability of operation, so for long-term operation it is worth providing a stabilizer. Also pay attention to the absence of sparking at the connection points of the wires.
⚠️ Attention: When starting for the first time, do not leave the compressor unattended. If within 5-10 seconds the engine does not return to operating mode or a burning smell appears, immediately turn off the power to the system. Prolonged humming without rotation burns out the windings in a matter of minutes.
Safety measures and common mistakes
Working with electricity and mechanical high-pressure devices requires strict adherence to the rules. The most common mistake is ignoring grounding. The compressor housing is metal, and if the insulation breaks down, it can have life-threatening potential.
Another mistake is using capacitors of the wrong type or with an expired expiration date. The electrolyte inside such parts may dry out, causing loss of capacity. It is also dangerous to connect wires by twisting without soldering, especially under vibration conditions characteristic of the operation of a piston unit.
Do not forget that the compressor is sealed and there may be refrigerant inside under pressure. It is prohibited to open the housing or cut through pressure tubes. If you are using an old unit, make sure that there is no acid in the oil that may have formed during the combustion of the windings in the past.
⚠️ Attention: Compressor specifications and electrical safety requirements may vary depending on the model and year of manufacture. Before starting work, check the official documentation of the manufacturer or the technical data sheet of a particular device, since circuit designs may differ.
Frequently asked questions (FAQ)
Is it possible to start a compressor without a condenser?
Theoretically, it is possible to start the engine by creating an initial rotation pulse manually, but for a refrigeration compressor this is not possible due to the high back pressure in the system. Without a capacitor or a starting relay, the motor will simply hum and overheat.
Which capacitor to choose: starting or running?
For most household refrigeration compressors, starting capacitors are used, which operate for a short time. However, in capacitor start circuits they may remain in the circuit. It is important to use specialized motor capacitors (CBB), and not ordinary electrolytes.
Why does the compressor work, but gets very hot?
Strong heating can be caused by several factors: incorrect capacitor capacitance (too large or small), low voltage in the network, lack of freon (if it is a refrigeration circuit) or wear of the mechanical part. Also check the cleanliness of the condenser (radiator), if any.
How to determine whether the compressor has burned out?
Test the windings with a multimeter. If the resistance between any of the contacts and the housing is zero (or close to it), then a breakdown to the housing has occurred. If the resistance between the contacts is infinitely high, the winding is broken. In both cases, the compressor must be replaced.