The situation when the refrigerator stopped working cool, and the diagnostics indicate a faulty start relay, often leaves the home mechanic with a choice: look for a rare spare part or use a temporary solution. In many cases, especially when urgently restoring the unit’s functionality or when testing the engine outside the housing, the direct start method via starting capacitoris used. This technology allows you to bypass standard automation, providing the necessary phase shift for rotor rotation.
However, it is worth understanding that this method is more of an emergency or diagnostic than a permanent solution for domestic use. Asynchronous motorinstalled in modern and old refrigerators, is designed for short-term operation of the starting winding. Long-term connection through a capacitor without proper protection can lead to overheating of the windings and eventual combustion of the motor, so it is important to strictly observe the time intervals and capacitance ratings.
In this article we will analyze in detail the physical principles of the circuit, select the necessary components and describe the step-by-step connection process. You will learn how it differs starting capacitance from the working one, how to correctly determine the terminals of the windings and what safety measures are critical when working with high voltage.
The principle of operation and the need for a capacitor
Electric motors used in refrigeration units are single-phase. The problem with a single-phase network is that it does not by itself create the rotating magnetic field necessary to start the rotor. Instead, a pulsating field is created that only hums, but does not rotate the shaft. To create the initial torque, a second winding is required, the current in which is shifted in phase relative to the main one.
This is where it comes in capacitor. This element creates a phase shift of the current in the starting winding, simulating the second phase. The result is an elliptical rotating field that causes the rotor to move. Without this component, it is almost impossible to start the motor with a load (piston group of the compressor).
There are two main types of connection of capacitors: starting and starting-operating. In the first case, the container is turned on only at the time of start and is turned off by a centrifugal switch or relay. In the second, the capacitor remains in the circuit constantly, which increases efficiency, but requires the use of special oil capacitors, designed for long-term operation under voltage.
⚠️ Attention: The use of paper or electrolytic capacitors as permanently switched operating elements is strictly prohibited. They can explode or leak, creating a fire hazard.
Understanding the difference between the start and run windings is critical to the success of the operation. An error in the connection will cause the motor to hum, overheat and quickly fail, since the current will not flow through the circuit that is intended to create a magnetic flux.
Required tools and components
Before starting work, it is necessary to prepare not only the capacitor itself, but also a number of auxiliary tools. The quality of execution directly affects safety and results. You will need a multimeter to test the windings, a set of screwdrivers, pliers and insulating materials.
The key element is the capacitor itself. Its capacity is selected experimentally or according to tables, based on engine power. Typically, for household refrigerators, capacitances are used in the range from 2 to 5 μF for starting ones and up to 30-40 μF for starting (short-term) ones. The rated voltage should be at least 400-450 Volts.
Also, I can’t do without a control button or a special starting relay. Since the starting winding cannot be kept energized for a long time, a mechanism is needed that will break the circuit 1-3 seconds after the start. In homemade circuits, they often use a button SB (start), which is held with your finger until the engine accelerates.
- 🔌 Multimeter - to measure the resistance of the windings and check the integrity of the capacitor.
- 🔩 Capacitor - with an operating voltage of at least 400V and a selected capacity.
- 🔘 Start button —normally open, rated for a current of at least 10A.
- 🧤 Dielectric gloves —required for protection against electric shock.
Do not forget about materials for insulating connections. Terminal blocks, heat shrink and electrical tape must be of high quality, since the compressor vibrates, and poor contact can cause sparking.
Identification of the terminals of the compressor windings
The most critical stage is the identification of contacts. There are usually three terminals on the compressor housing, covered by a terminal box. They may not be labeled, so you will have to use a logical method and measurements. On some models, such as Atlant or Biriusthe leads may be labeled, but you cannot rely on this.
Use the multimeter in resistance (Ohm) mode. You need to find pairs of contacts and measure the resistance between them. In total, you will have three measurements between three terminals (conventionally 1-2, 2-3, 1-3). The greatest resistance will be shown by the sum of the resistances of the starting and working windings, that is, the measurement between the extreme points.
| Pair of contacts | Resistance (Ohm) | Connection type | Purpose |
|---|---|---|---|
| Pin 1 - Pin 2 | 25-40 Ohm | Start winding | Thin wire, more turns |
| Pin 2 - Pin 3 | 10-15 Ohm | Working winding | Thick wire, fewer turns |
| Pin 1 - Pin 3 | 35-55 Ohm | Total | Total path through both windings |
The algorithm is simple: the total resistance (maximum) is measured between the two extreme terminals. The point that remains free (the middle pin in the circuit) is common wire. From the common wire to the terminal with lower resistance there is a working winding, and to the terminal with higher resistance there is a starting winding.
What to do if the resistances are the same?
In rare cases, especially on older or specific models, the resistances may be close. In this case, refer to the thickness of the visible part of the wire inside the terminal box, if visible, or use the short test run method with an ammeter. The no-load current on the working winding will be less than with an erroneous connection.
It is important to remember: the working winding always has less active resistance, since it is wound with a thicker wire to transmit the main power. The starting winding is thinner and creates a high resistance.
Connection diagram and step-by-step instructions
Once the pins have been determined, you can begin assembling the circuit. The connection diagram via a capacitor is extremely simple, but requires care. We will use a button to simulate the operation of the start relay.
First, connect the mains wire (220V) to the common terminal of the compressor and one of the button terminals. The second pin of the button is connected to one end of the capacitor. The remaining end of the capacitor is connected to the terminal of the compressor starting winding. The working winding is powered directly from the network (in parallel with the start circuit).
☑️ Checklist before switching on
The startup process looks like this: you supply power to the working winding and at the same time briefly press the button, supplying current to the starting winding through a capacitor. The engine starts to rotate. As soon as you hear a steady hum and see that the shaft has gained momentum (usually 1-2 seconds), the button must be released.
Connection diagram:Network (Phase) -> Compressor common terminal
Network (Zero) -> Working winding + Start button
Start button -> Capacitor -> Start winding
If motor does not start or hums, turn off the power immediately. Perhaps the capacitor capacity is too small or the windings are reversed. Prolonged humming without rotation will lead to insulation burning in a matter of minutes.
Choice of capacitance and type of capacitor
The correct choice of capacitance is the key to successful starting and long life of the engine. A capacitance that is too small will not create enough phase shift and there will not be enough torque to overcome the pressure in the system. Too large a capacitance will cause overheating of the windings and a sharp increase in current consumption.
For medium-power refrigeration compressors (100-200 W), the starting capacitance is usually 20-30 µF. Working capacitors, if the circuit assumes their constant operation, have a lower capacity - about 10-15 μF. However, the classic scheme for starting a refrigerator involves using only the starting mode.
- 📏 Capacity —selected at the rate of 4-5 uF for every 100 W of engine power.
- ⚡ Voltage —minimum threshold 400V, it is better to take with a margin of up to 450-500V.
- 🌡️ Temperature conditions —the capacitor must withstand the heat characteristic of the compressor compartment.
Often craftsmen use composite capacitors, connecting several pieces in parallel for obtaining the required amount of microfarads. This is a valid method, provided that all elements have the same rated voltage.
Pay attention to the type of dielectric. Electrolytic capacitors are suitable for starting circuits (but only for a short time!), and for workers - only paper or metallized polypropylene (series K78-17, MBGO, MBGP).
Safety measures and typical errors
Working with electricity and pressure requires increased caution. A compressor is not just a motor, it is a part of a sealed circuit where the refrigerant is under pressure. Incorrect actions can lead not only to electric shock, but also to mechanical damage.
One of the common mistakes is to ignore the grounding of the compressor, since if the insulation of the windings is broken, it can also be dangerous to leave it. the compressor is running without pressure control if it is not connected to the cooling system.
⚠️ Attention: Never start the compressor in a closed room without ventilation if the tubes are not sealed. The refrigerant may be toxic or displace oxygen.
Another common mistake is using too thin wires for connecting the starting current. compressor is 3-5 times higher than the nominal one. If the cross-section of the wire is small, it will heat up, the insulation will melt, and a short circuit will occur.
Do not forget about the thermal relay. In the standard circuit, it protects the motor from overheating when starting via a capacitor and a button, this protection is often excluded from the circuit, which makes manual control of the housing temperature necessary in the first minutes of operation.
Frequently asked questions (FAQ)
Is it possible to leave a capacitor in the circuit? constantly?
Technically, this is possible if you use a special working capacitor (oil-based) designed for continuous operation. However, for most household refrigeration compressors, such a circuit is not standard. Constantly turning on the starting winding can change the characteristics of the engine, increase noise and reduce the service life.
Which capacitor is better: dry or wet?
Modern dry polypropylene capacitors are best suited for compressor starting circuits. They are compact, reliable and do not require orientation in space. "Wet" (oil) capacitors of the old series are also reliable, but are afraid of temperature changes and can leak when overheated, which is dangerous in a closed environment. volume.
Why does the compressor hum but does not start?
This is a sign that the starting torque is not enough. Reasons: the capacitor capacity is too small, the starting winding itself is faulty (interturn short circuit) or the piston group is jammed. Also check the voltage in the network - if the voltage is low, the motor may not work. start.
Do you need a capacitor for a three-phase compressor?
If you connect a three-phase motor to a single-phase 220V network, then capacitors (starting and operating) are required to create an artificial third phase, but if the network is three-phase, then capacitors are not needed, the engine will start itself due to the phase shift in the network.