The situation when the refrigerator suddenly stops starting or makes only a humming sound without rotating the motor shaft often indicates a failure of the starting element. In most cases, the culprit of such a malfunction is starting capacitor, which provides the necessary torque to start the motor-compressor. Correct calculation and selection of this component are critical stages in restoring the functionality of household appliances.
Incorrect selection of capacitance can lead to overheating of the windings, activation of a thermal relay, or even complete combustion of an expensive compressor. Unit owners Indesit, Atlant or Beko need to understand the physical principles of operation of single-phase motors in order to avoid repeated breakdowns. Below we will analyze in detail the method for calculating parameters and the nuances of installation.
First, you should determine the type of your compressor, since the need for a starting capacity depends on this. Modern inverter models often do not have classic starting capacitors, operating according to a different scheme. If you have a classic unit with an asynchronous motor, then accurate calculation of capacity will be the key to successful repair.
The principle of operation of the starting capacitor in the refrigerator
Single-phase electric motors used in refrigeration equipment are not able to independently create rotating magnetic field at startup. To do this, they require a phase shift of the current, which is exactly what starting capacitorprovides. It is connected to the stator starting winding for a short time - exactly at the moment the rotor accelerates to operating speed.
After the motor shaft reaches about 75% of the rated speed, the centrifugal switch or relay opens the circuit and the capacitor is turned off. If this does not happen, the winding quickly overheats. In some circuits, especially in older models ZIL or Minsk, working capacitors can be used, which remain in the circuit constantly, but in modern household refrigerators it is the starting circuit that predominates.
It is important to understand the difference between the capacitance required to create a phase shift and the voltage that the component must withstand. Electric capacitance measured in microfarads (µF) and determines the strength of the trigger pulse. Insufficient capacitance will cause the compressor to hum but not start, and excess will cause overheating of the starting winding.
⚠️ Attention: Never use capacitors with an operating voltage below 250-300 Volts for a 220V network. Short-term power surges in the network can instantly break through weak insulation, which will lead to an explosion of the element housing.
Basic parameters for calculating capacity
Before starting mathematical calculations, it is necessary to collect initial data from the motor nameplate or technical documentation. The main parameter is the compressor power, which is usually indicated in watts (W) or horsepower (hp). The power factor (cos φ) and the efficiency of the motor are also critically important.
To accurately select an element, you need to know the supply voltage. Under standard conditions, this is 220-230 Volts, however, in some regions or when using generators, the voltage may differ, which will require correction of the calculations. The current frequency in our country is 50 Hz, which is also a constant in the formulas.
Particular attention should be paid to the type of winding connection circuit. Depending on the design of the motor, the windings can be connected in a star or delta configuration, which directly affects the final value of the required capacitance. An error in defining the circuit will lead to an incorrect calculation result.
Formula and methodology calculation
There are several approaches to determining the required capacity. The simplest, but less accurate method is empirical, based on engine power. It is believed that for every 100 W of power, approximately 7-8 µF of capacitance is required. However, for professional repairs it is better to use formulas that take into account electrical parameters.
For a star connection circuit, the calculation formula is as follows:
Cn = (2800 * I) / U, where I is current, U is voltage.
If the windings connected in a “triangle”, the formula changes:
Cn = (4800 * I) / U.
Current (I) can be calculated knowing the power (P) and voltage: I = P / (U * cos φ). Substituting this value into the basic formula, you will get the required capacitance in microfarads. The resulting value should be rounded up to the nearest standard value produced by industry.
Why can’t you use capacitors of larger capacity?
Using a capacitance significantly higher than the calculated one (more than 20%) will lead to a sharp increase in the inrush current. This can cause false operation of the protective relay or damage to the starter contacts, as well as accelerated aging of the insulation of the motor windings.
Selection table for capacitors based on compressor power
To simplify the task, technicians often use ready-made correspondence tables compiled on the basis of the average technical characteristics of popular compressors. Below is the data that is relevant for most household models of refrigerators.
| Compressor power (W) | Capacitor type | Capacity (uF) | Operating voltage (V) |
|---|---|---|---|
| 100 - 150 | Starter | 10 - 15 | 250 - 300 |
| 150 - 250 | Starter | 16 - 25 | 300 - 350 |
| 250 - 400 | Starter | 30 - 40 | 350 - 400 |
| 400 - 600 | Starter | 45 - 60 | 400 - 450 |
When selecting an element from the table, always pay attention to the tolerances. The standard accuracy of factory capacitors is ±5% or ±10%. If you find a part with a capacitance of 22 µF instead of the required 20 µF, this is an acceptable deviation. However, setting 30 µF instead of 20 µF is already considered risky.
⚠️ Attention: The characteristics of compressors from different manufacturers (for example, Secop versus Embraco) may differ even with the same power. Always check the markings on the engine itself, if they are readable.
Types of capacitors and their markings
There are many types of capacitors on the electronics market, but not all are suitable for refrigerators. The main requirement is the ability to work in alternating current (AC) circuits. Electrolytic capacitors, often used in audio equipment, are not suitable for this purpose, since they can explode when connected to a 220V network.
The most common are metallized polypropylene film capacitors (CBB60, CBB61, CBB65 series). They have the property of self-healing in case of breakdown and have a compact body. The marking on the case usually contains the capacitance value (for example, 20µF), voltage (450VAC) and tolerance (±5%).
There are also special starting capacitors in a black plastic case designed specifically for electric motors. They can withstand high inrush currents and short-term overloads. When replacing, try to use components from trusted brands, such as Jianghai or Run, avoiding nameless analogues.
Instructions for replacement and testing
The replacement process begins with completely disconnecting the refrigerator from the power supply. This is a basic safety rule and failure to comply may result in electric shock. After removing the plug from the retail outlet, you must remove the protective cover of the compressor compartment located at the back of the unit.
Next, you should carefully remove the starting relay and thermal protection. The capacitor is usually secured to the compressor housing or inside the relay using a clamp or glue. Before dismantling, it is recommended to discharge the old capacitor by shorting its contacts with an insulated screwdriver to avoid electric shock.
☑️ Algorithm for replacing the capacitor
Installation of the new element is carried out in the reverse order. It is important to securely fix the wires in the terminals to prevent sparking and heating of the contacts. After assembly, turn on the refrigerator and listen: the start-up should be smooth, without strong relay clicks or buzzing.
Frequent errors and fault diagnosis
One of the common mistakes is ignoring a visual inspection. A swollen housing, electrolyte leaks or melted terminals indicate that the capacitor has failed. However, sometimes an apparently serviceable element may not hold a capacitance, which can only be checked with a multimeter with a capacitance measurement function.
Another mistake is installation “by eye” or using the first capacitor you come across from stock. As already mentioned, a capacitance deviation of more than 20% in any direction is harmful to the engine. Also, do not forget to check the starting relay, which often fails simultaneously with the capacitor.
If after replacement the refrigerator works, but after a while it turns off again due to overload, perhaps the problem lies in the compressor itself (turn-to-turn short circuit) or in low voltage in the network. In such cases, simply replacing the capacitor will not radically solve the problem.
⚠️ Attention: Do not attempt to repair sealed capacitors by opening the case. This is not only ineffective, but also dangerous due to the possible content of harmful substances inside.
Questions and answers (FAQ)
Is it possible to use a capacitor with a higher operating voltage than specified in the specification?
Yes, it is possible and even necessary. If the design voltage is 300V and you find a part rated at 400V or 450V, this will only increase the safety margin and life of the element. The main thing is that the capacitance (uF) coincides with the calculated one.
Why does the compressor hum, but does not start after replacing the capacitor?
There may be several reasons: the capacitance is incorrectly selected (too small), the starting relay is faulty, the compressor itself is jammed, or there is a break in one of the motor windings. It is also worth checking the voltage in the outlet.
How to check a capacitor without a special device?
It is impossible to accurately measure the capacitance without a device. However, you can check it for breakdown or breakage using a multimeter in continuity mode (ohmmeter). When connecting the probes, the arrow (or numbers) should tremble and go to infinity (for analog) or show an increase in resistance (for digital). If it shows zero - breakdown, if immediately infinity - break.
Does the room temperature affect the operation of the capacitor?
Yes, it does. Most capacitors are designed to operate in the range from -40 to +85 degrees Celsius. If the refrigerator is placed near a hot stove or in direct sun, the life of the electrolyte inside the capacitor may be reduced, which will lead to its premature drying out and loss of capacity.
Does it need to be replaced preventively?
No, capacitors do not have a strict expiration date, like products. They are changed only when symptoms of a malfunction appear (compressor does not start, humming, machine knocks out) or when there is visible damage to the housing. Preventive replacement of a serviceable element does not make economic sense.