Starting a compressor is one of the most critical stages in the operating cycle of a refrigeration unit. It is at this moment that the electric motor must overcome the inertia of rest and create the necessary refrigerant pressure in the system. Without a special device capable of briefly increasing torque, the motor would simply hum without rotating, or would burn out from overload. This device is starting capacitorwhich plays the role of a kind of energy booster for an asynchronous motor.
Many users are faced with a situation where the refrigerator stops freezing, and the compressor makes only a short beep. Most often, this small cylindrical element is the culprit of such a breakdown. Understanding exactly how it interacts with the motor windings will help you quickly diagnose the problem and avoid an expensive call to a technician for a simple part replacement. In this article, we will analyze in detail the physical essence of the start-up process and the role of capacitance in the formation of the magnetic field.
It is worth noting that modern inverter models can use other control schemes, but classic refrigerators, which make up the majority of the equipment fleet, rely on a time-tested design with capacitor start. Starting capacitor is not just a consumable, but a key element that determines the service life of the motor. If it fails, the compressor will operate in emergency mode, which will quickly lead to its complete failure.
Physical basis of the operation of a single-phase motor
The electrical network in our homes provides single-phase alternating current. To operate a conventional electric motor, one phase is not enough, since it creates a pulsating rather than rotating magnetic field. In order for the rotor to start rotating, it is necessary to create a phase shift. Here it comes into play asynchronous motor with two windings: the main (working) and additional (starting) windings. The starting capacitor is connected in series with the additional winding and creates the necessary phase shift.
When the refrigerator is turned on, the current passes through both windings. Due to the presence of a capacitor, the current in the starting winding is phase shifted relative to the current in the working winding. This interaction of the two magnetic fields creates a resultant vector that causes the rotor to rotate. As soon as the engine reaches about 75% of the rated speed, the starting winding is turned off by a special relay, and further work occurs only on the working winding.
⚠️ Attention: An attempt to start the compressor without a working starting capacitor will lead to the fact that the engine will consume a huge starting current, which can lead to overheating of the windings and a fire hazard. situation.
It is important to understand the difference between the containers. Start capacitor it differs from the working one in that it is included in the circuit only for a short time - a few seconds required to accelerate the rotor. If it remained in the circuit constantly, it would lead to overheating and destruction of the dielectric. Therefore, the design and parameters of these elements are strictly regulated by equipment manufacturers.
Design features and parameters of the element
Externally, the starting capacitor is a sealed cylinder, usually enclosed in a plastic or metal case. Inside there are two aluminum foil plates, separated by a dielectric, rolled into a roll. The gap between the plates is filled with electrolyte or special paper. This design allows you to accumulate an electrical charge and release it at the right moment at high speed.
The main technical characteristics that you need to pay attention to when selecting an analogue are capacity and voltage. Capacitance is measured in microfarads (µF or µF) and determines the strength of the starting torque. Voltage (V or VAC) indicates the maximum threshold that the element can withstand without breakdown. For refrigerators, elements with a voltage of at least 250-450 Volts are usually used.
- 🔋 Capacity: varies from 30 to 150 uF depending on the compressor power.
- ⚡ Voltage: standard values 250V, 330V, 450V AC.
- 🌡️ Temperature range: ability to operate at low temperatures (down to -40°C), since the element may be located in an unheated area.
- 📏 Dimensions: diameter and height should allow installation in a standard mounting place.
There is also a concept ESR (equivalent series resistance), which is important for assessing the quality of the capacitor, although it is rarely checked in household repairs. More important is the self-healing breakdown parameter, which some modern models have. If you see a marking on the case +105°C, this means the maximum heating temperature that the element can withstand, which is a good indicator of reliability.
Interaction with the starting relay
The key partner of the capacitor in the starting circuit is the starting relay. This device is responsible for the timely connection and, more importantly, disconnection of the starting winding along with the capacitor. Older models used relays with a posistor (thermistor), which changed their resistance when heated, breaking the circuit. In more modern and powerful units, electromagnetic current relays are used.
The process is as follows: when voltage is applied, the current passes through the relay coil and the starting winding. The capacitor provides the phase shift. The motor begins to rotate, the current in the windings drops to operating values. At this point, the magnetic field of the relay coil weakens and the contacts open, eliminating the capacitor from the circuit. If the relay sticks in the closed state, the capacitor will burn out.
⚠️ Attention: A common mistake during repairs is replacing only the capacitor without checking the starting relay. If the relay is faulty, the new capacitor will also fail within a few startup cycles.
In some circuits there is a combined device where the relay and capacitor are located in the same housing. This simplifies installation, but increases the cost of replacement. When diagnosing such blocks, it is necessary to check the integrity of both components. Disassembling the combined unit requires care, as you can damage the plastic latches or contacts.
What is a posistor in a relay?
A posistor is a ceramic resistor, the resistance of which increases sharply when heated. When you turn on the refrigerator, it is cold and passes current to the starting winding. After 1-3 seconds, it is heated by the passing current, its resistance increases, and the starting winding circuit actually breaks. This is a simple and reliable method of shutdown that does not require mechanical contacts.
Symptoms and signs of malfunction
Diagnosing a faulty starting capacitor often does not require complex equipment. The first and most obvious sign is the characteristic sound when trying to start. The compressor may hum for a few seconds, click and turn off. This triggers a thermal protection relay, which saves the motor from combustion. If you let the refrigerator cool down and turn it on again, the situation repeats.
Visual inspection can also provide a lot of information. If the capacitor is swollen, leaking, or traces of burning are visible on its body, its replacement is definitely necessary. However, often there are no external defects, and the element looks perfectly intact, but does not perform its function. In this case, an instrumental check is required.
Let's consider the main symptoms in more detail:
- 🔊 Humming without starting: the motor is trying to start, but there is not enough torque.
- 🔥 Case heating: the compressor or the condenser itself becomes hot to the touch.
- 🔌 Knocking out plugs: a short circuit inside the capacitor causes a current surge.
- ❄️ Lack of cold: a consequence of the compressor not working.
Sometimes there is a situation when the refrigerator works, but consumes more electricity than usual. This may indicate that the capacitor capacity has dropped and the engine is running at low efficiency, constantly lacking the necessary impulse to operate efficiently.
Diagnosis and testing methods with a multimeter
For accurate diagnostics, you need a multimeter capable of measuring capacitance (mode Cx or F) or resistance. Before starting work, be sure to disconnect the refrigerator from the mains and discharge the capacitor by shorting its terminals with a screwdriver with an insulated handle to avoid electric shock.
The first method is to check for short circuits and open circuits. Set the multimeter to resistance (Ohms) measurement mode. Touch the leads to the leads. If the device shows zero or a value close to zero, the capacitor is broken. If the resistance is infinitely high at once, a break is possible. Normally, the needle of an analog device should smoothly deflect and return back, and a digital device should show changing numbers.
The second, more accurate method is measuring capacitance. Switch the multimeter to microfarad measurement mode. Connect the probes to the contacts. The readings must be as specified on the housing, subject to tolerance (usually ±5% or ±10%). If the actual capacitance is significantly lower than the nominal one (for example, instead of 50 µF the device shows 30 µF), the element will not be able to create sufficient starting torque.
| Check parameter | Normal value | Fault symptom | Action |
|---|---|---|---|
| Resistance | Increases from 0 to ∞ | 0 Ohm or constant ∞ | Replacement |
| Capacity | Nominal ±10% | Understatement of more than 20% | Replacement |
| Appearance | Smooth body | Bloating, drips | Replacement |
| Leakage current | Minimum | High leakage current | Replacement |
☑️ Checking the capacitor
Rules for selecting and replacing a component
When purchasing a new element for replacement, it is critical to comply with the parameters of the original. The basic rule is: the voltage of the new capacitor should be equal to or greater than that of the old one. You can safely put 450 Volts instead of 250 Volts, but not vice versa. As for the capacity, the spread here should be minimal.
The capacity deviation is allowed within 10-15% upward. For example, if there was a 30 uF capacitor, you can install 33 or 35 uF. This will even improve starting performance. However, a strong increase in capacitance (for example, 50 uF instead of 30) will lead to overheating of the motor windings, and a strong decrease will make it impossible to start under load.
⚠️ Attention: Technical characteristics of refrigerators may vary depending on the year of manufacture and model. Always check the markings on the body of your device or in the manufacturer’s technical documentation before purchasing spare parts.
The replacement process is simple: remove the old element, remember the connection diagram (or take a photo), and connect the new one. Polarity does not matter for non-polar starting capacitors, but if there is a marking 0 or ground symbol on the case, these contacts must be connected accordingly. After installation, secure the element with a clamp or terminal so that the vibration of the compressor does not break the wires.
Frequently asked questions and answers (FAQ)
Is it possible to start a refrigerator without a starting capacitor at all?
Theoretically, if you turn the compressor shaft manually at the moment of switching on, it can start, since a phase shift will be created mechanically. However, this is dangerous, requires removal of the casing, and is not a solution to the problem. Without a capacitor, the engine will not be able to develop the required power and will quickly burn out.
Why does a newly installed new capacitor burn out?
There may be several reasons: a faulty starting relay that does not turn off the winding; power surges in the network; or an incorrectly selected type of capacitor (for example, a working one was installed instead of a starting one). A short circuit in the compressor itself is also possible.
How long can a refrigerator with a faulty capacitor work?
If the capacitor has simply lost capacity, the refrigerator may work intermittently, taking a long time to gain temperature. If it is broken, the compressor will not start at all. Long-term operation in the “buzzing” mode (attempts to start) will lead to burnout of the motor windings within several hours or days.
What is the difference between Start and Run capacitors?
Start (starting) are designed for short-term operation and have a large capacity. Run (workers) work constantly and have a lower capacity, but a more durable dielectric. They cannot be confused: the starter in the operation circuit will explode, and the worker in the start circuit will not allow the engine to start.