The operating performance of a DC compressor in a low voltage environment will be significantly affected, which is closely related to the working characteristics of its motor. The motor of a DC compressor relies on a stable voltage input to maintain the rated speed. When the voltage is 10%-15% lower than the rated value, the motor output power will decrease as the voltage drops, which is manifested as a significant decrease in cooling or heating efficiency. For example, in a vehicle-mounted scenario, if the battery voltage drops below 10V (rated 12V) due to power loss, the compressor will experience speed fluctuations, and the cooling capacity may decrease by more than 30%, which cannot meet the temperature control requirements of the device. At the same time, low voltage will cause the motor current to increase, just like a car will increase the throttle when it is climbing a hill due to insufficient power. Continuous high current will increase the temperature of the motor winding, accelerate the aging of the insulation layer, and may cause the coil to burn out during long-term operation.
Low voltage will also affect the starting performance of the DC compressor, especially at the moment of a sudden voltage drop, the probability of starting failure will increase significantly. When the compressor starts, it needs to overcome mechanical inertia and system pressure. This process requires a large starting current, and low voltage will lead to insufficient starting torque, and the motor may be "stuck" - that is, the motor tries to rotate but cannot start successfully. At this time, the current will soar to 5-8 times the rated value, which may cause the motor to overheat and damage in just a few seconds. For example, when the grid voltage suddenly drops to 180V (rated 220V), if a household DC compressor is in the startup phase, it is likely to make abnormal noise and stop working, or even trigger the internal protection mechanism to cut off the power supply.
In response to the risks brought by low voltage, DC compressors are generally equipped with undervoltage protection function, which is the most basic voltage protection mechanism. This function monitors the input voltage in real time through the voltage detection circuit. When the voltage is lower than the set threshold (usually 85%-90% of the rated voltage), the control system will delay 1-3 seconds before cutting off the motor power supply to prevent the compressor from running in a low-efficiency state. For example, for a compressor with a rated voltage of 24V, the undervoltage protection threshold may be set at 20V. When the voltage is continuously lower than 20V, the protection mechanism is activated. The compressor will not restart until the voltage returns to normal and stabilizes for a period of time, preventing the impact caused by frequent start-stop.
In addition to passive power-off, some high-end DC compressors will use dynamic voltage compensation technology to actively deal with slight voltage fluctuations. This technology uses a built-in DC-DC converter to automatically adjust the output voltage when the voltage is slightly lower than the rated value (such as within the range of 10%-15%) to maintain a stable power supply to the motor. For example, when the input voltage drops from 12V to 10.5V, the compensation circuit will increase the output to 12V to ensure that the motor speed and power are not affected. However, this compensation has a certain limit. When the voltage is lower than the compensation range, the undervoltage protection will still be triggered to prevent the converter from being overloaded and damaged.
Overcurrent protection is an auxiliary protection mechanism in a low-voltage environment, which cooperates with undervoltage protection. As mentioned above, low voltage will cause the current to increase. The overcurrent protection circuit detects the motor current and immediately cuts off the power supply when the current exceeds 1.2-1.5 times the rated value and lasts for a certain period of time (usually 0.5-2 seconds). This mechanism is particularly suitable for scenarios where the voltage drops slowly. For example, when the battery is gradually depleted, the current will slowly increase. The overcurrent protection can intervene in time before the motor temperature is too high, making up for the possible response delay of the undervoltage protection, forming a double line of defense.
As the ultimate protection measure, temperature protection can deal with the risk of overheating caused by abnormal voltage. The DC compressor motor windings and power modules are equipped with temperature sensors. When the temperature exceeds the set value (usually 120-150℃), regardless of whether the voltage returns to normal, the power supply will be forcibly cut off until the temperature drops to a safe range (about 70-80℃) before restarting. This protection does not rely on voltage detection, but directly monitors the physical state of the device. It can effectively deal with the hidden overheating problem caused by low voltage. For example, the voltage is slightly low but the undervoltage protection is not triggered, but the motor is overheated for a long time, avoiding the melting of the insulation layer and causing a short circuit.
In multi-scenario applications, the voltage protection mechanism of DC compressor will be optimized according to the use environment. For example, the protection threshold of the vehicle compressor will adapt to the characteristics of the battery. When the voltage drops to the start protection threshold, it will prioritize the power required for the car to start and temporarily shut down the compressor; while industrial compressors may set a stricter undervoltage delay time to avoid false protection caused by instantaneous fluctuations in the power grid. In addition, some compressors also have a voltage fluctuation filtering function, which absorbs voltage spikes through capacitors or inductors, reduces the impact of instantaneous low voltage on the motor, and improves reliability in complex power grid environments. These refined designs allow DC compressors to ensure safe operation and maximize working performance in various low-voltage scenarios.
