The waterproof and airtight performance of energy storage battery systems is one of the important characteristics to ensure their reliable operation under different environmental conditions. In order to ensure that the energy storage system can withstand external environmental influences such as moisture, rainwater, etc., strict waterproof and airtightness tests must be conducted on it. Here are several common testing methods:
1 Pressure attenuation method:
This is one of the most commonly used methods for air tightness testing. Seal the shell of the energy storage battery and fill it with dry air or inert gas at a certain pressure, then cut off the gas supply and observe the changes in internal pressure for a period of time. Determine the sealing performance of the battery by creating a closed pressure environment inside or outside the battery, and then monitor the changes in pressure over time. If there is a leakage point in the battery, the compressed air inside the chamber will leak outwards through the leakage point, causing the pressure inside the chamber to gradually decrease. The detector will monitor changes in air pressure in real time and calculate the rate of pressure drop through internal algorithms. Based on the rate of pressure change, the leakage rate can be calculated.
Operation steps: Seal the opening of the energy storage battery system, and inject a certain pressure of dry gas into the system through the connecting inflation device. Stop inflation after reaching the set pressure to stabilize the system for a period of time. Afterwards, use high-precision pressure sensors to record the changes in internal pressure of the system over time. If the pressure drop rate is within the specified range, it indicates good airtightness. For example, for an energy storage battery system with a set test pressure of 30kPa, a pressure drop of no more than 1kPa within 10 minutes is considered qualified.
Applicable scenarios: This method is suitable for various specifications of energy storage battery systems, especially for systems with complex sealing structures that can be effectively tested.
2 Bubble observation method (water immersion method):
This method immerses the battery pack in water and then observes whether there are bubbles inside the battery pack. If there are bubbles, it indicates that the battery pack is leaking. However, this method has been replaced by pressure drop method and helium detection method due to its slow testing efficiency and poor accuracy.
Operation steps: Immerse the energy storage battery system in water except for the electrical interface (with waterproof protection), and determine whether there is a leak by observing whether bubbles are generated. For ease of observation, a small amount of surfactant can be added to water to reduce surface tension and make it easier for bubbles to form.
Applicable scenarios: This is a relatively intuitive method that is suitable for small energy storage battery systems or for use in the initial product testing stage, but may cause certain water stains on the product.
3 Helium mass spectrometer leak detector method:
Use helium as a tracer gas for trace leak detection. It has very high sensitivity and can detect extremely small leakage apertures. The specific method is to evacuate or fill the outer side of the tested component with background gas such as nitrogen, while injecting helium gas into the interior; If a leak occurs, helium atoms will enter the sensor cavity through the leak and be detected.
Operation steps: Fill helium gas into the energy storage battery system and use a helium mass spectrometer leak detector to detect it outside the system. Due to the strong penetrability of helium gas, if there is a leak point in the system, helium gas will leak out. The leak detector can detect extremely small amounts of helium gas to determine the location and amount of the leak.
Applicable scenarios: This method has extremely high accuracy and is suitable for energy storage battery systems that require high waterproof and airtightness, such as energy storage batteries used in underwater equipment or environments that are extremely sensitive to humidity.
4 Differential pressure comparison testing method
By applying a certain pressure to the battery pack and observing the pressure changes, the airtightness can be determined.
Operation steps: A standard leak free reference material is required to be tested simultaneously with the tested energy storage battery system. Simultaneously fill both with gas of the same pressure, and then use a differential pressure sensor to monitor the pressure difference between the two. During the testing process, if the differential pressure remains within a very small range, it indicates that the airtightness of the tested system is qualified.
Applicable scenarios: Suitable for energy storage battery systems that require high testing accuracy. This method is more effective when comparing the airtightness of different batches or models of products.
5 Direct inflation method:
Because there are usually reserved waterproof and breathable holes on the battery pack, the battery pack can be directly inflated for air tightness testing. Connect the airtightness detector to the waterproof breathable hole of the battery pack through a gas tube, so that a certain amount of compressed air can be filled into the interior of the battery pack. After three stages of inflation, stabilization, and testing, the airtightness detector can detect the gas changes inside the battery pack in real time, and judge whether there is a leak in the battery pack based on this.
6 Testing process:
Testing principle: Whether it is domestic or foreign airtight testing equipment, the testing process must go through the following four stages:
1. Inflation stage
The device's inflation/exhaust solenoid valve switches to inflation, the isolation solenoid valve opens, and the device begins to inflate the measured object. The pressure sensor pressure value gradually increases until it reaches the target pressure value.
2. Voltage stabilization stage
After the pressure value of the equipment pressure sensor reaches the target pressure value, the isolation solenoid valve closes, stops inflating, and the pressure value of the equipment pressure sensor decreases nonlinearly.
3. Testing phase
After the pressure sensor of the equipment stabilizes, it enters the linear descent stage. At this point, the equipment will reset the pressure drop value to zero, restart the calculation, and output the test results.
4. Exhaust stage
The isolation solenoid valve opens, the inflation exhaust solenoid valve switches to exhaust, the internal gas of the measured object is discharged, and the pressure sensor value of the equipment returns to 0.
Pressure drop standard and leakage rate standard: Generally, they are obtained by the development department through multiple immersion tests in the early stage of product development, combined with the calculation of the internal volume of the battery pack.
The process parameters for airtight testing: The setting of inflation time, stabilization time, and testing time need to be repeatedly debugged and verified based on the product structure and production cycle, and a large amount of data analysis needs to be collected.
Leakage rate formula
LRsccm=(V×∆p)/(Patm×t)
In the industry, the unit of leakage rate is generally: cc/min
Patm： Standard atmospheric pressure
t： Testing time
∆ p: pressure drop value
V： The volume of the object being measured can be calculated based on standard leakage holes
