Overcharging (charging voltage/time exceeding the rated range) and overdischarging (discharging below the minimum protection voltage) of UPS batteries can seriously shorten battery life and even cause safety risks such as leakage, bulging, and fire. To avoid such problems, it is necessary to start from multiple dimensions such as equipment design, usage habits, and maintenance management. Specific measures are as follows:
1、 Dependent on the protection mechanism of the device itself
Modern UPS systems typically have built-in Battery Management Systems (BMS) or protective circuits that work together through hardware and software to prevent overcharging and overdischarging. It is important to ensure that these functions are properly enabled:
Charging protection settings
UPS will preset charging parameters based on battery type (such as lead-acid, lithium):
Lead acid batteries: The termination voltage for charging is usually 13.5-14.7V (single cell). Exceeding this value will trigger "overcharge protection", automatically cutting off charging or switching to float charging (low current maintenance voltage).
Lithium battery: The charging termination voltage is about 4.2V (single cell), and the BMS will monitor the voltage in real time. When the threshold is reached, charging will be stopped to avoid lithium dendrite precipitation (short circuit risk).
Ensure that the UPS' charging mode 'is correct: select the mode that matches the battery (such as' standard charging' or 'float charging maintenance'), and avoid manually setting excessively high charging voltage/current.
Discharge protection setting
Overdischarge protection threshold: UPS will set the minimum discharge voltage (about 10.5V for lead-acid batteries and about 2.5-3.0V for lithium batteries). When the battery voltage drops to this value, UPS will automatically cut off the output (i.e. "power-off protection") to prevent deep discharge from causing plate sulfurization (lead-acid) or permanent capacity loss (lithium).
Avoid disabling the 'low voltage protection' function: Some UPS systems allow manual disabling of this protection (such as emergency extended power supply), but it can significantly damage the battery and should not be operated unless necessary.
2、 Standardize usage habits and reduce the causes of overcharging and overdischarging
Avoid "overcharging" scenarios
Not long term 'full charge idle': UPS will continue to float charge the battery (maintain full charge) when the mains power is normal. If it is not discharged for a long time (such as several months without power outage), lead-acid batteries may lose electrolyte due to 'overcharge gas evolution', and lithium batteries may accelerate capacity degradation due to 'full charge aging'. It is recommended to manually disconnect the mains power every 3-6 months and allow the battery to discharge to 50% -70% before recharging (simulating normal use).
Avoid "hybrid charging": Mixing batteries of different brands, capacities, and aging levels can lead to uneven charging (some batteries are overcharged, while others are undercharged), and it is necessary to ensure the consistency of the battery pack.
Prevent 'excessive discharge' scenarios
Control discharge depth: The optimal discharge depth for UPS batteries is 20% -80% (lead-acid batteries should avoid deep discharge below 20%), and it is necessary to avoid long-term discharge under load until automatic power-off. For example:
Priority should be given to shutting down non essential loads (such as printers and redundant lighting) during power outages, while only retaining core equipment (servers, monitoring) to reduce discharge current and time.
Advance estimation of power supply duration: Based on the battery capacity (such as 100Ah) and load power (such as 1000W), calculate the approximate power supply time (about 1 hour), manually power off in advance to avoid battery depletion.
Prohibit 'battery depletion storage': UPS that is not used for a long time must maintain a battery level of 50% -70% (lead-acid batteries should be recharged once a month, lithium batteries should be recharged every 3 months), otherwise it may cause over discharge due to self discharge (such as lead-acid battery plate vulcanization, which cannot restore capacity).
3、 Optimize environment and load management
Control the ambient temperature
Temperature is a key factor affecting charge and discharge efficiency:
High temperature (>30 ℃) can lead to a decrease in internal resistance of the battery, and the current during charging is easily too high, which may exceed the protection threshold and cause overcharging; At the same time, high temperature will accelerate battery self discharge and increase the risk of over discharge.
Low temperature (<5 ℃) can reduce the battery's ability to accept charging, which may lead to "virtual charging" (voltage reaching the standard but insufficient capacity), a sudden drop in capacity during discharge, and easy triggering of over discharge protection.
It is recommended to install UPS in a ventilated environment at 20-25 ℃.
Reasonably manage load
Avoid overloading discharge: The rated load power of UPS should be greater than the actual carrying power (it is recommended to reserve a 20% margin). If the load is too large and the discharge current surges, the battery voltage will quickly drop to the protection threshold. Although it may seem like "over discharge", it is actually a voltage drop caused by excessive current, which can damage the battery plates in the long run.
Avoid frequent short-term discharges: Frequent power outages (such as multiple times a day) can cause the battery to discharge again before it is fully charged, forming a "shallow charge shallow discharge cycle". However, it is important to pay attention to timely charging after each discharge to avoid cumulative power loss.
4、 Regular maintenance and monitoring
Battery status check
Voltage monitoring: Use a multimeter to detect the total voltage of the battery pack (in non charging state). If the voltage of the lead-acid battery pack is consistently below 90% of the rated value (such as 12V cells below 10.8V), there may be a risk of overdischarge; During charging, if the voltage rises abnormally (such as exceeding 14.7V/cell), it is necessary to check whether the protection circuit has failed.
Appearance inspection: If lead-acid batteries leak, bulge, or have corroded terminals, and lithium batteries bulge or have damaged shells, they need to be replaced immediately. The charging and discharging protection ability of such batteries has decreased and they are prone to overcharging and overdischarging.
Protection circuit testing
Regular testing of overcharge protection: Simulate continuous power supply from the mains and observe whether the UPS automatically switches to float charging (current drops to a low level) after the battery is fully charged, rather than continuous high current charging.
Regular testing of over discharge protection: Disconnect the mains power and allow the UPS to discharge with load. Record the battery voltage during automatic power-off. If it is far below the preset protection threshold (such as lead-acid battery cells below 10V), it indicates a fault in the protection circuit and requires repair or replacement of the UPS.
Timely replace aging batteries
Lead acid batteries typically have a lifespan of 3-5 years, while lithium batteries have a lifespan of 5-8 years. Aging batteries may experience capacity degradation, increased internal resistance, disordered charging and discharging characteristics, and potential failure of protective mechanisms. When the battery capacity drops below 60% of the rated value, it needs to be replaced as a whole (to avoid mixing old and new batteries) to prevent overcharging and overdischarging of the entire group due to poor performance of a single battery.
summarize
The core logic to avoid overcharging and discharging of UPS batteries is: relying on automatic device protection, standardizing usage scenarios, and regular maintenance monitoring. Among them, the Battery Management System (BMS) is the first line of defense, environmental control and load management are the basis for reducing risks, and regular inspections can timely detect the failure of protection mechanisms or abnormalities in the battery itself, reducing the probability of failure from the source.
