Four major misconceptions in battery maintenance

As an independent power supply, batteries are widely used in various industries. The uninterrupted power supply in the data center, communication power supply in the power industry, onboard power supply in rail transit, backup power supply in subway stations, and batteries all provide important energy support for their uninterrupted operation.

Like other industrial equipment, batteries also require regular maintenance. But many engineers do not have rich experience in this area, and there are still some misunderstandings about maintenance projects and methods.

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Several Misunderstandings in Battery Maintenance

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Myth 1: "Maintenance-free lead-acid batteries" do not require regular maintenance

Four major misconceptions in battery maintenance

The so-called "maintenance free" means that compared to traditional open batteries, there is no need to regularly add electrolyte or distilled water, but their "health status" needs to be checked regularly.

If these maintenance free batteries are not regularly inspected, they are very prone to deterioration and failure. Mild liquid leakage corrosion, internal short circuit; If severe, it will cause a local fire and cause a fire.

Myth 2: Maintaining a battery only requires monitoring the voltage

Four major misconceptions in battery maintenance

Due to cost factors, some engineers often use a multimeter to test the float charging voltage of batteries. Currently, online systems on the market also monitor and evaluate the health status of backup or energy storage batteries through the battery voltage. However, the floating charge voltage can only reflect whether the charger is working properly, but it cannot reflect the health status of the battery. When the battery capacity decreases, the float charging voltage is likely to remain artificially high due to the control of the UPS charger. This is why in many cases, the voltage display of the UPS is normal, but after a power outage, the battery pack quickly loses power and cannot discharge.

The open circuit voltage of the battery (the voltage after disconnecting the charger) can to some extent reflect the capacity status of the battery. However, as can be seen from the above figure, only when the battery capacity severely decreases will there be a significant change in the open circuit voltage. The change in internal resistance of the battery is much faster, and there will be a significant increase in internal resistance during the middle and early stages of capacity decline. Therefore, internal resistance detects battery degradation earlier than voltage.

During the initial and intermediate stages of battery degradation, there will be no significant changes in the float charging voltage, and it is only possible to detect problems through voltage detection when the battery is open or short circuited, or when the degradation is extremely severe, but it is likely too late.

So what are the items that need to be tested during maintenance? How to choose the testing frequency?

IEEE Std 1188 Maintenance Standard for Valve Regulated Lead Acid Batteries ™- 2005) can provide reference for engineers. It can be seen that in addition to the floating charge voltage, the internal resistance of the battery, the temperature of the negative pole, and the ripple voltage are all parameters that need to be paid attention to.

Four major misconceptions in battery maintenance

Myth 3: Measuring the internal resistance of a battery with a multimeter is enough

Four major misconceptions in battery maintenance

There are three reasons why a multimeter cannot be used to measure the internal resistance of a battery:

1. Method - As is well known, measuring resistance with a multimeter is based on Ohm's law, which only applies to metal conductors. But batteries belong to chemical batteries, and the internal chemical reactions cannot be calculated using Ohm's law, so the internal resistance value measured by a multimeter has no reference significance. At present, there are basically three methods for measuring the internal resistance of batteries: AC injection method, AC discharge method, and DC internal resistance discharge method. It is recommended that engineers choose professional instruments to accurately and reliably test the internal resistance of batteries.

2. Accuracy - The internal resistance of a battery is generally at the milliohm level, but the resistance resolution of an ordinary multimeter is around 0.1 Ω, which does not meet the testing accuracy requirements.

3. Safety - The resistance range of the multimeter does not allow voltage to exist on the measured object, but voltage always exists on both ends of the battery. Testing the internal resistance of a battery with a multimeter can easily burn out the multimeter.

Myth 4: Low battery voltage, no need to pay attention to the safety level of testing equipment

Four major misconceptions in battery maintenance

According to the International Electrotechnical Commission IEC61010-2-030 standard, the battery testing environment belongs to CATIII electrical environment. Due to the incomplete isolation of UPS or DC screens from the mains, instantaneous high-voltage impacts in the power grid (such as lightning strikes or capacitor cabinet switching) may be transmitted to the battery terminals and cause personal injury to testing personnel. Therefore, please use a battery internal resistance tester with at least CATIII 600V rating. The concept of CAT level is not alarmist, and its design requirements ensure that there is sufficient creepage distance between the exposed metal part of the instrument and the human hand when the test pen is subjected to instantaneous high voltage impact.

Please remember to always consider your own safety.