Battery life and UPS Reliability

Even if the UPS uses the same battery technology, the battery life varies from manufacturer to manufacturer, which is important to users because the cost of replacing the battery is high (30% of the price of UPS ). Battery failure can reduce system reliability, which is very annoying.

Battery temperature affects battery Reliability

Temperature has a great impact on the natural aging process of the battery. Detailed experimental data shows that the battery life is reduced by 10% every 5 degrees Celsius, so the UPS design should keep the battery temperature as low as possible. All online and backup/online hybrid UPS instances provide greater heat than the standby or Online Interactive UPS instances during operation (so the former requires fan installation ), this is also an important reason for the long replacement period of the battery of the backup or Online Interactive UPS. The apc ups battery has a minimum temperature, so it can better meet system reliability requirements.

Battery Charger design affects battery Reliability

Battery chargers are an important part of UPS. The battery charging conditions have a great impact on the battery life. If the battery remains in the constant voltage or "floating charge" battery charging status, the UPS battery life can be maximized. In fact, battery charging has a longer lifetime than simply storing it. Because battery charging can delay the natural aging process of the battery, the UPS should keep the battery recharged regardless of the running or stopped status.

All apc ups, regardless of whether the battery is in the charging status, many of the UPS on the market do not have this function. Although this can increase the UPS cost, if you consider the cost of replacing the battery, the overall use of UPS costs are reduced.

Battery voltage affects battery Reliability

A battery is composed of a single "original battery". The voltage of each original battery is about 2 volts. The original battery is connected in series to form a high voltage battery. A 12 volt battery is composed of six original battery, A 24 V battery consists of 12 batteries. When the UPS battery is charged, each connected source battery is charged. If the performance of the original battery is slightly different, some of the original battery will be charged with a higher charge ratio than other original battery, and the battery will aging in advance. As long as the performance of a source battery in connection decreases, the performance of the entire battery will also decrease. Test shows that the battery life is related to the number of battery in series. The higher the battery voltage, the faster the aging.

When the UPS capacity is certain, the minimum battery voltage should be made possible during the design, so that the longer the life of the UPS battery is, when the battery voltage is certain, a small number of battery series batteries should be selected, do not select multiple batteries with low voltage. Some manufacturers of UPS battery voltage is relatively high, this is because when the capacity is certain, the higher the voltage, the smaller the current, you can use a smaller wire and a smaller power semiconductor, this reduces UPS costs. The battery voltage of a 1 kVA UPS is generally 24-96 V. This type of capacity-level apc ups, such as Smart-UPS 1250, has the minimum battery voltage of 24 V.

The relatively low battery voltage of apc ups extends the battery life. The lifetime of apc ups is 3 to 5 years, while that of some UPS is only 1 year! During the ten-year period of use of UPS, the cost of replacing the battery is twice higher than the price of UPS! Although this type of UPS is easy to design and cost-effective, it is costly to replace the "potential" battery.

Impact of Ripple Current on battery Reliability

Ideally, to extend the life of the UPS battery, keep the battery in "floating" charging or constant pressure charging. In this situation, a fully-charged battery absorbs a small amount of charger current, which is called "floating" or "self-discharge. Despite the recommendations from battery manufacturers, some UPS design (many on-line) causes the battery to withstand some extra small currents, called ripple currents. Ripple current is generated when the battery continuously supplies power to the inverter. According to the energy conservation principle, the inverter must have input DC to generate AC output. In this way, the battery forms a small charge/discharge cycle, and the charge/discharge current frequency is twice the UPS output frequency (50 or 60Hz.

Normal standby, APC online interactive, or backup/ferromagnetic UPS do not have ripple currents, and other design UPS will generate ripple currents of varying sizes, depending on the specific design method. Check the UPS structure to see if the UPS can generate Ripple current.

If the battery of the online UPS is between the charger and the inverter, the battery will have ripple current, which is a common "dual-switching" UPS.

If the battery is isolated from the inverter using a cut-off diode, relay, converter, or rectifier, the battery will not have ripple current. Of course, this design of UPS is not always "online", so such UPS is called "hybrid backup/online" UPS.

Summary

Battery is the least reliable part of the UPS system, but the design of UPS directly affects the reliability of the battery. Keep the battery in charge (even if the UPS is stopped) to prolong the life of the battery, and avoid the use of UPS with high battery voltage. Some UPS design will generate Ripple current on the battery, causing unnecessary overheating of the battery. Most upss use almost the same battery, but the different UPS design will greatly affect the battery life.