UPS uninterruptible power supply

Battery Life

Even if the UPS uses the same battery technology, the battery life of different manufacturers can vary widely, which is very important to the user because of the high cost of replacing batteries (about 30% of the UPS selling price). Battery failures can reduce system reliability and can be very annoying.

Temperature influence

Temperature has a great influence on the natural aging process of batteries. Detailed experimental data shows that every time the temperature rises by 5 degrees Celsius, the battery life will drop by 10%, so the design of the UPS should keep the battery as warm as possible. All online and backup/online hybrid UPSs generate more heat than backup or line-interactive UPSs (so the former needs to install fans), which is also an important reason why backup or line-interactive UPS battery replacement cycles are relatively long.

Charge impact

The battery charger is a very important part of the UPS, and the charging conditions of the battery have a great influence on the battery life. UPS battery life is maximized if the battery is kept at constant voltage or "float" electrical charge. In fact, the life of the battery state of charge is much longer than that of the pure storage state. Because battery charging slows down the natural aging process of the battery, the UPS should keep the battery charged whether it is running or shut down.

Voltage influence

The battery is composed of a single "primary battery". The voltage of each primary battery is about 2 volts. The primary batteries are connected in series to form a battery with a higher voltage. A 12-volt battery is composed of 6 primary batteries, and a 24-volt battery is composed of 12. A primary battery composition and so on. When the UPS battery is charged, each primary battery connected in series is charged. A slight difference in the performance of primary batteries will cause some primary batteries to charge higher voltages than others, and these batteries will age prematurely. As long as the performance of a certain primary battery connected in series decreases, the performance of the entire battery will also decrease. Experiments have proved that battery life is related to the number of primary batteries connected in series, the higher the battery voltage, the faster the aging. When the UPS capacity is fixed, the battery voltage should be designed to be as low as possible, so that the battery life of the UPS is longer. When the battery voltage is fixed, a battery with a small number of primary batteries connected in series should be selected instead of a large number of primary batteries connected in series with a low voltage. battery. The battery voltage of some UPS manufacturers is relatively high. This is because when the capacity is constant, the higher the voltage, the smaller the current, so thinner wires and semiconductors with lower power can be used to reduce the cost of UPS. The battery voltage of a UPS with a capacity of about 1KVA is generally 24-96V.

Current influence

Ideally, in order to prolong UPS battery life, the battery should always be kept on "float" charge or constant voltage charge. In this state of charge, a fully charged battery draws a very small charger current, which is called the "float" or "self-discharge" current. Despite the battery manufacturer's recommendations, some UPS designs (many on-line) subject the batteries to some additional small current, called ripple current. Ripple current is generated when the battery continuously supplies power to the inverter, because according to the principle of energy conservation, the inverter must have input DC to generate AC output. In this way, the battery forms a small charge and discharge cycle, and the frequency of the charge and discharge current is twice the UPS output frequency (50 or 60Hz).

Ordinary backup, line-interactive or backup/ferromagnetic UPSs will not have ripple currents, and UPSs of other designs will generate ripple currents of varying sizes, depending on the specific design method. Just check the block diagram of the UPS to know whether the UPS can generate ripple current.

If the battery of the online UPS is between the charger and the inverter, then the battery will have ripple current, which is a common "double conversion" UPS.

If the battery is isolated from the inverter with a blocking diode, relay, converter or rectifier, then there will be no ripple current from the battery. Of course, the UPS of this design is not always "online", so this kind of UPS is called "hybrid backup/online" UPS.

Summarize

The battery is the most unreliable part of the UPS system, but the quality of the UPS design directly affects the reliability of the battery. Keeping the battery charged (even if the UPS is shut down) can prolong the life of the battery. Try to avoid using a UPS with a high battery voltage. Some UPS designs will cause the battery to generate ripple current, causing unnecessary overheating of the battery. Most UPSs use similar batteries, but differences in UPS design can greatly affect battery life. One battery is 12V, and the UPS needs to be connected to 96V, that is to say, it needs to be connected to 8 batteries. The server is 780W, plus 20%, about 1000W, 2 hours, each battery is about 20AH, and 8 batteries with a nominal capacity of 24AH can be used.

There are many brands. Most of the candidates choose domestic maintenance-free lead-acid batteries. Regular manufacturers guarantee quality, long service life and high cost performance.

Charging time

For backup batteries, the time required to fully charge the battery after the battery is powered is generally not less than 24 hours; for cycle batteries, if you know the last discharge capacity and initial charging current, you can press The following formula calculates the charging time required when the environment is 25°C.

A. When the discharge current is greater than 0.25C

Cdis

Tch = I +3 ～5

B. When the discharge current is less than 0.25C

Cdis

Tch = I +6 ～10

Note: Tch = time required to fully charge the battery (hours)

Cdis = the last discharge of the battery (Ampere Hours)

I = maximum initial charge current (amps)

Capacity Calculation

1. Calculate the maximum discharge current value of the battery:

Imax=Pcosф/(η*Ecritical*N)

Note: P →Nominal output power of UPS power supply

cosф → The output power factor of UPS power supply (UPS is generally 0.8)

η→ UPS inverter efficiency, generally 0.88~0.94 (0.9 can be taken in actual calculation)

E Critical → The critical discharge voltage of the battery pack (12V battery is about 10.5V, 2V battery is about 1.7V)

N → Quantity of each battery pack (determined by each brand and each series of products)

2. According to the backup time of the selected battery pack, find out the required discharge rate value C of the battery pack, and then according to:

The nominal capacity of the battery pack = Imax/C

3. Time and discharge rate C

4. Take the MTT series 300KVA delay for 30 minutes as an example:

It is known that the number N of MTT series UPS power supply batteries is 32, the power factor cosф is 0.8, and the inverter efficiency η is 0.9.

According to: Imax=Pcosф/(η*Ecritical*N),

Then the maximum discharge current = nominal power 300000VA×0.8÷ (0.9 efficiency * 32 cells * 10.5V discharge voltage per cell) = 794AH

It is also known that the discharge rate C of the battery in 30 minutes is 0.92,

According to: the nominal capacity of the battery pack = Imax/C

The nominal capacity of the battery pack = 794÷ 0.92C=863AH

The total capacity of the battery pack=863AH×32 cells×12V=331392AH

It can be seen that 6 groups of 150AH32 batteries are needed

6 battery cabinets size 800*900*2000

Powered & Powerful!

Distributors and OEM business are warmly welcome.

Get connected with professional lead acid battery manufacturer,

www.gembattery.com

sales@gembattery.com

WhatsApp: +8615959276199