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How To Calculate UPS Runtime Calculation

Power failure can happen due to many reasons which will cause the working voltage to drop at a certain level. With an uninterrupted power supply (UPS), the connected device will have the power even when the power source fails. When you use a UPS, you can easily power different devices including computers and the internet. It offers backup for a certain limited time as long as the power restores.

Why use a UPS?

When there is a power failure, continuous connectivity is lost. Many people require uninterrupted connectivity for performing different tasks. Loss of connectivity may lead to the loss of the unsaved project or loss of data feed. It can even be worse for people who work with live applications.

In many instances, people also tend to go offline when there is unreliable communication. For this reason, an uninterrupted power supply can be the perfect item for your workstation. It can be very helpful for web developers and other professionals. When you use a UPS, there will be uninterrupted internet connectivity.

Important UPS Specifications

Similar to different types of electronic products, UPS also comes with varying specifications. It is important to consider all the specifications carefully when you are looking to increase the battery capacity.

Battery: The battery capacity is measured in AH or Amp-hrs. Here the battery will have the capacity to store the charged power.

VA Power Rating:  VA stands for Volts and Amps. It is the maximum charge of the battery. The VA power rating is the power limitation accepted by the UPS.

Watts Power Rating: The Watts rating is the power output of the UPS. It determines the UPS’s real power and is measured in watts.

Surge Protection: When there is surge protection, you can prevent damage to the electrical equipment. It can be perfect to protect the device when there is an electrical surge.

Number of Outlets: Another factor to consider will be the number of power outlets. It all depends on the number of devices that you are looking to power.

Power Connection: UPS enables you to connect it into an alternating current or AC wall socket with the help of an AC connector. This helps to power the device and make sure that the battery receives full charging.

How long a UPS last?

The ability of the UPS to offer power is determined by many factors. Here are the factors that determine how long will the UPS battery last.

Battery Capacity: The battery capacity is the time in which the battery offers current at a certain voltage. We can say that it is the charge stored in the battery. Battery capacity is represented by AH.

DC Bus (V): DC Bus (V) is the voltage required to operate the inverter. The DC bus can begin from 12V and go up to 180V.

Power load of supported devices: The power load of devices being supported is measured in watts. It has to be noted that each device has its own power supply requirements. The UPS will support the individual devices according to the power requirement.

Battery Type: Another important consideration is that there are different types of batteries available. However, each of these batteries has varying discharge rates. A battery that discharges faster, determines the life of the uninterruptible power supply.

Power Factor: The power factor is the difference between the watts and VA power rating. It can lie between 0 and 1 and in many cases, the current will flow into and then back into the battery. In doing so, power delivery to the equipment will not be achieved.

UPS Efficiency: There can be instances when the battery’s energy is lost in connections and cabling. Even inverters tend to use some energy for running themselves. For this reason, it is essential to consider the efficiency factor. Additionally, batteries tend to lose their capacity when they are old. You must note that not all batteries will be able to run the load.

How to Calculate ups Runtime Formula?

UPS selection calculation is the power draw of the equipment. It is an extensive database for the measurement of actual power by the equipment. The UPS selection calculation has a database for different types of devices including the computer components. In doing so, it can determine the load power. However, it has to be noted that the supply runtime is according to different assumptions. Also, the batteries can vary significantly according to the manufacturers and battery life. UPS selection calculation is according to the specific features or runtime.

Calculate Theoretical Runtime using a UPS Runtime Formula

For calculating the UPS run time formula you will have to apply a certain formula. However, this formula has many key elements. While calculating, the UPS rating has got nothing to do with the battery capacity or the power load. To start the calculation, you will have to identify all the devices that require backup including modem, internet router, computer, and monitor. You will also have to calculate the devices’ power requirements by going through the technical specifications. In many cases, you may find the power requirements in voltage and not in watts.

However, there are many manufacturers where the power consumption is listed in watts. Another important factor will be to look for the wattage. It can be in AC or DC where AC has high voltages with low currents. On the contrary, DC tends to have higher currents with low voltages. The formula that we are going to apply is to calculate power consumption based on voltage and current requirements.

To sum up, it will be W = V X A.

The total load is represented by Wt which is the sum of the power consumption of all devices. It can be represented as Wt = W1 + W2 + …

Amperage calculation can be found by Total weight / volts. Here, the volt is the battery voltage.

A = Wt / V.

The UPS device runtime is the ratio of the over total load and battery capacity. It can be summed up as Time = AH / A

Here is a theoretical example of calculating the UPS run time.

A desktop computer requires 120 watts along with 10 watts internet and two 70 watts monitors. It will 120 + 10 + 70 + 70 = 270. The total of which will be 270 watts.

UPS that has a 12V battery with a capacity of 2.9 AH and 300 watts power rating can provide the load of the above configuration.

If we have to look at the amperage then it will be A = Wt / V. Here, 270 W / 12V = 22.5 A.

From the above, we can say that the expected UPS run time will be AH / A.

2.9 AH / 22.5 A = 7 minutes 44 seconds. You can easily calculate the time into hours minutes or seconds.

Calculate Runtime Using a Manufacturers UPS Discharge Curves

To be more specific on how much will the UPS last, you will have to look at the discharge curves provided by the manufacturer. Here is a practical example of the Cyberpower CP1500PFCLCD UPS.

  • Start by calculating the total load from all the devices in watts. You can refer to the formula Wt = W1 + W2 + W3…
  • Consider the discharge curve of the manufacturer.
  • Interpolate the runtime on the discharge curve from the load.
  • The estimated run time is 20 minutes.


By going through the above formula, you can get the approximate runtime of the uninterruptible power supply. Even though it is a simple formula, there are many factors to consider including the type of battery. For extending the runtime, the battery must be charged regularly. When it does not have enough power to hold, then the battery will be exhausted quickly.

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