The **UPS Runtime Calculator** is an essential tool for estimating how long your Uninterruptible Power Supply (UPS) system will provide backup power during a mains outage. By accurately inputting your battery specifications and connected load, you can ensure your critical systems have sufficient time for a safe shutdown.
UPS Runtime Calculator
Detailed Calculation Steps
UPS Runtime Calculator Formula
Where: T = Runtime (Hours), C = Battery Capacity (Ah), V = DC Voltage (V), $E_{dec}$ = Inverter Efficiency (decimal), P = Load Power (W).
Formula Source 1 (Eaton) | Formula Source 2 (APC)
Variables Explained
- Battery Capacity (Ah): The Ampere-Hour rating, representing how much charge the battery can deliver for a specific time.
- DC Bus Voltage (V): The total DC voltage of the battery bank (e.g., 12V, 24V, 48V, or higher).
- Total Load Power (W): The total power consumption of all connected devices in Watts.
- Inverter Efficiency (%): The percentage of DC power converted to AC power that reaches the load. Typically ranges from 80% to 95%.
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What is UPS Runtime Calculator?
A UPS Runtime Calculator determines the estimated duration (runtime) that a battery backup system can sustain the connected electrical load during an unexpected power outage. This calculation is crucial for planning your power infrastructure, ensuring that staff and systems have adequate time to shut down safely without data loss or hardware corruption.
Unlike simple battery capacity estimates, the runtime calculator incorporates key real-world factors, most notably the **inverter efficiency**. The inverter is the component inside the UPS that converts the battery’s DC power into the AC power needed by your electronics. This conversion process always involves some energy loss, which directly reduces the available runtime.
How to Calculate UPS Runtime (Example)
- Identify Inputs: A system has a battery capacity ($C$) of 200 Ah, a DC Voltage ($V$) of 48 V, a total Load Power ($P$) of 1,200 W, and an Inverter Efficiency ($E$) of 92%.
- Convert Efficiency: Convert the percentage to a decimal: $E_{dec} = 92 / 100 = 0.92$.
- Calculate Available DC Power: Multiply capacity by voltage: $200\ Ah \times 48\ V = 9,600\ Wh$. (Watt-Hours).
- Apply Efficiency: Multiply the available power by the efficiency: $9,600\ Wh \times 0.92 = 8,832\ Wh$ (Net Usable Energy).
- Calculate Runtime: Divide the usable energy by the load power: $T = 8,832\ Wh / 1,200\ W = 7.36\ Hours$.
Frequently Asked Questions (FAQ)
Calculated runtime often differs from reality due to several factors: battery age (capacity degrades over time), ambient temperature (batteries perform worse when hot or cold), and actual load (the load is often dynamic and may peak higher than estimated).
For modern, well-designed UPS systems, the inverter efficiency typically ranges between 85% and 95%. Using a default value of 90% is a reasonable approximation if the manufacturer’s specification is unavailable.
You must use the **actual load power in Watts (W)**. The VA (Volt-Amperes) rating of a UPS is its apparent power capacity and is higher than the actual power it can supply to the load. Using the VA rating will significantly overestimate your runtime.
For the same total stored energy (Wh), higher DC voltage allows for lower current draw (Amps) for the same load. While the Wh remains constant, higher voltage systems are often more efficient and allow for thinner wiring and longer battery strings, indirectly increasing overall system performance and sometimes, net runtime.