ELUPS runtime - How do I calculate it?
How to calculate UPS runtime (backup time): the formula for the battery capacity you need in Ah, with a worked example for an 8,000 W load.
One of the most important factors in choosing the right UPS is how much runtime we need the UPS to provide in the event of a power outage. The type and number of batteries in the UPS determine its runtime.
The calculation can be made with the following formula:
C = (P × T) ÷ (V × η × K)
where:
- C – Battery capacity, in amp-hours (Ah)
- P – Load power, in watts (W)
- T – Runtime, in hours (h)
- V – Nominal battery voltage, in volts (V)
- η – Efficiency of the battery inverter
- K – Battery discharge factor
- When the battery runtime is <3h, K = 0.6
- When the battery runtime is 3–5h, K = 0.8
- When the battery runtime is 5–10h, K = 0.85
- When the battery runtime is >10h, K = 1
For example, if the load is 8000W (8kW) and the required runtime is 1 hour, the batteries used in the UPS should have the following characteristics.
C = (8000W * 1)/(12V * 16 * 0.92 * 0.6) = 75.5Ah.
In other words, a 100Ah battery can guarantee about 1 hour of runtime.
It is important to note that batteries, like most electronic devices, wear with continuous use, and their runtime decreases over time. One solution is to buy batteries with considerably more capacity from the start (e.g., 50% more). Alternatively, it is very important to check the health of your batteries regularly or, in line with recent developments, to consider buying a new-generation (lithium) UPS, which offers longer runtime and a longer service life.
Tescom Hellas offers batteries for every type of UPS (learn more here), as well as battery testing and replacement services when needed.
If you need help calculating runtime or have more questions, contact the Tescom Hellas experts and they will be glad to help.
