One of the most common questions about UPS systems is "How long will it keep my equipment running?" The answer depends on several factors including battery capacity, load size, battery age, and environmental conditions.
Basic Runtime Formula
Runtime is primarily determined by the relationship between battery capacity (measured in Amp-Hours) and the load being supported (measured in Watts or VA). The basic formula is: Runtime (hours) = Battery Capacity (Ah) x Battery Voltage (V) x Efficiency / Load (Watts).
Factors That Affect Runtime
- Load percentage: Running at 50% load typically provides more than double the runtime at 100% load due to battery discharge characteristics.
- Battery age: Batteries lose capacity over time. A 3-year-old battery may only provide 80% of its original runtime.
- Temperature: High temperatures accelerate battery degradation. Every 10°C above 25°C roughly halves battery life.
- Discharge rate: Higher discharge rates reduce the effective capacity of lead-acid batteries (Peukert's Law).
Extending Runtime
Many UPS models support external battery packs for extended runtime. This is more cost-effective than oversizing the UPS itself. Always consult the manufacturer's runtime charts for accurate estimates based on your specific load and configuration.