UPS Runtime Calculation: The Exact Formula for Philippine Office Environments
The runtime figure on a UPS spec sheet is almost always stated at a specific load — usually full rated load (100%) or sometimes half load (50%). Your actual load is almost certainly different from these reference points, which means your actual runtime is different from the spec sheet figure.
Understanding the calculation — and the correction factors for Philippine conditions — lets you predict your actual runtime accurately before a brownout tests it.
The Basic Runtime Formula
Runtime (hours) = Battery capacity (Wh) × Efficiency ÷ Load (W)
Where:
- Battery capacity in Wh = battery voltage (V) × battery Ah rating
- Efficiency = typically 0.90–0.95 for online double-conversion UPS (losses in rectifier and inverter)
- Load (W) = your actual connected load in watts (not the UPS rated capacity)
Example: PROLINK PRO906WRS with 6 kVA / 5.4 kW rating. Internal batteries: 6 × 12V 9Ah = 648Wh total. At 1,500W actual load and 0.92 efficiency:
Runtime = 648 × 0.92 ÷ 1,500 = 0.398 hours = approximately 24 minutes
At 3,000W actual load: Runtime = 648 × 0.92 ÷ 3,000 = 0.199 hours = approximately 12 minutes
This is why running the UPS at a lower percentage of rated capacity significantly extends runtime — and why the spec sheet's "at full load" figure is often misleading for typical office deployments.
The Load Percentage Effect
Runtime is not linear with load — it is approximately inversely proportional. Halving the load roughly doubles (or more than doubles) the runtime because:
- Less current draw = less resistive heating in the battery = more energy extracted per cycle
- Battery chemistry: lead-acid batteries deliver more total energy at lower discharge rates (Peukert's Law)
Practical table for a 6 kVA PROLINK PRO906WRS (internal battery, approx. 648Wh):
| Actual Load | % of Rated | Approximate Runtime |
|---|---|---|
| 5,400W (full) | 100% | ~7 minutes |
| 3,000W | 56% | ~12 minutes |
| 1,500W | 28% | ~24 minutes |
| 800W | 15% | ~40 minutes |
The implication for Philippine offices: A server room with 1,500W of actual load on a 6 kVA UPS gets approximately 24 minutes of runtime — enough for generator startup and several minutes of buffer. The same office running 4,000W would get only 9–10 minutes.
This is why right-sizing your UPS matters. Too large a UPS for the actual load is not just a waste of money — it also means you never know your actual runtime because the reference load scenarios don't match your deployment. See our UPS spec sheet guide for understanding VA, watts, and power factor in the specification.
Philippine Correction Factors
The theoretical formula assumes:
- 25°C ambient temperature (standard test condition)
- New batteries at 100% rated capacity
- Standard-rate discharge (not extreme fast or slow discharge)
Philippine office conditions typically deviate from these assumptions. Two corrections apply:
1. Temperature Correction
Lead-acid battery capacity decreases as temperature increases — counterintuitively. The rated Ah capacity is at 25°C. At 30°C (a typical Philippine server room without adequate cooling), battery capacity decreases by approximately 5%. At 35°C, by approximately 10%.
Correction factor: Multiply battery Wh by 0.90–0.95 for typical Philippine ambient conditions.
This is why server room cooling is not optional for UPS installations. A server room at 35°C consistently will lose 10% of UPS runtime compared to spec, and will age batteries significantly faster. See our data centre cooling guide for the thermal management requirements.
2. Battery Age Correction
Lead-acid batteries lose rated capacity over time. A 3-year-old battery in Philippine conditions (higher ambient temperature, frequent partial discharge from brownouts) may retain only 70–80% of its original rated capacity.
Correction factor: For batteries 2+ years old, multiply theoretical runtime by 0.75–0.85.
Combined correction example:
- Theoretical runtime at 1,500W load: 24 minutes
- Temperature correction (30°C): × 0.95 = 22.8 minutes
- Age correction (2-year-old battery): × 0.80 = 18.2 minutes
Actual expected runtime: ~18 minutes, not the theoretical 24. This is why battery testing matters — see our UPS battery preventive maintenance guide for the replacement schedule.
Long Run Models: Extended Runtime
For Philippine offices where 15–25 minutes is insufficient — provincial locations with brownouts exceeding 30 minutes, or operations requiring longer graceful shutdown windows — PROLINK's Long Run variants address this with extended battery capacity.
The runtime calculation applies the same way; the difference is a larger battery Wh capacity:
- Standard PRO906WRS: ~648Wh
- Long Run equivalent: 1,200–2,400Wh (depending on model and external battery pack configuration)
At 1,500W load with 1,800Wh battery and 0.92 efficiency: Runtime = 1,800 × 0.92 ÷ 1,500 = 1.1 hours = approximately 66 minutes
PROLINK Professional II Series Long Run models are available through Technica Solutions Inc.
Practical Sizing Rule
To achieve a target runtime at your actual load:
Required battery Wh = Target runtime (hours) × Load (W) ÷ Efficiency × Temperature correction
For 30 minutes runtime at 2,000W load in a Philippine office: Required Wh = 0.5 × 2,000 ÷ 0.92 × (1 ÷ 0.95) = 1,144 Wh minimum
This determines whether you need an extended internal battery model, an external battery pack, or a Long Run variant.
Related reading: UPS spec sheet explained · UPS battery preventive maintenance · Brownout protection for provincial offices · Generator + UPS integration
For Philippine offices sizing UPS for specific runtime requirements — PROLINK standard and Long Run models available through Technica Solutions Inc. — get in touch.
Talk to our Power Systems team →
