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UPS Runtime

Estimate the backup minutes of a UPS from the load and the battery bank, accounting for inverter efficiency, depth of discharge (DoD) and aging. Includes an inverse mode to size the Ah you need for a target runtime.

What do you want to calculate
Load to back up
W
Battery bank
V
Ah
×

Ah and voltage per battery, at 20 °C. The bank energy is Vb × Ah × N.

DC→AC losses. Typical 85–95 %.

How much of the battery you use. Lead-acid 50–80 %; lithium up to 100 %.

Real capacity vs. rated. Used batteries ~80 %.

Examples
redzilla.cl — ups 
 
  
 
 
Estimated runtime
 
—
 
—
 
 
 
In minutes
 
—
 
—
 
 
 
Usable energy
 
—
 
after DoD, efficiency and aging
 
 
  
 
 Runtime —  
 
 Minutes —  
 
  
 
Calculation breakdown
 
 
  
ItemValueDetail
   
 
 
 
 How it is calculated · Wh, DoD and Peukert 
 
 1. Bank nominal energy:
Wh_bank = Vb × Ah × N.

 
 2. Energy actually deliverable to the load:
Wh_usable = Wh_bank × DoD × efficiency × aging
(each factor as a fraction).

 
 3. Runtime:
minutes = Wh_usable / load_W × 60, with
load_W = VA × PF if you enter VA.

 
 4. Sizing:
Ah = load_W × (min/60) / (Vb × DoD × eff × aging × N).

 
 ! This is an estimate.
            Real discharge is not linear: at high currents capacity drops
            (the Peukert effect), so the actual runtime is usually
            somewhat lower than calculated. Also consider temperature and the
            batteries' state of health.

 
 
 
 
 
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