Server Room UPS Runtime Calculator for ERP Servers
Power cuts and scheduled load reduction hit ERP servers, network gear and shop floor terminals. This calculator shows how long a battery bank will hold your load and how much capacity you need for a given outage.
Your numbers
Total real power drawn by servers, switches and storage.
Your results
Estimate only. Real runtime falls with battery age, temperature and high discharge rates. Have a qualified electrician size and install your system.
Runtime versus connected load
Sweeps Connected load from 200 to 4000, holding your other inputs fixed.
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Optional: talk through on-prem ERP and AI hosting that copes with unstable power.
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How to use the calculator
Enter the real power draw in watts, the battery bank voltage, the capacity of each string in amp-hours and the number of parallel strings. Set the usable depth of discharge and inverter efficiency, then enter the outage length you want to cover. The result shows runtime and the total amp-hours you need.
The formula
Usable energy in watt-hours equals bank voltage times total amp-hours times depth of discharge times inverter efficiency. Runtime in hours is usable energy divided by the load. Required capacity works backwards: load times outage hours, divided by voltage, depth of discharge and efficiency.
- Lithium banks often allow 80 to 90 percent depth of discharge
- Lead-acid banks are usually kept near 50 percent to protect life
- Inverters typically run 85 to 95 percent efficient
Reading the chart
The chart sweeps the load from 200 W to 4,000 W at your battery settings. Runtime falls quickly as the load rises, so removing non-essential devices from the protected circuit is often cheaper than adding batteries.
Common mistakes
Using the VA rating instead of real watts, ignoring cooling and lighting on the protected circuit, and counting full battery capacity as usable all lead to short runtimes. Also plan for graceful server shutdown rather than running until the battery is flat.
Frequently Asked Questions
Should I use watts or VA?
Use real power in watts. VA is apparent power and is higher than watts for most loads. Read the wattage from the device labels or a power meter, then add some margin for growth and start-up surges.
What depth of discharge should I choose?
Follow the battery manufacturer. Lithium iron phosphate batteries commonly allow high usable depth, while lead-acid batteries last longer if you keep discharge shallow. A lower value gives a safer, more conservative runtime.
Does this include GPU servers?
Yes, if you enter their full load. Multi-GPU servers can draw several kilowatts, which shortens runtime sharply. Many sites protect only the ERP and network and let heavy compute stop safely during an outage.
Is runtime linear with load?
Not exactly. Batteries deliver less usable energy at high discharge rates, so real runtime at heavy loads is often shorter than the simple formula shows. Treat results as a planning figure and confirm with the supplier's discharge curves.
If keeping ERP and shop floor systems available through outages is a concern, Netray can help design on-prem AI and ERP hosting that tolerates interruptions.
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