UPS Battery BackupsMulti-Mode Double-Conversion
Liebert 51SA050BAA UPS Battery Backup Manual
Setup, everyday use, maintenance and troubleshooting for the 50 kVA / 50 kW multi-mode double-conversion UPS, with verified specifications.
- Rating50 kVA / 50 kW
- TopologyMulti-Mode Double-Conversion
- Efficiency96.4%
- Runtime at half load10 min
About the Liebert 51SA050BAA
This guide covers the Liebert 51SA050BAA, a 50 kVA / 50 kW multi-mode double-conversion UPS listed as ENERGY STAR certified.
It can support up to 50 kW of connected equipment (50 kVA apparent power, a 1.00 output power factor). It is rated for 480 V, 60 Hz input, a three-phase service typical of data centers and large commercial buildings. Energy storage is a valve-regulated lead-acid (VRLA) battery (separate battery cabinet), with a 3-year warranty listed in the certification record.
ENERGY STAR weighted efficiency is 96.4%, and 96.6% at half load. With nothing connected it draws 339 W. Its weighted efficiency is higher than 86% of the 348 Multi-Mode Double-Conversion models in our database.
The manufacturer lists it for consumer, commercial, and data center applications.
Specifications
| Brand | Liebert |
|---|---|
| Model number | 51SA050BAA |
| Topology | Multi-Mode Double-Conversion |
| Apparent power rating | 50,000 VA |
| Real power rating | 50,000 W |
| Output power factor (W/VA) | 1.00 |
| Default normal mode | VFI (voltage and frequency independent) |
| Multiple normal modes | Yes |
| Intended applications | Consumer, Commercial, Data Center |
| Rated input voltage | 480 V |
| Rated output voltage | 480 V |
| Input frequency | 60 Hz |
| Battery technology | Valve-regulated lead-acid (VRLA) |
| Battery location | Separate battery cabinet |
| Runtime at full load | 5 min |
| Runtime at half load | 10 min |
| Battery warranty | 3 years |
| Weighted efficiency (ENERGY STAR) | 96.4% |
| Efficiency at 25% load | 95.9% |
| Efficiency at 50% load | 96.6% |
| Efficiency at 75% load | 96.4% |
| Efficiency at 100% load | 96.2% |
| Input power at no load | 338.7 W |
| Input power factor | 0.99 |
| Rack-mountable | No |
| Height | 78.7 in. |
| Width | 23.9 in. |
| Depth | 39.1 in. |
| Modular design | Yes |
| Communication ports | serial (RS-232), USB, Ethernet |
| Management protocols | Modbus TCP, HTTPS, HTTP, SNMP, Modbus RTU |
| Manufacturer take-back program | No |
Safety information
- Installation, wiring, battery-cabinet connection and start-up must be performed by qualified electricians or manufacturer-authorized field engineers in accordance with NFPA 70 (National Electrical Code) and local codes.
- Hazardous voltage is present from the battery and from any parallel or bypass sources even when the input breaker is open. Follow lockout/tagout procedures, verify absence of voltage, and wear arc-flash PPE appropriate to the labeled hazard level.
- Batteries can deliver dangerous energy even when the UPS is disconnected from utility power, and its output terminals may be live on battery power. Only trained service personnel should open cabinets or service battery strings.
- Install the UPS indoors in a clean, dry, well-ventilated location away from heat sources and direct sunlight. High temperatures shorten battery life sharply.
- Cabinets of this size must be moved upright with a pallet jack or proper rigging and anchored as the installation manual specifies, including seismic anchoring where local codes require it.
Installation and first-time setup
Base sizing on the critical load. Use the measured or calculated critical load from the electrical design, plus planned growth, and keep normal operation below about 80% of the 50 kW rating. Redundant (N+1) configurations should be sized so the load is still carried with one module out of service.
- Plan the site
Confirm floor loading, service clearances front and rear, cooling capacity and the ambient temperature (about 77 °F / 25 °C is the usual design point for battery life). The cabinet measures about 78.7 × 23.9 × 39.1 in. (H × W × D; 2,000 × 608 × 994 mm).
- Electrical design
Have the electrical engineer size the input and bypass feeders, breakers and grounding for 480 V three-phase service. A wrap-around maintenance bypass is strongly recommended so the load can stay powered during service.
- Install batteries
Position and interconnect the separate battery cabinets as specified; battery string connections must be made by trained personnel.
- Commission
Have the manufacturer's authorized service perform start-up: verifying wiring and phase rotation, configuring operating modes and alarms, and running load and battery tests.
Using your UPS
How this UPS protects your equipment
As an online double-conversion UPS, it continuously converts incoming AC to DC and back to clean AC, so connected equipment is isolated from voltage and frequency disturbances and there is no transfer time when the utility fails. Because it supports multiple normal modes, it can also run in a high-efficiency (eco) mode that passes filtered utility power through when conditions are good and switches back to double conversion when they are not. Its default operating mode is classified as VFI (voltage and frequency independent).
Battery runtime
According to the certification record, the tested battery configuration provides about 5 minutes at full rated load (50 kW) and about 10 minutes at half load (25 kW). Runtime is not linear — halving the load usually more than doubles it — and it falls as the battery ages or gets warm. Use the runtime to ride through short outages and to shut systems down cleanly during longer ones.
Monitoring and alerts
The UPS provides serial (RS-232), USB, and Ethernet communication. Supported management protocols include Modbus TCP, HTTPS, HTTP, SNMP, and Modbus RTU, so it can integrate with network-management and building-management systems. Configure email or SNMP alerts for on-battery, low-battery, overload and replace-battery events.
Alarms and everyday use
- An intermittent beep usually means the UPS is running on battery. Save your work; if the outage continues, shut down connected equipment before the low-battery alarm.
- A continuous tone or overload indicator means the connected load is too high. Unplug non-essential devices from the battery outlets.
- Leave the UPS switched on and plugged in at all times so the battery stays charged.
Care and maintenance
| When | What to do |
|---|---|
| Monthly | Check the front-panel status or software for alarms, confirm the load percentage, and make sure vents are clear of dust and obstructions. |
| Every 6 months | Run a self-test (or confirm the automatic self-test passed). Where supported, perform a runtime calibration during a maintenance window, as it discharges the battery. |
| Every 3–5 years | Replace VRLA batteries. Typical life is 3–5 years at 77 °F (25 °C); roughly every 15 °F (8 °C) above that can cut battery life in half. |
| Annually | Schedule preventive maintenance by authorized service personnel: thermal imaging of connections, capacitor and fan inspection, firmware updates and battery string testing. |
Troubleshooting
Use the front-panel indicators, display messages and event log to narrow down problems. For specific alarm codes, consult the manufacturer's manual or support line.
| Problem | Possible cause | What to try |
|---|---|---|
| UPS will not turn on | Battery disconnected or deeply discharged; input breaker or fuse open; no utility power. | Check the battery connection, verify the outlet or input breaker, and let the UPS charge for several hours before trying again. |
| Beeps and runs on battery with power present | Input voltage or frequency outside limits; loose input plug; generator power. | Check the input connection, try a different circuit, and adjust input sensitivity if the manual permits. |
| Overload alarm | Connected load above the rating; high inrush device on battery outlets. | Reduce the load below 50 kW and move printers or heaters off the UPS. |
| Short runtime or self-test failure | Aged or hot battery; battery not fully charged. | Charge fully and retest; replace the battery if runtime remains well below the rated figures. |
| Replace-battery indicator on | Battery at end of life. | Order the specified replacement battery and replace it as described in the manual (or by service for larger units). |
| Site wiring fault indicator | Missing ground or reversed hot/neutral in the building wiring. | Have a qualified electrician inspect the outlet and wiring before connecting equipment. |
| Computer does not shut down automatically | Communication cable not connected; software not installed or not configured. | Connect the USB or serial cable (or configure the network card), install the management software, and test with a simulated outage. |
| Unexpected transfers in eco mode | Utility disturbances causing the UPS to leave high-efficiency mode. | Review the event log; if transfers are frequent, consider keeping the UPS in double-conversion mode for that site. |
Energy use and running costs
A UPS uses energy as conversion and charging losses on top of what your equipment consumes. The Liebert 51SA050BAA has an ENERGY STAR weighted efficiency of 96.4%. The table estimates its losses if it supports a steady load 24 hours a day, 365 days a year, at $0.17 per kWh.
| Load | Efficiency | Power lost | Losses per year | Cost per year |
|---|---|---|---|---|
| 25% (12.5 kW) | 95.9% | 534 W | 4,681 kWh | $796 |
| 50% (25 kW) | 96.6% | 880 W | 7,708 kWh | $1,310 |
| 75% (37.5 kW) | 96.4% | 1,400 W | 12,268 kWh | $2,085 |
| 100% (50 kW) | 96.2% | 1,975 W | 17,301 kWh | $2,941 |
Even with nothing connected, the UPS draws about 339 W to keep its electronics and battery charger running — around 2,967 kWh ($504) a year.
Running in high-efficiency (eco) mode, where appropriate for your site, reduces these losses further. Loading a UPS very lightly lowers its efficiency, so choosing a unit sized reasonably close to your actual load keeps losses down.
Frequently asked questions
How much equipment can the Liebert 51SA050BAA power?
It is rated at 50 kW (50 kVA). Keep the connected load below that — ideally under about 40 kW — to allow for surges and battery aging.
How long will the Liebert 51SA050BAA run on battery?
The certification record lists 5 minutes at full load and 10 minutes at half load. Lighter loads run longer; older or warm batteries run shorter.
What type of UPS is the Liebert 51SA050BAA?
It uses a multi-mode double-conversion topology and defaults to VFI (voltage and frequency independent) operation. Double conversion gives the highest level of power conditioning with zero transfer time.
How efficient is the Liebert 51SA050BAA?
Its ENERGY STAR weighted efficiency is 96.4%. At half load (25 kW) it is 96.6% efficient, losing about 880 W — roughly $1,310 a year if run continuously at $0.17/kWh.
What battery does the Liebert 51SA050BAA use?
It uses a valve-regulated lead-acid (VRLA) battery (separate battery cabinet). The certification record lists a 3-year battery warranty.
Can the Liebert 51SA050BAA be monitored over the network?
Yes. It has an Ethernet connection and supports Modbus TCP, HTTPS, HTTP, SNMP, and Modbus RTU.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified ups battery backups dataset published by the U.S. Environmental Protection Agency (record certified January 22, 2019), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with Liebert. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact Liebert or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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