An elevator is not a normal backup load. It has a motor with a high starting current, a controller that must stay alive, a rescue sequence defined by the lift code, and a machine room that is often hot and small. A generic UPS quote rarely covers all four.
This guide explains the three backup layers, how to size the rescue circuit, and what the lift contractor and the power supplier must agree before the order.
What happens to a lift when the power fails?
A lift with a variable-frequency drive stops when the DC bus collapses. The passengers are inside the car, the controller may still be alive for a few seconds, and the brake sets. The rescue sequence then depends on the equipment installed:
- ARD (automatic rescue device): an internal battery and inverter move the car to the nearest floor and open the doors once.
- UPS on the controller: keeps the controller, door operator, communications and rescue circuit powered, but does not move the car unless the drive is also backed up.
- Generator: supplies the whole lift after 10–30 seconds, but the gap is exactly when the rescue is needed.
The practical design is usually a combination: the ARD handles the one-time rescue, a small UPS keeps the controller and communications alive, and the generator takes over for normal service.
UPS, ARD or generator: which layer do you need?
The three layers solve different problems and should not be substituted for one another.
| Layer | What it powers | Runtime | Typical use |
|---|---|---|---|
| ARD | Car movement to the nearest floor | One rescue cycle | Every passenger lift |
| UPS | Controller, doors, intercom, rescue circuit | 15–60 minutes | High-rise, hospital, hotel |
| Generator | Whole lift and building | Hours | Long outages, fire service lift |
If the building has a generator, the UPS only needs to cover the generator start and the rescue. If there is no generator, the ARD is the primary rescue path and the UPS is optional for the controller.
How do you size the elevator UPS?
Start with the load list from the lift contractor. The controller nameplate is only part of the load.
- Controller and drive control: typically 0.5–2 kVA.
- Door operator and lighting: 0.3–1 kVA.
- Intercom, CCTV and emergency lighting: 0.2–0.5 kVA.
- Rescue circuit and brake release: per the lift manufacturer.
- Design margin: add 25% for ageing, temperature and future load.
For a 2 kVA continuous load with 30 minutes of runtime at a 192 VDC bus, 0.85 inverter efficiency and 0.6 usable depth of discharge, the estimate is about 39 Ah. A 40–50 Ah bank or a 24 V lithium module covers it with margin. Confirm the charger current and the battery room before fixing the model.
| Building | Controller + rescue load | UPS size | Runtime |
|---|---|---|---|
| 6–10 floor office | 1–2 kVA | 2–3 kVA | 15–30 min |
| Hotel, 12–20 floors | 2–4 kVA | 3–6 kVA | 30–60 min |
| Hospital, fire-service lift | 3–8 kVA | 6–10 kVA | 60–120 min |
| High-rise, two cars | 4–10 kVA | 10–20 kVA | 30–60 min |
Can the UPS run the motor?
Usually not, and it should not be forced. A standard IT UPS is designed for a nonlinear electronic load, not for a motor with a 5–7 times starting current. A dedicated elevator UPS or a drive-rated inverter is different: it is sized for the motor, the starting method and the regenerative energy.
If the project needs the car to run on battery, use a lift drive that supports a battery input, a bidirectional converter or a braking resistor, and a UPS rated for the motor’s starting current. Confirm the drive manufacturer’s DC bus voltage and the UPS output configuration. A mismatch here is expensive and dangerous.
What should be in the specification?
A lift backup specification should state:
- The rescue strategy: ARD, UPS, generator or a combination.
- The load list and the runtime for each layer.
- The input voltage, phase and frequency (230 V / 400 V, 50 Hz or 220 V / 60 Hz).
- The battery chemistry and the machine-room temperature.
- The communication interface to the building management system (dry contact, RS485, MODBUS, SNMP).
- The test and handover procedure with the lift contractor.
Do not accept a quotation that lists only “elevator UPS 3 kVA”. The rescue circuit, the door operator and the battery room decide whether the system works on the day.
How does the battery room affect the design?
A lift machine room is often the hottest room in the building. VRLA life halves for roughly every 10 °C above 25 °C, so a 35 °C room turns a 10-year block into a 5-year block. LiFePO4 has a wider operating window and a longer cycle life, but it still needs ventilation and a BMS rated for the ambient.
If the room cannot be cooled, derate the battery and shorten the replacement interval. If the room is small, a rack or wall-mounted lithium module may fit where a lead-acid string does not.
Which standards and documents apply?
The lift is covered by EN 81-20 / EN 81-50 in Europe and ASME A17.1 / CSA B44 in North America, plus local rescue and emergency-power rules. The UPS is specified to IEC 62040-1/-2/-3, and the battery to IEC 60896-21/-22 for VRLA or IEC 62619 for lithium. A fire-service lift usually has an additional fire-rated supply requirement.
Ask for the model datasheet, the battery configuration sheet, the test report and the interface drawing. The lift contractor should confirm the rescue sequence and the load list in writing before the UPS is ordered.
Next step
Send the controller nameplate, the rescue load, the number of floors, the machine-room temperature and the required runtime. We will return the UPS size, the battery configuration and the interface list for the lift contractor.
Start with the elevator UPS product page, compare the three-phase UPS range for a high-rise, or use the sizing calculator for a first estimate.
