UPS for an elevator: online UPS or inverter with batteries
Author: Svitlo-Lux editorial team. Published , updated . Review (engineering): approved (Project owner).
A UPS for an elevator and pumps is chosen not by the power on the box but by behavior during motor start, switchover and the return of the grid. Below is a comparison of the two approaches, a list of questions and the reasons why approval from the elevator manufacturer cannot be skipped.
Two approaches: online UPS and inverter with batteries
A double-conversion online UPS constantly rectifies the input voltage and forms the output sine wave anew, so the load does not feel the switch to battery. An inverter with batteries and a charger in a typical scheme switches to battery power after the grid disappears, and the time of this switchover depends on the model. Both approaches can work, but they have different strengths and weaknesses.
| Criterion | Online UPS | Inverter with a battery |
|---|---|---|
| Behavior when the grid disappears | No break in power | There is a switchover time, depending on the model |
| Output voltage quality | Stable, isolated from the grid | Depends on the mode; often the grid passes through to the load |
| Motor inrush currents | Limited overload capacity, check against the datasheet | May have higher peak capacity, check against the datasheet |
| Bypass | Usually automatic and manual | Depends on the scheme and model |
| Scaling | Depends on the model | Modular options are common |
| Load type | Sensitive electronics, controls, communication | Motors and mixed lines, if confirmed by the manufacturer |
The load type determines the choice. For elevator control panels, dispatching and communication an online UPS is convenient, while for the power part with powerful motors both high-power UPS units and an inverter with batteries are considered, depending on the elevator manufacturer's requirements.
Bypass and switchover time
A bypass is a route that lets power reach the load around the converter, for example during maintenance or overload. For an elevator two questions matter: what happens when the motor start overloads the unit, and whether the load will be left without power during the transition. Also clarify whether the bypass passes poor-quality grid power to the load, if there is any, and whether that is acceptable for your drive.
Switchover time is measured from the grid disappearing to stable voltage appearing at the output. For a motor, a short break usually means the car stops, and the required reaction is set by the control scheme. So the time value is taken from the datasheet and agreed with the elevator manufacturer.
Inrush current and power headroom
Elevator drives and pump motors have inrush (starting) currents much larger than running ones. A benchmark from market reviews: from one and a half to three times, but the real value depends on the drive, see the datasheet. A frequency converter and soft start reduce the starting current, but add their own requirements for voltage quality and harmonics.
The platform calculates peak power by the "one motor starts, the rest run" scenario, multiplying the result by a starting margin. Simultaneous starting of several motors is not modeled, so a line with an elevator and pumps needs an engineering calculation. Do not select a UPS only by the motor power on the nameplate.
- Ask the elevator manufacturer or service organization for the starting power and power factor.
- Clarify whether there is regeneration and how the UPS or inverter should act when the motor returns energy.
- Ask the UPS supplier what overload capacity, and for how many seconds, it guarantees per the datasheet.
- Find out whether the calculation was done for the worst case: full car, upward travel.
Why elevator manufacturer approval is needed
An elevator is high-hazard equipment: its control scheme, brakes and emergency evacuation mode are designed for certain power parameters. A backup source that supplies an unexpected voltage waveform can change the behavior of the control panel or limiting devices. So connecting backup to an elevator should be agreed with the manufacturer or maintenance organization, and the relevant requirements and documents should be clarified with specialists.
A simpler scenario considered separately: powering only the device that returns the car to a landing floor. It needs less energy, but the scheme and requirements are again set by the manufacturer.
Pumps and water supply
Pump groups run in cycles, so the number of starts per hour and the operating mode of the frequency converter matter. For constant pressure it is better to account for both peaks and average consumption, and for whether the whole group needs backup or only one of the pumps. If the pumps are regulated by frequency converters, check their voltage requirements, and if they run on direct start, allow a larger power margin.
Supplier questions and acceptance
Questions before purchase
- What overload capacity and time apply to each overload level per the datasheet?
- What is the switchover time, and is there a no-break mode?
- How does the bypass work and under what conditions does it switch on automatically?
- What is the backup runtime at the stated load and under what assumptions?
- Is there written approval from the elevator and pump equipment manufacturer?
- Who performs service and battery replacement, and what is the inspection schedule?
Acceptance
- The test grid disconnection was carried out with the participation of the elevator maintenance organization.
- The behavior of the car and control panel after switchover is recorded in the act.
- Starting the pumps on the backup line was checked under real conditions.
- The return of the grid went without faults, and the bypass was checked.
- The OSBB has instructions for on-duty staff actions and a list of contacts.
It is convenient to start the list of critical loads and the capacity calculation with the backup power calculator. The result for elevators and pumps always carries a note that an engineering calculation is needed.
Frequently asked questions
- Can I use an ordinary office UPS for an elevator?
- You should not without written approval from the elevator manufacturer and a confirmed overload capacity. Motors have inrush currents that office models may not withstand.
- What is better for pumps: a UPS or an inverter with batteries?
- It depends on power, start type and the control scheme. For powerful motors an inverter with batteries is often considered, but the final choice comes from an engineering calculation.
Next steps
Backup power calculatorInverter power calculatorRegister an OSBB
This material is for general information only and is not a power supply design, legal or financial advice. Calculations are indicative; installation and protection selection must be done by qualified specialists only. The platform does not accept or hold funds.