Battery Application Solutions for Movable Bridge: Reliable Lift Power

A movable bridge that cannot lift is a navigational closure and a road closure at the same time, so its drive power is treated as a safety system rather than a convenience. Most spans draw from a grid feed that also serves lighting and traffic signals, and that feed is exactly what fails in a storm. Purpose-built battery application solutions give the operator an independent reserve that can complete a lift, hold the span, and bring it back down without waiting for the utility.

Why Bridge Lift Power Is a Safety System

Bridge operators work to published opening schedules and legal obligations to mariners. A failed lift during a scheduled opening strands vessels, and a span stuck in the raised position closes a road. The power system therefore has to be dependable on demand, not on average, and it has to be testable without disrupting traffic. Battery-backed drives meet both requirements: they carry the lift, and they can be exercised between openings on a regular cycle.

Load Profile of a Movable Span

The duty is short and violent. A bascule or swing span draws a large inrush as the drive breaks inertia, holds a moderate load through the travel, then regenerates on the way down for some drive types. That profile suits batteries well, but sizing has to follow the peak rather than the energy. A bank sized on average consumption will sag voltage at the moment of breakaway and trip the drive on undervoltage.

Choosing a Chemistry for the Pier Environment

Pier pits and machinery rooms are damp, salt-laden, and occasionally flooded. Lithium iron phosphate in a sealed, corrosion-rated enclosure is the common choice for new installations, because it handles the vibration of a driven span and gives decades of float life with no watering. Where the machinery room is unheated and exposed to freezing, the spec should include a heater and a low-temperature charge cutoff so the bank is never charged below its safe window.

Movable Bridge Power Comparison

Retrofitting an Existing Drive

Most retrofit work is electrical, not mechanical. The battery and a bidirectional inverter sit between the existing drive and the supply, or alongside it through a transfer scheme. The important checks are the drive’s tolerance for DC-link ripple, whether the existing motor starter can accept an inverter source, and what happens to regenerative energy during lowering. A supplier should survey the drive before quoting, because older DC drives behave very differently from modern variable-frequency units.

What to Ask a Supplier

Ask for the peak current the bank can sustain for the full travel time, the number of consecutive lifts available on battery alone, and how the system behaves if a lift is interrupted mid-travel. Insist on a commissioning test that completes three full cycles on battery power with the grid feed disconnected.

People Also Ask

How many lifts can a battery bank provide? Usually three to ten full cycles depending on span size and bank capacity. Specify the number you need rather than accepting a generic rating.

Can the system handle regenerative energy? Many spans generate power while lowering. Confirm the inverter or a braking resistor can absorb it, or the drive may trip on overvoltage.

Does a battery replace the standby generator? Not always. It covers the lift itself and short outages, but a generator may still be needed for extended grid failures that also affect lighting and signals.

How often should the bank be tested? Monthly exercise cycles catch faults early. The BMS should log each test so the operator has a record for the bridge inspector.

Written by Karl at China Battery Technology. Request a quote.