UPS systems sized for the load, the autonomy and the room they sit in

Online or line-interactive

In an online double-conversion UPS the load always runs from the inverter: incoming mains is rectified to DC and converted back to clean AC. When mains fails there is no transfer at all, and the load is isolated from dips, surges, frequency drift and noise. A line-interactive UPS feeds the load from mains through a voltage regulator and switches to its inverter when mains fails, which takes a few milliseconds.

Many online units offer an eco or high-efficiency mode that runs the load on mains and brings back a short transfer time. We state in the design where that is acceptable and where it isn't.

Every online UPS has a static bypass that moves the load to mains if the inverter fails or is overloaded. We also specify an external maintenance bypass, so the UPS can be isolated, repaired or replaced without shutting the systems down. Its interlocking and labelling are checked at commissioning, because a wrongly operated bypass is a common cause of outages during maintenance.

Sizing by load and autonomy

We start from a list of what must stay on: recorders, core and PoE switches (with the PoE power actually drawn), access controllers and lock power supplies, intercom servers, control room workstations and displays. Where the equipment is already running we measure it, because nameplate values add up to far more than the real load.

• Rating: UPS ratings are given in kVA and kW, and for modern IT loads with a power factor close to 1 the kW figure is the limit. We keep the steady load at around 70–80 % of the kW rating, leaving room for inrush and growth.
• Autonomy: set by what happens after the outage starts. With a generator the UPS only has to bridge start, transfer and stabilisation, but we add margin for a failed first start. Without one, autonomy is however long the site must keep operating on its own.
• End of life: batteries lose capacity as they age. We size so the autonomy still holds near the end of the battery's expected life, not only on the first day.
• Distribution: separate output circuits so a fault on one device doesn't take down the rest, with protection chosen to trip on the limited fault current an inverter can supply.

Runtime is not linear. Halving the load on the same battery more than doubles the runtime, which is one reason we separate critical loads from those that can wait for the generator.

Batteries, heat and testing

Valve-regulated lead-acid (VRLA) batteries are still the most common choice for UPS. Their life is rated at 25 °C and roughly halves for every 8–10 °C of sustained increase. A battery in a room that sits at 35 °C through a Saudi summer may need replacing in about half the time its datasheet suggests. Lithium-ion is increasingly used where space, weight or long life matter.

Cooling is part of the design: a battery room with its own air-conditioning on a reliable setpoint, not shared with an office unit that is switched off at night, and a temperature sensor that raises an alarm.

• Visual and connection checks: terminals, torque, swelling, leakage and corrosion.
• Impedance or conductance per block, trended over time to find weak blocks before they fail under load.
• Capacity (discharge) tests against a known load to confirm the real autonomy, at commissioning and periodically after.
• UPS checks: event log review, fans and filters, and a controlled transfer to bypass and back.

We provide design, installation, commissioning and maintenance services. The UPS and its batteries are procured by you or your contractor against our specification.