Which no-break power supply suits your business?

A no-break power supply is backup power that takes over your loads without a noticeable interruption when the grid fails. Three set-ups do this: a commercial battery system with an inverter-charger, a UPS with a generator, or a rotary no-break with a flywheel. For an SME, a farm or an office building, the battery is often the most logical choice. It covers the power cut and works for you the rest of the year. The choice depends on three measured numbers: the power of your critical loads, the switchover time they tolerate and the runtime.

The grid fails on a Tuesday at 10 am. The generator starts, as planned. But in those few seconds the servers have rebooted, the PLC has lost its running cycle and the line has stopped. The generator did its job, and you still lost the morning.

What many companies do not see: a generator covers the duration, not the moment itself. And a row of small UPS units behind every server costs replacement batteries, without earning anything between two outages. In Maasmechelen, a customer already had an emergency generator standing idle. Our semi-off-grid system finally makes it useful. The customer chooses the grid or the generator as the charger for a 30.8 kWh battery, with 24 kVA of charging power.

What is a no-break power supply, exactly?

No-break is a function, not a device: keeping your loads powered without a noticeable interruption when the grid fails. Three set-ups deliver it:

• A rotary no-break (DRUPS): a diesel engine, an alternator and a flywheel. The flywheel bridges the time until the engine runs. At Hitachi Hi-Rel, for example, the range runs from 500 to 3,000 kVA, without a battery. These are machines for large sites.
• A UPS with a generator: the UPS holds the loads while the generator starts.
• A battery system with an inverter-charger: the battery feeds the critical circuits directly and lasts for hours if it is sized for that.

For an SME, a farm or an office building, the third option is often the most logical. A UPS and a generator are two machines waiting for an outage. A battery with an inverter-charger takes over on its own and also works every day. Our commercial batteries range from SMEs to industrial sites, in modular systems up to 1 MW. Our media section has a video of a Victron backup system for an airport control tower.

What is the difference between a no-break supply and a backup generator?

A generator supplies power as long as it has fuel, but it first has to start and switch over. During that time your loads have no voltage. In the United States, the NFPA 110 standard gives a "Type 10" emergency generator 10 seconds to deliver power, as Cummins explains. Ten seconds is enough to stop servers, PLCs and a production line.

UPS units differ too. According to Vertiv, an online double-conversion UPS does not switch over: it feeds the load all the time. An offline UPS interrupts for about 6 to 8 milliseconds, a line-interactive UPS for 4 to 6 milliseconds.

Want to compare UPS, generator and battery on runtime, daily use and rules? Our article on backup power for businesses puts them side by side.

What switchover time can your equipment tolerate?

The Victron MultiPlus-II datasheet gives a takeover in less than 20 milliseconds, fast enough for computers and electronics. The Victron Quattro does the same. It also accepts two sources, for example the grid and a generator, and connects automatically to the active one.

In practice, sort your loads into three groups:

• No interruption: servers, network, alarms, process control. These go on the backup output of the inverter-charger.
• A few seconds acceptable: lighting, pumps, ventilation. These can wait for a generator if the duration requires it.
• Not critical: extra heating, EV chargers, machines that can wait. These stay on the grid and stop during the outage.

That split sets the size of your no-break system. Only the first group really needs zero seconds. For servers and racks, our article on the right inverter for a business compares solar inverters, battery inverters and UPS units.

How do you size a no-break power supply in kW and kWh?

You size a no-break power supply on two numbers: power and energy. You measure both, you do not guess them.

• Power (kW): which loads run at the same time, and which starting currents (compressors, motors) must the inverter absorb? According to its datasheet, a MultiPlus-II 48/5000 delivers 4,000 W continuous at 25 °C and 9,000 W peak. Up to six units work in parallel, also in three-phase.
• Energy (kWh): how long must the critical loads keep running? After a few hours, an auto-start generator or solar panels take over.

We always start from measured quarter-hour consumption, never from a rule of thumb. With our monitoring software we measure for a short period before the installation. After that, you follow the system in the app and in the Victron VRM portal.

Worked example: an SME that wants to run two hours without the grid

Illustrative example, values chosen for the demonstration. An SME with a cold room and a server room lists its critical loads:

• Energy: two hours at 12 kW, so 24 kWh.
• Battery: 60 kWh usable, half of it reserved for backup, so 30 kWh. That gives 2.5 hours at 12 kW, with a margin for losses.
• Inverter-charger: six MultiPlus-II 48/5000 units, two per phase, give 24 kW continuous and 54 kW peak. That is enough for the compressor start.
• Daily use: the other 30 kWh serve every day for own solar use and peak shaving.

You set the reserve in ESS on the Victron GX device. According to the ESS manual, the setting "Minimum SoC (unless grid fails)" fixes the lower limit in normal use. If the grid fails, the battery simply keeps feeding the loads. For a longer outage, the GX device can start and stop a generator on its own, according to Victron. Our article on the off-grid generator with a battery explains that set-up.

Is your critical load mainly cooling? Our article on the cold room during a power cut works out how long a battery keeps it cold.

What do the Belgian rules say about a no-break power supply?

The Belgian electrical code (AREI in Dutch, RGIE in French) is federal: it applies in Flanders, Wallonia and Brussels. It separates two cases, and your risk analysis decides which one applies.

• Safety installations keep running what protects people. Allowed safety sources include batteries, generators independent of the normal source, and UPS units. They switch on automatically, in a separate, ventilated room open only to instructed (BA4) or skilled (BA5) persons.
• Critical installations keep a function running for other reasons, such as a production line, a server room or a control room. The operator sets the replacement source and the required runtime per load in a risk analysis.

A second grid connection does not count as a safety source. A safety source needs at least one switchover test under load per year, with documented maintenance. And sources not designed to run in parallel must be protected against doing so.

The grid operator has a say too. Under the Synergrid C10/11 technical rules, a backup supply system may only run in parallel with the grid briefly. That is at most 5 minutes per switchover, recorded in a log. A battery that also shaves your peaks every day is a storage system. In Flanders you register it with Fluvius. In Wallonia, declaring it to ORES is a legal duty, batteries included, with a deeper study above 10 kVA. In Brussels, check with Sibelga.

How does a no-break battery earn its keep every day?

A UPS or a generator waits for the outage. A no-break battery can work every day, as long as the control protects the reserve. Three uses come up often:

• Peak shaving. With the peak shaving option in Victron ESS, the battery tops up the grid when your loads exceed the set current limit. In Flanders, the capacity tariff for households and small businesses depends on the highest quarter-hour peak each month, according to Fluvius. In Wallonia, sites with peak metering pay a capacity charge to ORES.
• Own solar use. Daytime surplus is used in the evening instead of being exported.
• A connection that is too small. A battery is often the fastest answer when the grid operator refuses an upgrade or asks for a cabin.

How the battery cuts your peaks is explained in our article on peak shaving with a battery. One step further, a semi-off-grid system feeds your circuits from solar and battery, with the grid as the reserve.