How to choose a UPS: how long will cameras and servers last during a power cut?

What does a UPS do, and what doesn't it do?

The moment the power goes out, a UPS keeps supplying devices from its own battery. The camera recorder does not stop recording, the server does not shut down, the network switch keeps the connection. In short outages nobody notices anything.

A UPS is not a generator designed for long outages. Its main job is to cover short outages and, in a long outage, give time for devices to shut down properly or for the generator to start. A recorder that shuts down suddenly can get a disk error and a server can lose data; a UPS reduces this risk.

In Şanlıurfa in summer, short outages and voltage fluctuations are common as the load increases. Online UPS units also filter these fluctuations.

Buildings that have a generator also need a UPS. The generator takes a few seconds to start; in the meantime the UPS powers the devices.

The difference between VA and watts

On a UPS label you see two values: VA (apparent power) and W (real power). The power your devices draw is calculated in watts, and the UPS's watt value must cover that total. Choosing by the VA value alone can cause a UPS that looks sufficient on paper to fall short in reality.

To find the total load, add up the power value on the label or technical document of each device to be connected. For example, if a recorder, a PoE switch and a modem will be connected together, write down the values of the three separately. The value of the PoE switch also includes the power drawn by the cameras connected to it; so as the number of cameras grows, the load grows too.

For the exact value, you need to look at the device's own document. If there is no document, the value on the adapter gives an idea of the upper limit; real consumption is usually below it. The most accurate result comes from measuring on site.

Expert note: Do not run the UPS at full capacity. Leaving a margin above the load you calculated both extends battery time and leaves room for devices to be added to the system later.

How long does it last in an outage?

The answer to this question depends on four factors, and no company can give a correct time without seeing them.

• Size of the load: The same UPS lasts long with a small load and short with a large load. The time does not decrease in direct proportion to the load; it drops faster as the load grows.
• Battery capacity: The battery inside the UPS or added external battery cabinets determine the time.
• Age of the battery: A battery loses capacity over the years. The time that was sufficient when it was new gets shorter after a few years.
• Ambient temperature: Battery life shortens in a hot room. That is why cooling of the server room also affects the choice of UPS.

How is the time calculated?

For each UPS model, manufacturers publish a table or calculation tool showing the relationship between load and time. After finding your total load in watts, you read from this table how long the model you chose will last at that load. If the time you want does not come out, either a larger model or an external battery cabinet is added.

You decide how long you need. If the aim at a workplace is to ride out short outages and shut the server down properly in a long outage, a margin of a few minutes may be enough. If you want a camera system to keep recording in long outages too, larger battery capacity or generator support is needed.

On servers, it is important to set up communication between the UPS and the server. When the battery drops below a certain level, the UPS sends a shutdown command to the server, so data loss is prevented even if nobody is there.

Topology: line-interactive or online?

Line-interactive UPS units, widely used in small offices and camera systems, normally supply from the mains and switch to the battery during an outage or a large fluctuation. They are suitable for small systems in terms of price and efficiency.

Online (double-conversion) UPS units, on the other hand, continuously supply devices with clean voltage they generate themselves. They are preferred where the mains fluctuates often and in server rooms. There is no transfer time during an outage. They produce more heat and take up more space.

Which type to choose depends on the sensitivity of the devices to be connected and the condition of the mains. Voltage fluctuations can be more frequent in industrial zones or in facilities where large motors run; in these environments an online UPS is a safer choice.

How is the calculation set up for a camera system?

Suppose that at a business the recorder, the PoE switch that powers the cameras and the internet modem sit in the same cabinet. The first step is to write down the power values of these three devices. The power drawn by each camera connected to the PoE switch is added to the switch's value. Cameras that turn on infrared light at night may draw more power than during the day, so do the calculation using the night value.

The second step is to decide which devices will actually be connected to the UPS. If the recorder and cameras are connected but the modem is not, recording continues, but remote viewing is cut. If you do not connect the monitor to the UPS, the load decreases and recording still continues.

The third step is to look up this total load in the manufacturer's runtime table. The table shows how long the model you chose will last at this load. If the result does not meet your expectation, you reduce the load or increase the battery capacity.

Maintenance and common mistakes

The most common UPS failure is the battery reaching the end of its life without being noticed. Everything looks normal until the power goes out; when an outage happens, the system shuts down instantly. Testing the batteries regularly and forwarding the UPS's warnings to someone prevents this surprise.

Other common mistakes: connecting high-power devices such as a printer or heater to the UPS, putting the UPS inside a cabinet with no ventilation, and exceeding the capacity with power strips behind the UPS.

You also need to be careful when choosing the UPS location. The weight of the batteries, the ventilation need and access to the back for service should be considered. Large UPS units are placed inside or next to a rack cabinet, on a floor that can carry the weight.

Desa Bilişim does the load calculation on site for camera, network and server systems and recommends the right UPS and battery capacity.

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