Correctly Plan and Calculate Power Supplies

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6 minutes
10. June 2024

At the technical core of every building lies the distribution board, where meticulous planning and precise calculation of power supply units are essential for the seamless functioning of automation technology.

Crafting the perfect power supply units for 24V devices within a distribution cabinet demands a blend of technical prowess and strategic foresight.

In this blog, we shed light on key considerations crucial for mapping out power supply units in building automation systems, delving into potential challenges that may surface along the way.

1. Calculate total output

The initial and pivotal step involves meticulously calculating the total power required by all 24V devices. This calculation must not only consider current demand but also anticipate future expansions. Undersized power supply units can result in overloading and subsequent failures. Conversely, oversizing often leads to the erroneous assumption of maximum total output for all devices, resulting in the installation of an excessive number of power supply units. This not only occupies unnecessary space in the distribution board but also incurs additional costs. One critical variable in this equation is the simultaneity factor.

The Loxone Project Planning tool calculates the required power fully automatically based on the planned components.

2. Simultaneity Factor

This is used for components such as lighting and audio and reflects the probability of how many of these components are 100% active at the same time. In private construction, we are talking about a factor of 0.3, i.e. 30% of the total power (with centralised power supply).

For the cabinet-based devices, such as the Miniserver and any Extensions, and also for all peripheral devices, such as Presence Sensors or Touch switches, 100% of the required power is calculated.


Light calculation example:

The 5m Loxone LED Strips has a maximum power consumption of 86W. In the Loxone Config, however, switching on is split between the three RGB channels and the W channel. This means that a maximum of 64W can be activated when using this 5m colour LED strip (2.66A instead of 3.58A).

Power consumption per channel and 5m strip:

Red: 20W
Green: 23W
Blue: 21W
Warm white: 22W
Max.: 86W


Real-life, measured values:
PWM spots as well as the Loxone Tree Spots, for example, require only 60% of the power at 80% of the brightness.

80% brightness – 4.92W
100% brightness – 7.5W

Audio calculation example:

An output of the Loxone Audioserver is calculated with an RMS power of 18W. This power would be required at maximum switch-on volume. However, only with very low-frequency music.

Real-life, measured values:
With quiet music, only 40%* of the total power is required at 100% volume.

Hotel California – Eagles
25% volume – 3.2W
100% volume – 9.6W

Animals – Martin Garrix
25% volume – 3.4 W
100% volume – 14.4W

Measured against the WALL Speaker.
*the values refer to the maximum measured current, as this is very dynamic with music.

3. Plan a power reserve

It is advisable to use a power reserve of at least 20% above the calculated total output. This reserve helps to absorb unexpected load peaks and provides scope for later expansions of the system.

The Power Supply and Backup can output 60A for 10 seconds instead of the maximum permissible 40A according to the datasheet.

4. Quality and reliability

The selection of power supply units should not only on the basis of their performance capacity. High-quality power supply units with good efficiency and protective functions such as short-circuit protection, overload protection and thermal protection are crucial for the longevity and safety of the entire system.

Electromagnetic compatibility (EMC):
Installing several power supply units in a distribution board can lead to electromagnetic interference. It is important to choose power supply units that perform well in terms of EMC and to take additional shielding measures if necessary.

5. Consider heat output

Components should be strategically placed within the cabinet to avoid overheating:

Power supply units: As one of the main sources of heat, power supplies should be positioned in well-ventilated areas. Avoid placing them next to other heat sources or in the center of the distribution board to minimize heat buildup. Ideally, they should be installed near ventilation slots or in locations with natural airflow.

Automatic switches (circuit breakers): These should be located at the beginning of the distributor for easy access, if possible. Since breakers generate less heat compared to power supply units or the control unit, their placement can be more flexible.

6. Cabling and connections

More power supply units mean more cabling effort. Every terminal, connection, and screw adds another potential source of error. In cabinet builds, a 2-5% margin of error for all connections is typically accounted for. Reducing the total number of connections not only cuts down installation time but also simplifies troubleshooting. Plus, it saves space in the cabinet overall.

Proper cabling and secure connections are crucial for reliable power supply. Ensure that cable cross-sections are adequately sized and all connections are firmly connected.

7. Maintenance and monitoring

In the event of a short circuit or overload of the cable, each outlet should be secured. To avoid lengthy troubleshooting, it makes sense to monitor these fuses so that you are notified when they have tripped. In addition, it makes sense to measure energy consumption in order to identify potential savings and avoid energy wasters. Our recommendation: the Power Supply & Backup as an all-in-one solution.

The biggest challenge is often the dynamics of the project. Changes in the planning phase, or unexpected extensions. To summarise, the planning of power supply units for building automation is a task that goes far beyond the simple addition of performance values. It requires a comprehensive understanding of the technical requirements, forward-looking planning and the ability to react flexibly to unforeseeable challenges.

Andreas Falkinger

Product Marketing: Energy, Loxone


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