Table of contents: Buyer's guide Top 5 KNX power supplies
A KNX power supply unit ensures a stable 30V power supply for all components. In the 1280 mA premium class, we compare the best power supply units from Enertex, Gira, MDT, Meanwell & Theben. Important: Enertex and MDT offer diagnostic functions.
Every KNX system requires at least one KNX power supply unit for a stable power supply that is in operation 24 hours a day, 365 days a year This quickly makes it clear what role a KNX power supply plays in ensuring stable continuous operation.
Because if this small component in the control cabinet fails, nothing works: switching and control processes no longer function and a smart building becomes a real “problem case”. What’s more, if the heating system has not been properly configured – see Top 5 heating actuators 140 to 290€ in comparison (comparison test) – it also gets bitterly cold in the house.
It doesn’t matter whether it’s a typical town hall, a large shopping center or a chic detached house. KNX power supply units are installed in the electrical switch cabinets everywhere to supply the entire system with a stable voltage. In larger buildings or villas, several KNX power supply units are always used, whether distributed across several control cabinets or in a single cabinet with several KNX lines. It is not uncommon for us to use 4, 5 or 6 KNX lines.
In addition to a stable power supply of 30 volts DC (direct voltage), which can drop to less than 24 volts at the last device with 64 KNX devices, a high level of short-circuit resistance is required today. This is because if the bus voltage is too low, it is not possible to program the relevant device. Does this often happen in practice? Yes and no.
KNX power supply units are currently offered by 69 manufacturers worldwide in various power classes – depending on the size of the house or apartment in each individual case. While 15 years ago the KNX industry was still cheering building owners with 160 mA KNX power supply units, today at least 960 mA or even better 1280 mA power supply units are required to satisfy the increased hunger for power of a KNX system.
Most KNX power supply unit failures occur in buildings when the current load is too high and too many components need to be supplied with power. The cause can then be quickly identified: The system was not designed properly and the KNX power supply unit was too weakly dimensioned/designed. Or retrofits have been carried out by building owners over the years without adapting/replacing the KNX power supply unit. If you want to do your programming quickly and yourself, take a look at our 8-hour click guide to KNX programming here.
Note: Like our other comparison tests, this article is updated regularly. This top 5 KNX power supply units is therefore a snapshot that may change over the coming weeks and months. This also applies to the prices.
Purchasing advice: KNX power supply units 1280 mA in this article
- Enertex KNX Dual Power Supply 1280
- Gira KNX power supply 1280 mA
- Meanwell KNX-40E-1280 Power supply unit
- MDT STC-1280.01 Bus power supply
- Theben PS 1280 KNX
Differences in the equipment of the KNX power supply units
- KNX power supply unit with 1280 mA current output (all have)
- KNX power supply unit with 1280 mA and second output (all have)
- KNX power supply unit with minimum space requirement (4 division units, Theben & Meanwell)
- KNX power supply unit with additional OLED display for status indication (Enertex only)
- KNX power supply unit with KNX diagnostic functions (Enertex and MDT only)
KNX power supply units with 1280 mA, which can even supply 1600 mA, 2000 mA or briefly up to 3000 mA of current in individual cases, are the top class today. The 2015 specification of Konnex in Belgium provides for KNX power supply units with a maximum of 1280 mA, after which the current limit is reached. Nevertheless, a 1280 mA KNX power supply unit provides a maximum continuous output of 39 watts at 30 volts DC. This is sufficient for many detached houses and larger apartments. Nevertheless, if you are building a new home or equipping an existing building with a KNX system, you should always opt for a KNX power supply unit with 1280 mA.
This raises the following questions for us: What do the top 5 KNX power supply units in the “1280 mA class” offer in this comparison test? What are the advantages of the individual candidates compared to the competition? Which features and functions are recommendable, and which can be safely dispensed with?
In this comparison test, the following compete against each other: The Meanwell KNX-40E-1280 power supply, the MDT STC-1280.01, the Gira KNX power supply 1280 mA (identical in construction to Jung KNX power supply 1280 mA and Hager TYFS110), the Enertex KNX Dual Power Supply 1280 and the brand new Theben PS 1280 KNX. All candidates are fairly new on the market, although Enertex already presented the first 1280 KNX power supply in 2020.
Basic functions of KNX power supply units
- 30 Volt power supply KNX bus or KNX system
- 1280 mA current load with choke as continuous load and thus 39 watts continuous power
- Second 30 volt voltage output (without choke)
- Various statuses via LED displays
- Protection against short circuit or overload
- KNX integration: Query bus parameters such as current, voltage, time stamp, etc. (optional)
KNX power supply units from 85 euros to 290 euros: What are the similarities and differences?
A simple look at the purchase price reveals a big difference right from the start: Meanwell offers the KNX-40E-1280, a KNX power supply unit with 1280 mA for well under 100 euros. Until recently, it was absolutely unthinkable that a manufacturer could offer such a “thick part” in this price range.
The other candidates offer their KNX power supply units in the range between 245 euros (Gira) and 290 euros (Theben). This makes it all the more important to find out, where the big price difference comes from and what the power supply units between 200 and 300 euros have in common. After all, no manufacturer in the KNX environment has anything to give away these days – see also Top 5 KNX switching actuators 24-fold in comparison.
Let’s start with what all KNX power supply units have in common: All candidates offer a 30 volt direct current (DC) output with choke. We explain exactly what this does in a paragraph below.
What are the benefits of the diagnostic function for KNX power supply units?
Among the five test candidates, the Enertex KNX Dual Power Supply 1280 and the MDT STC-1280.01 offer the option of sending diagnostic data to the KNX bus. Meanwell also offers a diagnostics-capable version with its KNX-40E-1280D power supply, although we did not include it in this test field.
This also means that this diagnostic data can be accessed remotely in encrypted form. This function is essential for KNX remote maintenance and fault diagnosis in order to avoid unnecessary travel costs and travel time. In our everyday work, we rely almost exclusively on remote maintenance for upmarket detached houses and villas in order to gain an initial overview of a KNX system.
If a KNX power supply unit can output diagnostic data such as bus voltage and bus current or time stamps for the last bus reset or bus failure, it is often possible to draw conclusions about failures or malfunctions of a KNX system. This can save a lot of time and testing effort in the run-up to an on-site visit. The table below lists all possible diagnostic functions in this test environment:
Diagnostic functions 1280 mA KNX power supply units (Enertex & MDT)
- Bus voltage (also with several outputs)
- Bus current (also with several outputs)
- Undervoltage warning
- last power failure
- Number of bus restarts
- Operating hours counter
- Temperature alarm
- Bus traffic, telegram rate
- Output statuses
- Additional functions such as logic functions, calendar, etc.
What does KNX power supply unit with built-in choke mean?
All KNX power supply units presented/tested here have a built-in choke, at least on the first voltage output. Basically the choke limits the short-circuit current. In order to transmit data, the voltage is briefly closed for a few microseconds by the respective bus subscriber, thereby pulling the voltage down. The choke prevents a rapid increase in current and therefore a short circuit in the power supply unit.
Although the component (shown in the picture below) costs little more than one euro in larger quantities, most power supply manufacturers only provide one voltage output with a choke. The only exception here in this comparison test is Enertex with its KNX Dual Power Supply 1280, which also provides its KNX voltage converter with a choke for the second 320 mA voltage output.
Overload capacity of KNX power supply units with 1280 mA
In many practical projects, situations arise where a KNX power supply unit suddenly has to provide more power than specified by the manufacturer. This is known as an overload, caused by too many connected KNX devices or simply short circuits in the green KNX cable. A modern KNX power supply unit must be able to withstand this without damage.
How often have we experienced this: If too many devices are connected to a KNX power supply unit that is too weak or if other cables were used for the power supply instead of the green KNX cable during installation, then the power requirement can increase immensely. For this reason, today’s KNX power supply can tolerate significantly higher current loads for short periods than was the case a few years ago. The quality of KNX power supply units has improved significantly with the increasing power requirements of KNX systems in recent years.
How much can a 1280 mA power supply unit be overloaded?
- Enertex KNX Dual Power 1280: 2000 mA (60 watts)
- MDT STC-1280.01: 1900 mA (57 watts)
- Gira power supply 1280 mA: 3000 mA (90 watts, short-circuit current)
- Meanwell KNX-40E-1280: 2800 mA (84 watts, short-circuit current)
- Theben PS 1280 KNX: no information from the manufacturer
1st place: Enertex KNX Dual Power Supply 1280
Enertex is the real pioneer among KNX power supplies with 1280 mA. The background: The Franconian manufacturer launched the Enertex KNX Dual Power Supply 1280, the first product in this power class, back in 2020. The OLED display, which provides all important operating data such as voltages and currents at the three outputs, operating temperature and telegrams (load) at the touch of a button, is still unique in the competitive environment.
This is particularly important for people like us to get all the important “diagnostic data” of a running KNX system at a glance. And all this without having to call up a bus monitor via the ETS software!
It offers three voltage outputs with 30 volts direct current (DC) like no other candidate in the test environment: One with 1280 mA including choke and two with 320 mA each (only one output with choke). In practice, this could be a second KNX line and the power supply for an electric door, for example, which are operated with this single power supply unit.
As the power supply unit is fully integrated into KNX, bus resets can be triggered via group addresses or bus telegrams can be sent for various statuses (voltages, currents, temperature, etc.). The extent to which additional functions such as timers and logic functions are relevant in individual cases is something that everyone has to decide for themselves. And for those who like encryption, for example in outdoor areas, there is“KNX Data Secure“, which can be activated in the ETS software.
What we have observed at Enertex in recent years: There are software updates for the power supply unit at irregular intervals, which are imported into the KNX power supply unit using Enertex’s own tool.
Enertex KNX Dual Power Supply 1280 Rating
Overall ranking: 1st place
2nd place: Meanwell KNX-40E-1280 power supply unit
Meanwell has been known as a manufacturer of power supply units for decades. The pure KNX power supply units have not been on the market for that long. However, Meanwell offers really competitive prices that no other manufacturer can even come close to. Meanwell is based in Taiwan and produces its power supply units in China.
The Meanwell KNX power supply unit is also available as a diagnostic version in the KNX-40E-1280D variant. However, it then costs more than twice as much at approx. 180 euros and is still significantly cheaper than the comparable competition with and without diagnostic functions.
The highlight: 4 division units – equivalent to 72 mm width – like the Theben, means very little space required in the switch cabinet, a possible short-circuit current of up to 2800 mA, so there is definitely an upward buffer for the already powerful power supply unit ex works in the event of peak loads.
The second voltage output of 30 volts – without a choke, of course – is worth mentioning in connection with the low price of just under 80 euros.
As with most other candidates, there is a bus reset button. A status LED indicates the bus voltage with three colors green = 28 to 31 V, orange = higher 31 V and red = lower than 28 V. A second status LED also indicates the current load with three colors green = lower 1280 mA, orange = 1280 to 1600 mA and red = overload greater than 1600 mA.
A status LED indicates the bus voltage with three colors green = 28 to 31 V, orange = higher than 31 V and red = lower than 28 V. A second status LED also indicates the current load with three colors green = lower 1280 mA, orange = 1280 to 1600 mA and red = overload greater than 1600 mA.
Meanwell KNX-40E-1280 Power supply rating
Overall ranking: 2nd place
3rd place: MDT STC-1280.01 bus power supply
In addition to many other KNX components, MDT has recently started offering a KNX power supply unit with 1280 mA. The debut of the Enertex power supply unit in this power class is likely to have been the decisive factor in MDT also offering a power supply unit in the top class with the STC-1280.01. Of the five power supply units in this comparison, it is the second voltage converter alongside the Enertex to be equipped with diagnostic functionality.
This makes it particularly interesting for the group of buyers who also use these functions and therefore cannot consider any other power supply unit. We can therefore compare the MDT STC-1280.01 directly with the Enertex KNX 1280 Dual Power Supply: Both candidates require 6 division units of space in the control cabinet on the top-hat rail. However, the MDT STC-1280.01 power supply “only” has two voltage outputs, one with 1280 mA including choke and a second with 320 mA without choke.
Important statuses such as “temperature alarm”, “bus error”, “device error/failure” and excessive “bus traffic” are displayed via a total of 8 LEDs. This is by no means standard among KNX power supply units, but some candidates in the “premium class” offer functions that are not available in the smaller classes.
MDT STC-1280.01 Power supply rating
Overall ranking: 3rd place
4th place: Theben PS 1280 KNX
The Theben PS 1280 KNX is the latest addition to the market among all the test candidates and has only been available for a few days in April 2024. Like all other candidates in this league, it has a second voltage output with 30 volts direct current (DC), albeit without a choke. It is just as compact as the Meanwell with a width of 4 division units and uses LEDs to indicate various statuses such as current overload and bus data overload.
As it has no diagnostic functions, it also offers no parameters for setting in the ETS software. It is a solid power supply for Theben’s own “Luxor Living” system or for use as a pure KNX power supply unit. Theben is denied a top 3 position because it offers too few features and functions in the price segment up to 300 euros.
Theben PS 1280 KNX rating
Overall ranking: 4th place
5th place: Gira KNX power supply 1280 mA
The KNX power supply unit from Gira in the top version, the Gira 1280 mA power supply, has also only been on the market for a few months. It is completely identical in construction to the Jung KNX power supply 1280 mA and the Hager TYFS110. It takes up 6 pitch units of space on the top-hat rail and, like all the other test candidates, has two 30 V DC voltage outputs. As is usual with most test candidates, only the first output is equipped with a choke. Gira specifies the highest short-circuit current as 3000 mA in the entire test environment. We will test that!
The Gira 1280 mA power supply also lacks a little in terms of features to be in the top league here. We are aware that power supply units such as the Gira are priced differently in the project business – especially when it comes to the in-house KNX Light System “Gira One” – than is the case in individual sales. In other areas of KNX components, it can be seen how loose and flexible Gira is in its pricing and how it can offer lower prices than its competitors.
Gira KNX power supply 1280 Rating
Overall ranking: 5th place
Conclusion
Let’s get to the heart of the individual test candidates in the 1280 mA premium class: If you’re on a tight budget, then the Meanwell KNX-40E-1280 KNX power supply is the best choice. For just under 80 euros, you can get a powerful and compact KNX power supply with two 30 volt outputs, the first of which is equipped with a choke.
If you want KNX (remote) diagnostic functions, need three voltage outputs – two of which are equipped with a choke – and can enjoy an OLED display, then the Enertex KNX Dual Power Supply 1280 is the perfect choice. This makes the thick Enertex KNX Dual Power Supply 1280 including display for 270 euros the clear performance winner and the Meanwell KNX-40E-1280 the price banger in the premier class of KNX power supplies. The Enertex impresses with its (status) display, which is unrivaled in this environment.
We also recommend the MDT STC-1280.01 for 260 euros, which offers slightly fewer features than the Enertex at almost the same price. The recent price increases at MDT have left their mark here. In contrast, the Gira KNX power supply 1280 for 245 euros and the Theben PS 1280 KNX for 290 euros offer far too few features, especially no diagnostic functions, for a comparatively high price in this premium KNX power supply class. However, with both of the latter candidates, it should be borne in mind that they are sold in project business or bundle offers at even more favorable prices via electrical wholesalers such as Sonepar or FEGA & Schmitt.
All candidates can supply a KNX line with at least 64 devices – or even a few more components – with sufficient power. That is enough for many single-family homes indoors. If necessary, the Enertex can even be used for a second line with its second 320 mA output.
And how long does a KNX power supply unit last? In our experience, it is easily 15 to 20 years in continuous operation. The ageing capacitors (cent items) on the circuit board are usually to blame for the final failure. If these were replaced, operation would immediately continue for many years.
1st place
2nd place
3rd place
4th place
5th place
Frank Völkel & Smartest Home Team
Since 2007, we have been testing KNX components for functionality and practical suitability in order to use only the best products in our customers' homes and villas
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