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Two DIN-Rail Power Supply Concepts in Comparison: XT40 vs QT40
In a time when it is becoming less and less the case that the engineers are involved in running companies and making decisions on the use of devices, it is important that the required characteristics of a device are specified with precision. The desire of those running companies for costeffective solutions is understandable as well as necessary. For engineers and system planners, however, the task of specifying power supplies is becoming more and more difficult.
There is a choice between too many offers with different device features, which can only be assessed with special knowledge or experience. In addition, there is a desire for the most simple and cost-effective solutions. How lean and streamlined the specification of a power supply unit may be, this article will address what features can be designed in and out based on two 960W power supply units of PULS, the semi-regulated XT40 device and the fully regulated QT40.
|When looking at costs it is important to compare the overall costs in the system fairly and not to simply reduce them to the savings in the procurement of the power supply itself. It only works if you actually have the option to choose between different power supplies or power supply concepts. With PULS, there are two devices in the 960W class with different approaches for different tasks.
The XT40 series was mainly developed for drive tasks or loads where motors are involved and converts the 3-phase input voltage with a semi-regulated resonance converter into an output DC voltage of either 24V, 36V, 48V or 72V. This single-stage concept is very cost-effective, compact and highly efficient, but makes minor compromises in the input voltage range, the ripple and noise voltage and in the hold-up time in the event of power failures.
The alternative to these devices are the newly rolled out units of the QT40 series. This series is fully regulated and equipped with many features that can in turn save costs in the overall calculation.
|QT40 - QT40 device with 3 in-built fuses save installation costs and space.|
The advantage of a high efficiency level is obvious and is not an objective in itself for manufacturers of power supplies. It is in fact a tool which serves to achieve a number of characteristics such as: low power losses, small design, less space required on the DIN-Rail, low heat gen-eration, low operating costs, light weight, low temperature stress on component parts in the complete control cabinet, long lifetime, high level of reliability and much more.
In these disciplines the two devices are leaders and stand out from their competitors. In the 24V variant, the XT40 is only 96 mm wide and achieves efficiency of 95.5%. The QT40 achieves 95.3% and requires only 110 mm on the DIN Rail. With these efficiency values, the power losses of the 40A devices are reduced to a level of several standard 10A devices. This means that 4 times the useable performance is achieved with the same volume of heat waste. Another benefit of the QT40 units is the optimized efficiency across the entire load range. So far, it has been important to optimize efficiency at maximum load.
This facilitates the small design, with¬out exceeding the maximum allowed temperatures of components. As systems and machines seldom run continuously at full load, efficiency at partial load is alsoof practical use. For these characteristics,complex control circuits and algorithmsare required, and theseare easiest to realize using digital circuits, microprocessors and software. In a device such as the QT40, there is a total of 3 microprocessors working hand-in-hand.
|input Voltage Range|
A broad input voltage range increases the immunity to fluctuations in the supply voltages and facilitates global use in the event of differing mains voltages. However, the wide input voltage range is complex and costs money. When the total system is supplied through a matching transformer or the power supply is only being used in a regional project, there is nothing to be gained from this feature.
With the XT40 Series, separate devices are required for the 400Vac and the 480Vac mains networks but the QT40 Series covers the entire range with one device. Another distinguishing feature is the behavior when one phase fails. The QT40 is good-natured in this respect and even at reduced current can also be operated permanently on just two phases. The XT40 device on the other hand, protects itself and switches off in these circumstances.
|Overload Capacity, Parallel Connection and Charging of Batteries|
Both devices have generous overload reserves integrated that make it easier to start motors or connect capacitive loads. The QT40 supplies 50% “bonus current” for 4 seconds (BonusPower®) and then limits the current automatically to the nominal current. The semi-regulated XT40 has a 25% PowerBoost integrated.
Whereas the QT40 supplies constant current when there is an extended overload, the XT40 switches the output off after a certain period of time. Parallel connecting of outputs or charging of batteries is only possible with the QT40 devices. To achieve an uniform distribution of the load current when multiple power supplies are connected in parallel, the QT40 even has a special feature for passive current share included.
In the Parallel Use mode the output voltage is controlled in such a way that it is about 5% higher at no load than at nominal load. With this feature an overload of one single device is avoided and almost even temperatures between the parallel-connected power supplies are achieved, which is beneficial for the lifetime of the individual devices.
The hold-up time or ride-through time is the time between the loss of input voltage and the dropping of the output voltage. With the QT40, some half-waves of the sinusoidal input voltage can be bridged, depending on load current. With the XT40, the voltage drops immediately after the loss of input voltage.
You must be certain whether or not a bridging is required. If motors are being supplied with power, short mains voltage interruptions generally do not result in a fault as the rotating masses capture these. However, controls react very sensitively to short interruptions. If they are not supported by a DC-UPS or a buffer module, supply with the XT device is not recommended.
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