The subject of 'redundancy' is on everyone's lips, as high availability is a must for more and more applications. However, with the redundant power supply it was mostly the output that was of interest, until now the input had hardly been taken into consideration. Schroff offers a redundant solution with a 1U power supply plug-in unit.
The trend to utilise the last available unit height in an electronic enclosure has not changed. This is the reason why in many applications the available space has become insufficient to house two redundant 19" power supply plug-in units in a 3 U subrack. Within the framework of a customer project, Schroff was asked to develop a power supply unit of only 1U height with a capacity of up to 400 W, which would be suitable for the assembly in 19" and also ETSI cabinets. The condition for this development was redundancy for input and output. Schroff succeeded in fulfilling the demands and transformed them into an effective and competitively priced system, which it introduced into its standard range.
Secure redundant input
Until recently, as a rule, the uninterrupted operation through a secure input voltage was achieved by the use of classic battery back-ups. In case of a network failure, the stored energy in the batteries provided the uninterrupted function of the systems. Disadvantages were: high requirement for space, the cost, as batteries are expensive; and, the costly maintenance through the required cyclical exchange of batteries.
The new unit from Schroff enables the use of a second independent power supply. The 1U power supply plug-in unit shown in the accompanying photo (4,45 x 40,4 x 23,8 cm: H x W x D) is configured in such a way, that on the input side, two independent power supplies (90 V to 254 V) can be connected. In case of the failure of power supply 1, the electronics will switch to the second unit within milliseconds. The complete switching process is guaranteed to be shorter than the failure measures of the power supplies. In this way the output voltage remains stable, whichever power unit is supplying the voltage. The available output is indicated via potential-free relay contacts.
As the power supply connectors are assembled at the rear, ie, connectors with accessible contacts, special precautions had to be taken. It had to be ensured that the contacts always remained voltage-free after being unplugged. Special relays with dual contacts in series were used, which, even during failure, guarantee that no power voltages are apparent on the input connectors. A further switch relay prevents a short circuit occurring between the two input power supplies. The complete switching is arranged in such a way that the power supplies can be operated between 90 V and 265 V and with this, unlimited worldwide usage is possible.
40 to 400 W capacity
From the front, the 1 U unit offers the possibility to plug in two power supplies as 19" plug-in units. The unit is arranged so that the user can utilise all 3U/6 HP Schroff power supplies, eg, slimpower SLE, ecopower SEK/SEM/SEC and maxpower. Therefore, a capacity range from 40 W to 400 W can be covered. The output voltage range available lies between 5 V and 67 V. In total, the unit offers five DC ports and signal connections; furthermore, it is possible to charge a battery with the power supply. Through the de-coupling elements, which are integrated on the port, the output voltage of the system is available redundantly. A passive and active current-sharing principle is supported with this system, whereby the individual power supplies are used evenly, which increases their life span.
A well thought-out cooling concept guarantees the balanced cooling of the unit. Two DC fans in the front area between the units, suck in air through the perforated front. The fresh air stream branches out in a T-formation to the power supplies and the warm air is expelled through the side perforations.
Cableless wiring
The electronics driving the switching from power supply 1 to power supply 2, as well as the signals which inform the operator about the status of the network voltages and the output voltages of the two power supplies, are integrated into a single board. With conventional backplane technology it was not possible to house the electronics in a 1U unit. However, the T-shape backplane design mounts the required interference suppression capacitors, switches, fans, signals, fuses, input and output pins directly to the backplane.
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