Plug & Play Designs benefit railway applications

What does plug & play mean, in the context of railway applications?

“Plug & play” is a term that is used in various fields to describe a product that meets all the requirements for operating an application, without any additional effort on the part of the user. At the baseline, plug & play products for railway applications must be able to survive in the operating environment. Unlike consumer power supply that operates in the benign surroundings of a home or office, a railway DC/DC converter must function reliably for many years under extreme conditions such as heat, cold, shock, and vibration.

The converter must meet the requirements of EN50155 (and all other related standards), and the performance standard for electronic equipment used in rolling stock—basically all rail vehicles that move, including locomotives, passenger wagons, light railways, and freight trains. EN50155 prescribes the minimum requirements for the electrical and mechanical operating environment, equipment reliability, and expected useful life of converters. These requirements are above the capabilities of “off-the-shelf” modular DC/DC converters.

For example, the nominal system voltage in a railway application can vary between +25% to -30%, with dips down to 60% of nominal and surges up to 140% of nominal. For a 110V nominal system, this means that an input voltage range of 77V–137.5V, with dips and surges, can expand up to 66V–154V.

Plug & play railway power supplies

A DC/DC power supply designed for a railway application will qualify as plug & play if it meets all the applicable electrical and mechanical standards “out of the box”. The result is a power supply that can be immediately integrated into a railway application without any extra design work, thereby saving time and system cost.

RECOM’s RMD500-EW is the first converter in the standard range of plug & play DC/DC converters for rail applications such as traction and propulsion auxiliary supplies, braking, monitoring, safety, HVAC and door control systems, data loggers, and many more.

What makes the RMD500-EW plug & play?

For one, the RMD500-EW incorporates all the features required by EN50155: reverse polarity protection, EMC and surge filtering, inrush current limiting, 10ms hold-up time, and output ORing diode. These features would otherwise have to be accomplished by adding external components.

The power supply meets all the relevant rail environmental standards for conducted and radiated EMI, mechanical shock and vibration, thermal shock, temperature cycling, isolation coordination, and fire protection. Featuring a wide 4:1 (43–154VDC) input range (170V peak) and 24V output with reinforced isolation based on 5,5mm air creepage distances (OVCIII / PDII), the RMD500-EW is suitable for nominal 72V and 110VDC inputs with tolerance and surges within the limits prescribed by EN 50155.

The output power is 500W up to 95°C baseplate temperature without derating. This allows operation within an ambient temperature of -40°C to +70/85°C, with only natural convection cooling, which meets EN50155 OT4 (-40°C to +70°C) with ST1 and ST2 (+85°C) conditions. Efficiency is as high as 95.5% down to light loads over a wide input range, allowing high power density in a compact 209 x 141 x 48mm package. The RMD500-EW can be mounted in any orientation; screw terminals are provided for convenient input and output connections.

The product is certified to fulfill EN 62368-1 and EN 50155 (S2) regulations, with a 3.5kVAC rated isolation. It is extremely reliable, robust, and fully protected against short-circuits, output over-voltage, over-current, and over-temperature.

Figure 2 shows the internal block diagram of the RMD500-EW. The design uses a forward topology with an active clamp reset circuit to minimize switching losses and a secondary-side synchronous rectifier to ensure higher efficiency. Plug & play features include an integrated input filter, a reverse blocking diode, and a hold-up time module.

Other standard features include DCOK volt-free relay contacts, remote ON/OFF, and active power sharing with OR-ing diodes for parallel operation when increased power or n+1 redundancy is required. The nominal 24V output voltage of the RMD500-EW can be trimmed between 19.2VDC and 25.2VDC by using an external tri resistor. The eco-friendly RMD family is designed without encapsulation and so the weight is considerably lesser than that of potted products.

Additional products in the series are in the pipeline for launch later in 2022, with power ratings of 600–1000W as well as 300W and 150W, to accommodate a wider variety of rolling stock and trackside applications.

If these do not meet the needs of a particular railway application, RECOM’s sister company, PCS, has extensive experience in custom designs that meet EN51055 requirements. The PCS portfolio also includes rack-mounted AC/DC and DC/DC converters for rolling stock and trackside applications, from low power up to 18kW with DC, single-phase, or three-phase AC inputs. The battery charger families are designed as modular concepts. In the 1,5kW, 5kW, or 18kW class, all units are cascadable and can operate parallelly to increase the availability and reliability of the converters. They are ideal solutions for redundant n+1 power units, and for safety-relevant and reliable rolling stock applications. The battery chargers come with excellent efficiency and functionality features such as temperature-regulated output voltages and analog or digital interfaces.

To learn more—and to access a handy FAQ with helpful tips - visit the RMD500-EW product page.