Railway Power Supplies

Over the last few years, RECOM has greatly extended its product portfolio of EN50155-certified components and now offers a huge range of AC/DC and DC/DC converters for railway. With the acquisition of the Italian power specialist Power Control Systems, RECOM is able to provide customized power solutions up to 18kW.

Over the years, RECOM has expanded its portfolio of DC/DC converters for the railway industry from 8W to 240W and can now offer the broadest portfolio of EN50155 certified products available on the market. The railway-certified series pack up to 240W in compact case sizes for a power density of up to 4.5W/cm³ - one of the highest available on the market. For superior thermal performance, RECOM also offers the 12W RP12-AR, 20W RPA20-AW and 30W RPA30-AW series in a 1”x1” case and the 60W RPA60-FW series in a 2”x1” case.

These regulated DC/DC converters with their 4:1 wide input voltage range are specially designed for railway applications. The RPA100H-RUW and RPA200H-RUW series even offer an impressive 10:1 input voltage range to cover all input voltages from nominal 24VDC up to 110VDC in a single product. The RP40Q-RUW and RP60Q-RUW series even go beyond that and accept 12:1 inputs. All series are EN50155 certified* and designed for use in harsh environments or on rolling stock. Since they are UL/cUL60950 certified, they are also a reliable choice for industrial and telecommunication applications.

RECOM introduced evaluation platforms for its DC/DC railway converters up to 240W. They are available in either high voltage (-1) or high current (-2) layouts and include a RIA12 surge stopper.

The RSPxxx-168 are surge protectors designed to protect railway DC/DC converters from excessive voltage surges of up to 385VDC. Besides 3.3V, 5V, 12V and 15V single outputs, dual ±12V and ±15V outputs are available. The control pin logic can be chosen to be positive or negative. With efficiencies of up to 93%, cooling by natural convection is typically all that is needed, but if required, the modules are also available with a pre-mounted heatsink. The modules come with RECOM’s standard 3 year warranty.

For higher power railway DC/DC applications, the RECOM RMD series provides 40W to 500W of output at nominal 24V, 36V, 48V, 72V or 110V with five input ranges covering 14.4V to 170VDC. The high-efficiency design is type tested to railway standard EN 50155.

DC/DC converters are used in railway environments to convert DC battery voltages to a lower voltage for usage in a variety of control and energy circuits. This is because railway rolling stock uses a DC power distribution system so that batteries can be used to maintain electrical power in the event of a generator failure. These converters need to be constructed according to EN 50155 to ensure harsh environmental conditions do not influence its mode of operation.

Heat, frost, vibration, mechanical impact – they all can cause serious damage to electronic assemblies. DC/DC converters used in railway technology are exposed to extremely tough conditions and must work properly and reliably for their entire service life. Engineers are therefore looking for DC/DC converters that can withstand these exceptional conditions and are certified for railway applications.

The EN50155 (Railway Applications - Electronic equipment used on rolling stock) specifies carefully defined requirements for information systems and electronic components used in railway engineering. This also applies for DC/DC converters which have to function as reliable power supplies for many years under extreme conditions such as heat, cold, shock and vibration.

EN50155 is a performance standard for electronic equipment used in rolling stock (basically all rail vehicles that move; including locomotives, passenger wagons, light railways and freight trains). It lays down minimum requirements for the input voltage range, electrical isolation, operating temperature, shock and vibration, humidity and EMC, as well as equipment reliability and expected useful life. Electronic equipment used on rolling stock is expected to have a very long operational life of up to 20 years, therefore the environmental testing should be thorough. Besides the normal operating temperature tests, additional thermal cycling, dry heat and damp heat testing is specified. Only a fully potted or sealed DC/DC converter can meet these requirements.

In the summer, temperatures can reach +60°C or more. In the winter, they frequently drop to -30°C or even lower. Where converters are operated in rolling stock, they are exposed to heavy vibration. All this pushes conventional DC/DC converters to the limits. The new EN50155 standard defined six different operating temperature ranges and also include testing the operating temperatures and the extended temperature limits during start-up.

EN 50155 gives general guidelines: relative humidity of 75% on average, followed by 30 consecutive days with 95% relative humidity. For the electronic equipment this means in most cases watertight cases or lacquered assemblies.

Railway electronics must work properly even in extremely unfavourable electromagnetic environments. On the one hand, they are exposed to strong magnetic fields generated by electric motors and transformers. On the other, they must be able to withstand interference emitted from the pantographs. And there are numerous additional sources of interference, brought on board by passengers carrying mobile phones and laptops. None of these sources of interference must in any way impair the function of highly sensitive components such as drive assemblies, motor control units and displays.

To ensure this, EN 50155 repeatedly makes reference to collateral standard EN 50121-3-2 "Railway applications – Electromagnetic compatibility – Rolling stock – Apparatus", which defines clear limits for radiated and conducted interference as well as stringent requirements with regard to resistance to overvoltage and transients. To meet these EMC requirements, an EMC filter is needed to protect the DC/DC converter and absorb any conducted emissions.

For historical reasons, a large number of different supply voltages are used in railway applications. The most common ratings are 24VDC, 48VDC, 72VDC, 96VDC and 110VDC. The latest version of EN50155 defines seven different standardized DC voltages, although 110VDC is the most commonly used on trains. The 24V thru 48V is often used on light railways, trams and trolley buses. In order to meet these requirements for nominal input voltages, railway application developers opt for 4:1 converters such as the RP20-FR and RP40-FR series from RECOM, as they cover the entire nominal input voltage range with 3 different converter models only.

Nominal Input Voltage	EN50155			RECOM RPxx-FR Serie
	Input Range	Min. Input (0,1s)	Max. Input (1s)	Input Range	Min. Input	Max. Input (1s)
24V	16.8-30V	14.4V	33.6V	9-36V	9V	50V
48V	33.6-60V	28.8V	67.2V	18-75V	18V	100V
72V	50.4-90V	43.2V	100.8V	43-160V	43V	170V
96V	67.2-120V	57.6V	134.4V	43-160V	43V	170V
110V	77-137.5V	66V	154V	43-160V	43V	170V

EN50155 states that the nominal input voltage may fluctuate between 0.7 and 1.25 times the rated voltage, and permits short-term deviations between 0.6 and 1.4 times that value. This means that a 48V DC/DC converter must cater for a voltage range of 28.8V to 67.2V. Until recently, there was a consensus that 4:1 converters had reached their limits with regard to efficiency and cost-effectiveness. This is now all changing with the latest 100W and 200W DC/DC converters from RECOM. The RPA100H and RPA200H feature a broad 10:1 input to cover all common voltage ratings in one module.

DC/DC railway converters are often referred to as bricks, half-bricks, and quarter-bricks. A full-brick measures 4.6 x 2.4 x 0.5 inches, a half-brick measures 2.3 x 2.4 x 0.35 inches, and a quarter brick measures 2.3 x 1.45 x 0.35 inches. But there are also DIP24, 1’’x1’’ and 2’’x1’’ cases for lower power converters. Newer switched-mode power supplies in quarter-brick format deliver an electrical output of 250 watts or higher. This is a significant improvement in the slot that was previously needed and means more room for features that can now be added to the product. The specification also includes the pin output; therefore, when using DC/DC railway converters that meet the standard, products can be easily replaced if the designer so desires.