The Automated Warehouse: A RECOM Story

RECOM recently helped a customer develop a power solution for an automated warehouse application. The client’s core expertise is in high-precision mechatronic solutions and complex software for the storage and handling of goods. To minimize development costs and reduce time-to-market (TTM), they use off-the-shelf industrial components wherever possible for electronic blocks such as motor drives, sensors, controllers, CPUs, cameras, lasers, interfaces, and wireless communication systems. This combination causes high shock and vibration stress on the electronics.

Efficient use of power throughout these systems ensures logistics companies provide reliable and rapid service. But the special requirements of this type of application make it difficult to find any standard power supply solution. For efficient operation and 24/7 availability, the transport vehicles ride on rails and experience fast acceleration and deceleration.

An additional challenge comes from harsh temperature conditions in a warehouse; temperatures can range from -20°C or lower in cool houses up to over 50°C in hot regions. For safe operation without special isolation protection, the rail is limited to a maximum voltage of 60V. A higher voltage could endanger warehouse personnel: potentially generate enough current flow to cause respiratory arrest or ventricular fibrillation. The rail has a resistance which, although small, is not zero; the DC voltage available at a transport vehicle therefore depends both on the distance between the vehicle and the current flowing in the rail. The rail voltage is generated by a high-power, industry-standard, three-phase DIN rail power supply with the output trimmed up to 60V to compensate for large voltage drops on the long rails.

The power for the motors comes directly from the rail. The high power needed for the motors, and therefore the high currents on the long rails, causes significant voltage drops and ground shifts. In addition, there can be intermittent contact between rails, wheels, or sliding contacts, which can result in voltage dropouts or transients, which are buffered by capacitors. Standard 24VIN industrial equipment is used to minimize cost, so the power supply of the transport unit must be able to work across the wide input voltage range supplied by the rails. Total power required by the electronics is 200W.

Due to the special power requirements, the customer had used a complex, discrete, custom design in the past, which was designed and produced by an external supplier. For the new design, though, the customer was looking for a simpler solution with fewer components and lower NRE. RECOM suggested an off-the-shelf solution from our large catalog and worked closely with the customer from the early concept stage to the final design.

The early engagement with RECOM allowed the customer to keep NRE costs low by focusing their efforts on what they do best — the mechanical and electrical design. This way, the customer was able to avoid any redesigns, setbacks, or unexpected surprises normally associated with discrete custom designs.

Figure 2 above shows the blocks powered by the 24V system bus. The harsh electrical environment with its widely varying input voltage, voltage transients, and ground shifts requires an isolated DC/DC converter. RECOM’s solution uses the RPA200H-11024SRUW/P at the heart of the onboard power delivery system. This DC/DC converter delivers an output voltage of 24 V DC over an input voltage range of 16.5 V to 140 V DC. The ultra-wide input range can easily cover the widely varying supply voltage on the rail and can handle the occurring under voltages and over voltages.

The DC/DC converter is a member of the RPA200H series half-brick DC/DC converter family that is designed to meet the needs of the railway industry. Power supplies in automated warehouse vehicles and power supplies for railway rolling stock must meet many of the same challenges: extended lifetime operation in an environment that includes temperature extremes, high levels of shock and vibration, and voltage transients. Plus, of course, they both run on rails.

The RPA200H-11024SRUW/P has a consistently high efficiency over the entire input voltage range and comes with a metal baseplate to permit a wide operating temperature range from -40°C to +93.5°C when baseplate cooled. The case is fitted with threaded inserts to allow secure mounting to the PCB or bulkhead for use in high shock and vibration environments. The converter is certified to UL/IEC/EN60950 and comes with a three-year warranty.

RECOM helped in other ways, too. The RPA200H-11024SRUW/P datasheet already has a fully-validated EMI filter solution that meets the tough EN 50121-3-2 standard; RECOM supported the design by offering to make measurements of the total solution in RECOM’s EMI lab for the customer.

Another big advantage for the customer was that the previous discrete design had hundreds of different components, including magnetics, that could be difficult to source; the RECOM solution reduced the sourcing effort down to one converter module plus a few components for the filter.