Use Space-Saving DIN Rail AC/DC Supplies and E-Fuse to Reliably Deliver Industrial DC Power

Designers or specifiers of AC/DC power supplies for industrial, factory, building, and process automation; power generation and distribution; infrastructure; and data and telecom applications face numerous electrical, physical, deployment, maintenance, safety, and compliance challenges. These challenges can be addressed by carefully selecting readily available DIN rail supplies and fusing specifically designed for these applications.

This article provides a brief overview of the challenges encountered when implementing these supplies. It then introduces a line of DIN rail AC/DC and DC/DC power supplies and a supporting fuse from RECOM Power, which reliably and safely deliver industrial-grade DC power.

The industrial power challenges

Power supplies for industrial applications must be compact, accept a wide range of three-phase AC or high-voltage DC inputs, be highly efficient, meet numerous regulatory mandates, support parallel operation for redundancy, and provide robust user and system protection. They must also satisfy performance specifications across a wide temperature range while using only passive cooling, demonstrate overall ruggedness with a high mean time between failures (MTBF), and be cost-effective to deploy and maintain.

The requirements of these applications preclude custom designs and form factors, favoring DIN rail mount supplies and fuses. The challenge now shifts to careful selection to optimize for the application.

Power supplies: start with packaging

Power supplies are often underappreciated for their critical role in system integrity. Their design starts with the packaging, which affects electrical, mechanical, and thermal performance in industrial settings. This is why, in nearly all cases, industrial supplies are designed for standard DIN rail mounting (Figure 1).

Figure 1: An industrial cabinet with a wide range of module types mounted on DIN rails allows convenient front-side module installation and removal, as well as ready access to wiring. (Image source: Hackaday)

The rail is attached to the rear panel of the equipment cabinet or enclosure. All electrical modules, such as motor drives, loop controllers, power, signal interfaces, safety subsystems, and communications interfaces, are mounted to this rail, with all power and signal connections accessible from the front.

The DIN rail approach contrasts sharply with the 19" rack with front and back connections for modules. This rack is widely used in lab instrumentation and test/measurement systems. The DIN rail is more convenient and practical, as cabinet space is often at a premium due to the number of modules it must house.

Many AC/DC supplies in industrial applications operate from a three-phase, 320 V_AC to 575 V_AC line input and must deliver a clean, stable, transient-resistant 24 V_DC or 48 V_DC to loads such as a motor controller. In addition, many applications now require operation from a high-voltage DC source of 430 V to 815 V. Using a DC source is well-suited for microgrid-based factory automation applications and for renewable energy solutions, including biogas, photovoltaics, and wind installations.

To meet the challenging requirements of powering industrial applications using DIN rail mounting, designers can use RECOM Power’s three-phase RACPRO1 family of AC/DC power supplies. These can also be used with high-voltage DC inputs.

For example, the RACPRO1-T240/24, RACPRO1-T480/24, and RACPRO1-T960/24 (Figure 2, left to right) deliver power levels of 240 W, 480 W, and 960 W, respectively, with 24 V outputs. Versions are also available with a 48 V output but are otherwise identical. In addition, the nominal output voltages of these supplies can be adjusted up to 28 V from 24 V and 56 V from 48 V.

Figure 2: The compact RACPRO1-T240/24 (left), RACPRO1-T480/24 (center), and RACPRO1-T960/24 (right) DIN rail power supplies deliver 240 W, 480 W, and 960 W, respectively. (Image source: RECOM Power)

An important feature of these modules is their compact form factor. Specifically, the width of each supply is 43 mm, 52 mm, and 80 mm (1.69", 2.05", and 3.15"), respectively. All three modules are 135 mm (5.31") high, while their depth varies by model, ranging from 140 mm to 156 mm (5.51" to 6.14"). An important feature for installers and technicians is that the modules are designed for fast, easy, toolless installation and removal, using push-in wire-cage clamps with +25° push-in connectors.

The high efficiency of the RACPRO1 series lowers operating costs and reduces heat generated by the power supply. Therefore, a smaller heatsink and less surface area for thermal dissipation are needed.

These supplies do not require forced-air cooling with fans or other active systems; they are designed to be cooled solely by natural convection, another advantage in industrial environments. Each module incorporates two separate airflow flue channels to maximize the “chimney effect” for cooling.

The small size and high efficiency of this series are achieved through a smart layout and component selection. The RACPRO1-T960/24 unit has an efficiency of 96%; the RACPRO1-T240/24 and RACPRO1-T480/24 have efficiencies of 94.1% and 95%, respectively. Furthermore, despite delivering hundreds of watts, these supplies require only about 1 W at no load.

The efficiency and cooling of these supplies enable them to be rated for high operating temperatures. The 960 W RACPRO1-T960/24 supply can deliver its full output-power rating to +60°C; the 240 W RACPRO1-T240/24 has a slightly higher top-range extension to +70°C.

High temperatures are not the only concern; many systems, such as outdoor HVAC equipment, are also subject to extreme cold. To address this need, RACPRO1 supplies are rated for operation at -40°C.

Electrical performance and features

A power supply for industrial environments must do more than just deliver the nominal value of voltage over a range of input voltages and loads. Other required attributes include high return-voltage immunity, extended surge immunity, and power boost capability:

• When powering or depowering a non-resistive load, such as a motor, there can be backflow (also called backfeeding) into the power supply's output. Return voltage immunity is the ability to withstand backflow voltage. In RACPRO1 supplies, the 24 V output has return voltage immunity to 35 V, while the 48 V output has immunity to 63 V.
• For line surges, these units feature extended surge immunity to 6 kV as defined by applicable industry and regulatory standards.
• These supplies provide a power boost capability to accommodate loads that briefly require more than the rated output power. For example, the high-power RACPRO1-T960/24 can boost power to 150% for 6 seconds (s), thus eliminating many disruptions due to transient load conditions.

Another user-friendly feature of the 480 W and 960 W RACPRO1 units is a simple, single vertical LED line (Figure 3) that indicates the percentage of the rated output power the supply is delivering.

Figure 3: The 480 W and 960 W RACPRO1 modules include a convenient indicator that shows the percentage of the rated output power the supply is delivering. (Image source: RECOM Power)

Reliability by analysis, design, and evaluation

Every application requires reliability. For RACPRO1 units, high efficiency reduces heat dissipation, thereby improving component reliability. Also, the RACPRO1 series is engineered for maximum performance and efficiency, addressing key metrics including thermal performance, MTBF, and built-in protective features. Furthermore, integrated protective features, including overvoltage, short-circuit, and thermal-shutdown protection, enhance durability and ensure continued operation in harsh industrial environments.

To validate long-term reliability, RECOM subjects each model to rigorous lifetime testing, including extended stress simulations, shock and vibration tests, and high-temperature endurance assessments. Modeling, analysis, and testing indicate that the lifespan of these supplies is approximately 80,000 hours at 40˚C under the most stressful condition, full load.

Nonetheless, there are applications where even a rare failure, whether due to internal or external factors, is unacceptable. For these applications, the RACPRO1-T480/24 and -T960/24 models allow for parallel connection of two or more units for redundancy or increased output capacity (Figure 4).

Figure 4: The RACPRO1-T480/24 and RACPRO1-T960/24 can be used in parallel to provide backup redundancy or boost the power output rating. (Image source: RECOM Power)

This arrangement provides redundancy and also supports load sharing, with both supplies distributing power evenly. These features prevent system downtime and maintain stable power in industrial automation environments and other operations where interruptions can impact productivity and safety. In addition, the well-defined constant-voltage/constant-current (CV/CC) output characteristics of these supplies enable battery charging for additional backup.

Meeting regulatory mandates

Power supplies, like other electronic products, are subject to numerous regulatory mandates. Some of these relate to operational aspects such as power factor (above 0.9 for these supplies), electromagnetic interference (EMI), efficiency at different power levels, and no-load power dissipation. Other mandates are safety-related.

Among their many electrical performance certifications, these supplies comply with EN 61000-6-4 Class B (emissions) and EN 61000-6-2 (immunity). The units are also certified according to the global safety standards IEC/EN/UL 62368-1, IEC/EN/UL 61010-1, and IEC/EN/UL/CSA 61010-2-201.

Add a fuse, just in case

Given the many protective features of these supplies, a fuse that “trips” in response to a severe overcurrent seems unnecessary. That might be true, but designers may want one installed just in case, or, more likely, it is mandated by the electrical code in effect at the time of installation.

To fulfill this need, the RACPRO1 series is supported by the RACPRO1-4SP/24V/5A DIN rail electronic fuse (e-fuse) module (Figure 5), which is fully approved for use in place of a conventional thermal fuse or circuit breaker. Note that this unit can be used with any power supply, not just the RACPRO1 family.

The RACPRO1-4SP/24V/5A is compact, measuring 110.2 mm × 72.0 mm × 61.9 mm (4.34" × 2.83" × 2.44"), and functions as a monitoring element connected to the main DC rail. This 5 A module (a 10 A version is also offered) distributes 24 V_DC to four separately controlled load channels with independent overcurrent limit control and real-time output current indication.

Figure 5: The RACPRO1-4SP/24V/5A DIN rail e-fuse module has four independent electronic fuses rated at 5 A each. (Image source: RECOM Power)

The channels power up sequentially to reduce input inrush current with a pre-settable time delay. Under system overload conditions, the channels will disconnect the loads in reverse sequence, keeping essential functions running to the end. Although the channels may be operationally linked, each channel can be switched ON or OFF independently to facilitate fault diagnostics or maintenance.

The e-fuse module is much more than just a simplistic replacement for the classic thermal “open on overcurrent” fuse. It is controlled by internal logic circuits to protect and prioritize loads and power supplies, detecting and reacting dynamically to overcurrent, undervoltage, and overvoltage conditions.

Each channel is protected independently, so overload or fault conditions on an individual load do not affect overall system reliability or functionality. In addition to the basic 5 A maximum channel current, the module delivers a 150% power boost for 5 s and can handle more than 150% overload for up to 100 ms to prevent nuisance tripping. These are all important considerations in industrial installations, where load shifts, motor stalls, start-up current spikes, and other disruptive events are expected and unavoidable.

As an added troubleshooting feature, each channel has an LED bar for status indication (Figure 6). It shows the output-current status as it changes from green to yellow (current within limit) to orange (current at limit) to red (overcurrent or short circuit).

Figure 6: Each of the four e-fuses has a multicolored LED strip indicator that quickly conveys a significant amount of information about channel status. (Image source: RECOM Power)

As complements to the RACPRO1 power supplies, these e-fuses also have a lifetime expectancy greater than 80,000 hours at +40°C and feature easy wiring with toolless push-in and lever-release terminals.

Conclusion

Power supplies for industrial applications must reliably and efficiently deliver lower-voltage DC from higher-voltage AC mains or a DC rail in a compact form factor. The DIN rail mount RACPRO1 modules  from RECOM Power meet these requirements while simplifying installation and maintenance. The complementary four-channel e-fuse module provides independent channels while allowing them to be linked for more effective operation and improved fault detection and management.

Related Content

1. How the Simple DIN Rail Solves for Modularity, Flexibility, & Convenience in Industrial Systems
2. RECOM Power RACPRO1 Series DIN Rail Power Supplies PIO (video)