Alternative to Shooters How to Reduce the Space Required for High-Current Switches

PCB relays with higher current-carrying capacity and integrated fault detection offer an alternative to contactors for rated currents ranging from 50 to 300 A. Here’s what you need to keep in mind when making the switch.

The trend toward electrification is driving up demand for upgrades and modernizations across all infrastructure—from solar and wind power plants to end-use locations. Power control is a crucial aspect of this. Devices intended for use in residential buildings face significant cost pressures. Miniaturization is required to enable unobtrusive designs. In industrial electrification, on the other hand, reliability and error handling are the primary requirements. Advances in efficiency, however, are in demand everywhere.

Switching High Currents: Contactors vs. Relays

When it comes to handling high currents and voltages, electromechanical switches such as contactors and relays are the preferred choice. This is because they offer high rated values and safely isolate inactive loads.

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Contactors typically have larger electromagnetic coils than relays, as well as spring-loaded contacts for breaking the circuit. They are primarily used in applications where extremely high currents must be controlled. Contactors also typically feature built-in detection to determine whether the contacts have welded together. This prevents the main contacts from becoming stuck and unable to open. This is usually achieved using a set of auxiliary contacts that mirror the main contact structure.

Due to their auxiliary contact mechanism, higher coil power, and spring force, contactors are generally larger than elementary relays and have a lower maximum switching frequency. Connections are typically made via screw terminals, which must be installed manually.

In today's electrified world, new direct current (DC) switching applications include large inverters for photovoltaic generators and battery energy storage systems in the power grid, high-speed EV chargers and wall boxes, as well as uninterruptible power supplies (UPS).

These new applications are turning the old order upside down and require the high current-carrying capacity and safety features of contactors, but with a smaller size and lower power consumption in devices that are compatible with mass-production techniques. Similar requirements apply to alternating current (AC) loads such as lighting, heating, ventilation, and cooling, and factory automation, where power density is increasing and the need for smaller and more compact devices is growing.

When Relays Switch Higher Loads

New developments in relay technology enable rated currents ranging from 50 to 300 A. As a result, these components offer an alternative to contactors in many residential, industrial, and utility applications. Current components also detect welded contacts and issue a fault message, thereby providing comparable system protection. The auxiliary contact mechanism shown in Figure 1 ensures reliable isolation with a dielectric strength of 2.5 kV or a minimum contact gap of 0.5 mm (approximately 0.020 in), even after the coil has been de-energized, should the main contacts weld together.

Among the inherent advantages of relays are smaller component dimensions, which allow for more compact and flatter housings. This is equally important for consumer applications as well as for industrial and power supply applications, which face the challenge of installing more and smarter infrastructure amid increasing space constraints. A comparison of the characteristics of a typical contactor with those of a comparable relay shows a weight reduction of more than 66%, as well as a height reduction of more than 60% and a volume reduction of 85%.

The smaller size and generally lower weight of elementary relays allow high-power switches to be mounted on the printed circuit board, which simplifies device assembly and makes it more efficient.

Printed circuit board assemblies are compatible with automated production processes, allowing circuits to be assembled at high speeds using in-line placement machines. Through subsequent automated soldering, device manufacturers can eliminate the need for conventional, bulky, and expensive components such as busbars and screw terminals, which must be fastened manually. In addition to faster and more efficient assembly, soldered connections prevent human errors such as incomplete tightening of screws or incorrect torque, resulting in more consistent production quality.

Switch to High-Current PCB Relays

The transition from established design practices and production processes—which previously relied on traditional, manually assembled contactors—to relay assemblies for printed circuit board (PCB) mounting literally requires a return to hand-drawn design to create a new PCB layout. PCB design guidelines include ensuring sufficient copper thickness to carry the intended current levels. Increasing the pad size helps improve heat dissipation.

In applications that require extremely high current levels, a heat sink or an insulated metal substrate helps protect the printed circuit board. Furthermore, for high-power PCB relays, implementing a hold-up circuit or a PWM drive circuit to minimize power consumption can effectively simplify thermal management and potentially reduce the drive power by 25%.

Electronics manufacturers can offset the investment in redesigning their printed circuit boards by increasing sales through the offering of smaller, lighter PCB assemblies that meet market demands.

The production area may also need to be restructured to reduce or eliminate manual workstations and switch production to automated machines for through-hole assembly. A comparison of manufacturing techniques shows that soldered connections can reduce the bill of materials (BOM)—including busbars and screws—by up to 35% and lower the costs of the assembly process by up to 50%. The benefits of automated assembly become even more significant as production volumes increase.

In addition, switching to PCB relays can boost product performance and improve energy efficiency. Their lower contact resistance results in reduced I2R losses and less heat dissipation, which increases contact reliability. The lower coil power also contributes to higher efficiency.

Among the high-current PCB relays is the single-pole G9KA-1A1B-E, which can switch currents up to 300 A and has a contact resistance of less than 0.2 mΩ. The design and selected materials contribute to the low resistance and also enable a contact spacing of 4.0 mm (approximately 0.16 in), ensuring high performance while maintaining safety. Integrated 30 V/1 A mirror contacts enable the detection of contact welding in accordance with IEC 60947-4-1, the international standard for electromechanical contactors and starters, including motor protection switches.

Overall, while the transition to printed circuit board assembly requires an initial investment, suppliers benefit significantly in the long term from cost savings as well as greater efficiency and reliability.

More Compact and Cost-Effective Power Control

Circuit breakers have long been considered the “kings” of high-current switching and cover a wide range of rated currents up to several hundred amperes. Among their strengths are auxiliary contacts for fault detection. Disadvantages include the large and heavy coil and the corresponding closing mechanism, which require a lot of space and limit the switching frequency. Manual assembly processes slow down production and leave room for human error.

New requirements are driving developments in PCB relays. This opens up a new option for rated currents ranging from 50 to 300 A, enabling more compact, reliable, efficient, and cost-effective power control. 

*Takato Nabeshima is the Product Marketing Manager for Relays at Omron Electronic Components Europe in Hoofddorp, Netherlands