Types of PCB Power Relays
Electromagnetic Relays
Electromagnetic relays are the most commonly used type in printed circuit boards (PCBs), operating through an electromagnetic coil that mechanically opens or closes contacts. These relays are widely used in industrial control systems, household appliances, and automotive systems for switching high loads using low signal voltage.
Key specs include:
- Coil voltage (e.g., 5V, 12V, 24V DC)
- Contact ratings for current and switching voltage
- Fast response times and durable mechanical components
Solid-State Relays
Solid-state relays (SSRs) use semiconductor devices instead of mechanical contacts. They offer faster switching, zero contact bounce, and longer lifespan, making them ideal for low-power components, AC control functions, or compact relay setups in sensitive electronic devices.
While more expensive than electromagnetic relays, SSRs are noise-free and provide seamless power flow in applications like lighting, HVAC, and automation.
Hybrid Relays
Hybrid relays combine the benefits of both electromagnetic and solid-state technologies. Typically, an SSR is used to trigger the load initially, while the mechanical contacts maintain conduction. This improves contact longevity and reduces coil power consumption, especially in high switching frequency scenarios.
They are ideal for lighting systems, battery energy storage systems, and building automation requiring consistent switching performance.
Thermal Relays
Thermal relays use a bimetallic strip to detect heat generated by current flow. When excessive heat indicates an overload, the relay trips to protect the circuit. These are useful in motor windings, distribution systems, and circuit breakers, especially in industrial power relays with inrush current risk.
Often paired with electromagnetic PCB relays, they provide dual protection for load circuits and power supplies.
Operational Classifications of Relays
SPST – Single Pole Single Throw Relays
SPST relays are the simplest relay type. They allow a single circuit to be connected or disconnected. These are commonly used for basic ON/OFF control in low-voltage applications and are found in compact PCBs where limited space is a concern.
SPDT – Single Pole Double Throw Relays
SPDT relays can route a single input to one of two outputs. This makes them ideal for signal switching, fail-safe setups, and automated control sub-systems. They’re also used in automotive PCB relays, such as 5-pin SPDT switches, where reversing or alternate routing is needed.
DPST – Double Pole Single Throw Relays
DPST relays control two separate circuits simultaneously with a single actuation. These are useful in AC coil applications and industrial machinery where parallel switching of power and control lines is required.
DPDT – Double Pole Double Throw Relays
DPDT relays are highly versatile, allowing two input signals to each switch between two output terminals. Found in boards in power systems, test devices, and control logic circuits, these relays are a go-to solution for differential relays or direction-sensitive devices.
Design Considerations for PCB Power Relays
Relay Integrations in Circuit Design
When integrating a relay into a PCB layout, engineers must consider:
- Contact and coil isolation
- Proper load circuit and primary circuit separation
- Thermal dissipation and ambient temperature ratings (e.g., -40°C to +85°C)
- Adequate distance between coil contacts to prevent arcing
Correct design of relay circuits ensures safe, long-term functionality across all voltage applications.
Protection Mechanisms
Key protective features to look for in PCB power relays include:
- Withstand voltage ratings for high-spike environments
- Flux proof and sealed contact structures to prevent flux ingress during soldering
- Use of auxiliary contacts for feedback and redundancy
- Mechanical contact sets with force-guided relays contacts for enhanced safety
Standards such as IEC 61810-7 and RoHS compliance are essential for quality assurance and global compatibility.
Control Function Implementation
PCB relays are central to control functions such as:
- Switching between normal and backup power in power supplies
- Triggering alarms or safety disconnects in protective devices
- Handling high-voltage DC contactor events in storage system applications
- Managing signal flow in bus system actuators or AV devices
Advanced models now feature ceramic sealing technology, plug-in PCB terminals, and support for DC-1 utilization categories, offering robust performance across diverse applications.
Operational Insights
Soldering Techniques for PCB Relays
Proper soldering techniques are essential for the long-term stability of PCB power relays. Most miniature relays are flux-proofed or sealed to protect internal mechanisms during wave or reflow soldering.
Key tips include:
- Use bifurcated terminals or plug-in PCB terminals for consistent joints
- Maintain recommended preheating and cooling cycles to prevent internal component stress
- Avoid excessive soldering time to reduce contact resistance and preserve coil integrity
For high-current PCB relays, follow relay-specific temperature profiles found in datasheets (e.g., HF115FP-012DC Relay or OMRON G8PM series).
Testing Procedures for Reliability
To ensure reliability and consistent switching performance, manufacturers recommend:
- Mechanical life testing: repeated switching to test for wear
- Electrical endurance testing: verifying switching capability under load
- Measurement of contact resistance, withstand voltage, and coil power consumption
- Verifying response time, contact bounce, and insulation resistance
These procedures confirm that the relay meets safety standards such as IEC 61810-7 and is safe for use in critical load circuits.
Key Features and Specifications
50A Miniature High-Power Relays
Relays in the 50A miniature class are designed for heavy-duty use in industrial machinery, HVAC, and electric vehicle control units. Despite their compact form, they offer:
- High switching capacity (AC or DC)
- Reinforced contact materials and low contact bounce
- Flux-sealed cases for board washing
- Built-in auxiliary outputs in some variants
They are ideal for battery energy storage systems, load switching, and inrush current management.
25A Miniature High-Power Relays
25A power relays provide a balance between compact design and respectable current handling. These are often used in household appliances, lighting systems, and control subsystems in automotive electronics.
Specifications include:
- DC or AC coil voltage from 5V to 48V
- RoHS compliance and optional ceramic sealing
- Excellent contact gap and double-break structures for safety
Safety Approvals and Standards
Leading relays meet international safety approvals including:
- UL, VDE, TUV certifications
- RoHS compliant construction
- Adherence to IEC/EN 61810-7, IEC 60947, and other functional PCB relay criteria
These ensure safe operation in high-voltage environments, with standardized design criteria for manufacturers and installers.
Applications of PCB Power Relays
Industrial Applications
PCB power relays are essential in control cabinets, automation systems, electronic manufacturing, and machinery operation. Their ability to safely switch power allows them to control:
- Electric motors, solenoids, and contactors
- Distribution boards and panel-mounted systems
- HVAC and process control
They’re also frequently used in force-guided relay contact configurations for added safety.
Household Applications
In home electronics, relays are found in:
- Washing machines, microwaves, water heaters, and air conditioners
- AV devices and smart control panels
- Compact and low-power relays ensure quiet operation, long lifespan, and thermal efficiency
Energy Market Applications
In renewable and energy storage sectors, PCB relays control:
- DC switching in solar inverters
- Load disconnection in energy meters
- Power routing in BESS (battery energy storage systems)
Relays with high withstand voltage, low contact resistance, and certified safety approvals are crucial for these applications.
Specifications and Model Options
OMRON Relay Options
OMRON offers a comprehensive lineup including:
- G8PM, G2RL, G5Q, and G7L series
- Variants with 5V/12V/24V coils, SPDT/DPDT configurations, and flux-sealed or fully sealed enclosures
- Automotive relays rated for 40A–70A, with compact footprints
Each model is tested for ambient temperature tolerance, contact closure reliability, and electromagnetic compatibility.
Consultations with Catalogues and Whitepapers
Engineers and OEMs are encouraged to consult:
- Manufacturer datasheets for exact switching voltage, contact ratings, and current capacity
- Technical whitepapers covering design in power systems, control functions, and relay circuit boards
- Application-specific guides like lighting relay selection, battery isolation, or industrial contactors
These resources ensure correct product selection, safety compliance, and optimal performance in the final application.
