An SPDT 5-pin relay works by using an electromagnetic coil to switch a single common contact between two output positions — Normally Open (NO) and Normally Closed (NC) — allowing one low-power control signal to switch high-power loads up to 30A at 240VAC. In industrial applications, this mechanism enables automation controllers, PLCs, HVAC systems, motor drivers, and power distribution panels to manage heavy electrical loads with precision, speed, and electrical isolation. The HLS-T91(16F)-3 from Ningbo Helishun Electron Co., Ltd. is a purpose-built high power relay that delivers exactly this capability in a compact PCB-mount form factor rated for demanding environments from -40°C to +85°C.

This article explains the operating principles of the SPDT 5 pin relay, walks through the full electrical and mechanical specifications of the HLS-T91(16F)-3, and provides practical guidance for industrial PCB mount relay design — from coil voltage selection to contact form selection and layout best practices.

How an SPDT Electromagnetic Relay Works: The Core Principle

An electromagnetic relay operates on the principle of electromagnetic induction. When DC voltage is applied to the coil terminals, current flows through the coil winding and generates a magnetic field. This field attracts a ferromagnetic armature, mechanically moving the common contact (COM) away from its resting Normally Closed (NC) position and onto the Normally Open (NO) contact. When coil voltage is removed, a return spring resets the armature and the contact returns to NC.

In an SPDT (Single Pole Double Throw) configuration, this single switching action controls two distinct circuit paths simultaneously — making it highly versatile. The 5-pin layout of the HLS-T91(16F)-3 maps as follows: Pin 1 and Pin 2 are the coil input terminals, Pin 3 is the Common (COM), Pin 4 is the Normally Open (NO), and Pin 5 is the Normally Closed (NC). This standard 5-pin footprint is fully compatible with industrial PCB relay socket standards, simplifying integration and field replacement.

The T91 relay architecture is designed for high-current switching — the contact form 1A variant supports 30A at 240VAC, which covers the majority of industrial single-phase load switching requirements. The operate time is rated at a maximum of 15ms and release time at a maximum of 10ms, making the HLS-T91(16F)-3 responsive enough for time-critical automation sequences while remaining immune to transient noise pulses shorter than 10ms.

Full Electrical Specifications of the HLS-T91(16F)-3 Power Relay

The HLS-T91(16F)-3 is engineered to serve as a 30A power relay in demanding industrial, HVAC, automotive auxiliary, and automation control applications. Its specification set is comprehensive and consistent with international industrial relay standards, holding TUV and CQC safety certifications and full compliance with EU RoHS requirements.

Several specifications deserve particular attention from design engineers. The 2000VAC coil-to-contact dielectric strength is a critical safety parameter, ensuring that in the event of a high-voltage surge on the load side, the coil circuit and its controlling microcontroller or PLC output remain fully isolated. The -40°C to +85°C ambient temperature range makes the HLS-T91(16F)-3 suitable for outdoor enclosures, industrial cold-chain equipment, and automotive auxiliary systems where temperature extremes are a regular operating condition. The 10 million mechanical operation life at no-load demonstrates the robustness of the spring-armature mechanism and supports applications with high switching frequency.

Coil Voltage Options and Selection Guide

The HLS-T91(16F)-3 is available in six standard DC coil voltage options: 5V, 6V, 9V, 12V, 24V, and 48V, covering virtually every common control voltage found in industrial and embedded electronic systems. All coil variants share a nominal coil power consumption of 0.93W, which is consistent across the range and simplifies power supply design — the operating current is simply 0.93W divided by the rated coil voltage.

How to Use the Coil Data Table

The Max Operate Voltage is the minimum coil voltage required to guarantee energization across worst-case temperature, tolerance, and supply variation conditions — engineers should ensure the control supply voltage at the relay coil pins always exceeds this value during operation. The Min Release Voltage defines the threshold below which the coil magnetic field is too weak to hold the armature, causing the relay to drop out; this is typically very low (0.25–2.8V depending on variant), confirming that once de-energized by the control circuit, the relay releases reliably without residual hold. The Max Applied Voltage is the absolute maximum coil voltage the relay can sustain without coil thermal damage — never exceed this value, even momentarily.

The 12VDC and 24VDC coil variants are the most widely used in industrial automation and building management systems, as these voltages correspond directly to standard PLC output modules and industrial 24VDC bus systems. The 5VDC variant interfaces directly with microcontroller GPIO pins via a transistor driver stage, making it the preferred choice for embedded system and IoT gateway designs.0

Mechanical Robustness: Vibration, Shock, and Environmental Ratings

Industrial applications subject relays to mechanical stresses that laboratory-grade components cannot survive. The HLS-T91(16F)-3 is specifically rated for the following mechanical and environmental conditions, which are directly relevant to its use in factory automation, transportation, and outdoor control panels.

• Shock resistance (malfunction): 10G — the relay maintains correct contact state under shock pulses up to 10 times gravitational acceleration, preventing false switching in environments with mechanical impacts.
• Shock resistance (destruction): 20G — physical integrity of the relay housing and contact mechanism is maintained up to 20G shock, beyond which structural damage may occur.
• Vibration resistance: 10–55Hz, 1.5mm double amplitude — covers the primary vibration frequency range of industrial machinery, HVAC compressors, and vehicle powertrains.
• Ambient humidity: 40–85% RH — suitable for humid factory environments, though not condensing conditions. Enclosure protection should be added for outdoor applications with condensation risk.
• Ambient temperature: -40°C to +85°C — one of the widest operating ranges in the T91 relay class, enabling deployment in cold-room control systems, rooftop HVAC panels, and automotive auxiliary fuse boxes.

The combination of wide temperature range and 10G malfunction shock resistance is particularly significant for transportation applications — automotive auxiliary relays, EV charging equipment, and railway control cabinets all experience temperature extremes and vibration simultaneously. The HLS-T91(16F)-3's PCB mount form factor also means it can be soldered directly to the control board rather than mounted in a separate relay socket, reducing the mechanical vibration path and improving long-term reliability in mobile applications.

Key Industrial Applications for the HLS-T91(16F)-3 High Power Relay

The HLS-T91(16F)-3's specification profile — 30A contact rating, wide temperature range, PCB mount form factor, multiple coil voltages, and dual safety certifications — makes it well suited to the following industrial application categories.

HVAC and Building Automation

HVAC compressor contactors, fan motor starters, and zone valve actuators all require reliable 30A power relay switching at 240VAC. The HLS-T91(16F)-3's electrical life of 100,000 rated-load operations supports typical HVAC cycle counts over a multi-year service life. In building automation systems using 24VDC control buses, the 24V coil variant interfaces directly with BACnet and Modbus output modules.

Industrial Automation and PLC Output Stages

PLC relay output modules commonly use T91-class high power relays to switch motor starters, solenoid valves, heating elements, and pilot lights. The PCB mount relay format allows relay output modules to be manufactured as compact, high-density PCB assemblies rather than bulky DIN rail socket designs. The 10ms maximum release time is fast enough for most PLC scan cycles while providing adequate noise immunity.

Household and Commercial Appliances

Washing machine controllers, dishwasher heating element switching, electric oven timer circuits, and air conditioner PCBs all use 30A SPDT relays for main load switching. The Ag alloy contact material provides low initial contact resistance (100mΩ max) and good arc erosion resistance, supporting the high inrush currents typical of resistive heating loads and motor starting.

Telecommunication Power Systems

Telecommunication base stations and data center power distribution units require relay switching for battery backup transfer, rectifier output switching, and alarm-triggered load shedding. The 100MΩ minimum insulation resistance and 2000VAC coil-to-contact dielectric strength of the HLS-T91(16F)-3 meet the isolation requirements of telecom power system standards, and the 48VDC coil variant is directly compatible with standard -48VDC telecom battery systems (using appropriate polarity).

PCB Layout and Design Best Practices for T91 Relay Integration

Correct PCB layout is critical for maximising the performance and safety of the HLS-T91(16F)-3 PCB mount relay. The following guidelines reflect best practices for high-current relay PCB design.

• Contact trace width: For a 30A rated relay, the PCB traces connecting to the Common, NO, and NC pins should be a minimum of 6mm wide on 35μm copper, or 4mm on 70μm copper, to keep trace temperature rise below 10°C at rated current.
• Creepage and clearance: Maintain a minimum of 3mm PCB clearance between high-voltage contact traces and low-voltage coil traces to comply with IEC 60664 for 250VAC working voltage in Pollution Degree 2 environments.
• Flyback diode: Always place a fast-recovery flyback diode (e.g., 1N4007 or 1N4148) in reverse-parallel across the coil pins to suppress the inductive voltage spike on relay de-energization. Mount the diode within 10mm of the coil pins to minimize loop inductance.
• Driver transistor: Use an NPN transistor (e.g., 2N2222 for low-voltage coils, BD139 for 24-48V coils) with a base resistor sized to ensure full saturation at the logic output voltage. Place the transistor close to the coil pins.
• Thermal relief: Use thermal relief pads on the high-current contact through-holes to facilitate reliable hand soldering and reduce thermal stress during wave soldering.
• Ground plane separation: Keep the high-current return path and the logic/control ground plane physically separated on the PCB, connecting them at a single star-ground point to prevent load-switching transients from coupling into the control circuitry.

The HLS-T91(16F)-3 is available in a standard 5-pin PCB footprint consistent with T91-family relay socket and PCB layout conventions, enabling straightforward drop-in replacement in existing designs and compatibility with widely available relay socket accessories for socketed (non-soldered) mounting configurations.

About Ningbo Helishun Electron Co., Ltd.

Ningbo Helishun Electron Co., Ltd. was founded in 2000 and is located in Ningbo City — a major industrial and export hub on the East China Sea coastline. The company now covers 8,800 square meters of manufacturing and R&D space, specialising exclusively in researching, developing, and producing relays. Over more than two decades of operation, Helishun has established an important position in the global relay market under its registered HELISHUN trademark.

The company has adopted advanced technology and testing equipment from both domestic and international sources, and has built a dependable quality management system certified to ISO9001:2015. Products comply with international mounting and characteristic standards, and carry certifications including UL, TÜV, CE, and CQC, with full compliance to EU RoHS requirements. These certifications cover the breadth of major global markets and make Helishun relays a priority replacement choice across product categories.

HELISHUN relays are sold across domestic and international markets and are widely used in household electrical appliances, telecommunication systems, automation control equipment, automobiles, and instruments and meters. The company pursues quality through all-round management and has built lasting customer trust through careful manufacturing and consistent product performance. Helishun welcomes customers and OEM/ODM partners worldwide to explore cooperative opportunities.

Frequently Asked Questions