High-frequency PCB board refers to the electromagnetic frequency of the higher special circuit boards for high-frequency (frequency greater than 300MHZ or wavelength of less than 1 meter) and microwave (frequency greater than 3GHZ or wavelength of less than 0.1 meters) in the field of PCB, is in the microwave substrate copper-clad laminate boards on the use of ordinary rigid circuit boards manufactured using some of the processes or the use of special treatment methods and the production of circuit boards.

High-frequency PCB layout and wiring design specifications

1.Isolation and grounding principles

• Strictly separate digital and analog circuit areas
• Ensure that all RF alignments have a complete ground plane reference.
• Prioritize the surface layer alignment for RF signal transmission

2.Wiring Priority Order

RF lines → baseband RF interface lines (IQ lines) → clock signal lines → power lines → digital baseband circuits → ground network

3.Surface treatment specification

• High-frequency single-board (>1GHz) is recommended to eliminate the green oil cover in the microstrip line area.
• Low and medium frequency single board microstrip line is recommended to retain the green oil protective layer

4.Cross wiring specification

• Strictly prohibit digital/analog signal cross-wiring.
• RF lines and signal lines need to be met when crossing:
  a) Preferred option: add an isolated ground plane layer
  b) Second choice: Maintain 90° orthogonal crossings.
• Parallel RF line spacing requirements:
  a) Normal wiring: Maintain 3W spacing.
  b) When parallelism is necessary, insert a well-grounded isolated ground plane in the center.

5.Mixed Signal Processing

• Duplexers/mixers and other multi-signal devices are required:
  a) RF/IF signals are routed orthogonally.
  b) Isolated ground barrier between signals

6.Alignment Integrity Requirements

• Overhanging ends of RF alignment are strictly prohibited.
• Maintain transmission line characteristic impedance consistency

7.Vias Handling Specifications

• Avoid changing layers of RF alignment as much as possible.
• When a layer change is necessary:
  a) Use the smallest hole size (recommended 0.2mm)
  b) Limit the number of vias (≤ 2 per line)

8.Baseband interface wiring

• IQ line width ≥ 10 mil
• Strict equal length matching (ΔL ≤ 5 mil)
• Maintain uniform spacing (±10% tolerance)

9.Control line wiring

• Route length optimized for termination impedance
• Minimize proximity to the RF path
• Prohibit the placement of ground vias next to control wires

10.Interference protection

• 3H spacing between digital/power supply alignments and RF circuits (H is the thickness of the dielectric)
• Separate shielding area for clock circuits

11.Clock wiring

• Clock wiring ≥ 10 mils
• Double-sided grounded shielding
• Ribbon wire structure is preferred

12.VCO wiring

• Control lines ≥2mm from RF lines
• If necessary, implement full ground wrap treatment

13.Multilayer design

• Prefer a cross-layer isolation scheme
• The second choice of the orthogonal crossover solution
• Limit parallel length (≤λ/10)

14.Grounding System

• Ground plane completeness of each layer >80
• Grounding hole spacing <λ/20
• Multi-point grounding in critical areas

Note: All dimensional specifications should be adjusted according to the wavelength (λ) of the actual operating frequency, and it is recommended that three-dimensional electromagnetic field simulation be carried out to verify the final design.

High-speed high-frequency PCB key performance parameters technical specifications

1.Dielectric Characteristic Parameters

1.1 Dielectric constant (Dk)

• Typical requirement: 2.2-3.8 (@1GHz)
• Key Indicator:
• Numerical stability (±0.05 tolerance)
• Frequency dependence (<5% variation from 1-40 GHz)
• Isotropy (X/Y/Z axis variation <2%)

1.2Dielectric loss (Df)

• Standard range: 0.001-0.005 (@10GHz)
• Core Requirements:
• Low loss characteristics (Df <0.003 preferred)
• Temperature stability (-55℃~125℃ variation <15%)
• Surface roughness impact (Ra <1μm)

2.Thermo-mechanical properties

2.1 Coefficient of thermal expansion (CTE)

• Copper foil matching requirements:
• X/Y axis CTE: 12-16ppm/°C
• Z-axis CTE: 25- 50 ppm/°C
• Reliability standard:
• 300 thermal cycles (-55℃~125℃) without delamination

2.2 Heat resistance index

• Tg point: ≥170℃ (preferably 180-220℃)
• Td point: ≥300℃ (5% weight loss temperature)
• Delamination time: >60min (288℃ solder test)

3.Environmental stability

3.1 Moisture absorption characteristics

• Saturated water absorption: <0.2% (24h immersion)
• Dielectric parameter drift:
• Dk change <2%
• Df change <10%

3.2 Chemical resistance

• Acid and alkali resistance: 5% concentration solution immersion 24h without corrosion
• Solvent resistance: Passed IPC-TM-650 2.3.30 test.

4.Electrical Performance

4.1 Impedance control

• Single-ended line: 50Ω±10%.
• Differential pairs: 100Ω±7%
• Key control points:
• Tolerance of line width ±5%
• Tolerance of dielectric thickness ±8%
• Copper Thickness Tolerance ±10

4.2 Signal Integrity

• Insertion loss: <0.5dB/inch@10GHz
• Return Loss: >20dB@Operating Band
• Crosstalk rejection: <-50dB@1mm spacing

5.Mechanical Reliability

5.1 Peel Strength

• Initial value: >1.0N/mm
• After thermal aging: ＞0.8N/mm (125℃/1000h)

5.2 Impact strength

• CAF resistance: >1000h (85℃/85%RH/50V)
• Mechanical shock: Pass 30G/0.5ms test

6.Special Performance Requirements

6.1 High Frequency Stability

• Phase consistency: ±1°@10GHz/100mm
• Group delay: <5ps/cm@40GHz

6.2 Surface Finish

• Copper foil roughness: Rz＜3μm
• Soldermask effect: Dk variation <1%

Notes:

1. All parameters should be tested according to IPC-TM-650 standard methods.
2. Batch sampling is recommended for key parameters.
3. High frequency application should provide Dk/Df with a frequency variation curve.
4. Multilayer boards should be evaluated for Z-axis parameter consistency.

High-Frequency PCB Material Dk/Df Testing Technical White Paper

1. Classification and Selection Principles of Testing Methods

1.1 Testing Method System

• IPC Standard Methods: 12 standardized testing protocols
• Industry Custom Methods: Proprietary solutions from research institutions and manufacturers
• Practical Selection Criteria:
  • Frequency matching (±20% of operating band)
  • Electric field direction consistency (Z-axis/XY plane)
  • Correlation with manufacturing processes (raw material/finished board)

1.2 Method Selection Matrix

2. Detailed Explanation of Core Testing Techniques

2.1 X-Band Clamped Stripline Resonator Method (IPC-TM-650 2.5.5.50)

• Test Structure:
  ┌─────────────────┐
  │ Ground Plane │
  ├─────────────────┤
  │ DUT (Z-axis) │
  ├─────────────────┤
  │ Resonator Circuit│
  ├─────────────────┤
  │ DUT (Z-axis) │
  ├─────────────────┤
  │ Ground Plane │
  └─────────────────┘
• Technical Characteristics:
  • Frequency range: 2.5–12.5 GHz (increments of 2.5 GHz)
  • Accuracy: ±0.02 (Dk), ±0.0005 (Df)
  • Error sources: Fixture air gaps (~1–3% deviation)

2.2 Split Cylinder Resonator Method (IPC-TM-650 2.5.5.13)

• Key Parameters:
  • Testing direction: XY-plane properties
  • Resonance peaks: 3–5 characteristic frequency points
  • Anisotropy analysis: Can compare with Z-axis data

2.3 Microstrip Ring Resonator Method

• Circuit Requirements:
  • Feedline impedance: 50Ω ±1%
  • Ring gap: 0.1–0.15 mm (requires lithography control)
  • Copper thickness tolerance: ±5 μm compensation needed

3. Test Error Analysis and Compensation

3.1 Major Error Sources

• Material Dispersion: Frequency-dependent Dk (typical: -0.5%/GHz)
• Copper Roughness Impact: Roughness Level Dk Deviation Rz < 1 μm <1% Rz = 3 μm 3–5% Rz > 5 μm >8%
• Process Variations:
  • Plated copper thickness (0.3% error per 10 μm deviation)
  • Solder mask influence (0.5–1.2% variation due to green oil coverage)

3.2 Data Correction Methods

• Frequency Compensation Algorithm:
  Dk(f)=Dko​⋅(1−α⋅log(f/fo​))
• Surface Roughness Correction: Hammerstad-Jensen model
• Anisotropic Material Handling: Tensor analysis method

4. Engineering Application Guidelines

4.1 Testing Plan Development Process

1. Determine operating frequency band (center frequency ±30%)
2. Analyze primary electric field direction (microstrip/stripline)
3. Evaluate manufacturing process window (copper thickness/line width tolerance)
4. Select a testing method with >80% matching accuracy

4.2 Data Comparison Standards

• Valid Comparison Conditions:
  • Same testing direction (Z-axis or XY plane)
  • Frequency deviation < ±5%
  • Consistent temperature conditions (23±2°C)
• Typical Material Parameter Variations: Testing Method Dk Variation Df Variation Fixture vs. Circuit 2–8% 15–30% Z-axis vs. XY Plane 1–15% 5–20%

5. Evolution of Testing Standards

5.1 Emerging Testing Technologies

• Terahertz time-domain spectroscopy (0.1–4 THz)
• Near-field scanning microwave microscopy (10–100 GHz)
• AI-assisted parameter extraction systems

5.2 Standardization Trends

• Multilayer board testing methods (IPC-2023 draft)
• 5G mmWave-specific testing protocols (28/39 GHz)
• Dynamic thermal cycling test standards

Note: All tests should be conducted in a controlled environment (23±1°C, 50±5% RH). Automated test systems integrating vector network analyzers (VNA) and probe stations are recommended. Test data must include 3σ statistical analysis.

Surface Mount Technology (SMT) represents the core of modern electronics assembly, transforming traditional discrete through-hole components into compact leadless or short-lead chip devices mounted directly onto printed circuit board surfaces. This technology enables high-density, highly reliable, miniaturized, cost-effective electronic product assembly while supporting automated manufacturing processes.

Overview of Surface Mount Technology

Surface Mount Technology (SMT) has revolutionized modern electronics manufacturing by replacing bulky through-hole components with compact, leadless chip devices that mount directly onto printed circuit boards. As the industry’s dominant assembly process, SMT enables automated production of high-density, ultra-reliable, and miniaturized electronic devices at reduced costs. This transformative technology has become ubiquitous across computer systems, communication equipment, and countless electronic products, with its adoption continuing to expand as traditional through-hole component usage declines. The ongoing advancement of SMT processes and components has firmly established it as the gold standard in electronics assembly, driving innovation while meeting the growing demand for smaller, more powerful, and cost-efficient electronic devices across all market sectors.

Evolution and Technical Background of SMT

Technological Development Context

The trends toward intelligent, multimedia, and networked electronics have driven three core requirements for assembly technology: high density, high speed, and standardization. These demands prompted the revolutionary shift from traditional Through-Hole Technology (THT) to Surface Mount Technology.

Global Development History

SMT originated in the 1960s and has progressed through four key phases:

1. Initial Exploration (1970s): Primarily used in hybrid integrated circuits and consumer products like electronic watches and calculators
2. Rapid Growth (Mid-1980s): Increasing maturity and expanded applications
3. Widespread Adoption (1990s): Became mainstream assembly technology, gradually replacing THT
4. Continuous Innovation (21st Century-Present): Advancing toward higher density, smaller size, and better performance

Current Status in China

SMT technology was introduced to China in the 1980s, initially for television tuner production before expanding to consumer electronics like video recorders and cameras. Since 2000, with the rapid development of the electronics information industry, SMT equipment imports have grown substantially, establishing China as the world’s largest SMT manufacturing base.

Core Advantages of SMT Technology

1. High-Density Assembly: Reduces product volume by 60% and weight by 75%
2. Exceptional Reliability: Solder joint defect rates one order of magnitude lower than THT, with superior shock resistance
3. Excellent High-Frequency Characteristics: Minimizes parasitic capacitance and inductance while reducing electromagnetic interference
4. Efficient Automation: Simplifies production processes and improves efficiency
5. Significant Cost Advantages: Lowers total production costs by 30-50%

Key Technological Trends in SMT

Component Packaging Innovations

Packaging technology continues evolving toward smaller sizes, more I/Os, and higher reliability, with major trends including:

• Multi-Chip Module (MCM) integration
• Chip resistor network development
• System-in-Package (SiP) technology
• System-on-Chip (SoC) integration
• Silicon-on-Insulator (SOI) applications
• Nanoelectronic device research

Production Equipment Advancements

Modern SMT equipment is progressing toward efficiency, flexibility, and environmental sustainability:

• High Efficiency: Dual-lane board feeding and multi-head designs boost productivity
• Intelligent Systems: Vision inspection and digital controls enhance precision and speed
• Flexible Configurations: Modular designs accommodate diverse production needs
• Eco-Friendly Solutions: Noise reduction and pollution control for green manufacturing

Circuit Board Technology Innovations

Surface Mount Board (SMB) development trends:

• High precision: 0.06mm line width, 0.08mm spacing
• High density: 0.1mm minimum aperture
• Ultra-thin designs: 6-layer boards at 0.45-0.6mm thickness
• Buildup multilayer boards: 30-50 layer high-density interconnects
• Increasing flexible board applications
• Widespread ceramic substrate use
• Lead-free surface coating technologies

Core Components of SMT Processes

Primary Process Types

1. Solder Paste-Reflow: Simple and efficient for miniaturized products
2. SMT-Wave Soldering: Combines through-hole and surface mount components
3. Double-Sided Solder Paste-Reflow: Enables ultra-high density assembly
4. Hybrid Assembly: Integrates multiple technological advantages

Key Production Line Processes

1. Solder Paste Printing: Precise application to PCB pads
2. Component Placement: High-accuracy mounting of SMDs
3. Reflow Soldering: Creates reliable electrical connections
4. Cleaning & Inspection: Removes residues and verifies quality

Three Critical Process Details

1. Paste Application: Automated or semi-automated printing for even distribution
2. Component Placement: Micron-level positioning via precision placement systems
3. Reflow Soldering: Precise temperature profiling for optimal soldering

Electrostatic Discharge (ESD) Protection Management

ESD Risks

Static electricity can cause immediate or latent damage to electronic components, with latent defects accounting for 90% of failures and posing significant quality threats.

Protection Measures

1. Personal Protection Systems: Anti-static wrist straps, garments, and footwear
2. Environmental Controls: ESD-safe flooring and work surfaces
3. Operational Protocols: Strict ESD management procedures in production areas

SMT three core process technology details

1. Solder Paste Application Process

As the first critical process in SMT production lines, solder paste application quality directly impacts subsequent operations. Modern solder paste printing primarily utilizes stencil printing technology with key technical aspects including:

• Printing Equipment:
• Fully automatic printers with vision alignment systems achieve ±12.5μm positioning accuracy
• Semi-automatic models suit medium/small batch production
• Process Control:
• Squeegee angle is typically maintained at 45-60°
• Printing speed controlled between 20-80mm/s
• Printing pressure maintained at 5-15kg range
• Stencil Design:
• Thickness selection: 0.1-0.15mm for standard components, 0.08mm for fine-pitch
• Aperture design: Area ratio >0.66 ensures proper paste release
• Paste Management:
• Requires a minimum 4-hour reconditioning before use
• 2-3 minutes of mixing achieves optimal viscosity
• Ambient conditions: 23±3°C, 40-60% RH

2. Component Placement Technology

The core of SMT manufacturing, modern placement machines deliver ultra-precise automated assembly:

• Equipment Types:
• High-speed placers: Up to 250,000 CPH for small components
• Multi-function machines: Handle odd-form components at ±25μm accuracy
• Modular systems: Flexible configurations for diverse needs
• Critical Technical Parameters:
• Placement accuracy: ±30μm@3σ (high-end machines achieve ±15μm)
• Minimum component size: 0201 (0.25×0.125mm) or smaller
• Component recognition: High-resolution CCD (up to 0.01mm/pixel)
• Key Process Controls:
• Nozzle selection and maintenance
• Feeder calibration
• Placement force control (10-500g adjustable)
• Vision alignment system calibration

3. Reflow Soldering Process

The critical process for reliable solder joints requires precise temperature control:

• Temperature Profile Zones:
• Preheat: Ambient→150°C at 1-3°C/s ramp rate
• Soak: 150-180°C for 60-90 seconds
• Reflow: Peak temperature 220-245°C for 30-60 seconds
• Cooling: Rate <4°C/s
• Equipment Types:
• Convection reflow: Excellent temperature uniformity
• Infrared reflow: High thermal efficiency
• Hybrid systems: Combine both advantages
• Critical Process Controls:
• Oxygen content (<1000ppm)
• Conveyor speed (0.8-1.5m/min)
• Thermocouple placement and monitoring
• Profile optimization for different pastes
• Common Defect Prevention:
• Tombstoning: Optimize pad design, control ramp rate
• Bridging: Adjust stencil apertures, squeegee parameters
• Cold joints: Ensure proper peak temperature/duration

These three processes form the technological core of SMT manufacturing. Each requires precise process control and strict quality management to ensure final product reliability and consistency. Modern SMT lines implement MES systems for full-process data monitoring, ensuring parameter traceability and process stability.

50A fuse is a core component designed for circuit protection, widely used in the electrical system of automobiles, construction machinery and other equipment, which can effectively prevent damage caused by circuit overload and short circuit.

Product Characteristics and Parameters

1. Electrical parameters

Rated current: 50A (Ampere)
Operating voltage: low voltage applicable (specific voltage range can be customized according to actual demand)

2. Physical Characteristics

Structure: Standard plug-in design (supports various specifications)
Fusing Characteristics: Fast blowing type (F type)
Temperature range: -40℃ to 120℃ (operating temperature range)

3. Performance Characteristics

Adoption of high-quality alloy fusing material
Precise fusing characteristic curve
Stable electrical performance
Resistant to vibration and shock

50 Amp Fuse Function

A 50 Amp (50A) fuse is a critical circuit protection component that is primarily used to prevent damage to electrical systems and equipment caused by current overloads and short circuits, as well as to safeguard usage. Its main functions include:

1. Overload protection
   When the current in the circuit exceeds the rated value of 50 amperes, the fuse will blow quickly, cutting off the current path and avoiding the risk of overheating of wires, damage to equipment or even fire due to overloading.
2. Short circuit protection
   In the event of a short-circuit fault, the short-circuit current may surge instantaneously, far exceeding the normal load current. 50A fuse can be blown in a very short time, effectively preventing the short-circuit current from impacting on the circuit and equipment, and reducing the risk of fire.
3. Personal safety protection
   By cutting off the abnormal current in time, the fuse can reduce the safety risk of electric shock and electric shock caused by circuit failure, providing additional protection for operators and equipment.
4. Circuit Stability Maintenance
   The fast response of the fuse can effectively suppress current fluctuation, prevent overload or short circuit from affecting the normal operation of other related equipment, and ensure the stability and reliability of the entire electrical system.

Principle of operation

1. Basic Structure Composition

The 50 ampere fuse is mainly composed of the following two parts:

• Conductor part: made of highly conductive metal materials (such as copper, silver or its alloy) to ensure low impedance characteristics under normal operating current
• Protective casing: Usually made of high-temperature resistant ceramic or glass, with the following functions
• Provide mechanical protection
• Prevent the spread of electric arcs
• Insulate from external environmental influences

2. Normal working conditions

When working within the rated current (50A):

• Joule heat generated by the conductor (I²R) is effectively dissipated through the housing
• The overall temperature is maintained within safe limits (typically below 80°C).
• The conductor remains fully energized, and the circuit operates normally.

3. Overload protection mechanism

When the current exceeds the rated value:

• Heat build-up phase:

• The increase in current results in a square-fold increase in heat generation (Q=I²Rt).
• Conductor temperature rises rapidly

• Fusing threshold:

• The melting point of the conductor material is reached (copper: 1083°C, silver: 961°C).
• Specific alloy formulations ensure precise fusing characteristics

• Circuit break protection:

• Conductor vaporization to form a circuit breaker gap
• Simultaneously, the housing effectively curbs any arcing that may occur.

4. Short-circuit protection characteristics

In the face of short-circuit currents (up to thousands of amperes):

• Fusing times can be reduced to milliseconds.
• Enhanced arc extinguishing by special designs (e.g., quartz sand filling).
• Ensure that the fault current is cut off within the first cycle.

5. Key technical parameters

• Fusing curve: under IEC 60269 standards
• Breaking capacity: up to 10kA (depending on the specific model)
• Time-current characteristic: ensures selective protection
  This sophisticated protection mechanism allows the 50 amp fuse to differentiate between normal inrush currents and dangerous overcurrents in milliseconds, providing reliable protection for electrical systems.

Fuse voltage tolerance

1. Basic Concepts of Voltage Ratings

The voltage rating (Un) of a 50-ampere fuse is the highest circuit voltage at which it can operate safely and reliably. This parameter is critical because:

1. voltage rating directly affects insulation performance
2. exceeding the rated voltage may result in:

• Risk of insulation breakdown
• Continued arcing during fusing
• Failure of protection

2. Typical Voltage Classification

• Low-voltage type (32V DC) Main applications: Automotive electrical systems.

• Main applications: Automotive electrical systems
• Common types:
  • Plug-in type (ATO/ATC)
  • Miniature glass tube (10 x 38mm)
• Features:
  • Designed for 12V/24V vehicles.
  • Vibration-resistant construction

• Medium Voltage Type (125V AC/DC)

• Main applications:
  • Construction machinery
  • Industrial equipment
• Common types:
  • Fork-bolt type (MEGA/J-CASE)
  • Bolt-on type
• Features:
  • Higher breaking capacity
  • Enhanced arc extinguishing design

3. Key Selection Parameters Comparison Table

4. Precautions for use

• Principle of voltage matching

• It must be ensured that the circuit operating voltage ≤ fuse rated voltage
• DC rating should be paid special attention to DC system.

• Special Considerations: Transient voltage peaks should not exceed the rated voltage.

• The peak transient voltage should not exceed 120% of the rated voltage.
• Derating should be considered for altitudes over 2000m

• Safety margin recommendation

• Conventional applications: retain 20% voltage margin
• Harsh environment: keep more than 30% margin.

5. Clarification of Common Misconceptions

• Misconceptions about the current/voltage relationship. Misconception: “50A” is a good choice for the current/voltage relationship.

• Misconception: “A 50A fuse can be used for any voltage.”
• Fact: Current rating and voltage rating are independent of each other and need to be satisfied at the same time.

• AC/DC applicability: Most automotive fuses are labeled for D only.

• Most automotive fuses are labeled with DC ratings only.
• Most automotive fuses are only labeled with DC ratings.

It is recommended to always refer to the detailed specifications provided by the manufacturer for actual selection, especially for special application scenarios (e.g., electric vehicles, photovoltaic systems, etc.), which may require customized high-voltage solutions.

50A Fuse Maximum Current

1. Core current parameter description

• 1. Rated current (In)

• Standard value: 50A (nominal operating current)
• Definition: Maximum continuous current that can work stably for a long period under standard test conditions
• Test conditions:
  • Ambient temperature 23±5°C
  • At rated voltage
  • Natural convection cooling

• 2. Actual operating current range

• Recommended operating current: ≤80% In (i.e. 40A)
• Critical operating area: 80-100% In (subject to derating factor)

2. Overload Characterization

Note: Refer to IEC 60269 time-current curves for specific data.

3. Special Type Differences

1. Conventional blown fuses

• Strict limitation: Continuous current must not exceed 50A
• Instantaneous withstand: 200% of inrush current for <100ms

1. Periodic resettable fuse (PPTC)

• Operating limit: 50A (steady state)
• Trip current: usually 200-300% of rated value
• Reset Characteristics: Automatic recovery after troubleshooting

4. Key influencing factors

1. Ambient Temperature Correction Factor Ambient Temperature Current Correction Factor 25℃ 1.0 50 ℃ 0.85 70 ℃ 0.75
2. Influence of installation method

• Confined space requires an additional 15-20% derating.
• Parallel use requires professional design (not recommended for parallel use)

5. Suggestions for Selection

1. Industrial applications **It is recommended to choose IEC standard products.

• It is recommended to choose IEC standard products.
• Focus on breaking capacity (at least 10kA)

1. **Automotive electronics

• Prefer SAE-certified products
• Attention to vibration resistance

1. **Special Needs

• High-frequency pulse scenarios: choose gg/gL type
• Motor protection: AM type is more suitable

IMPORTANT NOTE: Any use in excess of the rated current of 50A will significantly shorten the life of the product. In critical operating conditions, it is recommended that a higher specification (e.g. 63A) be used to ensure reliability. A complete durability test must be carried out before actual application.

Precautions for Use (Professional Version)

1. Selection key elements

1. Principle of current matching

• Calculation formula: Fuse rated current ≥ 1.25 x maximum continuous current of the circuit
• Special scenarios:
  • Motor circuit: consider the starting current (recommended 1.5-2 times the rated current)
  • Capacitive loads: add 30% margin

1. Voltage rating selection

• Basic requirements: Fuse rated voltage ≥ maximum circuit operating voltage
• DC system special attention:
  • DC ratings need to be specified
  • Polarity-sensitive fuses need to be installed correctly.

2. Performance Parameter Considerations

1. Breaking capacity classification | Application Scenarios | Minimum Breaking Capability Application Scenarios Minimum Breaking Capacity Requirements Automotive Electronics 1kA Industrial Controls 10kA Photovoltaic Systems
2. Fusing Characteristics Selection Guidelines

• Fast Fusing (FF):
  • Application: semiconductor device protection
  • Characteristics: ≤0.1s fuse at 200% overload
• Slow fusing type (TT):
  • Applicable: Motor circuit
  • Characteristics: Can withstand 5-7 times In for 1 second.

3. Environmental adaptability requirements

1. Temperature Compensation Coefficients Table Ambient Temperature Current Carrying Capacity Correction ≤25℃ 100% 50 ℃ 85% 70 ℃ 70%
2. **Special Environmental Countermeasures

• Vibration: Select spring-loaded mounting
• Humid environment: Select sealed products (IP67).

4. Installation Specifications

1. Standard Operating Procedure 1.
2. Power off and check the power (use a multimeter to confirm)
3. Remove the oxidized layer on the contact surface.
4. Use a torque wrench to install (reference value: 2.5 N-m)
5. Conductivity test
6. Prohibited items

• Prohibit the use of copper wire across the connection.
• Prohibit mixing of different specifications.
• Do not modify the mounting bracket without authorization.

5. Maintenance Management

• Troubleshooting Procedure

• First fuse: Replace with a new product of the same specification.
• Second fuse: check load current (use clamp meter)
• Third fuse: System-level troubleshooting

• Life Cycle Management

• Routine inspection cycle: 6 months/times
• Mandatory replacement cycle: 5 years or after 3 fuses

6. Certification Requirements

• Industry Certification Standards Comparison

Important: When using 50A fuses in new energy vehicles (EV) or photovoltaic systems, it is important to select products with appropriate DC voltage approvals (e.g., UL2750) and to consider arc suppression design. It is recommended that a fuse replacement log file be established to track the root cause of each blowing event.

Fuses are widely used in various circuits to protect electrical equipment from overloads and short circuits. Choosing the right fuse needs to be based on the rated current, voltage, and melting time of the circuit. The rated current is the value of the current that the fuse can continuously pass, and the fuse will blow if it exceeds this value; the voltage should generally be less than or equal to the operating voltage of the circuit; the melting time refers to the time from the current exceeding the rated value to the melting time, which is usually determined by the material and design parameters of the fuse. In addition, there are some special types of fuses, such as fast blow fuses and delayed blow fuses, which are used to respond quickly to overload conditions and to allow current to pass for a while under brief overload conditions, respectively.

50 Amp Fuse FAQs

Q1: Why does the fuse blow so often when I use the air conditioner in my house?

A: This is a typical overload problem. When using multiple high-power appliances at the same time (e.g., air conditioner + heater), the total current may exceed 50A. suggestions:

1. Calculate the total power of all electrical appliances (1P air conditioner ≈ 8A, electric heater ≈ 10A)
2. Staggered use of high-power appliances
3. If you need to use high load for a long time, we suggest you to upgrade the circuit instead of just replacing the fuse with a bigger one.

Q2: What should I do if the fuse blows occasionally when the equipment starts up?

A: This is caused by pulse current shock. The following measures are recommended:

1. Replace the fuse with a slow-blowing fuse (model number with “T” mark)
2. Check whether the starting current of the equipment is abnormal
3. Ensure that the fuse is securely installed (recommended torque 2- 3 N-m)
4. Consider installing a soft start device.

Q3: What are the signs of poor fuse contact? How to solve it?

A: Common symptoms include:

• Black discoloration of the fuse holder
• Smell of burnt plastic
• Intermittent power failure

Solution:

1. clean contact surfaces after power failure (use fine sandpaper or contact cleaner)
2. Check for loose terminals
3. Replace badly oxidized fuse holders
4. Check contact resistance periodically (annually)

Q4: What are the possible causes of instantaneous fuse blowing?

A: It is most likely a short circuit fault and should be immediately:

1. Disconnect all electrical appliances
2. Use a multimeter to measure the line resistance (normal should be > 1MΩ)
3. Focus on checking:

• Damaged wires
• Water inlet socket
• Short circuit inside the appliance

1. Do not replace the fuse until the problem is solved.

Q5: How can I tell if a fuse needs to be replaced?

A: Fuses should be replaced in the following cases:

1. It has been in use for more than 5 years (even if it has not blown).
2. The surface is oxidized or deformed
3. It has been blown more than 3 times
4. Measured resistance value exceeds 15% of the new product

It is recommended to set up a replacement record and replace it once every 3-5 years in a normal environment.

Professional Tips: Be sure to disconnect the power before all maintenance operations! If the same problem occurs repeatedly, please consult a professional electrician for a systematic check. Increasing the fuse size arbitrarily may cause the line to overheat and cause a fire.

What is an Automatic Charging Relay

An automatic charging relay is a type of relay used to automatically control the charging process, usually in electric vehicles or other devices that require automatic charging. Its main function is to automatically cut off the charging circuit when the battery is fully charged to prevent overcharging, thus protecting the battery and prolonging its service life.
Relay (English name: relay) is a kind of electric control device, is the change of input quantity (excitation quantity) to reach the stipulated requirements in the electrical output circuit to make the controlled quantity undergo a predetermined step change in a kind of electrical appliance. It has an interactive relationship between the control system (also called the input circuit) and the controlled system (also called the output circuit). Usually used in automated control circuits, it is a kind of “automatic switch” that controls the operation of large currents with small currents. Therefore, it plays the role of automatic adjustment, safety protection, and a conversion circuit in the circuit.

Types of Automatic Charging Relays

The main types of automatic charging relays include electromagnetic relays, thermal relays, time relays, and speed relays. These relays are categorized according to their principle of action, structural feature,s and type of load.

1.Electromagnetic Relay

Electromagnetic relays are the most common type of relays that control the on-off of a circuit through electromagnetic effects. When the coil is energized, it generates a magnetic field that attracts the iron core, causing the contacts to close or break, thus realizing the control of the circuit.
Main functions: the control circuit and load circuit are completely isolated to improve safety, can control high current or high voltage circuits, simple mechanical structure, and long life. If you need to select the type, you need to consider the voltage, current, contact type, and other parameters to ensure the best performance.

2.Thermal Relay

Thermal relay is a commonly used electrical protection device, which is mainly used to prevent motor or electrical equipment from being damaged due to overload. When the current in the circuit exceeds the set value, the thermal element heats up and bends and deforms the bimetal, which triggers the mechanical mechanism to disconnect the circuit and ensure the safety of the equipment.
Main function: precise overload protection, simple and reliable structure with strong anti-interference ability. The action current can be adjusted according to the demand of equipment, not directly cut off the main circuit, only control the contactor coil, high security.

3.Time relay

Time relay is a kind of control device with a time delay function, which can automatically connect or disconnect the circuit after a set time, and is widely used in automation system that needs precise time control.
Main function: precise control to meet different needs. Can be matched with contactors, PLC, etc. to realize complex timing control, electronic high precision, and to adapt to different environments.

4.Speed Relay

Speed relay (also known as speed relay) is a kind of automation component used for detecting the speed of motor or rotating equipment, which can automatically turn on or off the control circuit according to the preset speed value, and is widely used in motor speed regulation, braking control, and equipment protection system.
Main functions: prevent motor damage due to overspeed or low-speed blocking, with an inverter to realize closed-loop speed regulation, non-contact electronic anti-vibration, maintenance-free, suitable for harsh environments.

Relay Circuit Symbols

1.Circuit representation of relay coils

A standardized representation of relay coils is used in circuit diagrams:
Basic symbol: A single coil is represented using a long box graphic
Double coil representation: When a relay has two coils, two long boxes are drawn side by side.
Labeling norms: The text symbol “J” (from the pinyin initials of “relay”) must be labeled inside or next to the long box.

2.Two ways of drawing relay contacts

Centralized drawing method
Characteristics: All contacts are drawn on the same side of the long box representing the coil.
Advantage: Visualize the complete structure of the relay
Applicable scenarios: simple circuit design, teaching schematic diagrams.
Decentralized drawing method
Characteristics: According to the actual circuit needs, the contacts will be scattered in different positions.
Labeling requirements:
Ensure that the coil and the corresponding contacts use the same symbol (e.g. J1).
Add a number to each contact group (e.g. J1-1, J1-2)
Advantage: Makes the wiring of complex circuits clearer and easier to read.

3.Three types of relay contacts

1. Normally open contacts (type H)
Symbol identification: indicated by the letter “H”.
When the coil is de-energized, the contact remains open:
When the coil is de-energized, the contact remains open.
When the coil is energized, the contact closes and conducts.
Typical applications: circuit start-up control, equipment energized switching.
2.Normally closed contact (D type)
Symbol identification: indicated by the letter “D”.
Symbolization: The letter “D” is used to indicate the operating characteristics:
When the coil is de-energized, the contact remains closed.
When the coil is energized: the contact is open
Typical applications: safety protection circuits, emergency stops.
3.Change-over contact (Z type)
Symbol identification: indicated by the letter “Z”.
Structural features:
Contains 3 contacts: 1 movable contact + 2 static contacts.
Form two contact pairs
Operating characteristics:
When the coil is not energized, the movable contact is closed to one of the static contacts and disconnected from the other.
When the coil is energized, the position of the movable contact is switched to change the connection state.
Typical applications: circuit switching control, motor forward and reverse control.

Automatic charging relay function

1.Intelligent charging management and precise on-off control

Automatic charging relay plays a key role in the field of power control, and its excellent on-off performance provides a solid guarantee for charging safety. Taking the electric vehicle charging pile as an example, the relay system can
Precise control: Achieve ma illisecond response to ensure stable power on when charging is initiated.
Safe disconnection: Reliable disconnection of the circuit when charging is completed or under abnormal conditions.
Mode switching: Intelligent switching of fast/slow charging modes according to the control instructions, supporting advanced functions such as charging reservation.
Efficiency optimization: significantly improve energy utilization efficiency by dynamically adjusting charging parameters.

2.Multiple circuit protection mechanisms

The modern automatic charging relay integrates a full range of protection functions, building multiple safety barriers for the charging system:
Core protection function:
Over-current protection: real-time monitoring of the current, beyond the safety threshold, cuts off immediately
Over-voltage protection: automatic disconnection in case of abnormal grid voltage
Power failure protection: Responding to sudden power failure to ensure the safety of the equipment
Temperature monitoring: prevent equipment damage caused by overheating
Protection Advantage:
Response time <20ms, far exceeding mechanical switches
Programmable protection parameters, adapting to different equipment needs
Failure self-diagnosis function, improve maintenance efficiency

3.Intelligent monitoring and remote control system

As the core component of the intelligent charging system, the automatic charging relay has a strong data interaction capability:
Monitoring function:
Real-time collection of key parameters such as charging current, voltage, temperature, etc.
Data sampling accuracy of ± 0.5%, to ensure the accuracy of monitoring
Instant alarm for abnormal status, supporting a hierarchical warning mechanism.
Control features:
Support 4G/5G/WiFi and other communication protocols.
Remote start/stop, mode switching, and other operations can be realized.
Cooperate withthe cloud platform to realize charging pile cluster management.
Open API interface for system integration
Through these three core functions, the automatic charging relay not only guarantees the safety and reliability of the charging process but also promotes the development of the charging infrastructure in the direction of intelligence and networking, and provides key technical support for power management in the new energy era.

Automatic charging relay working principle

Automatic charging relay is a kind of intelligent control device based on electromagnetic principles, and its core function is to realize the automatic on-off control of the charging circuit. The following is its detailed working principle:

1.Charging start-up phase

When the charging process starts
The control system applies a working voltage to the electromagnetic coil of the relay, which generates a strong electromagnetic field after being energized. The electromagnetic force overcomes the spring resistance and attracts the armature to act, and the movable and static contacts are closed reliably to form the charging circuit.

2.Charging Holding Stage

In the normal charging process
The electromagnetic coil is continuously energized to maintain the magnetic field, and the contacts are kept closed to ensure stable current transmission and the control system monitors the charging parameters (voltage, current, temperature, etc.) in real time.

3.Charging termination stage

When the charging completion signal is detected
The control system cuts off the power supply to the electromagnetic coil, the electromagnetic field disappears rapidly, the spring mechanism pushes the armature to reset, the movable contact and the static contact are separated quickly, and the circuit is completely disconnected.
This intelligent on-off control not only ensures the safety and reliability of the charging process but also effectively extends the service life of the battery, which is an indispensable key component in modern charging equipment.

Advantages and disadvantages of automatic charging relays

1.Advantages

Automatic control: can automatically detect the battery status and cut off the charging circuit, reducing manual intervention.
Battery protection: prevent overcharging and over-discharging, prolong the service life of the battery.
Safe and reliable: reduce safety accidents caused by improper charging.

2.Disadvantages

Higher cost: Compared with ordinary chargers, automatic charging relays increase the complexity and cost of the system.
Complex maintenance: requires regular inspection and maintenance of the relay and its control system.

‌Application of automatic charging relays on PCBs

1.Expanding the control range
Automatic charging relay can control the data signal through multiple points of contact, to ensure that a certain value, you can press the point of contact group of different methods, in addition to replacing, opening, and closing, connecting multiple circuits.
2.Increase load capacity
Automatic charging relay can use a very small amount of control, control a large output power circuit. For example, dexterous relays and intermediate relays can control high-power supply circuits with a small amount of control.
3.Integrated Data Signal
When multiple control data signals are input to a multi-winding relay in the required manner, it can undergo comparative integrated type processing to ensure the desired control effect.
Automation control: Automatic charging relays can be formed with other electrical products to operate program control lines for automation control. For example, relays on protection equipment can be combined with other electrical products to form an operation program control line for automated control operation.

‌Automatic charging relay in PCB design considerations

1.Select the right relay model
Select the right 5V relay module according to load capacity, response time, and life time, etc. 5V relay modules are widely used in automation control, smart home, industrial production line, and other fields due to their moderate voltage and direct compatibility with most microcontrollers.
2.Design the control circuit of the relay
The control circuit of a relay involves signal input, processing, and output. The input side can receive signals from various control devices, such as the GPIO output of the microcontroller, sensor signals, and so on. The outputs are then connected to the load circuit being controlled. The control terminal is usually part of the relay coil. When the control terminal is driven by an appropriate voltage, the coil generates a magnetic field, which in turn causes the relay to operate.
3.Optimize solenoid coil design
The solenoid coil is one of the core components of the relay, and its design needs to ensure that the electromagnetic force generated by the coil when it is energized is sufficient to drive the mechanical structure while minimizing energy consumption.
Ensure a reliable electrical connection: In PCB design, contacts are connected to various parts of the circuit through holes in the PCB board, a connection that is not only convenient but also provides a reliable electrical connection.

Application areas of automatic charging relay

1.New Energy Vehicles
In new energy vehicles, the automatic charging relay is mainly used to control the switching of the battery pack, motor, charging port, and other components. Specifically, it can control the on-off of the circuit, to realize the functions of starting, accelerating, decelerating, and stopping of the vehicle. In addition, when the vehicle is charging, the automatic charging relay can also control the switch of the charging port to ensure the safety and stability of the charging process.
2.Charging gun and charging post
Relays also play an important role in charging guns and charging piles. For example, Hongfa’s HF161F relay is widely used in charging guns and charging piles to control the on-off of the circuit. Another Hongfa HF179F relay is used to control the on-off of the circuit to ensure the safe operation of the charging equipment. In addition, Aohi’s 3.5/4kW intelligent charging and discharging guns also have built-in relays to provide a variety of protection functions, such as over-voltage protection and over-current protection.
3.Solar Power Generation System
In a solar power system, the automatic charging relay can control the switch of the solar panel and protect the circuit to prevent the panel from being damaged by too much or too little current. At the same time, the relay can also be used in conjunction with the solar controller to realize the intelligent management of the solar power generation system.

Frequently asked questions about automatic charging relays

1.Relay fails to engage (does not work)
Possible causes:
Insufficient supply voltage (coil voltage does not match).
Control signal failure (e.g. microcontroller does not output a signal).
The relay coil is broken or aging.
Poor wire contact (e.g., loose terminals, oxidation).
Solution:
Check whether the rated voltage of the coil matches the input (e.g,. 12V/24V).
Measure the control signal with a multimeter to see if it is normal.
Test the coil on/off, infinite resistance needs to be replaced.
Clean the terminals and retighten the connecting wires.
2.Relay is engaged but charging abnormally
Possible causes:
Contact resistance is too high due to contact ablation or oxidation.
Load current exceeds relay rating (e.g. battery short circuit or overload).
Charging control logic error (such as voltage detection is not allowed).
Solution:
Check if the contacts are blackened or pitted and replace if necessary.
Confirm the load current and select a higher specification relay (e.g. 30A instead of 10A).
Check voltage sensor or charge controller settings.
3.Relay continues to engage/fails to disengage
Possible causes:
Control signal stuck (e.g. program bug or relay drive circuit failure).
Contacts sticking (high current leads to fusion welding).
Mechanical structure stuck (dust or wear).
Solution:
Disconnect the control signal and observe if it releases; check the drive transistor / MOSFET.
Replace the relay and troubleshoot the cause of the overcurrent (e.g., reverse battery).
Clean or replace mechanical parts.
4.Severe relay heating
Possible causes:
Increased resistance due to poor contact.
Prolonged overload operation.
Poor heat dissipation conditions (e.g., confined space).
Solution:
Measure the contact voltage drop and replace it when abnormally hot.
Increase relay current margin (e.g. use automotive grade relays).
Improve ventilation or install a heat sink.
5.Coil burnout
Possible causes:
Input voltage is too high (e.g. 24V mistakenly connected to 12V coil).
Coil short circuit (insulation broken).
Overheating due to frequent switching.
Solution:
Check the voltage specification and add an over-voltage protection circuit (e.g. voltage regulator diode).
Replace the relay and check the wiring insulation.
Reduce the switching frequency or select a solid-state relay (SSR).
6.Noise or vibration
Possible causes:
Coil voltage fluctuation (e.g., unstable PWM signal).
Installation is not secure.
AC relay used for DC scenario (or vice versa).
Solution:
Ensure that the voltage is smooth and add filter capacitors if necessary.
Reinforce the mounting bracket or use anti-vibration pads.
Select a DC-specific relay (DC coil).
7.Malfunction (random on-off)
Possible causes:
Electromagnetic interference (e.g., nearby motor, inverter).
Control signal interference (e.g,. long wires not shielded).
High ambient humidity leads to leakage.
Solution:
Connect the relay coil in parallel with a current-continuing diode.
Use shielded wires and keep away from interference sources.
Select the moisture-proof model or do a triple-proof treatment.