Case Study: 120W AC-DC Power Adapter in Siemens S7-1200 PLC Systems

Practical Tips for PLC Applications

Ventilation and Placement
- Place adapters in ventilated enclosures to reduce heat and prevent derating
Planning for Transients
- Include power margin for inrush currents from relays, motors, and sensors
Cable Selection
- Use proper gauge cables to minimize voltage drop and maintain effective power margin
Multi-Stage Distribution
- AC-DC adapter powers PLC bus; downstream DC-DC converters can supply sub-modules if required
Temperature and Aging Considerations
- Monitor environmental conditions; derating curves should be considered
- Long-term component aging reduces available output power, reinforcing the need for adequate margin

Conclusion

Selecting the right 120W AC-DC adapter is critical for industrial PLC applications. By combining:

Accurate peak load estimation
Recommended industrial margin
24V/5A industrial AC-DC adapter

… engineers can ensure reliable, expandable, and efficient PLC systems.

Next Steps:

Visit our 120W AC‑DC industrial Power Adapter page

Project Overview

An industrial automation system integrator was developing a PLC-based control system using Siemens S7-1200 controllers for machinery and manufacturing applications.

The system integrated multiple components including CPU modules, digital I/O modules, analog modules, communication modules, and expansion units. Reliable DC power was essential to ensure stable control operation, prevent unexpected downtime, and support future system expansion.

Based on the system load analysis, XJK Power provided a 24V DC / 5A (120W) industrial AC-DC power adapter solution designed for PLC automation applications.

The project focused on:

Providing stable 24V DC power for PLC systems
Maintaining sufficient power margin for peak loads
Supporting startup current demands from connected devices
Improving reliability in industrial environments
Allowing future system expansion

Component	Quantity	Typical Power Consumption
Siemens S7‑1200 CPU 1214C	1	~5 W
16-Point Digital I/O Module	2	~20 W
8-Point Analog I/O Module	1	~15 W
Ethernet Communication Module	1	~8 W
Expansion I/O Modules	2	~24 W
Total Estimated Peak Load	—	~72 W

Project Type	Industrial Automation Power Solution
Application	PLC Control System
Industry	Industrial Automation & Manufacturing
PLC Platform	Siemens S7-1200
Power Requirement	120W
Output Specification	24V DC / 5A
Power Supply Type	Industrial AC-DC Power Adapter
Input Voltage	90–264VAC
Typical Load	Approximately 72W
Recommended Power Margin	30–40%
Operating Environment	Industrial Control Cabinets
Protection Features	OVP / OCP / SCP
Safety Standards	CE / UL / IEC EN 62368 Support

Typical Power Architecture

Customer Challenge

The customer required a reliable power solution for an industrial PLC control system operating in manufacturing environments.

Several engineering challenges needed to be addressed.

1. Stable Power Supply for PLC and Expansion Modules

The control system consisted of multiple components:

Siemens S7-1200 CPU 1214C
Digital input/output modules
Analog modules
Communication modules
Expansion I/O units

The estimated system power demand was:

Component	Typical Power Consumption
Siemens S7-1200 CPU	~5W
Digital I/O Modules	~20W
Analog I/O Module	~15W
Communication Module	~8W
Expansion Modules	~24W
Total Peak Load	~72W

The customer required a power supply that could maintain stable output while supporting all connected modules.

2. Insufficient Power Margin Risks

In industrial automation systems, selecting a power supply based only on nominal load can create reliability risks.

The system needed additional margin for:

Startup current
Relay and sensor activation
Future expansion modules
Component aging
Temperature-related output reduction

The customer required a solution that could operate below maximum capacity during normal operation.

3. Industrial Environment Reliability

PLC systems are commonly installed inside control cabinets where conditions may include:

Elevated temperature
Long operating hours
Limited ventilation
Continuous operation

The power supply needed reliable thermal performance and stable output under industrial conditions.

4. Voltage Stability Requirements

PLC CPUs, communication modules, and I/O devices require stable 24V DC power.

Voltage fluctuation or excessive ripple could potentially cause:

Communication errors
PLC faults
Unexpected system interruptions

The customer required low ripple and regulated DC output.

5. Future System Expansion

Industrial systems are often upgraded after initial deployment.

The power solution needed enough capacity margin to support:

Additional I/O modules
Extra sensors
Communication devices

without replacing the power supply.

XJK Engineering Solution

24V 5A (120W) Industrial AC-DC Power Adapter

Based on the PLC system power analysis, XJK Power recommended a 24V DC / 5A 120W industrial AC-DC power adapter.

The selected power rating provided sufficient capacity for current requirements while maintaining a practical reliability margin.

1. Optimized Power Margin Design

The PLC system peak load was approximately:

72W

Recommended industrial margin:

30–40%

Required power:

72W × 1.3 ≈ 94W

The selected:

120W AC-DC adapter

provided approximately:

48W additional capacity

This margin supported:

Startup surges
Temperature variation
Future expansion
Long-term reliability

2. Stable 24V DC Output

The adapter provided:

24V DC output
5A rated current
Low ripple performance
Stable voltage regulation

This ensured reliable operation of:

PLC CPU
I/O modules
Communication devices
Industrial sensors

3. Industrial Safety and Reliability Design

The power solution was designed for industrial applications with:

Wide input voltage range (90–264VAC)
Industrial protection features
Reliable component selection
OVP / OCP / SCP protection

4. Improved Thermal Performance

High conversion efficiency helped reduce:

Internal power losses
Heat generation
Thermal stress

This improved reliability in enclosed industrial cabinets.

5. Flexible System Integration

The adapter supported integration requirements including:

Industrial control cabinets
Automation equipment
PLC-based systems
OEM machinery

Parameter	Specification	Description
Output Power	120W	Sufficient for PLC system peak load + margin
Output Voltage	24V DC	Standard industrial PLC voltage
Output Current	5A	Corresponding to 120W full load
Input Voltage	90–264VAC	Suitable for global industrial applications
Type	Enclosed Industrial AC-DC Adapter	Stable and dust-proof
Operating Temperature	-20°C ~ +60°C	No derating in high temperature
Efficiency	>88% @ full load	Reduces heat, extends lifespan
Certifications	UL, CE, IEC/EN 62368, RoHS	Industrial safety standards
Output Ripple	<1%	High stability for critical loads

How We Develop a Custom Power Supply

Our engineering process helps device manufacturers move efficiently from requirement definition to production-ready power solutions.

Step1
Requirement
Review

Review voltage, current, connector, plug type, installation environment, and medical device requirements.

Step2
Engineering
Evaluation

Electrical feasibility assessment, connector matching, and product configuration planning.

Step3
Prototype
Development

Prototype recommendation or customized sample preparation based on project requirements.

Step4
Compliance &
Validation

Review safety expectations, EMC considerations, and application-specific requirements.

Step5
Sample
Approval

Functional verification and customer-side evaluation before production.

Step6
Production &
Delivery

OEM production support for customized healthcare power solutions.

Technical Design Considerations

During PLC power system design, several engineering factors were considered.

1. Power Margin Calculation

Industrial power supply selection should consider more than rated load.

The calculation included:

Maximum steady-state load
Startup current
Environmental conditions
Future expansion requirements

Maintaining 30–40% margin improves system reliability.

Calculating Power Margin

Step 1: Identify Maximum Load

Estimated Peak Load = 72 W

Step 2: Apply Recommended Industrial Margin

Recommended margin: 30–40%

Required Power ≈ 72 W × 1.3 ≈ 94 W

Step 3: Select Suitable Power Adapter

Chosen adapter: 24V / 5A 120W AC‑DC Industrial Adapter

Provides margin for:
- Startup surges
- Temperature derating
- Expansion modules
- Long-term component aging

Power Margin Visual:

Peak load: 72W

Adapter rating: 120W

Margin: ~48W (~40%), ensuring safe operation under worst-case conditions

2. Transient Load Handling

PLC systems may experience temporary power increases caused by:

Relay activation
Sensors
Communication modules
Expansion devices

The power supply must respond without significant voltage drop.

3. Thermal Management

Industrial cabinets often have limited airflow.

Design considerations included:

Efficiency
Temperature rise
Installation location
Ventilation

4. Cable and Voltage Drop Considerations

For 24V systems, cable selection is important because voltage drop increases with:

Longer cable distance
Higher current
Smaller conductor size

Proper cable sizing helps maintain effective power margin.

5. Long-Term Reliability

Continuous industrial operation requires consideration of:

Component aging
Operating temperature
Load percentage
Protection mechanisms

Operating below maximum capacity extends service reliability.

Project Result

After implementing the 120W industrial AC-DC power adapter solution, the customer achieved:

Stable PLC System Operation

The Siemens S7-1200 control system operated reliably with stable 24V DC power supply.

Improved System Reliability

The additional power margin reduced risks caused by:

Peak load events
Startup surges
Voltage instability

Simplified Future Expansion

The reserved power capacity allowed additional modules and peripherals to be added without replacing the power supply.

Reduced Downtime Risk

Stable power delivery helped prevent unexpected PLC interruptions and improved overall equipment availability.

Key Technical Highlights

24V DC / 5A output
120W industrial AC-DC adapter
Designed for PLC automation applications
Wide input voltage range 90–264VAC
Low ripple output
88% efficiency
OVP / OCP / SCP protection
CE / UL / IEC EN 62368 support
OEM customization available

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FAQ

1. Why use a 120W power adapter for Siemens S7-1200 PLC systems?

A 120W adapter provides sufficient margin for PLC modules, expansion units, startup surges, and future system upgrades.

2. How much power margin should a PLC system have?

For industrial applications, a 30–40% power margin above peak load is commonly recommended.

3. Can one 120W adapter power multiple PLC modules?

Yes. Multiple PLC modules can be powered as long as the total peak load remains within the adapter capacity with sufficient margin.

4. Why is 24V DC commonly used in industrial automation?

24V DC is widely adopted because it provides a balance between safety, efficiency, and compatibility with industrial sensors and control devices.

5. Can the industrial adapter be customized?

Yes. XJK Power supports customization of output voltage, connectors, cables, mechanical design, and application requirements.

Need a Reliable 24V Industrial Power Supply for Your Automation System?

Industrial automation systems require stable power, sufficient margin, and long-term reliability.

XJK Power provides customized industrial AC-DC power solutions for:

PLC systems
Automation equipment
Control cabinets
Manufacturing machinery

Contact our engineering team to discuss your industrial power requirements.

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