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H1: Selecting a Power Supply for Industrial Automation: 24V Systems
URL: /selecting-power-supply-industrial-automation-24v/
Meta Description: Engineering guide to selecting 24V power supplies for industrial automation equipment. PLC power requirements, servo drive considerations, cable voltage drop, and reliability specifications for OEMs.
Category: Application Guide
Tags: industrial automation, 24V power supply, PLC system, servo drive, control cabinet, automation OEM, desktop adapter industrial
Featured Image Concept: Desktop power adapter connected to a PLC/HMI system in an industrial control cabinet, clean professional shot
Word Count Target: 1800 words
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INTRO
Industrial automation systems operate 24 hours a day, 365 days a year, in environments where a power supply failure directly translates to production downtime. The 24V DC bus that powers PLC racks, HMI panels, sensor networks, and actuator controllers must deliver stable, reliable power across the system’s full operating temperature range and service life.
This guide covers the specific considerations for selecting 24V power supplies for industrial automation equipment: load profiling for mixed PLC/sensor/actuator systems, inrush current management for capacitive and inductive loads, voltage drop over cable runs in large installations, and the reliability metrics that differentiate industrial-grade supplies from commercial alternatives.
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H2: How Do You Profile the 24V Load of a Typical Automation System?
A modern industrial automation system draws power from the 24V DC bus through multiple device types, each with distinct current profiles. Understanding the aggregate load is the foundation of power supply selection.
Typical 24V load composition for a small-to-medium automation cell:
– PLC CPU unit: 0.3–0.8A (300–800mA) depending on processor speed and integrated I/O
– Digital input modules (16-channel): 0.05–0.15A each, depending on input type (sinking/sourcing)
– Digital output modules (16-channel): 0.1–0.5A each, plus connected load current
– Analog input/output modules: 0.1–0.3A each
– HMI panel (7–10 inch): 0.5–1.2A depending on backlight brightness and touch interface
– Proximity sensors (inductive/capacitive): 0.01–0.03A each
– Solenoid valves: 0.1–0.5A each during activation, holding current 30–50% lower
– Small DC motor or actuator: 0.5–3.0A depending on size and load
A practical example: a system with one PLC rack (0.8A), 4 input modules (0.4A total), 3 output modules (2.0A total with load), one HMI (0.8A), 20 proximity sensors (0.4A total), and 8 solenoid valves (2.4A peak) has a continuous load of approximately 6.8A. With 30% margin, the recommended power supply rating is 8.9A or approximately 215W at 24V.
Why This Matters
▸ The total 24V load is often 2–3× higher than initially estimated because field devices (sensors, valves) are frequently omitted from the initial power budget.
▸ Output modules draw current based on the connected field loads, not just the module’s own electronics—the load current must be itemized per channel.
▸ Adding margin at the specification stage avoids costly field retrofits when the system expands. A 30% margin is industry standard for industrial automation.
What OEMs Should Do Now
▸ Create a load inventory table with columns: device type, quantity, unit current, total current, and notes on transient or inrush behavior.
▸ Distinguish between continuous current and peak/transient current. The power supply must handle both—continuous rating for steady state, peak capability for transients (typically 120–150% of rated for 1–5 seconds).
▸ Verify the startup sequence: do all modules and field devices power up simultaneously, or is there a sequence that reduces peak inrush?
Mini Q&A
Q: Should I include the PLC backplane power in the adapter budget?
A: PLC backplane power is typically supplied by the PLC’s own power supply module (usually integrated or a dedicated backplane supply). External 24V adapters power the input modules’ load side, output modules’ load side, field devices, and HMI. Check the PLC manufacturer’s power distribution specification.
Q: How much inrush current does a typical automation system draw at power-on?
A: A system with multiple output modules driving capacitive loads (solenoids) can draw 150–300% of rated current for 10–100ms during power-on. The power supply must have sufficient peak current capacity or the system should implement startup sequencing.
Useful Links
→ /industrial-automation/ (Application page: Industrial Automation Power Solutions)
→ /how-to-choose-industrial-power-adapter/ (Related article: How to Choose the Right Power Adapter)
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H2: 24V vs 48V Architecture Decisions in Composite Automation Systems
While the 24V DC standard is dominant in industrial automation, many automation cells also include servo drives, spindle motors, or high-power actuators that operate at 48V or higher. The decision to use a single 48V bus with DC-DC converters for 24V loads, or separate 24V and 48V power supplies, has engineering trade-offs.
A single 48V adapter at 500W delivers 10.4A, compared to 20.8A for a 24V system at the same power. The reduced current at 48V means:
– Cable gauge requirements are smaller: 14 AWG is adequate for 10A at 48V over 30m, while 24V at 20A requires 10 AWG for the same distance
– Voltage drop at 30m is 1.2V (2.5% loss) at 48V 10A versus 2.4V (10% loss) at 24V 20A
– I²R losses in connectors and cabling are reduced by approximately 75%
However, adding a 48V-to-24V DC-DC converter adds $15–40 per converter, reduces overall system efficiency by 3–8%, and introduces additional failure points. For systems where most loads are 24V, separate supplies are typically more reliable and cost-effective.
Why This Matters
▸ 48V power distribution is preferred for systems with long cable runs (>20m) or high total power (>300W continuous).
▸ DC-DC converters must be rated for the same industrial temperature range and reliability as the main power supply—an undervalued converter can become the system’s weakest component.
▸ Some servo drives accept 24–48V DC input and draw more current at lower voltage, meaning a 48V bus actually reduces total cable ampacity requirements.
What OEMs Should Do Now
▸ Map all system components by voltage requirement. Count 24V loads separately from 48V loads. If 48V loads exceed 50% of total power, evaluate a single 48V distribution strategy.
▸ For mixed-voltage systems, calculate the breakeven point: if the cost of DC-DC converters plus their inefficiency exceeds the cost of separate 24V and 48V adapters, use separate supplies.
▸ Consider future expansion—a 48V bus can power higher-wattage components without rewiring, while a 24V system may require additional power supplies as loads increase.
Mini Q&A
Q: Can I use a 48V power adapter to charge a 24V battery backup system?
A: No, directly. Charging a 24V battery requires a charger circuit with appropriate voltage and current limits (typically 27.6V for lead-acid float charging). A separate 24V charger or a DC-DC converter with charging profile is required.
Q: What is the maximum power typically available from a single 24V DIN rail power supply?
A: Single-unit DIN rail supplies commonly range from 60W to 480W (2.5A to 20A at 24V). For higher power, industry practice is to use multiple supplies in parallel or a single larger 48V supply with DC-DC distribution.
Useful Links
→ /industrial-automation/ (Application page: Industrial Automation Power Solutions)
→ /products/desktop-adapters/ (Product page: Desktop Adapter Series)
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H2: What Cable and Voltage Drop Considerations Apply to 24V Distribution?
Voltage drop over DC distribution cabling is a common source of field issues in industrial automation systems. At 24V, a 10% voltage drop (2.4V) can cause sensitive equipment to malfunction or reset, while an overcurrent condition may not be detected due to the higher wire resistance.
Voltage drop at 24V:
– 24V, 5A, 14 AWG, 30m one-way: 2.1V drop (8.7%)
– 24V, 5A, 12 AWG, 50m one-way: 1.6V drop (6.7%)
– 24V, 10A, 10 AWG, 30m one-way: 1.9V drop (7.9%)
– 24V, 10A, 12 AWG, 20m one-way: 1.3V drop (5.4%)
Most industrial equipment operates within 24V ±10% (21.6V to 26.4V). Some sensitive devices require 24V ±5% (22.8V to 25.2V). The voltage at the device terminals should be measured or calculated, not assumed equal to the power supply output voltage.
For long runs or high-current branches, using multiple power supplies at strategic cabinet locations (distributed power architecture) is more effective than increasing wire gauge on a single central supply.
Why This Matters
▸ A 24V system with voltage drop exceeding 10% causes intermittent resets and erratic sensor readings that are extremely difficult to diagnose—field service technicians may replace components unnecessarily.
▸ Voltage drop increases with load current (I²R loss), meaning the worst-case voltage is at maximum load, not during the commissioning test at light load.
▸ Distributed power architecture (local 24V supplies at each cabinet or machine section) eliminates long-distance voltage drop issues and simplifies cable routing.
What OEMs Should Do Now
▸ Calculate voltage drop for the longest cable run at full load current using the formula V_drop = 2 × L × R_cable × I (where R_cable is resistance per meter for the selected gauge).
▸ If calculated voltage drop exceeds 5%, either increase wire gauge by 2 AWG, shorten the run by repositioning the supply, or add a local power supply.
▸ Specify 24V power supplies with remote sense capability for long cable runs (>20m) to compensate for line losses at the power supply output.
Mini Q&A
Q: What is remote sensing on a 24V power supply and when should I use it?
A: Remote sensing adjusts the power supply output voltage to compensate for cable voltage drop by measuring voltage at the load (sense wires) rather than at the supply terminals. It’s recommended for runs longer than 20m or where ±5% regulation is required at the device.
Q: How do I calculate the correct wire gauge for a 24V 10A run at 25m?
A: Using the formula V_drop = 2 × 25m × R × 10A: for 3% drop target (0.72V), R must be ≤0.00144Ω/m. 12 AWG (0.0052Ω/m) gives 2.6V drop—too high. 10 AWG (0.0033Ω/m) gives 1.65V drop (6.9%)—borderline. 8 AWG (0.0021Ω/m) gives 1.05V drop (4.4%)—acceptable. This illustrates why distributed power is often more practical.
Useful Links
→ /products/desktop-adapters/ (Product page: Desktop Adapter Series)
→ /how-to-choose-industrial-power-adapter/ (Related article: How to Choose the Right Power Adapter)
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[In-Content CTA Block]
Designing a 24V automation system? Contact our engineering team for power supply sizing assistance and distributed power architecture recommendations.
→ /contact/
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H2: What Protection and Reliability Features Are Critical for Industrial 24V Supplies?
Industrial automation power supplies should include protection features beyond basic overcurrent limiting. The specific protection functions and their thresholds directly affect system uptime and maintenance response.
Required protection features:
– Overcurrent protection (OCP): Trip at 105–150% of rated current. Automatic recovery (hiccup mode) preferred for transient loads
– Overvoltage protection (OVP): Typically activates at 28–30V for 24V outputs. Latching or auto-recovery depends on application criticality
– Overtemperature protection (OTP): Thermal shutdown typically at 85–100°C internal temperature. Auto-recovery when temperature drops below threshold
– Reverse polarity protection: External diode or MOSFET-based. Critical for field-wired systems where polarity mistakes occur during maintenance
– Short-circuit protection: Immediate current limiting with low power dissipation during fault
Reliability indicators for industrial 24V supplies:
– MTBF: ≥100,000 hours at 40°C (MIL-HDBK-217F methodology)
– Capacitor technology: 105°C rated, ≥5,000 hour lifetime at rated temperature
– Full-load burn-in: 100% of units tested at rated load at elevated temperature (40°C minimum, 4+ hours)
– Surge protection: IEC 61000-4-5 Level 3 (±2kV line-to-line, ±4kV line-to-ground)
Why This Matters
▸ An automation cell with a 24V supply lacking OVP can destroy $5,000–50,000 of PLC and HMI equipment if the supply fails in an overvoltage condition.
▸ MTBF is a statistical projection, not a guarantee—but a supply with published MTBF data has demonstrably undergone reliability engineering evaluation.
▸ Burn-in testing catches infant mortality failures (typically the first 100–500 hours of operation) at the factory rather than in the field.
What OEMs Should Do Now
▸ Create a protection function specification table for your 24V supply, listing each protection type, the required threshold, and the response behavior (latching vs. auto-recovery).
▸ Request MTBF data calculated per MIL-HDBK-217F with the calculation temperature specified (MTBF at 25°C is not useful—request 40°C or your operating temperature).
▸ Verify that the manufacturer performs 100% burn-in testing on every unit and can provide the test specification (load percentage, duration, temperature, pass/fail criteria).
Mini Q&A
Q: Should the overvoltage protection latch or auto-recover for an industrial 24V supply?
A: Latching OVP is preferred for critical systems because it prevents the supply from cycling on and off into an overvoltage fault, which can cause unpredictable system behavior. Auto-recovery OVP is acceptable for non-critical loads. The choice should align with the system’s safety risk assessment.
Q: What surge protection level is adequate for factory floor installations?
A: IEC 61000-4-5 Level 3 (±2kV line-to-line, ±4kV line-to-ground) is the minimum for fixed industrial installations with separate power distribution. Level 4 (±4kV/±4kV) is recommended for outdoor or remote equipment subject to lightning-induced surges.
Useful Links
→ /power-supply-thermal-management-design-considerations/ (Related article: Power Supply Thermal Management)
→ /contact/ (CTA: Discuss Your Requirements)
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H2: Redundancy and Parallel Operation Considerations
Critical automation systems that cannot tolerate downtime may require redundant power supply configurations. The two primary approaches are 1+1 redundancy (two supplies, each capable of handling the full load) and N+1 redundancy (N+1 supplies sharing the load, with any one failure covered by the remaining units).
For 1+1 redundancy at 24V 10A: two 24V 10A supplies are connected through decoupling diodes or an OR-ing module. Each supply independently powers the full load. If one fails, the other seamlessly takes over. The OR-ing diodes introduce approximately 0.5V forward voltage drop, meaning the load sees approximately 23.5V instead of 24V. Some supplies include integral OR-ing MOSFETs with lower forward drop (0.1–0.2V).
Parallel operation (N+1) requires supplies with active current sharing capability. Supplies connected in parallel without active sharing may not share current equally—one supply may deliver 80% of the load while the other delivers 20%, defeating the redundancy purpose. Current sharing accuracy of ±10% is typical for supplies with active sharing.
Why This Matters
▸ Without decoupling (OR-ing) diodes, a failed supply’s output shorts can drag down the entire 24V bus, causing system failure despite the redundant supply.
▸ Active current sharing (±10% accuracy) typically requires a dedicated current-share bus connection between supplies and is only available on specified parallel-capable models.
▸ Redundant configurations increase system cost by 100% (1+1) to 25–50% (N+1) and should be justified by the cost of downtime: if 1 hour of downtime costs >$10,000, redundancy is likely justified.
What OEMs Should Do Now
▸ Calculate the cost of downtime per hour for your automation system. If it exceeds $5,000/hour, evaluate redundant power architecture.
▸ If using redundant supplies, specify OR-ing diodes or parallel-capable supplies with current sharing. Do not simply wire two standard supplies in parallel through a Y-cable—this provides no protection against output short failures.
▸ Consider a power supply with an integrated alarm/status relay that indicates AC input, DC output, and overtemperature status for remote monitoring in the PLC system.
Mini Q&A
Q: Can I use standard 24V desktop adapters in a redundant configuration without OR-ing modules?
A: No. Without decoupling, a failed supply’s shorted output would pull down the entire bus. OR-ing modules (external or integrated) are mandatory for any redundant power architecture.
Q: What is the typical voltage drop across an OR-ing diode at 10A?
A: A Schottky OR-ing diode drops approximately 0.4–0.6V at 10A, resulting in a 23.4–23.6V bus voltage from a 24V supply. MOSFET-based ideal diode modules drop 0.05–0.2V. The trade-off is cost—MOSFET OR-ing modules cost $15–50 more than diode-based solutions.
Useful Links
→ /products/desktop-adapters/ (Product page: Desktop Adapter Series)
→ /contact/ (CTA: Discuss Your Requirements)
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CONCLUSION
Selecting a 24V power supply for industrial automation requires a systematic approach: accurate load profiling of all PLC, I/O, HMI, and field devices, voltage drop calculation for cable runs, specifying appropriate protection features, and evaluating redundancy requirements based on downtime cost. The industrial environment—extended operating hours, elevated ambient temperatures, and electrical noise—demands power supplies designed for continuous industrial service rather than commercial or consumer equipment.
For automation OEMs and system integrators, YHYadapter offers 24V and 48V desktop adapters from 12W to 300W with aluminum-case construction for improved thermal performance, 100% burn-in tested, with UL 62368-1, CE, FCC, and additional certifications available by model.
[Button: “Discuss Your Automation Power Requirements →” /contact/]
[Secondary: “View Industrial Desktop Adapter Series →” /products/desktop-adapters/]
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INTERNAL LINKS:
– Application Page: /industrial-automation/
– Product Page: /products/desktop-adapters/
– Related Article: /how-to-choose-industrial-power-adapter/
– Related Article: /power-supply-thermal-management-design-considerations/
– CTA: /contact/
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