When Rated Power Isn’t Enough

In secondary systems such as protection and control, station communication, and industrial automation, DC switch-mode power supplies are standard. Yet engineers often encounter an odd problem: the load power is below the supply’s rating, but the unit still trips into overcurrent or overload protection at startup.

The issue isn’t always poor quality—it’s usually poor matching. Subtle transient conditions can create “invisible overloads.” This article explains the real causes and selection principles behind stable power-supply design.

Learn more about ODES’s PSMU Series power supplies and other DC system solutions at www.odes-electric.com

1. Common Causes of “False” Overload Protection

1.1 Inrush current and short-term current peaks

Capacitive loads, devices with motors, or large input capacitors can draw multiple times the steady-state current during startup. If the power supply’s surge-current capability or current-limiting behavior doesn’t match the load, protection trips before steady operation begins.

1.2 Power factor and current waveform distortion

Loads with poor PF or high harmonic content can raise RMS current and apparent power even when average power is within limits. This leads to excessive heating and unstable control loops, triggering internal thermal or overload protection.

1.3 Voltage and current mismatch or input sag

Power supply “rating” is not just about watts. Output voltage and current must align with the load’s true operating parameters. On the input side, operating near AC110 V can raise current stress on components as the converter compensates, resulting in overheat or undervoltage shutdown.

2. Engineering-Based Selection Guidelines

Step 1 – Provide 20–50% Power Margin

Choose a supply rated at 1.2–1.5× the maximum load power. Confirm that the short-term overload and current-limit curve can accommodate inrush peaks, not just the nominal load.

Step 2 – Match Output Class and Input Conditions

• Output: Verify nominal voltage and confirm the required current margin and voltage regulation tolerance.

• Input: Prefer supplies with 85–265 VAC / 88–370 VDC wide-range input for better grid compatibility and tolerance to low-voltage operation.

3. The ODES PSMU Series in Real Applications

Scenario A – 24 V Systems for Protection, Control, and Communication

Load characteristics: Distributed circuits, ripple-sensitive devices, continuous operation. Recommendation: PSMU 24 V models (available in 30 W, 72 W, 120 W, 240 W, and 480 W). DIN-rail mounting supports standardized cabinet integration and effective heat dissipation.

Scenario B – 48 V Systems for Switches, Gateways, and I/O Modules

Load characteristics: Communication hardware with transient surges and power-loss sensitivity. Recommendation: PSMU 48 V models (72–480 W). Evaluate startup surge and short-term overload capacity to ensure bus stability.

Scenario C – Compact or Board-Level Installations (24 V / 48 V)

Load characteristics: Space-constrained systems requiring PCB or enclosure integration. Recommendation: PSMD board-mount versions with full overload, overvoltage, and short-circuit protection—ideal for devices not suited for DIN-rail mounting.

4. Why Engineers Choose the ODES PSMU Series

• Comprehensive coverage: 24 V and 48 V outputs across multiple power ratings (30–480 W) meet everything from low-power control loads to mid-range communication equipment.

• Strong input tolerance: Wide-range 85–265 VAC / 88–370 VDC input for diverse and unstable grid conditions.

• High reliability: High efficiency, full overload/overvoltage/short-circuit protection, EMC Level IV, −40 °C to +70 °C temperature range, DIN-rail installation.

• Proven field performance: More than 20 years of reliability data with top-tier system integrators and utilities.

A supply that appears correctly sized on paper can still fail in practice if transient conditions or voltage environment are ignored. Proper power-margin design and surge-current matching are as important as rated wattage.

The ODES PSMU Series offers an engineering-grade solution for stable, resilient DC power—combining wide input tolerance, strong protection, and a proven track record in secondary systems worldwide.

Avoid false overloads and unpredictable startups.

• Request the PSMU selection guide and wiring examples by sharing your voltage (24 V / 48 V), load current, and ambient temperature.

• Consult our engineers for surge, load, and heat design verification.

• Power your systems with reliability designed and proven in the field.

Contact: 📩 tonyzhang@odes-electric.com

Or visit: www.odes-electric.com

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