28.06.2026 by Viktor Siebert
Power-One SPM3D2K Power Supply. When the 24 V Output Collapses Under Load
A Small Power Supply with a Major ImpactA machine shutdown is not always caused by a servo drive or frequency inverter. In many cases, what appears to be a simple component can bring an entire production process to a standstill. That was exactly the case with this repair of a Power-One SPM3D2K DC Power Supply.
The industrial customer reported a fault that was initially difficult to reproduce. After power-up, the power supply operated completely normally. The 24 V output remained stable, and all connected control components were supplied correctly. However, after a certain operating time and under increasing load, the output voltage suddenly collapsed. This resulted in intermittent machine failures and unpredictable production interruptions.
Since the fault did not occur immediately after startup or during no-load operation, it was already clear during the initial inspection that the problem was temperature or load dependent. These types of failures are among the most challenging issues encountered in industrial electronics repair.
Initial Diagnosis
During the first inspection it became apparent that this power supply was designed to a very high standard. The Power-One SPM3D2K features a sophisticated switched-mode power supply architecture with numerous monitoring and protection functions. Devices of this class react to even minor irregularities within the voltage regulation circuit and automatically protect both themselves and the connected equipment.
During no-load testing the power supply operated perfectly. Neither the output voltage nor the current consumption showed any abnormalities. Only after the unit had been operated for an extended period under realistic load conditions did the behaviour begin to change.
As temperature and power demand increased, the output voltage gradually began to drop until the internal protection circuitry intervened and the power supply could no longer maintain stable output voltage.
Because this fault only appeared under thermal stress, the power supply was operated for several hours under defined load conditions while all operating parameters were continuously monitored.
Root Cause Analysis
After extensive electrical measurements, the root cause could be clearly identified.
The following conditions were detected:
- Temperature-dependent instability within the power stage
- Multiple aged electronic components with degraded electrical characteristics
- Progressive voltage drop under high current load
- Internal protection circuits prevented complete failure by shutting the unit down safely
- Several components had already drifted outside their original specifications
In high-power industrial power supplies, failures rarely occur suddenly. Instead, the electrical characteristics of individual components gradually change over many years of operation. As long as sufficient design margin remains, the unit appears to function normally. Only under elevated temperature or high output power does this safety margin disappear, causing the regulated output voltage to become unstable.
This type of failure is particularly critical because standard bench tests without load often reveal no abnormalities.
Repair Procedure
After completing the diagnostic process, the power supply underwent a complete overhaul.
The repair included:
- Replacement of numerous age-sensitive electronic components
- Replacement of thermally stressed components
- Inspection and reworking of all solder joints
- Thorough cleaning of the complete electronic assembly
- Cleaning of all cooling surfaces
- Complete verification of all voltage regulation circuits
- Inspection of both primary and secondary power stages
- Recalibration of the output voltage under various load conditions
Because the SPM3D2K incorporates multiple internal protection systems, the repair focused on more than simply correcting the immediate fault. Additional critical components were replaced as a preventive measure to significantly improve the long-term reliability of the power supply.
For high-quality industrial power supplies, this additional effort is justified because another unexpected production shutdown would often result in significantly higher costs than a comprehensive preventive overhaul.
Load Testing Under Real Operating Conditions
After completing the repair, the most important stage of the process began.
The power supply was operated on our in-house test bench for several hours under varying load conditions.
The following parameters were continuously monitored:
- Input voltage
- Output voltage
- Output current
- Internal temperature
- Voltage stability
- Load response
- Protection circuit operation
Throughout the entire endurance test, the output voltage remained completely stable. Even under high current load, no further voltage collapse could be reproduced.
Only after successfully completing all load and endurance tests was the unit approved for return shipment.
Return to the Customer
Following the successful final inspection, the Power-One SPM3D2K was prepared for industrial service once again.
By combining fault elimination, preventive replacement of critical components and extensive load testing, the customer received a thoroughly inspected power supply ready to reliably provide the 24 V supply required by the machine.
A stable power supply is the foundation for reliable operation of PLCs, sensors, industrial control systems and all downstream electronic equipment.
To mentioned Mitsubishi Drive: Power-One SPM3D2K Industrial Switching Power Supply
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Technical Specifications
| Specification | Value |
|---|
| Manufacturer | Power-One |
| Model | SPM3D2K |
| Device Type | Industrial Switching Power Supply |
| Input Voltage | 110 / 220 VAC |
| Output Voltage | 24 VDC |
| Maximum Output Current | 32 A |
| Maximum Output Power | 800 W |
| Cooling | Passive heatsink cooling |
| Protection Functions | Overcurrent protection, Overvoltage protection, Short circuit protection, Thermal protection |
| Application | Industrial automation, CNC machines, PLC systems, Machine control power supply |
Operating Environment & Compatible Equipment
The Power-One SPM3D2K is designed to provide a highly stable 24 VDC power supply for industrial automation equipment and machine control systems.
Typical applications include:
- CNC machine tools
- Industrial automation systems
- PLC control cabinets
- Robotics
- Production lines
- Packaging equipment
- Special-purpose machinery
- Industrial test systems
Typical connected equipment includes:
- PLC controllers
- Digital and analog I/O modules
- Sensors
- Safety relays
- Industrial PCs
- Communication modules
- Solenoid valves
- Machine control electronics
Functional Description
The Power-One SPM3D2K converts the incoming AC mains voltage into a regulated 24 VDC output suitable for demanding industrial applications.
The internal regulation continuously monitors:
- Input voltage
- Output voltage
- Output current
- Internal temperature
- Overload conditions
- Short circuit conditions
- Voltage regulation stability
If abnormal operating conditions are detected, the integrated protection circuitry intervenes automatically to protect both the power supply and the connected equipment.
These protection mechanisms are particularly important in industrial environments where a stable 24 VDC supply is essential for reliable machine operation.
Typical Fault Symptoms & Troubleshooting
| Symptom | Possible Cause | Recommended Inspection | Recommended Action |
|---|
| Output voltage collapses under load | Aged electrolytic capacitors or thermally stressed components | Perform full-load testing | Replace degraded components |
| Stable at no load but unstable under load | Reduced performance margin caused by component aging | Extended load test | Inspect power stage |
| Intermittent shutdowns | Thermal overload or protection circuit activation | Monitor internal temperature | Replace heat-stressed components |
| No output voltage | Primary power stage failure | Verify AC input voltage | Inspect primary circuit |
| Output voltage fluctuates | Voltage regulation instability | Measure output ripple | Repair regulation circuit |
| Power supply repeatedly restarts | Internal protection repeatedly activated | Disconnect external load and retest | Identify root cause |
| Excessive operating temperature | Increased internal power dissipation | Perform thermal inspection | Replace stressed components |
| Output voltage decreases after extended operation | Temperature-dependent failure | Perform long-duration load test | Complete preventive overhaul |
| Stable only at low load | Reduced power stage capability | Increase load gradually | Inspect power components |
| Repeated failures after years of operation | Natural component aging | Complete preventive inspection | Replace critical aging components |
Main Internal Assemblies
| Assembly | Function | Inspection Recommendation |
|---|
| Input Rectifier | Converts AC input into DC | Measure input voltages |
| Primary Power Supply | Supplies internal control electronics | Verify supply rails |
| Switching Power Stage | Main energy conversion | Perform full-load testing |
| Regulation Circuit | Maintains constant output voltage | Verify voltage stability |
| Power Output Stage | Supplies high output current | Measure output current |
| Protection Circuit | Overcurrent and thermal protection | Functional verification |
| Output Filter | Reduces output ripple | Measure ripple voltage |
| Heat Sink Assembly | Dissipates heat | Check operating temperature |
Preventive Maintenance Recommendations
To maximize the service life of industrial power supplies, we recommend:
- Regular cleaning of cooling surfaces
- Inspection of ventilation openings
- Operating the power supply within its specified load range
- Periodic visual inspection for thermal discoloration
- Preventive replacement of aged electrolytic capacitors in older units
- Periodic load testing during scheduled maintenance
- Verification of output voltage under rated load
- Inspection and tightening of all power connections
Industrial power supplies often operate continuously for many years. Preventive maintenance significantly reduces the risk of unexpected production downtime.
Conclusion
This repair case of the Power-One SPM3D2K demonstrates that failures in industrial switching power supplies often become visible only under realistic operating conditions. During no-load testing, the unit initially appeared to function normally, while the output voltage collapsed only after extended operation under increasing load. Only comprehensive long-term load testing allowed the fault to be accurately identified.
Following the replacement of multiple age-related components, a complete electronic overhaul and several hours of load testing, the power supply was successfully restored to reliable operating condition.
Professional repair and preventive refurbishment of high-quality industrial power supplies significantly improve operational reliability, reduce unplanned production downtime and extend the service life of both the power supply and the entire machine.