Description
1. At-A-Glance Executive Brief
- Model: 6ES5955-3LF42
- Brand: Siemens
- Part Type: Power Supply Module (PS 955)
- System Compatibility: SIMATIC S5-135U, S5-155U, and EU 185U racks
- Lifecycle Status: Discontinued / Legacy Mature
- Weight: ~2.1 kg
2. Technical Introduction
Legacy control racks demand stable, continuous power delivery to prevent intermittent faults and unexpected shutdowns across continuous process lines. Sudden power supply degradation in an aging SIMATIC S5 architecture frequently triggers false trip conditions or corrupts processor memory registers.
The 6ES5955-3LF42 power supply unit is engineered to accept 120/230V AC input and deliver regulated internal DC voltages—including a robust 5V 40A output—directly to the S5-135U or S5-155U backplane bus. Securing tested replacement hardware ensures voltage stability without forcing an expensive, high-risk system migration.
- Problem: Aging electrolytic capacitors inside legacy power supplies dry out over decades of continuous operation, leading to voltage ripple, thermal trips, and dropped backplane communication.
- Agitation: Waiting for a total component failure risks protracted plant downtime while trying to source obsolete hardware on short notice.
- Solution: Installing a verified, fully tested PS 955 module restores clean power rails and protects sensitive legacy CPU and I/O cards from voltage spikes.
3. Core Technical Specifications
| Parameter | Value |
| Manufacturer | Siemens |
| Product Family | SIMATIC S5 |
| Module Type | Power Supply Unit (PS 955) |
| Input Voltage | 120 / 230 V AC |
| Output Current | 5 V DC, 40 A |
| Compatible Racks | S5-135U, S5-155U, EU 185U |
| Lifecycle Phase | Discontinued / Spare Parts |
| Environmental Tolerances | Please refer to the OEM datasheet for complete environmental tolerances. |
4. Field Engineer’s Tech Notes
- Thermal Clearance and Heat Dissipation: This power supply generates substantial heat under high backplane loads. Ensure that the upper and lower ventilation slots on the S5 cabinet frame are unobstructed, and verify that adjacent rack modules leave sufficient spacing for natural convection cooling.
- Inrush Current and Line Protection: Due to high capacitive inrush currents upon initial startup, verify that upstream circuit breakers are properly rated (curve C or equivalent) to prevent nuisance tripping during cold power-up sequences.
5. Adaptive QA & Testing Protocol
Our testing procedure for power supply modules involves mounting the unit to a live S5 backplane simulator and applying variable line voltages through an autotransformer. We measure DC output ripple under simulated heavy loads using an oscilloscope, validating that the 5V rail remains strictly within tolerance limits. Overload protection and thermal cutoff circuits are verified under load. Complete functional test logs are available upon request prior to shipment.
6. Buyer’s FAQ
- What warranty is included with this power supply?
All units include a comprehensive 12-month operational warranty covering all electrical and mechanical functions.
- Are these modules tested under full load?
Yes. Every PS 955 module undergoes bench load testing to verify output stability and ripple suppression prior to packaging.
- What packaging is used for transit protection?
Units are wrapped in anti-static shielding and packed securely inside high-density foam cartons to withstand international freight handling.
- How quickly can this part ship for emergency plant outages?
Expedited same-day shipping options are available for in-stock items to get your process line back online quickly.
