Siemens 6ES5931-8MD11 PS931 Replacement for SIMATIC S5

Product Overview

Siemens 6ES5931-8MD11 PS931 Replacement for SIMATIC S5: Seamless Transition & Compatible Upgrade

The Siemens 6ES5931-8MD11 is the PS931 power supply module designed for the SIMATIC S5 programmable logic controller platform — one of Siemens’ most widely deployed industrial automation systems across manufacturing, process control, and utility infrastructure. As the S5 series has reached end-of-life and spare parts become increasingly scarce, facilities running legacy S5-115U, S5-135U, S5-150U, and S5-155U systems face mounting pressure to source reliable replacement power supply modules without triggering a full system overhaul.

TOPNLMS maintains verified stock of the 6ES5931-8MD11 to support your retrofit, emergency replacement, and planned migration projects. Each unit is tested prior to shipment and backed by a 12-month warranty, giving procurement teams and maintenance engineers the confidence to plan around a reliable supply chain.

Compatibility Comparison Table

Seamless Upgrade Solutions

A power supply replacement rarely happens in isolation. When your facility is migrating from an aging SIMATIC S5 installation or responding to an unplanned PS931 failure, the surrounding system components must be evaluated in parallel to ensure a stable, fully operational control system after the swap.

In most S5-135U and S5-155U installations, the 6ES5931-8MD11 powers a central rack populated with CPU modules such as the 6ES5948-3UA23 (CPU948) or 6ES5928-3UB21 (CPU928B), alongside digital I/O modules like the 6ES5420-7LA11 (32-channel digital input) and 6ES5430-7LA11 (32-channel digital output). These modules draw regulated 5 V and 24 V from the PS931 backplane bus — confirming that the replacement power supply’s output current capacity matches the aggregate load of all installed modules is a critical pre-commissioning step.

For systems using SINEC H1 or PROFIBUS-DP communication, the rack may also house CP5430 TF or CP5431 FMS/DP communication processors. These modules are sensitive to power rail stability; a degraded or undersized power supply is a common root cause of intermittent communication faults on aging S5 networks. Replacing the 6ES5931-8MD11 with a verified unit often resolves these phantom communication errors without requiring any changes to the CP module configuration or network topology.

In control cabinets where the S5 rack shares enclosure space with external 24 V DC loads — such as relay coils, solenoid valves, or distributed I/O terminal modules like the ET 200U — it is advisable to audit the total 24 V current draw before commissioning the replacement PS931. If the aggregate load approaches the module’s rated output, adding a dedicated SITOP PSU100S or equivalent DIN-rail power supply for auxiliary 24 V loads will improve system stability and extend the service life of the PS931.

For facilities planning a phased migration from S5 to SIMATIC S7-300 or S7-400, maintaining a functional S5 system during the transition period is essential. The 6ES5931-8MD11 supports this bridge strategy by keeping the legacy rack operational while new S7 hardware — including CPU315-2 DP or CPU416-3 DP/PN controllers — is installed in parallel and validated against the production process. Programming cable adapters such as the PC Adapter USB A2 (for S7) alongside legacy PG 720/PG 740 programmer interfaces (for S5) are typically required during this dual-system commissioning phase.

Where analog signal conditioning is part of the S5 installation, analog input modules such as the 6ES5464-8ME11 (8-channel analog input) depend on clean, stable power from the PS931. Signal drift or measurement errors on analog channels are frequently traced back to power supply degradation rather than sensor or wiring faults. A fresh 6ES5931-8MD11 restores baseline power quality and eliminates this variable from your troubleshooting process.

Retrofit Guidance FAQ

Q: Can I replace the 6ES5931-8MD11 without rewiring the terminal block?
A: In most cases, yes. The PS931 uses a standard screw terminal block with a consistent pinout across S5 power supply revisions. Before removal, photograph or document the existing wiring, then transfer connections terminal-by-terminal to the replacement module. No changes to the control cabinet wiring harness are typically required.

Q: Will replacing the power supply affect my S5 program or CPU memory?
A: The CPU module retains its program in battery-backed RAM or EPROM independently of the power supply. A clean power cycle during the PS931 swap will not corrupt the user program, provided the CPU’s backup battery is functional. Always verify battery status before performing the replacement.

Q: Is the 6ES5931-8MD11 compatible with both S5-135U and S5-155U racks?
A: Yes. The PS931 is designed for the standard S5 central rack (ZG) used across the S5-115U, S5-135U, S5-150U, and S5-155U families. Verify the rack slot designation and output current requirements against your specific system configuration before installation.

Q: What communication protocols are supported after the power supply replacement?
A: The PS931 is a power supply module and does not participate in communication protocols. All existing PROFIBUS-DP, SINEC H1, or serial communication configurations managed by CP modules in the rack remain unchanged after the power supply swap.

Q: How do I verify the replacement PS931 is functioning correctly after installation?
A: After installation, check the module’s LED status indicators for normal operating state. Verify DC 5 V and 24 V output voltages at the backplane using a calibrated multimeter. Confirm that all CPU and I/O modules power up normally and that the CPU transitions to RUN mode without fault codes.

Q: Can this module be used as a long-term spare for a planned S5-to-S7 migration?
A: Yes. Holding verified spare PS931 units in inventory is a standard risk mitigation strategy for facilities operating legacy S5 systems during a phased migration. TOPNLMS can supply multiple units with consistent firmware and hardware revisions to support your spares management program.

Warranty Assurance

Every 6ES5931-8MD11 shipped by TOPNLMS is covered by a 12-month warranty from the date of delivery. Prior to shipment, each unit undergoes functional testing to verify output voltage regulation, current capacity, and module communication on the S5 backplane bus. Units that do not meet specification are quarantined and not offered for sale.

In the event of a warranty claim, TOPNLMS provides replacement or repair support with a target response time of 1–3 business days. Our technical team can assist with failure diagnosis, installation guidance, and compatibility verification to minimize your system downtime. Warranty coverage applies to manufacturing defects and functional failures under normal operating conditions; it does not cover damage resulting from incorrect installation, overvoltage events, or physical mishandling.

For procurement teams requiring documentation, TOPNLMS can provide test reports, shipment records, and warranty certificates upon request. We support standard industrial procurement workflows including purchase order processing, proforma invoice issuance, and export documentation for international shipments.

Stock is available for immediate shipment from Xiamen, China. Lead time for in-stock units is typically 3–7 business days to major industrial regions. Contact our team to confirm current availability, request a quotation, or discuss volume pricing for spares programs.