ABB TB840A 3BSE037760R1 Retrofit-Compatible Battery for AC800M

ABB TB840A 3BSE037760R1 Retrofit-Compatible Battery for AC800M Legacy Systems

The ABB TB840A (part number 3BSE037760R1) is a battery backup unit designed for the AC800M controller platform — one of ABB’s most widely deployed process automation controllers in oil & gas, power generation, pulp & paper, and chemical processing industries. As the AC800M platform ages and OEM support windows narrow, facilities running PM861, PM864, PM866, or PM891 processor modules increasingly face the challenge of sourcing reliable battery backup units to sustain SRAM memory retention and real-time clock functions during power interruptions.

NINERMAS supplies the TB840A 3BSE037760R1 as a retrofit-compatible replacement for aging or end-of-life battery units within existing AC800M controller cabinets. Each unit undergoes pre-shipment functional testing to verify charge capacity, connector integrity, and compatibility with the AC800M backplane before dispatch. A 12-month warranty is included with every shipment.

For engineers managing legacy DCS or hybrid PLC/DCS architectures, the TB840A is a critical component in sustaining controller uptime without requiring a full platform migration. Replacing a degraded battery unit is one of the lowest-risk interventions available — provided the replacement unit is correctly specified and the installation procedure is followed precisely.

Upgrade Compatibility Table

Retrofit Planning for Existing Automation Systems

When planning a battery replacement within an AC800M-based control system, the scope of work extends beyond the TB840A unit itself. Engineers must assess the broader controller assembly to ensure the replacement does not introduce unintended disruptions to the running process.

The AC800M controller cabinet typically houses a PM864 or PM866 processor module paired with a TB840A battery, an SM810 or SM811 communication interface module for MMS or PROFIBUS connectivity, and one or more CI854 or CI858 fieldbus communication interface modules handling PROFIBUS DP or Foundation Fieldbus segments. Before removing the battery, confirm whether the processor module is operating in redundant mode — if a redundant PM8xx pair is configured via the TP830 redundancy module, the battery swap can often be performed on the standby unit without interrupting the active control loop.

For non-redundant installations, the replacement window must be coordinated with operations to allow a controlled shutdown of the affected controller. During this window, engineers should also inspect the SD802 or SD803 power supply modules feeding the controller rack, verify that the SB821 or SB822 battery supervision board (where fitted) is not reporting pre-existing faults, and confirm that the CI840A or CI840 S800 I/O communication interface is not in a degraded state that could complicate restart.

If the facility is also planning a broader migration from AC800M to AC800xA or a third-party platform, the TB840A replacement can serve as a bridge measure — extending the operational life of the existing controller while the migration project is scoped, budgeted, and scheduled. In such cases, it is advisable to simultaneously audit the TB807 termination unit connections and the TB811 or TB825 I/O terminal bases to identify any wiring or labelling deficiencies that should be corrected before the migration cutover.

All units supplied by NINERMAS are sourced from verified industrial channels, inspected upon receipt, and tested prior to shipment. Stock availability is maintained to support both emergency replacement and planned maintenance schedules. Contact our team to confirm lead time and arrange expedited dispatch where required.

Downtime Control During System Migration

Battery-related controller faults — including memory loss on power cycle, RTC drift, and unexpected warm-restart behaviour — are among the most disruptive failure modes in AC800M-based systems because they can corrupt the resident application program or cause the controller to enter a safe-state that halts the process. Proactive replacement of the TB840A before battery end-of-life is the most effective way to prevent these events.

For facilities that cannot afford unplanned downtime, NINERMAS recommends maintaining at least one TB840A 3BSE037760R1 unit as a certified on-site spare. This eliminates the lead time variable entirely and allows the maintenance team to execute the replacement during a planned outage window — typically a 15–30 minute procedure for a trained technician familiar with the AC800M platform.

During the replacement, the existing application program, hardware configuration, and communication parameters stored in the PM8xx processor’s flash memory are not affected by the battery swap — only the SRAM-resident runtime data (such as retentive variable values) may be lost if the battery has already fully discharged. Engineers should therefore export a current snapshot of retentive variable values from ABB Control Builder M before initiating the replacement, and verify that the HMI screens connected via OPC DA or OPC UA to the AC800M are configured to handle a brief controller restart gracefully.

After reinstalling the TB840A and powering up the controller, confirm that the SM810 or CI854 communication modules re-establish their fieldbus links within the expected timeout window, and that the S800 I/O modules — including AI810, AO810, DI810, and DO810 — report healthy status in the hardware tree before releasing the unit back to automatic control. This structured restart sequence minimises the risk of process upsets and ensures that the control system returns to its pre-maintenance state without requiring manual intervention at the field level.

Retrofit Support FAQ

Q1: Is the TB840A 3BSE037760R1 a direct replacement for the older TB840 (3BSE013208R1)?
Yes. The TB840A is the current-generation successor to the TB840 and is a form-fit-function replacement. It mounts to the same connector on PM861, PM864, PM866, and PM891 processor modules without any mechanical or electrical modification. No software changes are required in Control Builder M.

Q2: Will replacing the battery cause the controller to lose its application program?
No. The application program is stored in flash memory and is not affected by a battery swap. Only SRAM-resident retentive variable values may be lost if the battery has fully discharged prior to replacement. We recommend exporting retentive variable values before the procedure as a precaution.

Q3: How do I confirm the battery is the cause of my AC800M fault before ordering?
In ABB Control Builder M, navigate to the hardware tree and check the battery status indicator on the PM8xx module. A “Battery Low” or “Battery Fault” diagnostic event in the system log confirms the TB840A requires replacement. Physical inspection of the battery connector for corrosion or swelling is also recommended.

Q4: What is included with the NINERMAS TB840A supply and what warranty applies?
Each TB840A 3BSE037760R1 supplied by NINERMAS is individually tested for charge capacity and connector integrity before shipment. The unit is supplied with a 12-month warranty covering manufacturing defects and functional failure under normal operating conditions. Expedited shipping options are available for emergency replacement requirements. Contact sale@ninermas.com or +0086 187 5021 5667 for stock confirmation and lead time.