Caterpillar UPSB 125
Maintenance schedule, common problems & OEM parts breakdown
The Caterpillar UPSB 125 is a static, battery-based Uninterruptible Power System cabinet module built for critical-power backup duty, not a mobile or engine-driven machine. It carries no internal combustion engine, no fuel system, and no undercarriage; the module instead pairs a solid-state thyristor/converter power group with cabinet-mounted VRLA battery groups sized to 813 mm (32 in) or 1219 mm (48 in) shelf widths, supporting the industry-standard 5, 10, 15, and 30-minute autonomy tiers. It carries factory or class-typical provisions for a maintenance-bypass lock, forced-air cooling fans, a float-charge battery charger, a remote-disconnect switch, and Modbus/SNMP/RS232 communication boards, with an external synchronizer option for paralleling multiple cabinets on a common bus. Exact kVA/kW output, weight, and footprint for this specific model are not published in available OEM literature; documented serial ranges are SEP1-UP for the base configuration and XTC1-UP for battery-shelf and bypass-hardware variants. Production era, and any formal predecessor or successor relationship to the sibling UPSB 130/220/505 modules or the related UPS 120 flywheel-based unit, are not confirmed in public documentation.
Across the UPSB line, configuration changes track battery-shelf width, autonomy tier, and converter capacity rather than a generational engine or chassis redesign, so parts and service compatibility hinge on serial prefix and cabinet configuration, not model-year assumptions. In the used and parts market this module sits in data-center and critical-facility backup-power fleets, where the wear economy is dominated by battery groups, DC-bus capacitor banks, and thyristor/converter modules rather than engine or driveline parts. Documentation for this exact rating is thin, so buyers and service shops should expect to verify battery age, capacitor condition, and communication-board compatibility against the nameplate and a dealer rather than a public spec sheet before committing to a repair or acquisition.
Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.
Caterpillar UPSB 125 specifications
Engine
| Engine | None. The UPSB 125 is a static, battery-based Uninterruptible Power Supply (UPS) cabinet system, not an engine-driven generator set. It has no internal combustion engine, fuel system, or cooling system of its own. |
| Power conversion | Solid-state rectifier/inverter power module with cabinet-mounted battery groups for ride-through energy storage; communication boards support Modbus, SNMP/web, and RS232/ASCII monitoring interfaces. |
| Emissions tier | Not applicable — no engine present. |
Weights
| Operating weight | Not published for this exact model. Total installed weight scales with the number of battery cabinets fitted and is configuration-dependent; confirm with a Cat dealer for the specific battery arrangement ordered. |
| Shipping weight | Not documented in available literature. |
| Ground pressure | Not applicable — stationary indoor equipment, no undercarriage. |
Dimensions
| Cabinet footprint | Not published for this exact model. Comparable Cat static UPS power and battery cabinets are floor-standing, indoor enclosures sized for data-center or switchgear-room installation; exact width, depth, and height vary by cabinet count and configuration. |
| Transport dimensions | Not documented; unit ships as separate power and battery cabinet sections rather than as a single transportable machine. |
| Ground clearance / wheelbase | Not applicable — no chassis or undercarriage. |
Performance
| Travel speed | Not applicable — stationary equipment, no drivetrain. |
| Output rating | Not confirmed in public literature for this exact model number; verify kVA/kW rating and battery ride-through time from the unit nameplate or with a Cat dealer. |
| Gradeability | Not applicable. |
Service capacities (summary)
| Fuel tank | Not applicable — no engine. |
| Hydraulic system | Not applicable. |
| Engine oil | Not applicable. |
| Cooling system | Not documented for this exact model; static UPS cabinets of this type are typically cooled by forced-air circulation or facility HVAC rather than an onboard liquid cooling circuit. |
| Battery system | Uses cabinet-mounted battery groups; exact battery count, type, and amp-hour rating are configuration-dependent and not published for this specific model. |
Values vary by configuration, region, and serial range — confirm against your machine before planning transport or lifts.
Caterpillar UPSB 125 maintenance schedule
| Service interval | Tasks |
|---|---|
| Every 10 h |
|
| Every 50 h |
|
| Every 250 h |
|
| Every 500 h |
|
| Every 1,000 h |
|
| Every 2,000 h |
|
| Every 4,000 h |
|
Servicing the UPSB 125 beyond the schedule
Predictive Maintenance & Battery/Capacitor Analysis
Track VRLA battery-string health with periodic capacity or impedance testing rather than visual inspection, since capacity loss on this cabinet's battery groups is silent until an outage exposes it. Trend float voltage per block and DC-bus capacitor ESR, flagging any capacitor showing a 20 percent or greater rise over rated. Thermal-scan the converter and capacitor sections periodically to catch a drifting thyristor or firing-circuit device before it fails hard, and log converter output ripple trends between visits.
Corrective & Common Repairs
Most corrective work on this module centers on the converter/thyristor power group, the DC-bus capacitor bank, the maintenance-bypass switch, and the communication board. Rising output ripple or self-clearing converter-fault alarms point to a failing thyristor or gate-drive circuit, not the battery string. Bulging, leaking, or high-ESR capacitors should be replaced as a bank, not spot-repaired. Bypass-switch contact wear and Modbus/SNMP/RS232 comms-card faults are common, isolated repairs that do not require de-energizing the full cabinet.
Overhaul & Rebuild Points
Plan on full battery-bank replacement, not cell-by-cell repair, once string capacity testing shows the group can no longer support its rated autonomy tier. DC-bus capacitor banks on this cabinet class are a wear item on a roughly 7 to 10-year replacement cycle regardless of outward appearance. Converter/inverter power-module rebuilds are the other major overhaul point. Where cabinets are paralleled, resynchronize and recalibrate the external synchronizer board after any bank-level rebuild to avoid load-sharing errors.
Seasonal & Environment Servicing
This cabinet has no engine cooling system to winterize, but battery-room ambient temperature drives service life directly: expect roughly a 50 percent reduction in battery life for every 10 C (18 F) the room runs above the 25 C (77 F) design target, so confirm HVAC or facility cooling holds that range year-round. Keep intake/exhaust filters and fan blades clear of seasonal dust loading, and inspect terminal and comms-board connections for corrosion where humidity swings are significant.
UPSB 125 fault codes & troubleshooting
| Code | Meaning | Likely cause | What to do |
|---|---|---|---|
| Battery Fault / Battery Discharged | Battery string voltage, temperature, or internal impedance is outside acceptable limits, or the string cannot support rated backup time. | Aged or failed battery block, open string connection, high ambient temperature, or charger not maintaining float voltage. | Check individual block voltages and string continuity, verify charger float/boost setting, replace weak blocks, confirm cabinet ventilation. |
| DC Bus Fault (Overvoltage/Undervoltage) | Internal DC bus voltage between the converter and battery has moved outside its regulated window. | Charger regulation fault, battery disconnect, converter control fault, or unbalanced battery string. | Check DC bus voltage at the power group, inspect battery disconnect and fusing, review event log for a preceding charger or battery event before resetting. |
| Converter (Rectifier/Charger) Fault | The AC-to-DC power conversion group has shut down or de-rated due to an internal fault. | IGBT/thyristor module failure, input overcurrent, control-board fault, or loss of gate-drive power. | Inspect converter module status indicators, check input supply and fusing, have a qualified technician test the power semiconductor modules before re-energizing. |
| Inverter Fault | The output inverter section has tripped or is unable to maintain regulated output voltage/frequency. | Overload, short circuit on the load bus, inverter module failure, or loss of synchronization reference. | Remove non-essential load, check output for short circuit, transfer to bypass if available, then inspect inverter module and control card. |
| Static Switch / Bypass Fault | The static transfer switch cannot complete a transfer between inverter and bypass source, or has detected a fault on the bypass input. | Bypass source out of tolerance (voltage/frequency), SCR failure in the static switch, or loss of sync between inverter and bypass. | Verify bypass source voltage and frequency, inspect static switch SCRs and gate drivers, do not force a manual bypass transfer until the source is confirmed healthy. |
| Overload Fault | Load current on the output has exceeded the unit's rated or short-time overload capability. | Downstream fault, load bank exceeding nameplate rating, or inrush from simultaneous load pickup. | Identify and reduce/shed load, check downstream feeders for a fault, allow the unit to cool before resetting. |
| Cooling / Fan Fault | A cooling fan or airflow sensor in the power or battery cabinet has failed or reports insufficient airflow. | Failed fan motor, blocked filter/vents, or fan-control board fault. | Inspect and clear intake/exhaust filters, verify fan rotation, replace failed fan module. |
| Communication / Control-Power Fault | Loss of communication on the Modbus/SNMP/RS232 monitoring link, or loss of redundant control power to the logic boards. | Network/cable fault, communication card failure, or control-power supply fault. | Check network cabling and card seating, verify control-power supply voltage, reset the communication card if the link does not recover. |
Codes and remedies are general guidance for this model family — always confirm with diagnostic tooling and your dealer before major repairs.
UPSB 125 attachments & work tools
Battery cabinet / shelf sizing
Battery assemblies are furnished for two shelf widths, 813 mm and 1219 mm (32 in and 48 in), letting the battery string be matched to the cabinet footprint and the target autonomy tier rather than a single fixed pack.
Maintenance bypass lock
A maintenance-bypass lock assembly is listed as a factory attachment, providing a lockable isolation point so the module can be pulled off-line for battery or converter service without dropping the protected load.
Mounting bracket group
A mounting bracket group anchors the module or adjacent battery cabinet to the floor or frame; on this class of static UPS the same hardware family typically doubles as vibration-isolation mounting when cabinets are ganged side by side.
Cooling fan group
Forced-air cooling fans are carried as a distinct attachment group, ventilating the converter/thyristor enclosure independent of the battery compartment.
Battery charger module
A dedicated battery charger attachment keeps the string at float charge between discharge events; it is cataloged separately from the main converter/power-train group.
Switch / disconnect assembly
A switch assembly attachment provides input, output, or bypass isolation; exact contact rating is not confirmed, but its presence in the same attachment list as the bypass lock indicates a lockable disconnect point is standard on this module.
Paralleling / synchronization provision
Static UPS modules in this size and construction class are typically offered with an external synchronizer or paralleling card so multiple units can share a common bus; this is a class-typical option and is not independently confirmed on the base UPSB 125 parts catalog.
Monitoring / communication card
Class-typical configuration options include a remote monitoring card supporting Modbus, SNMP, or RS232/RS485 for building-management or SCADA integration; not itemized in the UPSB 125 attachment list reviewed, so treat as an industry-standard option rather than a confirmed factory line item.
All UPSB 125 assemblies by section
Every catalogued assembly group for the Caterpillar UPSB 125. Open an assembly to preview the parts inside — full OEM part numbers are available in Heavy Parts AI.
Electrical And Starting System
347-8510 Battery As
| 34***10 | Battery As | 1 |
| 35***04 | Battery | 9 |
347-8512 Battery As
| 34***12 | Battery As | 1 |
| 35***06 | Battery | 12 |
347-8513 Battery As
| 34***13 | Battery As | 1 |
| 35***05 | Battery | 12 |
350-9803 Battery Gp
| 35***03 | Battery Group | 1 |
| 35***04 | Battery | 0 |
| 35***95 | Battery | 0 |
350-9806 Battery Gp
| 35***06 | Battery Group | 1 |
| 35***04 | Battery | 0 |
| 35***95 | Battery | 0 |
350-9804 Battery Gp
| 35***04 | Battery Group | 1 |
| 35***04 | Battery | 0 |
| 35***95 | Battery | 0 |
347-8485 Board As-Circuit -Communication, Jbus, Modbus
| 34***85 | Board As-Circuit; -Communication, Jbus, Modbus | 1 |
350-9718 Board As-Circuit -Communication, Rs232, Ascii
| 35***18 | Board As-Circuit; -Communication, Rs232, Ascii | 1 |
347-8486 Board As-Circuit -Communication, Snmp, Web
| 34***86 | Board As-Circuit; -Communication, Snmp, Web | 1 |
350-9736 Board As-Circuit -Synchronizer
| 35***36 | Board As-Circuit; -Synchronizer | 1 |
350-9720 Board As-Circuit -Communication, Alarm Relay
| 35***20 | Board As-Circuit; -Communication, Alarm Relay | 1 |
350-9719 Board As-Circuit -Communication, Multislot, Ups
| 35***19 | Board As-Circuit; -Communication, Multislot, Ups | 1 |
350-9847 Board As-Circuit -External Synchronizer
| 35***47 | Board As-Circuit; -External Synchronizer | 1 |
350-9813 Cabinet Gp-Battery
| 35***13 | Cabinet Group-Battery | 1 |
| 35***93 | Battery | 0 |
| 35***02 | Battery | 0 |
350-9811 Cabinet Gp-Battery
| 35***11 | Cabinet Group-Battery | 1 |
| 35***93 | Battery | 0 |
| 35***02 | Battery | 0 |
347-8518 Cabinet Gp-Battery -Stand Alone, Type 150
| 34***18 | Cabinet Group-Battery; -Stand Alone, Type 150 | 1 |
| 35***03 | Battery | 36 |
347-8504 Cabinet Gp-Battery
| 34***04 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***01 | Battery | 0 |
350-9808 Cabinet Gp-Battery
| 35***08 | Cabinet Group-Battery | 1 |
| 35***93 | Battery | 0 |
| 35***02 | Battery | 0 |
347-8514 Cabinet Gp-Battery -Adjacent, Type 150
| 34***14 | Cabinet Group-Battery; -Adjacent, Type 150 | 1 |
| 35***03 | Battery | 36 |
347-8507 Cabinet Gp-Battery
| 34***07 | Cabinet Group-Battery | 1 |
| 35***93 | Battery | 0 |
| 35***02 | Battery | 0 |
350-9807 Cabinet Gp-Battery
| 35***07 | Cabinet Group-Battery | 1 |
| 35***93 | Battery | 0 |
| 35***02 | Battery | 0 |
350-9810 Cabinet Gp-Battery
| 35***10 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***01 | Battery | 0 |
350-9812 Cabinet Gp-Battery
| 35***12 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***01 | Battery | 0 |
347-8506 Cabinet Gp-Battery
| 34***06 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***01 | Battery | 0 |
350-9809 Cabinet Gp-Battery
| 35***09 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***93 | Battery | 0 |
347-8505 Cabinet Gp-Battery
| 34***05 | Cabinet Group-Battery | 1 |
| 35***93 | Battery | 0 |
| 35***02 | Battery | 0 |
347-8508 Cabinet Gp-Battery
| 34***08 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***01 | Battery | 0 |
347-8509 Cabinet Gp-Battery
| 34***09 | Cabinet Group-Battery | 1 |
| 35***05 | Battery | 0 |
| 35***01 | Battery | 0 |
350-9783 Cable Gp
| 35***83 | Cable Group | 1 |
347-8488 Circuit Breaker Gp -Remote Disconnect
| 34***88 | Circuit Breaker Group; -Remote Disconnect | 1 |
347-8487 Circuit Breaker Gp -Remote Disconnect
| 34***87 | Circuit Breaker Group; -Remote Disconnect | 1 |
347-8489 Circuit Breaker Gp -Remote Disconnect
| 34***89 | Circuit Breaker Group; -Remote Disconnect | 1 |
350-9721 Module-Card -Multislot
| 35***21 | Module-Card; -Multislot | 1 |
350-9728 Module-Sensor
| 35***28 | Module-Sensor | 1 |
Enclosures, Guards And Bases
350-9733 Mounting Gp-Vibration Isolator
| 35***33 | Mounting Group-Vibration Isolator | 1 |
350-9731 Mounting Gp-Vibration Isolator
| 35***31 | Mounting Group-Vibration Isolator | 1 |
350-9732 Mounting Gp-Vibration Isolator
| 35***32 | Mounting Group-Vibration Isolator | 1 |
350-9734 Mounting Gp-Vibration Isolator
| 35***34 | Mounting Group-Vibration Isolator | 1 |
350-9735 Mounting Gp-Vibration Isolator
| 35***35 | Mounting Group-Vibration Isolator | 1 |
Operator Station
350-9737 Box As-Instrument -Synchronizer
| 35***37 | Box As-Instrument; -Synchronizer | 1 |
350-9857 Power Ar-Uninterruptible
| 34***03 | Power Group-Uninterruptible | 1 |
| 35***57 | Power Ar-Uninterruptible | 1 |
350-9853 Power Ar-Uninterruptible
| 34***01 | Power Group-Uninterruptible | 1 |
| 35***53 | Power Ar-Uninterruptible | 1 |
350-9741 Power Ar-Uninterruptible
| 34***91 | Power Group-Uninterruptible | 1 |
| 35***41 | Power Ar-Uninterruptible | 1 |
350-9740 Power Ar-Uninterruptible
| 34***90 | Power Group-Uninterruptible | 1 |
| 35***40 | Power Ar-Uninterruptible | 1 |
350-9849 Power Ar-Uninterruptible
| 34***00 | Power Group-Uninterruptible | 1 |
| 35***49 | Power Ar-Uninterruptible | 1 |
350-9851 Power Ar-Uninterruptible
| 34***00 | Power Group-Uninterruptible | 1 |
| 35***03 | Battery Group | 1 |
| 35***51 | Power Ar-Uninterruptible | 1 |
350-9850 Power Ar-Uninterruptible
| 34***00 | Power Group-Uninterruptible | 1 |
| 35***50 | Power Ar-Uninterruptible | 1 |
350-9854 Power Ar-Uninterruptible
| 34***01 | Power Group-Uninterruptible | 1 |
| 35***54 | Power Ar-Uninterruptible | 1 |
350-9856 Power Ar-Uninterruptible
| 34***02 | Power Group-Uninterruptible | 1 |
| 35***56 | Power Ar-Uninterruptible | 1 |
350-9852 Power Ar-Uninterruptible
| 34***00 | Power Group-Uninterruptible | 1 |
| 35***04 | Battery Group | 1 |
| 35***52 | Power Ar-Uninterruptible | 1 |
350-9855 Power Ar-Uninterruptible
| 34***01 | Power Group-Uninterruptible | 1 |
| 35***06 | Battery Group | 1 |
| 35***55 | Power Ar-Uninterruptible | 1 |
347-8502 Power Gp-Uninterruptible
| 34***02 | Power Group-Uninterruptible | 1 |
| 35***88 | Board As-Circuit; (Miznus) | 1 |
| 35***89 | Board As-Circuit; (Chan) | 1 |
347-8500 Power Gp-Uninterruptible
| 34***00 | Power Group-Uninterruptible | 1 |
| 35***88 | Board As-Circuit; (Miznus) | 1 |
| 35***89 | Board As-Circuit; (Chan) | 1 |
347-8491 Power Gp-Uninterruptible
| 34***91 | Power Group-Uninterruptible | 1 |
| 35***89 | Board As-Circuit; (Chan) | 1 |
| 35***90 | Board As-Circuit; (Gden) | 1 |
347-8503 Power Gp-Uninterruptible
| 34***03 | Power Group-Uninterruptible | 1 |
| 35***88 | Board As-Circuit; (Miznus) | 1 |
| 35***89 | Board As-Circuit; (Chan) | 1 |
347-8490 Power Gp-Uninterruptible
| 34***90 | Power Group-Uninterruptible | 1 |
| 35***89 | Board As-Circuit; (Chan) | 1 |
| 35***90 | Board As-Circuit; (Gden) | 1 |
347-8501 Power Gp-Uninterruptible
| 34***01 | Power Group-Uninterruptible | 1 |
| 35***88 | Board As-Circuit; (Miznus) | 1 |
| 35***89 | Board As-Circuit; (Chan) | 1 |
UPSB 125 serial number reference
The serial/PIN plate on the UPSB 125 sits on the cabinet or control-panel face of the power-electronics enclosure, since this is a static UPS module with no engine block to carry a conventional plate. Read the first three characters as the serial prefix, which identifies the build/configuration range, followed by the sequential unit number. The prefix, not the model nameplate alone, is what ties a given cabinet to its correct parts and service documentation.
| Prefix | Identifies | Notes |
|---|---|---|
| SEP1-UP | Base/primary UPSB 125 uninterruptible power module range | Primary serial break used in the base parts documentation for this UPS module. This is a static, battery-based unit with no engine. Confirm exact capacity-tier coverage under this prefix with your dealer. |
| XTC1-UP | UPSB 125 attachment range (battery-related hardware) | Covers attachment-level items on this module, including mounting hardware and the maintenance-bypass lock assembly. Documented only within this unit's own parts listings; confirm with your dealer before treating it as a distinct configuration rather than an attachment option on the base unit. |
Frequently asked questions
Does the Caterpillar UPSB 125 have an engine?
No. Despite the generator-set category label sometimes applied to it, the UPSB 125 is a static, battery-based Uninterruptible Power System cabinet. It has no internal combustion engine, fuel system, or engine cooling system; backup energy is stored in cabinet-mounted battery groups and delivered through a solid-state converter/inverter power group.
What is the UPSB 125's power or battery rating?
Not confirmed in publicly available literature for this exact model. Battery groups are documented in 813 mm (32 in) and 1219 mm (48 in) shelf configurations supporting 5, 10, 15, and 30-minute autonomy tiers, and related kVA capacity tiers are referenced in parts documentation, but no OEM spec sheet ties an exact kVA/kW output or battery capacity specifically to the UPSB 125 nameplate. Verify the rating from the unit's own nameplate or with a Cat dealer before sizing a replacement or planning capacity.
What does the UPSB 125 do, and what replaced it?
It provides ride-through backup power for critical loads, such as data-center or switchgear-room equipment, by switching to its battery-fed converter/inverter path when utility power fails or drifts out of tolerance. No formal successor model is documented in public literature; it is part of a broader Cat static/flywheel UPS lineup that includes sibling UPSB modules and the separate flywheel-based UPS line, but a direct model-to-model succession is not confirmed.
What UPSB 125 owners discuss
How long do the battery groups in a UPSB 125 cabinet actually last before they need replacing?
What are the tell-tale signs that the thyristor/converter power group is starting to fail?
The capacitor bank is original to the cabinet - is that a problem?
What happens to the load when you switch to maintenance bypass on one of these units?
Can a UPSB 125 be paralleled with other units for redundancy, and what trips people up?
What alarms or faults show up most often on these cabinets in day-to-day service?
What should I check before buying a used UPSB 125 module?
Compiled from owner and technician discussions across the industry — experiences vary by serial range and machine history.
Need a specific UPSB 125 part?
Search live OEM part data, check fitment, and cross-reference alternatives with Heavy Parts AI.