Open Rack V3 BBU Shelf Specification, Rev 1.1

Overview

The document defines the second half of the Open Rack V3 power architecture: a centralized, scalable power shelf and a BBU shelf that feed payload devices over a common busbar. A BBU shelf carries a PMI (Power Monitoring Interface) module and six 3 kW BBU modules in 5+1 redundancy. On an AC outage the shelf supplies up to the power shelf's maximum rating for a specified time, long enough to switch sources (utility to utility, or utility to generator) and to drain or migrate applications.

In the electrical section the discharge output is 48.0 V at no load, 47.75 V at 50%, 47.5 V at 100% and 47.25 V at 150% load (0.5 V droop). Shelf output power is 18 kW (27 kW peak) and output current 379.2 A (568.8 A peak), with at most 60 mF output capacitance per shelf. The backup-time condition is a 15 kW discharge longer than 240 seconds at the PCM threshold (for example 3.9 V per cell) after 4 years at 35 C. During transfer from power shelf to BBU shelf the busbar must stay above 46 V.

On the charge side the shelf accepts 49-53 V input and at most 33 A (5.5 A per BBU, six modules); charge current is variable and programmable. Several BBU shelves can run in parallel for more load or longer backup, daisy-chained through PMI RJ45 connectors and using BBU_ISHARE, SYNC_START_L, SYNC_STOP_L and CAN. BBUs are hot-swappable in a live shelf; the shelf is hot-pluggable into a live busbar but must not be hot-removed, because of connector and busbar damage risk.

Mechanical and environmental sections give implementation detail: a 2OU envelope of 537 x 92.3 x 787.5 mm, 1.0-1.2 mm hot-dip zinc-coated steel, UL 94-V0 plastics, and shelf deflection under 1.3 mm with rectifiers installed. Any configuration with fewer than six BBUs needs a blank slot cover to channel airflow. Ambient is 0-40 C (15-35 C long-term standby), 10-90% RH non-condensing, storage -20 to +60 C. The revision history records the maximum shelf output rising from 15 kW to 18 kW.

Key points

1. Each BBU shelf holds one PMI module and six 3 kW BBU modules in 5+1 redundancy.
2. Discharge output is 48.0 V at 0% and 47.5 V at 100% load; droop 0.5 V (1%); total regulation 47.0-48.1 V.
3. Maximum output 18 kW (27 kW peak) and 379.2 A (568.8 A peak); output capacitance at most 60 mF per shelf.
4. A 15 kW discharge must last more than 240 seconds at the PCM threshold; BBU life at least 8 years.
5. Busbar must stay above 46 V in the power-shelf-to-BBU-shelf transition; startup time at most 2 ms.
6. Charge input 49-53 V, at most 33 A (6 x 5.5 A); the output return must not be grounded to the shelf enclosure.
7. Shelves may be paralleled; ORing on every output gives N+1, with no capacitors on the shared bus after the ORing devices.
8. BBUs are hot-swappable; the shelf is hot-pluggable into a live busbar but not hot-removable.
9. 2OU shelf of 537 x 92.3 x 787.5 mm; fewer than six BBUs require a blank slot cover.
10. Operating ambient 0-40 C (15-35 C long-term), 10-90% RH, storage -20 to +60 C; the power system must keep working if the monitoring module fails.

Using it in design

• Model ORV3 in-rack BBU as an alternative to a central UPS and check that generator start and transfer time fit inside the roughly 4-minute window at rated load per shelf.
• Where longer autonomy is needed, plan parallel BBU shelves and verify ORing and N+1 conditions.
• Reserve 2OU per BBU shelf in rack elevations and fit blank covers in unused BBU slots.
• Use the 0-40 C operating and 15-35 C long-term standby limits in room thermal checks.
• Apply UL 9540A-based fire-safety review to distributed rack batteries as to central battery rooms.
• Add the shelf charge input (up to 33 A) to the busbar and feed capacity calculation.

Who should read it

Power and rack engineers designing or procuring Open Rack V3 style in-rack backup, and BBU shelf manufacturers.

Document contents

1. License
2. Compliance with OCP Tenets
3. Scope
4. Introduction
5. Electrical Requirements
6. BBU Shelf Discharge Mode Output Parameters
7. BBU Shelf Charge Mode Input Parameters
8. Power Shelf to BBU Shelf Transition
9. Grounding
10. BBU Shelf Operation Modes
11. BBU Physical Addressing
12. BBU Shelves Parallel Operation and Hot Swap
13. Mechanical Requirements
14. BBU Shelf Physical Dimensions
15. Front Latch & Bumper
16. Construction, Materials and Fasteners
17. BBU Slot Blank
18. Monitoring & Control Interface
19. Shelf Electrical Connections
20. Environmental Requirements
21. Compliance requirements

Related standards

• OCP Open Rack V3 48V BBU Module Specification
• OCP Open Rack V3 Power Shelf Specification
• UL 9540A
• IEC 62368-1

Read the document

Publication details

Authors

Sun, D.; Shapiro, D.; Kim, B.; Athavale, J.; Mercado, R. (Meta)

Publisher

Open Compute Project Foundation

Year

2022

Document number

Rev 1.1

Document language

English

Source type

Industry body

Access

Open licence — downloadable

Licence

OWFa 1.0 — Open Compute open specification licence; redistribution permitted

Licence evidence

www.opencompute.org

Citation