Battery rack: design, materials and manufacturing

A battery rack is a structure with a chemistry attached. The steel is straightforward: four tiers, a known mass, a beam span and a floor. The chemistry is what catches people out. Vented lead-acid cells release acid mist on boost charge, VRLA blocks release hydrogen under fault, and both sit in a room where the rack is expected to be earthed and to stay painted for fifteen years.

Start with the number that decides the design. A rack of twenty 200 Ah monoblocs at 60 kg each carries 1,200 kg, and with the frame that is about 1,300 kg over a footprint of roughly 1.05 × 0.62 m, or 0.65 m². That is 20 kN/m² on the floor. A raised data hall floor is typically rated at 7.5–12 kN/m², so the rack is a point-load problem before it is a beam problem.

This guide covers the open battery rack used for UPS and DC systems: tier layout, sections, finish, bonding and the cut-form-weld-coat route. It uses a four-tier, twenty-block rack in 2.0 mm CRCA as the worked example. A 19-inch equipment rack is a different part with a different standard, and its frame design guide covers the 482.6 mm interface.

What does a battery rack have to carry?

Three loads, and they do not peak together. The dead load is the blocks plus the frame: 1,300 kg in the example, spread over four tiers at 300 kg each. The maintenance load is a technician leaning on a shelf or lifting a 60 kg block onto the top tier, which is a 1 kN point load at the front edge. The fault load is the one that sizes the anchorage: a short circuit produces electromagnetic forces between cables, and a seismic event or a forklift impact produces a lateral load at the base.

Take 0.2 g lateral as the anchorage case in a moderate seismic zone. On 13 kN of mass that is 2.6 kN at the centre of gravity, about 925 mm up, giving an overturning moment of 2.4 kN·m. Resisted by two anchors at 620 mm centres, the tension per side is 3.9 kN, which an M10 mechanical anchor in 25 MPa concrete handles with margin. The rack does not need a structural engineer for the gravity case; it does for the anchorage if the building is in a high seismic zone or the rack sits on a raised floor.

The beam check is ordinary. A 300 kg tier is 2.94 kN shared between two beams, so 1.47 kN per beam as a uniformly distributed load over a 1,000 mm span. The maximum moment is wL/8, or 184 kN·mm. A 60 × 40 × 2 mm CRCA beam has a section modulus near 3,600 mm³, giving 51 MPa, and a deflection near 1.0 mm, which is L/1000 against a limit of L/200.

Battery rack design limits for the drawing

The load path: beams, uprights and the floor

Beams carry the tier, uprights carry the sum

The beams are the easy part and the uprights are the part that gets drawn by eye. Four uprights share 13 kN, so 3.2 kN each in compression, which is 11 MPa on a 300 mm² section. The check that matters is buckling: a 1,850 mm upright in 2.0 mm CRCA has a radius of gyration near 12 mm on its weak axis, so a slenderness of about 154 and an elastic buckling stress near 87 MPa. At 11 MPa the upright is not close to buckling, provided the frame is braced.

Bracing is what stops a four-tier rack behaving as a mechanism. A bare rectangular frame with moment connections in 2.0 mm sections has very little lateral stiffness, and a 1 kN push at the top will move it several millimetres. Weld a diagonal or fit a back panel, and the rack becomes a shear panel. If the rack is free-standing in the middle of a room, the diagonal belongs on the drawing; if it stands against a wall, the wall bracket is not a substitute for frame bracing, because the wall is not part of the rack.

The floor is usually the limiting member

Each foot of the example carries about 3.3 kN. A 600 mm raised-floor panel is normally rated for a point load of that order with a spreader, and for a uniform load well below 20 kN/m². Two fixes work: a 200 × 200 × 6 mm steel spreader under each foot, which turns the foot into a plate bearing on the panel, or a continuous plinth that picks up the load across several panels and transfers it to the slab.

Neither fix changes the average floor pressure. What they change is the local pressure that the panel and the pedestal see, and that is what fails first. If the room has a structural slab, skip the plinth and anchor directly, but still specify the foot plate so the anchor group has something to bear on.

Chemistry decides material and finish

VRLA, vented lead-acid and the coating that suits each

A VRLA room is a clean, dry environment with a small hydrogen risk under fault. CRCA at 2.0 mm with 60–80 µm of polyester powder over seven-tank pretreatment is the correct, economical finish, and it meets a C3 environment to ISO 12944-2 indoors without trouble.

A vented lead-acid room is not that room. Acid mist settles on the shelves and on the floor around the cells, and polyester powder at 70 µm will chalk, lift at the edges and let acid reach the steel within a year or two of boost charging. The specification has to name an acid-resistant system at 120–150 µm, or a stainless tray under the cells. This is a case where the drawing's finish note decides the maintenance cost for a decade.

Stainless, galvanised or painted

Pre-galvanised 2.0 mm sheet is a reasonable choice for a humid room with VRLA blocks: the cut edges expose steel, so the edges need a zinc-rich touch-up, and the laser cut leaves a zinc oxide that has to be removed before any painting. The galvanised degreasing guide covers that edge case.

Stainless 304 is the right answer for trays under vented cells and for wash-down rooms. It is not the right answer for the whole rack unless the budget allows, because the frame is mostly stiffness and 304 at 1.5 mm costs more than CRCA at 2.0 mm for the same duty. Aluminium is the wrong answer: it corrodes in acid mist, and a bolted aluminium frame is difficult to bond to the earth bar reliably.

Ventilation, clearance and spill containment

IEC 62485-2 covers the safety requirements for stationary battery installations, including ventilation, protection against electrolyte and accommodation of the battery. The rack drawing does not have to reproduce the standard, but it does have to leave room for what the standard requires.

Leave 100 mm clear around the blocks so air can move and so a cell can be inspected and replaced without dismantling the tier. Leave 150 mm behind the rack for cable radius and for the earth conductor. Leave front clearance for the longest block: a 200 Ah monobloc is about 520 mm long, so a 700 mm aisle is the minimum that lets a technician withdraw one.

Where vented cells are used, the rack needs a containment tray under each tier. Size it to the electrolyte volume of the largest cell, which is 10–15 L for a 200 Ah cell, with a 150 mm lip and a drain point. A tray that only catches drips is not containment; it is a stain.

Earthing and bonding across a painted frame

A battery rack is a metal structure near a DC system, and it is bonded for two reasons: fault current and static. Powder coating defeats both if the contact faces are coated.

Mask an M8 stud on each upright, plus a 20 mm ring around it, and bond each tier to the upright with a braided link. Then bond the frame to the building earth bar with a conductor sized for the DC fault current. After assembly, check continuity from the farthest tier to the earth bar at 0.1 Ω or less. A reading above that is usually a coated joint, not a bad conductor.

Do not rely on the anchor bolts for bonding. They go into concrete, their contact is unpredictable, and nobody checks them after installation.

Battery racks and enclosures at Ganesh

Rack uprights, beams, trays and foot plates are cut on the 12 kW fibre laser with the 40 ft × 16 ft bed, formed on the 200 T 5-axis brake with the 4,450 mm bed, and welded on three CLOOS robotic MIG cells or at the 30+ manual stations. Fixtures are designed and built in the tool room, so a batch of frames comes off square and the holes stay on the datum. Coating runs through seven-tank pretreatment into the 18 ft × 14 ft powder booth, and DFT and cross-hatch adhesion are recorded per batch.

The same route builds 19-inch rack frames, PDU brackets, blanking panels and electrical enclosures, which is why a battery rack and its cable management can arrive from one supplier. The data centre rack range lists the family, the racks and enclosures hub collects the related guides, and the rack load calculator is the quickest way to check a tier layout before the drawing is finished.

Inspection before dispatch

• Frame dimensions and diagonal on a checking fixture, at 3 mm on a 1,850 mm frame.
• Tier pitch, measured from the top face of each beam, at ±1.0 mm, because the block sits on that face.
• Weld: leg size, undercut and spatter at every beam-to-upright joint; the toe of that joint carries the tier load.
• Coating: DFT on a flat face, cross-hatch adhesion to ISO 2409 at Gt0 or Gt1, and salt spray to the method and duration in the specification where corrosion is called out.
• Earthing: continuity from the farthest tier to the earth bar, recorded, not assumed.
• Anchorage holes: position and diameter checked against the floor layout, because a rack that does not match the anchor template delays the whole installation.

What to put on the drawing

1. Block make, model, mass and dimensions, plus the number per tier and the tier count.
2. Floor loading limit and the foot detail: spreader plate size or plinth.
3. Section sizes for uprights and beams, and the deflection limit for each tier.
4. The finish system by chemistry: powder for VRLA, acid-resistant coating or stainless for vented cells.
5. Earthing stud positions and the continuity limit.
6. Clearances: 100 mm around blocks, 150 mm behind, front withdrawal dimension.
7. Anchor positions and the template, with the concrete strength assumed.
8. Inspection and traceability: heat number, welder, coating batch and continuity record.

When this route is wrong

A welded CRCA rack is right for most UPS and DC rooms. It is wrong where the room is a high-seismic site and the rack needs a designed anchorage and a tested bracing system; that is structural engineering work, not sheet metal. It is wrong where the battery is a lithium cabinet with its own enclosure and fire rating, because then the rack is the cabinet supplier's scope. And it is wrong where the rack has to be carried through a 700 mm door and up a stair: a knock-down bolted rack, or a set of modules bolted on site, is the only way in, and the drawing has to show the joint and the site tolerance.

Ganesh does not design the ventilation system or the DC protection, and does not galvanise in-house. Send the block datasheet, the floor limit and the room chemistry with the drawing, and the quotation will state the sections, finish and anchorage it assumes.