Aluminum Compression Plates for Prismatic Cells, LFP 280Ah to 320Ah and Sodium-ion (Pair)

Use Cell Compression to Get Maximum Life From Your LFP and Sodium-ion Cells

Large prismatic LFP and sodium-ion cells swell as they cycle. Left loose, they bulge, lose capacity faster and pull on your busbars. OGS aluminum compression plates clamp a row of cells at the pressure the cell makers test them at, so your pack gets the cycle life on the datasheet. They fit the standard 174 x 72 x 204 mm case used by today's 280Ah, 304Ah, 314Ah and 320Ah cells from EVE, CATL, REPT, Hithium, Trina, Gotion, Lishen and others.

Each plate is laser cut and press-brake formed from 0.100 in 5052-H32 aluminum, a marine-grade alloy, with a flange along the top and a slotted mounting foot along the bottom. Those two bends make a thin plate stiff enough to stay flat under clamping load. Aluminum does not rust, and each plate weighs less than half as much as our old steel version. Choose natural aluminum or black anodized. Designed in Michigan, made in the USA.

At a glance

• Fits: prismatic LFP and Sodium-ion cells with a 174 x 204 to 207 mm face and 72 mm thickness (280Ah to 320Ah class)
• In the box: 2 plates (one pair clamps one battery row). Threaded rod sold separately, because rod length depends on your cell count.
• Rods: holes sized for 1/4-20 or M6 threaded rod
• Material: 5052-H32 marine-grade aluminum, 0.100 in thick. Will not rust.
• Finishes: Natural Aluminum or Black Anodized
• Widths: 1 cell wide (single row) or 2 cells wide (two rows side by side)
• Mounting: slotted foot bolts down to strut channel, a shelf or a rack
• Made in USA: ships from Michigan

Key features

• No rust. Aluminum forms its own protective oxide layer instead of rusting. Garages, sheds, cabins, vans and boats are all fine.
• Light. About 0.5 kg (1.1 lb) per 1 wide plate, less than half the weight of 14 gauge steel. Easier to handle and cheaper to ship.
• Right-sized, not over-built. The formed flanges keep the plate flat well past the clamping loads cell makers specify, so there is no need for heavy 1/2 in flat plate.
• Two finishes. Natural aluminum for a clean industrial look and the best value. Black anodized for installs where the battery is on display.
• Slotted mounting foot. Bolt the pack to 1-5/8 in strut channel (Unistrut style) or directly to a shelf. The slots give you room to adjust spacing.
• Sized for the most common DIY cell. One design covers the EVE LF280K, LF304 and MB31 (314Ah), CATL 280Ah and 314Ah, REPT 280Ah to 320Ah, Sodium-ion (160Ah, 200Ah, 210Ah), and other cells in the same case.
• Reusable. Change cell count, rebuild the pack or move it to a new rack. The plates stay the same; only rod length changes.

Choose your options

Width

If you are building a 16S 48V battery and want a shorter footprint, two rows of eight in a 2 wide set is about 60 cm long instead of about 120 cm.

Finish

Not sure? Pick Natural Aluminum. It does the same job and is the better value. Black Anodized is a looks choice.

Why prismatic LFP cells need compression

A large prismatic cell is a tightly stacked or wound set of electrode layers inside a thin aluminum can. As lithium moves in and out, those layers grow and shrink a little on every cycle, and the stack slowly thickens over the life of the cell. The can alone is not strong enough to hold the layers together.

Cell makers design for this. They specify their cells, and run their cycle-life tests, with the cell held in a fixture under steady pressure. The 6,000 to 8,000+ cycle ratings you see on current datasheets describe cells that were clamped. Left loose, a cell can bulge, the internal layers can lose contact, and capacity fades faster. A bulging can also pushes and pulls on busbars and terminals every cycle.

Compression plates put your cells back in the conditions they were rated for.

How much pressure is right?

Numbers from EVE's published specifications for its 280Ah to 314Ah cells, which share the 173.7 x 204.6 mm face:

NOTE: Always review your cell datasheet. These EVE figures are an example, and sodium-ion cells publish their own fixture specs.

The practical target for a DIY pack is about 12 psi, or roughly 300 kgf total, with some give in the stack so pressure stays in range as the cells breathe. EVE also recommends leaving 2.0 to 2.5 mm of expansion room per cell in the module design, which is why foam dividers or springs belong in the stack (see the FAQ).

How to assemble a compressed pack

1. Start at storage charge. Clamp the cells at roughly 30 to 50% state of charge, which is how most cells arrive. LFP cells get slightly thicker as they charge.
2. Insulate. Place an epoxy divider or EVA foam divider between every cell, and an insulating sheet between each plate and the end cells. The blue wrap on the cells is thin and scuffs easily.
3. Stand the plates at each end with the slotted foot at the bottom.
4. Run the rods. Slide 1/4-20 threaded rod through the plate holes. Sleeve each rod with heat shrink or PVC tubing along the length of the cells.
5. Tighten evenly. Put a 1 in OD fender washer under every nut, on both ends. The rod holes sit just outside the edge of the cell, so a small washer lets the plate curl around the hole as you tighten. A 1 in fender washer reaches past the cell edge and pushes straight into the stiff edge of the cell case, so the plate stays flat. Tighten in a cross pattern, a little at a time, until the stack is snug and square. See the FAQ for torque guidance.
6. Mount it. Bolt the feet to strut channel or your shelf.
7. Add busbars last, after the stack is compressed and square, so the cell spacing does not shift under them.
8. Check again after the first few full cycles.

Threaded rod length

Rod length depends on how many cells are in the row. These lengths assume 3 mm foam dividers between cells and leave room for a washer and nut plus a few threads on each end:

For any other count: (cells x 72 mm) + (divider thickness x gaps between cells) + 55 mm. Hardware stores sell 1/4-20 rod in 36 in and 72 in lengths; cut it with a hacksaw and run a nut off the cut end to clean the threads.

2 wide sets need all six rods, including the center pair that runs between the two cell rows. The center rods are what keep the wide plate flat. Leave a gap of at least 10 mm between the rows for the sleeved rod.

Hardware shopping list

• 1/4-20 zinc-plated steel threaded rod, cut to length: 4 for a 1 wide pair, 6 for a 2 wide pair. Use stainless rod on boats and in salty air.
• 1/4-20 nuts: 8 for 1 wide, 12 for 2 wide
• 1/4 in x 1 in OD steel fender washers, at least 0.060 in (1.5 mm) thick: 8 for 1 wide, 12 for 2 wide. Required, one under every nut. Do not use washers larger than 1-1/8 in OD; they will hang past the edge of the plate.
• Heat shrink or PVC tubing to sleeve the rods
• Optional: compression springs, for constant pressure as cells expand
• Dividers for every gap between cells (foam or epoxy)

Technical specifications

What's in the box

• 2x aluminum compression plates in your chosen width and finish

Threaded rod, nuts, washers and dividers are sold separately.

Frequently asked questions

Do LiFePO4 prismatic cells really need compression?
For long life, yes. Cell makers specify and cycle-test their prismatic cells under clamping pressure, and the cycle-life ratings assume it. Unclamped cells can bulge, lose internal layer contact and fade faster, and the movement stresses busbars and terminals. A pack that stays below full charge and sees gentle currents will be more forgiving, but clamping is cheap insurance on cells that cost far more than the plates.

How much pressure should I apply?
About 12 psi across the cell face, which is roughly 300 kgf (660 lbf) total on a 280Ah to 314Ah cell. That is the force EVE uses in its test fixture. EVE's MB31 314Ah spec gives a wider recommended module preload of 3,000 to 7,000 N and says never to exceed 10,000 N.

Is the spec 300 kPa or 300 kgf?
300 kgf. It is a total force, not a pressure. Spread over the 174 x 205 mm face it works out to about 83 kPa (12 psi). Reading it as 300 kPa would mean clamping about 3.6 times harder than the spec.

How tight should I tighten the nuts?
Lighter than most people expect. With four dry, zinc-plated 1/4-20 rods, about 8 in-lb per nut lands near 300 kgf total, and about 10 in-lb lands near 3,500 N. That is a small nut driver or a light touch on a 1/4 in drive torque wrench, not a ratchet. Torque-to-force conversion can be off by 40% depending on thread condition and lubrication, so treat it as a starting point. On a 2 wide set with six rods, use about 11 in-lb per nut to reach roughly 300 kgf per cell row. Always use a 1 in OD fender washer under each nut on the aluminum plate. For a measured result, use calibrated springs on the rods and tighten to a known spring length.

Should I use a fixed clamp or springs? Do I need foam between cells?
Use some give in the stack. A perfectly rigid clamp at fixed length lets force climb as the cells thicken with age, and EVE recommends leaving 2.0 to 2.5 mm of expansion room per cell. The two common ways to add it are 3 mm EVA foam dividers between cells, or compression springs under the nuts. Either one keeps pressure in range as cells breathe. The plates do the job of spreading the load evenly; the foam or springs keep the force steady.

Is 0.100 in aluminum strong enough? Why not 1/2 in plate?
Yes. A flat plate needs to be thick because it bends like a diving board. These plates get their stiffness from the two formed flanges, which is the same reason builders bolt angle iron across flat plates after they watch them bow. We made the aluminum plate thicker than the old 14 gauge steel and the flanges taller, so it is at least as strong as the steel version. By our engineering calculations, the plate deflects about 0.02 mm at the recommended clamping force and holds more than 10 kN (2,250 lbf) per cell row, which is EVE's maximum momentary force. A thicker plate would add weight and cost without a practical benefit.

Will the plates short my cells? Do I need insulation?
Cell cases can carry voltage, aluminum conducts electricity, and the factory wrap is thin, so insulate. The anodized finish is a thin surface layer and is not a substitute for insulation. Put an insulating sheet (epoxy board, FR4 or similar) between each plate and the end cell, place a divider between every cell, and sleeve the threaded rods with heat shrink or PVC tubing where they run alongside the cells.

Will these fit my 314Ah or 320Ah cells?
Almost certainly. Most 280Ah, 304Ah, 314Ah and 320Ah LFP cells use the same case, about 174 x 72 x 204 mm (207 mm including terminal insulation). Check your cell datasheet. If the face is 174 x 204 to 207 mm, these fit.

Will these fit sodium-ion prismatic cells?
Yes, if the cell uses the same 174 x 72 x 207 mm case. That includes our 160Ah NFPP and 200Ah layered oxide sodium-ion cells, and other 210Ah NFPP cells in the same case. Follow the sodium cell maker's fixture pressure spec.

What about 500Ah+ cells like the EVE MB56 628Ah?
Those use a larger case, so these plates do not fit. Contact us with your cell model for a custom size.

How many cells can one pair of plates hold?
As many as your rods are long. The plates only go at the two ends of a row. 4, 8 and 16 cell rows are all common. For long rows, two rows of eight in a 2 wide set are easier to handle and fit more shelves than one 1.2 m row.

Why are threaded rods not included?
Rod length depends on your cell count and divider thickness, and shipping 50 in rods adds cost. You can buy 1/4-20 rod at any hardware store. See the rod length table above.

Natural Aluminum or Black Anodized?
Both are the same plate, and neither will rust. Natural Aluminum is the better value and works anywhere. Black Anodized is for looks: a black finish for indoor installs where the battery is on display. It costs more because it goes through an extra process, and it is made in batches, so it takes longer to ship.

Will the steel rods corrode the aluminum plates?
Not in a normal indoor or garage install. Zinc-plated steel rods, nuts and washers on aluminum are a common, low-risk pairing in dry conditions. On boats or near salt water, use stainless steel rods, nuts and washers.

Can I use wood or flat plate instead?
You can. Flat aluminum needs to be around 1/2 in thick to stay flat, and flat steel around 1/4 in, which is heavy and bulky. Plywood works indoors but can compress over time and absorbs moisture. Formed aluminum plates give you a thin, light, flat, mountable part that does not rust or change with humidity.

What state of charge should cells be at when I clamp them?
Around 30 to 50%, which is how most cells ship. Cells are slightly thicker at full charge, so avoid setting clamp force on a fully charged pack.

Do I need to re-tighten later?
Check the rods after the first few full cycles and then once a year. With foam dividers or springs in the stack, you are checking that nothing has loosened, not trying to add more force. Do not keep tightening a stack that feels firm.

My cells are already swollen. Will compression fix them?
No. Compression slows normal expansion in healthy cells. A cell that has puffed from overcharging, over-discharging or overheating is damaged, and pressing it flat does not repair it. Set correct cell voltage limits in your BMS and charger to prevent it.

Do you make custom sizes?
Yes, for other prismatic cell formats and for battery modules. Contact us and send us your cell model and dimensions.

What overcharging does to an unprotected cell

These cells were overcharged. Compression plates do not prevent this kind of damage. A correctly set BMS does.

Related products

• EVA foam dividers for prismatic cells, 203 x 172 mm, 3 mm, V0 flame retardant
• Insulating epoxy dividers for prismatic cells, 0.5 mm
• Flexible busbars for 280Ah prismatic cells, 200A
• JK BMS for LFP battery packs

Why we switched from steel to aluminum

The first versions of these plates were made from steel. Structurally they did the job, but we kept hearing the same complaint from customers: rust. Battery packs live in garages, sheds, cabins and vans, where humidity and big temperature swings are normal. A cut edge or a small chip in the finish was all it took for rust to start, and nobody wants orange streaks next to a battery they just spent good money on.

So we went back to the drawing board. We redesigned the plate in 5052-H32 aluminum, the same marine-grade alloy used for boat hulls and fuel tanks, because it simply does not rust. Aluminum is less stiff than steel, so we made the plate thicker and the formed flanges taller to keep it at least as strong as the steel version. The new plate still weighs less than half as much, which also brings your shipping cost down.

Same fit, same rod holes, same mounting foot. No rust. Thank you to everyone who sent us feedback on the steel plates. This version exists because of you.

Questions about your build? Contact us.