Drawing set ZM‑CELL‑01 · Rev C · Units: mm unless noted · Sheet 8: 2S2P block

Zn‑MnO₂ Cell Module

Construction drawings for one replaceable cell of the 12 V, 10-cell salt-water battery: a sealed polypropylene box holding 5 cathode plates and 6 zinc plates in compressed felt, with bolt-hole terminal lugs on the lid.

Nominal voltage: 1.3 V
Capacity: 70 Ahdesign target · 40–70 Ah estimated
Outside size: 167.6 × 26.88 × 175+ lugs to 182
Mass: ≈ 1.52 kgfilled
Resistance: 3–6 mΩestimated
Voltage window: 0.90–1.50 Vcharge limit unverified, see sheet 7

General arrangement

Front elevation looking through the front wall, with the nearest zinc plate shaded. Balloons match the item numbers in the bill of materials on sheet 6.

Polypropylene Zinc Cathode mix Titanium Ni-plated brass PP felt Electrolyte

Height budget (inside, 170)

Bottom ribs	3
Plates	140
Felt overhang above cathode	3
Electrolyte above felt	≈ 5
Tabs, straps, risers	19

Plate positions

Plates are centered across the 165.2 inside width, leaving 2.6 each side. Zinc plates stand on the ribs. Cathode plates sit 0.88 higher, on the folded felt. Cathode tabs are 20 from the left (+) end, zinc tabs 115 from the left.

TitleGeneral arrangement · front elevation

Sheet2 of 8

Scale1:1 approx. on screen

RevC

Lid plan

Seen from above. The wide guide rail marks the + end, so the module can only go into its slot one way. The vent and fill port sit on the centerline. The lug holes sit 3 off center so each riser can pass through the lid beside its nut.

TitleLid plan · terminals, vent, fill port

Sheet3 of 8

Scale1:1 approx. on screen

RevC

Section A‑A · plate stack

Cut through the middle of the cell, looking toward the + end. Thickness is drawn about 9 times larger than the elevation so every layer shows. Zinc plates are at both walls, so each of the 10 cathode faces faces zinc.

TitleSection A‑A · layer stack

Sheet4 of 8

Scale≈ 20:1 horizontal

RevC

Part details

The + lug riser comes up beside the strap center, passes through an EPDM sleeve in the lid slot, and bends over the boss so its hole sits above the captive M6 nut. The epoxy well around the riser is the main seal. Weld titanium only to titanium.

TitlePlates, felt envelope, lug feedthrough

Sheet5 of 8

ScaleAs noted

RevC

Bill of materials · one cell

Item	Part	Material	Size	Qty	Mass / note
1	Module box	Polypropylene	167.6 × 26.88 × 172 ext. 1.2 walls, 2.0 bottom, three 4 × 3 ribs. Guide rails: 6 wide on + end, 3 wide on − end, 1.4 proud	1	≈ 85 g
2	Lid	Polypropylene	167.6 × 26.88 × 3.0, two lug bosses 3.0 high, vent seat, fill thread, lift ridges 8 wide × 6 high	1	Hot-plate welded
3	Cathode plate	75% MnO₂ / 25% carbon + 4% PTFE on Ti mesh	160 × 140 × 2.90, 50% porosity, tab 25 × 16	5	90.91 g MnO₂ + 30.30 g C + ≈ 4.8 g PTFE
3a	Cathode collector	Expanded titanium mesh, Gr 2	160 × 140 × 0.2 with solid tab 25 × 16	5	≈ 8.1 g
4	Zinc plate	99% zinc sheet	160 × 140 × 0.20, tab 25 × 16	6	32.0 g + tab
5	Felt envelope	PP needle felt ≈ 1.2 thick, Triton X‑100 treated	Flat 165 × 290, folded, sides heat-sealed 2 wide. 0.88 compressed	5
6	Cathode strap	Titanium Gr 2	22 × 6 × 3	1	Welds to 5 tabs + item 8
7	Anode strap	Nickel-plated brass	22 × 6 × 3	1	Solder or weld to 6 tabs + item 9
8	+ terminal lug	Titanium Gr 2	4 × 25 riser, bent to 20 × 25 pad, Ø6.5 hole	1	≈ 0.13 mΩ
9	− terminal lug	Nickel-plated brass	3 × 20 riser, bent to 20 × 20 pad, Ø6.5 hole	1
10	Captive nut	316 stainless	M6 hex, pressed into boss	2
11	Lug seal	EPDM sleeve + epoxy	Sleeve in lid slot, epoxy well 2 deep	2
12	Vent valve	EPDM umbrella valve	Opens 1.5–2.5 psi, splash baffle molded under lid	1
13	Fill plug	Polypropylene + EPDM O-ring	Ø16 head, threaded into lid	1
14	Electrolyte	2 M ZnSO₄ + 0.1 M MnSO₄	359 mL, fill to 151 above inside floor	1	≈ 500 g
15	Barrier film (optional)	Cellophane, 25 µm	Envelope 165 × 300 over item 5 (zinc side)	5	Felt drops to ≈ 0.85

Electrolyte batch · 400 mL

Zinc sulfate heptahydrate	230.0 g
Manganese sulfate monohydrate	6.76 g
Distilled water	to 400 mL

Dissolve the manganese sulfate first, then the zinc sulfate in batches (the mix turns cold). Top up to 400 mL once back at room temperature. Use 359 mL in the cell.

Active material per cell

MnO₂	454.54 g
Carbon powder	151.51 g
PTFE binder (4%)	≈ 24 g
Zinc	191.9 g
Titanium mesh	≈ 40 g

TitleBill of materials

Sheet6 of 8

ScaleNone

RevC

Build sequence and checks

Treat the felt
Soak felt in 0.1–0.5 wt% Triton X‑100 in isopropyl alcohol for 5 minutes. Hang until fully dry.
CheckWater drop soaks in within seconds
Cut the zinc plates
Cut six 160 × 140 plates with a 25 × 16 tab at 115 from the left edge. Deburr every edge and degrease with alcohol.
Check0.20 ± 0.02 thick, no burrs by fingertip
Mix the cathode
Per plate: dry-blend 90.91 g MnO₂ with 30.30 g carbon, then knead in PTFE dispersion (≈ 4.8 g solids) to a dough.
CheckUniform black, no dry streaks
Form the cathode plates
Roll the dough to two 1.35 sheets, lay one each side of the Ti mesh (tab at 20 from the left), and press or roll to 2.90.
Check2.90 ± 0.05 thick, ≈ 134 g with mesh
Make the envelopes
Fold each 165 × 290 felt around a cathode plate, fold at the bottom edge, and heat-seal both sides 2 wide. Add the optional cellophane envelope over it.
CheckNo exposed cathode edge
Stack the cell
Zinc, cathode, zinc, cathode … ending in zinc (6 zinc, 5 cathode). Line up the cathode tabs on the left and zinc tabs on the right.
CheckTabs never cross over
Clamp
Squeeze the stack between two flat plates to 24.48 and hold it with a clamp.
Check24.48 ± 0.1 across the full face
Weld the straps
Weld the 5 cathode tabs to the Ti strap and the 6 zinc tabs to the brass strap. Weld the + riser to the Ti strap and the − riser to the brass strap.
CheckNo cathode-to-zinc short (meter reads open)
Box the stack
Slide the clamped stack into the box until it rests on the ribs, then release the clamp.
CheckPlates sit square, felt touches both walls
Fit the lid
Thread the risers through the lid slots with EPDM sleeves, hot-plate weld the lid, bend the risers over the bosses onto the captive nuts, and fill the wells with epoxy.
CheckLugs flat, holes line up with nuts
Leak test
With the vent capped, pressurize through the fill port to 1.0 psi and brush soapy water over every seam and lug.
CheckNo bubbles for 5 minutes
Fill
Add 359 mL of electrolyte in 3–4 pours, 15 minutes apart, up to the fill line. Fit the plug.
CheckLevel at 151 above the inside floor
Wet out
Let the cell rest for 24 hours.
CheckRest voltage steady, about 1.3–1.5 V
Form
Cycles 1–2: 1.4 A discharge to 14 Ah or 1.05 V, charge at 1.4 A. Cycles 3–4: 3.5 A discharge to 35 Ah or 0.90 V, CC/CV charge. Record the capacity of each cycle.
CheckCapacity rises or holds each cycle
Baseline
Charge fully, rest 24 hours, and log the voltage drop. This is the self-discharge figure to compare against later.
CheckLogged with the cell serial number

Open items before building a full pack

Charge voltage. The design limits charge to 1.50 V. Published Zn‑MnO₂ cells in sulfate electrolyte usually charge to 1.8–1.9 V. Form this first cell at 1.50 V, then try 1.80 V and compare recovered capacity.
Felt width. The envelope is 165 wide. Earlier notes said 166, which does not fit the 165.2 inside width, and note.txt is now corrected.
Cold limit. The electrolyte freezes at about −6 °C. Keep the cell above that.
Pressing force. A full 160 × 140 plate pressed flat at once needs tens of tonnes. Roll the sheets or press in tiles.

TitleAssembly procedure · quality checks

Sheet7 of 8

ScaleNone

RevC

2S2P block · four-cell variant

Two sealed compartments in one printed box, each holding two standard plate stacks in parallel. Cell 2 is turned 180°, so its + lug sits beside the − lug of cell 1 and a short link bar on top of the lid joins them. Plate stacks, felt, straps, lugs and seals are the same parts as the single module (sheets 2–7) unless noted here. Model: cell_module_case.scad with cells_series = 2, cells_parallel = 2.

Block data

Nominal voltage	2.6 V
Capacity (estimate)	80–140 Ah
Outside size	167.6 × 107.52 × 175
Slots in the pack case	4
Compartment inside	165.2 × 48.96 × 170
Electrolyte	718 mL × 2
Mass, filled	≈ 6.1 kg
Resistance (estimate)	3–6 mΩ
Printed case (PETG)	≈ 550 g

Schematic

Parts that change

Plate stack kits (items 3–5)	4
Ti strap / brass strap, 46 × 6 × 3	2 / 2
+ lugs / − lugs (items 8, 9)	2 / 2
Link bar, Ni-brass 3 × 20 × 69	1
Spacer, Ni-brass Ø14 × 1	1
Captive nuts, M6 316 SS	4
Bolts: M6 × 16 (link) / M6 × 12, × 10	2 / 1, 1
Vent valves / fill plugs	2 / 2

10S2P pack from five blocks

Build differences

Leak test the empty box, then fill one compartment at a time with water and check the other stays dry for 24 h. The partition must never be drilled or notched.
Clamp the two stacks of each cell side by side to 48.96. Join all 10 cathode tabs to one 46-long Ti strap and all 12 zinc tabs to one 46-long brass strap.
Turn the cell 2 stack 180° before boxing it, so its cathode tabs are at the − end of the block.
Fit one lid over both compartments. Epoxy fills every lip gap; check the bead closes over the partition top, because it is the only seal between the cells.
Bolt the link bar across the link pad with the 1 mm spacer on the brass side, then measure each cell separately: 1.3–1.5 V each, 2.6–3.0 V across the block.
Fill each compartment with 718 mL through its own port.

Pack size

A 10S2P pack needs 20 slots (537.6), twice the length of the original 10-slot case. Use a longer case or two 10-slot cases side by side.

Title2S2P block · lid, section B‑B, pack layout

Sheet8 of 8

ScaleAs drawn

RevD

General arrangement

Height budget (inside, 170)

Plate positions

Lid plan

Section A‑A · plate stack

Part details

Bill of materials · one cell

Electrolyte batch · 400 mL

Active material per cell

Build sequence and checks

Treat the felt

Cut the zinc plates

Mix the cathode

Form the cathode plates

Make the envelopes

Stack the cell

Clamp

Weld the straps

Box the stack

Fit the lid

Leak test

Fill

Wet out

Form

Baseline

Open items before building a full pack

2S2P block · four-cell variant

Block data

Schematic

Parts that change

10S2P pack from five blocks

Build differences

Pack size