A lead-acid plate is made in four steps: cast a lead-antimony grid, press lead oxide paste into it, cure the pasted plate in warm humid air, then convert it to lead dioxide or sponge lead by a long formation charge. Each cell needs one more negative plate than positive, so a six-cell battery built from four positive and five negative plates per cell needs 54 plates.
Part of Battery Building and Maintenance
The sequence from molten lead to a formed battery plate, with the plate counts and quality checks that tie the steps together.
Four Steps Turn Lead Into A Working Plate
The grid is the backbone: a lead frame with a mesh of ribs and a lug at the top, which holds the active material and carries current to the terminal (Plate Casting covers the mold and pour). The paste is lead oxide mixed with dilute sulfuric acid, pressed into the grid openings. Curing hardens and bonds the paste. Formation charging then turns the cured paste into lead dioxide on the positive plates and sponge lead on the negative plates; the carrier calls it the single most important step, because under-formed plates mean poor capacity.
Each step has its own article here: Grid Casting, Lead-Antimony Alloy, Plate Pasting and Plate Curing and Formation.
Plate Count Follows From Cells And Plate Pairs
The carrier’s 50 Ah target uses 4 positive and 5 negative plates per cell. Plate Casting works a 100 Ah example at 9 positive and 10 negative per cell. Both start and end the stack with a negative plate. The reason is general knowledge, not from the other articles: it puts a negative plate against both faces of every positive plate, so no positive face is left unused.
Neither source ties a plate size to an ampere-hour figure, because capacity depends on plate area, paste mass and how fully the paste reacts. The plate count above is a starting design, to be checked by a discharge test on the first finished cell (Lead-Acid Chemistry shows the minimum material per ampere-hour).
What You Need
- Lead — scrap, cable sheathing or salvaged battery grids, and an antimony source (Lead-Antimony Alloy)
- A crucible and a heat source — lead melts at 327°C (Crucibles)
- A grid mold — iron or steel (Mold Making is a brick mold and is not the grid pattern; the grid mold is in Plate Casting)
- Lead oxide — for the paste
- A warm, humid place — for curing
- Dilute sulfuric acid and a DC source — for formation
Method: From Ingot To Formed Plate
Step 1: Prepare the alloy and cast the grids, rejecting any with cold shuts, porosity or incomplete ribs.
Step 2: Make the paste and press it into the grids, a little proud of the surface.
Step 3: Cure under cover in warm humid air so the paste bonds to the grid and hardens.
Step 4: Immerse the plates in dilute acid and form them at the low charge rate described in the curing article. A positive plate is ready when it is uniformly dark brown, a negative when it is uniformly gray.
Worked Example: Plates For One Battery
A six-cell battery on the carrier’s 50 Ah design: 6 cells × (4 positive + 5 negative) = 6 × 9 = 54 plates, of which 24 are positive and 30 negative. On the 100 Ah design in the plate-casting article: 6 × (9 + 10) = 114 plates, 54 positive and 60 negative, matching that article. Casting a battery’s worth of plates in a single session is practical; that article estimates 3 to 4 hours for an experienced caster on the 114-plate design. Add a margin for rejects.
Common Mistakes
- Skipping the weight check — plates varying by more than ±5% in a batch point to an inconsistent pour, per the plate-casting article
- Pasting then using immediately — uncured paste sheds (Plate Curing and Formation)
- Forming and not testing — a plate that looks right can still be under-formed; measure capacity on the finished cell
Safety
Molten lead and lead dust are the hazards of this stage
Melting lead gives off toxic fume, especially above 450°C, and the lead oxide for paste is a fine powder that is inhaled and carried home on hands. Cast outdoors or under a strong exhaust hood, keep tools and molds completely dry because water meeting molten metal throws it (general knowledge, not from the other articles), wash hands before eating, and keep children and pregnant people away (Lead Exposure Prevention).
What’s Next
- Learn next: Grid Casting — the first step of the sequence
- Combine with: Cell Assembly — what the formed plates go into