Connect a lead-acid cell by joining all positive plate lugs with one cast lead strap and all negative lugs with another, then link cells in series, positive of one to negative of the next, so six cells make a 12 V battery. Make each joint by lead burning or a clean bolted clamp, keep every joint tight and corrosion-free, and fuse the bank, because a short across a battery carries a very large current at very low voltage.
Part of Battery Building and Maintenance
Joining plates into cells and cells into a bank with lead straps, bus bars and bolted terminals.
Lugs, Straps And Links Make One Circuit From Many Plates
Inside a cell, every positive lug is joined to one lead strap and every negative lug to another; the carrier says to connect them with a cast lead bus bar. Between cells, the positive terminal of one cell goes to the negative of the next. Voltages add and capacity stays the same (Cell Voltage), so six cells make a nominal 12 V battery. The lead-acid article names two ways to make the joint: lead burning, which is welding with a propane torch and a lead rod as filler, or a mechanical bolt or clamp connection.
Connections are where resistance builds. A poor joint gets warm under load, wastes energy and, on a battery that is charging, can spark. Continuity Test gives the benchmark for a good screwed terminal: under 0.01 Ω is good, over 0.1 Ω is suspicious, and over 1 Ω must be replaced. A white or green crust at terminals is corrosion and increases resistance; the energy-storage article cleans it with baking-soda paste and water and coats the clean terminal with grease or petroleum jelly.
What You Need
- Lead strap material — cast from the same lead as the grids
- Link conductors — heavy copper cable or lead links, sized by current (Wire Selection, the copper-and-aluminium ampacity article)
- A torch and filler rod — for lead burning, or bolts and clamps for a mechanical joint
- A fuse or breaker on the bank — Fuse Design
- Insulated tools, a resistance meter
Method: Connect A Bank
Step 1: Join the lugs. Fit the plate lugs into a strap or a bus bar, then lead-burn or clamp them. Check the joint is solid by pulling gently on a plate.
Step 2: Place the cells in a row, ensuring terminals of adjacent cells alternate positive and negative so the links are short.
Step 3: Link in series. Connect positive to negative with the heavy link, bolted tight. Do not connect the last two terminals (the bank’s main terminals) until everything else is done.
Step 4: Test each joint with the resistance meter before the bank is charged or loaded.
Step 5: Fit a fuse in the main lead from the bank, close to the positive terminal, and then connect the load. Size it to protect the wire, not the load (Wire Selection: a fuse protects the wire).
Step 6: Protect the terminals with a thin coat of grease once clean.
Worked Example: Why A Short Is Not A Small Event
The Cell Voltage article’s example cell has an internal resistance of 0.05 Ω. A short across one such cell gives I = 2.05 ÷ 0.05 = 41 A. Six cells in series, with 6 × 0.05 = 0.3 Ω of internal resistance and 12.6 V, give I = 12.6 ÷ 0.3 = 42 A. Heating in the wire or tool follows P = I²R: a 0.01 Ω steel spanner carrying 42 A gives 42² × 0.01 = 17.6 W of heat concentrated in the contact points. A larger bank has a much lower internal resistance, so a larger short current: Battery Bank Sizing warns that a bank of village size can deliver hundreds of amps into a short and melt metal. The 0.01 Ω tool figure is assumed for the example.
Common Mistakes
- Loose terminals — heat and sparks; retighten on every inspection
- Copper wire clamped directly on lead without cleaning — corrosion raises resistance (Maintenance and Reconditioning)
- No fuse — the wire becomes the fuse in a short
- Mixed old and new cells in one bank — the weakest cell sets the whole bank’s limit (Battery Bank Sizing)
Safety
A bank is a short-circuit hazard of a different kind from mains
The voltage is low but the current is enormous, so a dropped spanner across two terminals welds in place and can rupture a cell; the energy-storage article warns of exactly this. Remove watches and rings, which can heat and burn through skin when they bridge a terminal, wrap tools in insulation, and never lay metal on a bank. A spark at a loose terminal can also ignite hydrogen at the top of a charging cell (Hydrogen Gas Hazard).
What’s Next
- Learn next: Charging Circuits — putting current back in
- Combine with: Bus Bars — copper bars for the distribution side