Battery Supply Line
The wiring that takes the kit's power directly from the battery terminal rather than from another consumer inside the vehicle. A supply taken from an intermediate point rides on top of that line's own load and voltage drop, which leads to unstable operation. The fuse on the line is positioned as close as possible to the battery terminal in order to limit the short-circuit risk.
A correct supply line provides three things together: adequate cross-section, a short route and correctly positioned protection.
- Cross-section: at 12V a 3% voltage drop limit leaves only 0.36 V of margin. For a 10 A load and a 3 m one-way distance a 4 mm² cross-section is recommended; 2.5 mm² stays within the limit at this load up to about 2.5 m.
- Fuse location: the fuse protects the cable, not the load. The section between the battery and the fuse is unprotected, so this distance is kept as short as possible.
- Routing: the cable is run away from the exhaust and hot surfaces, protected with a grommet where it passes sharp sheet-metal edges, and must not rub against moving parts.
For the LFT20 the manufacturer declares an average current of 10 A; this value is the starting point for both the cross-section and the fuse calculation. Since the high temperature in the engine area increases the resistance of copper, margin must be left in the calculations. When the supply is taken from the terminal, the kit's voltage is least affected by the switching of the vehicle's other consumers.
Context in which this term is used: Converting a tractor hydraulic lever to electronic control