Undersized battery cables cause efficiency losses, overheating, voltage drop, and fire risk. Correct cable sizing is essential for safety and performance in any battery installation.
>The Key Formula
Voltage Drop = (Current x Cable Length x 0.019) / Cross-sectional Area (mm2)
Where: Current in amps, Cable Length in meters (one way), 0.019 = resistivity of copper.
Recommended Maximum Voltage Drop
- Battery to inverter DC cables: Maximum 1-2% voltage drop
- Solar panel to charge controller: 2-3% acceptable
- Grounding conductors: Sized per local electrical codes
Cable Size Examples (48V System)
- 3kW inverter (62A at 48V): 3m distance, 1% drop = (62 x 3 x 2 x 0.019) / 0.01 = 70.7mm2. Use 70mm2 cable or 2x35mm2 in parallel.
- 5kW inverter (104A at 48V): 3m, 1% = (104 x 3 x 2 x 0.019) / 0.01 = 118.6mm2. Use 120mm2 or 2x70mm2.
- 10kW inverter (208A at 48V): 5m, 1% = (208 x 5 x 2 x 0.019) / 0.01 = 395.2mm2. Use 400mm2 bus bars.
Standard Cable Sizes
- 16mm2: Up to 70A over short distances
- 25mm2: Up to 100A
- 35mm2: Up to 125A
- 50mm2: Up to 150A
- 70mm2: Up to 200A
- 95mm2: Up to 250A
- 120mm2: Up to 300A
Always consult local electrical codes for minimum cable sizing requirements.