Voltage Drop Calculator
Determine voltage drop with precision using our free Voltage Drop Calculator. Enter your system voltage, current, cable length, and wire size to find accurate voltage loss, percentage drop, and final load voltage. Ideal for campervan, off-grid, and solar power installations.
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Understanding the Voltage Drop Calculator
Voltage drop is a critical factor in any low-voltage electrical system—especially in campervans, off-grid setups, and solar power systems. This calculator helps you determine the voltage drop, percentage loss, voltage at load, and cable resistance for a given run of copper wire. By entering system voltage, current, cable length, and wire size, you’ll get accurate feedback on whether your circuit meets industry-recommended limits.
For a full breakdown of safe wiring practices, see our detailed guide on campervan electrical systems.
Assumptions and Key Points
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Material: This calculator assumes stranded copper wire with resistance values adjusted to 60°C—reflecting real-world conditions in enclosed spaces with mutual heating (e.g. flat-touched cables).
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Voltage Type: Works for both DC and single-phase AC circuits, assuming a round-trip cable path (2x one-way distance).
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Wire Sizes: Based on standard metric mm² wire sizes commonly used in Europe and globally. Resistance values are taken from Victron’s specifications.
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Temperature Adjustment: Resistance values reflect copper’s increased resistivity at 60°C using a correction factor of ~1.16 over baseline 20°C values.
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Voltage Drop Limit: Industry best practice is to keep voltage drop below 3% for critical circuits and below 10% for non-essential or long cable runs.
Formulas Used
The primary formulas used in this calculator are:
1. Total Cable Resistance:
Resistance (Ohms) = 2 × Length (m) × Resistance per meter (Ω/m)
2. Voltage Drop:
Voltage Drop (V) = Current (A) × Resistance (Ω)
3. Voltage Drop (%):
Voltage Drop (%) = (Voltage Drop ÷ System Voltage) × 100
4. Voltage at Load:
Voltage at Load (V) = System Voltage − Voltage Drop
Why Correct Wire Sizing Matters
Even small voltage losses can cause serious issues in 12V and 24V DC systems, including:
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Reduced appliance efficiency
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Flickering lights or inverter shutdowns
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Overheating cables and potential fire risks
This calculator ensures you’re designing safe, reliable circuits with minimal power loss—essential for mobile, off-grid, and battery-powered systems.
Disclaimer
The information provided by this calculator is for general informational purposes only. While we strive to provide accurate calculations, we recommend seeking professional advice for specific electrical needs. TheVanConversion.com assumes no liability for any errors or discrepancies in the results.