What Is DC Voltage Drop?
DC voltage drop occurs when electrical current flows through a wire and loses energy due to the wire's internal resistance. Unlike AC systems which can fluctuate slightly, DC systems (like 12V automotive or 24V marine systems) are highly sensitive to even small voltage losses.
This calculator uses the standard round-trip calculation method (2 × Distance) because DC requires a complete return path for the current to flow back to the battery.
How to Calculate DC Voltage Drop (The Formula)
To calculate the drop manually, use the following formula which is the industry standard for low-voltage DC wiring:
Vd = (2 × R × I × D) / 1000
- 2: Constant for round-trip return path.
- R: Ohms per 1000 feet of wire (based on AWG size).
- I: Current draw of the device (Amps).
- D: One-way distance from source to load (Feet).
Recommended DC Limits
Depending on how critical your component is, you should aim for the following percentage limits:
- 3% Limit: Critical systems like circuit breakers, primary power leads, and main charge cables.
- 10% Limit: Non-critical lighting and accessory circuits (radios, general cabin lights).
General Questions
Does wire temperature affect DC voltage drop? +
Yes. Resistance increases as wire gets hotter. This calculator assumes standard room temperature (approx 25°C). For hot engine bays, you should always oversize your wire by one gauge for safety.
Can I use this for 12V and 24V? +
Absolutely. The formula works for any DC source including 12V, 24V, 48V, and even high-voltage DC arrays.