Trolling Motor Wire Size Calculator

Wire Size Formula:

\[ A = \frac{I \times L \times 2 \times \rho}{Vd} \]

Current (I):

amps

Length (L):

meters

Resistivity (ρ):

ohm-m

Voltage Drop (Vd):

volts

Wire Cross-Section Area (A):

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1. What is the Trolling Motor Wire Size Calculation?

The wire size calculation determines the appropriate cross-sectional area of wire needed for a trolling motor installation based on current, wire length, material resistivity, and acceptable voltage drop. Proper sizing ensures efficient power delivery and prevents overheating.

2. How Does the Calculator Work?

The calculator uses the wire size formula:

\[ A = \frac{I \times L \times 2 \times \rho}{Vd} \]

Where:

\( A \) — Wire cross-section area (mm²)
\( I \) — Current in amps
\( L \) — Length of wire in meters (one way)
\( \rho \) — Resistivity of wire material (ohm-m)
\( Vd \) — Acceptable voltage drop in volts
The factor of 2 accounts for round-trip current path

Explanation: The equation calculates the minimum wire size needed to maintain voltage drop within acceptable limits for the given current over the specified distance.

3. Importance of Proper Wire Sizing

Details: Correct wire sizing prevents excessive voltage drop (which reduces motor performance), minimizes power loss as heat, and reduces fire risk from overheating wires.

4. Using the Calculator

Tips:

Enter the maximum current your trolling motor will draw (check specifications)
Measure the total one-way distance from battery to motor
Use 0.0000000172 ohm-m for copper wire (default value)
Typical acceptable voltage drop is 3% of system voltage (about 0.36V for 12V systems)

5. Frequently Asked Questions (FAQ)

Q1: Why is voltage drop important?
A: Excessive voltage drop reduces motor power and efficiency, and can cause overheating in both motor and wiring.

Q2: What's a typical resistivity value for copper?
A: Copper resistivity is approximately 0.0000000172 ohm-m (the default value in the calculator).

Q3: How do I account for temperature?
A: For warm environments, increase resistivity by about 4% per 10°C above 20°C or use larger wire.

Q4: What about aluminum wire?
A: Aluminum has higher resistivity (about 1.6× copper) - use 0.0000000282 ohm-m and verify ampacity ratings.

Q5: Should I round up the calculated wire size?
A: Yes, always round up to the next standard wire gauge size for safety margin.