The wire size for your trolling motor depends on several factors.
To determine the appropriate wire size, you should consider the following factors:
- Voltage: Higher voltage systems will generally require smaller wire sizes than lower voltage systems because of reduced current draw.
- Current draw: The higher the current draw of your trolling motor, the larger the wire size you will need to ensure minimal voltage drop and prevent overheating.
- Length of the wire: The longer the distance between your trolling motor and battery, the larger the wire size you need to account for voltage drop.
To determine the size of the wire we are going to use several online calculators. I will explain the reasoning with an example below:
Step 1: Determine the Voltage and Current of the motor
Determining the voltage is easy. You will find this on the salespage of the motor or just your common knowledge. If you already have a motor and run it on a 12V battery, then it’s a 12V motor.
The current is a little harder to find out. We need to look for the Max amp (current) draw of the motor. This is the amount of amps the motor is going to draw when it’s going full throttle.
In this example, I will use a Minn Kota Ultrex:
- Voltage: 12V
- Current: 52A max
Now that we know these values we can move on to finding out the length of the wire.
Step 2: Find out the length of the wire
If the batteries are in the back of the boat, and the motor is in the front, it will take a few feet of wire to get there. Due to the resistance of the wire, the voltage will drop. These are losses that we want to avoid. A voltage drop of 3% is acceptable.
Let’s say our wire length (one way) is 10ft from the batteries to the motor. It’s safe to have a little bit extra.
Now we will finally move on to calculating the wire size.
Step 3: Calculating the wire size
We first need to create a safety factor of 125%. We do this by multiplying the current by 1.25
We will then open up this calculator and use the values we have found.
- Wire diameter size: We will adjust it once we have entered our own details.
- Wire/cable length: we will enter in 10ft.
- Current type: DC (this means direct current, which batteries use).
- Voltage in volts: enter the voltage of your motor.
- Current in amps: enter the current we have calculated using the 125% safety margin.
When you press calculate, the ‘percentage of voltage drop’ will be very high. We now need to adjust this to be under 3%.
When you select a 4AWG wire (25mm²), the voltage drop will be under 3% and will be suited for your system.
I recommend using a popular brand Ancor for marine wires. Check their wires out here.
What gauge wire for 24v trolling motor?
Let’s use the same current draw but with a 24V motor. We will see that the wire size will be reduced because the higher the voltage, the lower the voltage drop is.
- Voltage: 24V
- Current: 50A*1.25=65A
- Length: 10ft
We can now see that we need a 6AWG or 16mm² wire instead of the bigger 4AWG or 25mm² wire from the 12V motor.
There you have it. That is how you calculate the wire size for a trolling motor.
Interested in reading my expert guide on the best trolling motor batteries? Read it here.