Dead batteries and broken props aren’t the biggest problems with trolling motors; bad wiring is. On most boats, weakest link in the electrical system is wire itself. At hardware store, you see a cable, grab it and go. You hope for the best, but you never know if you have enough size. Then you get melted insulation, lost thrust and frustration.
The chart above explain wire sizes in relation to power draw and distance. It takes the guessing out of installations. Ampacity ratings is more than just a technical spec; they represent a safe operating limit. When peak current exceed what the copper can safely carry without getting hot, the insulation will start to degrade. Heat build-up doesn’t make any noise… Until it’s too late.
How to Wire Your Trolling Motor Correctly
Thin wire also create voltage drop which diminishes thrust. Voltage drop waste battery power converting energy into heat instead of pushing water forward. For most anglers, its a physics problem that isn’t addressed until things fail.
American Wire Gauge (AWG) is something you have to invert your thinking on because the gauge size goes opposite than what you think. The smaller the AWG number, the thicker the wire (higher capacity). So 10 gauge are thinner than 4 gauge. And 4 will carry almost twice as much before getting hot.
That’s important when running power long distances like across a big deck. Every foot from the battery bank to the motor mount is another foot of loss in the power run. The further away you are the bigger copper needs to be to overcome the loss for distance. Running thick wires gives the motor the ability to get enough volts to run effective.
If you’re not sure how much wiring you’ll need, don’t skimp on size. Thicker wire won’t waste as much power long term and it will run cooler. Eight gauge versus ten gauge doesn’t make that big a difference when it comes to pricing compared to a fire hazard or a new battery. Overheating wire from being undersized can melt the adjacent insulation which poses a very dangerous situation in a tight area. Always go heavier than necessary with your cable installation.
Another consideration is what voltage system your boat is set up in. If you have a low-thrust motor, like on some lightweight jon boats and kayaks, then a lower voltage system of 12 will be just fine. But if you’re running bigger equipment on a bigger boat, you’ll want to step up to something higher such as 24 or 36-volt systems. Running that same amount of power through a higher voltage system uses thinner wire. The connections between everything should still be beefy, though. You don’t want to fight electricity right out of the gate by going with an undersized system. Make sure your motor needs matches the size of your battery bank.
Selecting the right gauge is only part of the picture for proper installation. Carefully take note of how far the cable will actualy need to be run. Account for distance from the positive leg out, as well as the return path back into boat for negative. Remember, a ten foot run really amounts to twenty feet of wire you’ll have to size up.
Standard auto cables are not made for marine environments and will corrode very quickly in humid, salty air. The corrosion increase resistance where it connects. It ruins your purpose for using heavy gauge cable. Be sure to crimp terminals properly using a good ratchet crimper. Wires twisted together form poor contact points that will eventually fail when vibrated.
Always use a circuit breaker on your boat and install it no further than 18 inches from the positive side of the battery. That way if there’s a short somewhere in your system, the breaker will trip before a ton of damage is done downstream.
Once everything is wired up, run the motor at wide open throttle and check the voltage drop. You should never exceed a 3% drop, because if you do then the gauge wire is too small for carrying current over the given distance with that load. Do this correctly and you’ll have an electric trolling motor that works reliably every time. That means not having to troubleshoot electrical problems in the middle of the lake when you could of be catching fish.