“What Size Battery Cable is Needed for my Motor/Engine?” is the most common question our 12 AWG marine primary wire experts get on a day-to-day basis. We always do our best to assist clients in figuring out the proper size.
The most typical questions about battery cable sizes relate to either the engine, motor, inverter, or trolling motor. Each will have its own set of variables that we must determine to make the proper calculation. In this post we’ll cover engines.
When starting an engine, it will momentarily experience a massive inrush of current to get the motor moving. Once the engine starts to spin, it will draw considerably lower current throughout its cranking cycle.
Our recommendation for battery capacity will be based upon engine displacement. It will also be based on a number of variables, and established protocols, that we have arrived at over years of experience. The cold cranking capacity of the battery ought to be at the minimum of 1 amp/cubic inch of displacement, for more effective engine sizes like an 8 cylinder. For a 6 cylinder engine, 1.5 amps/cubic inch of displacement is appropriate. A 4 cylinder engine is effective at 2 amps/cubic inch of displacement. Those ratings are for a battery capacity, the capability for delivering current in order to start the motor. It is logical to use these as a guideline to determine the battery cable size.
With regard to voltage drop, we have discovered that under 5 percent is a firm target to ensure easy starting. Voltage drop should be absolutely under 10 percent if you want to squeak by using the minimum. The lower the voltage drop the better.
12 AWG marine primary wire is specifically designed to survive the rough marine environment. The single conductor 12 AWG gauge wiring is a fine stranded copper with every strand fully tin-plated. Tinned copper resists corrosion and ensures secure and safe operation for years to come.
