Always use wires rated for the power requirements of your load. Q: SO, how do we know what gauge wire we should use? A: A simple equation. CM =(K x I x L) / E ----------------------------------------- CM = Circular Area of Conductors K = 10.75 (Constant representing the mil-foot resistance of copper) I = Current (amps) L = Length (feet) E = Voltage drop (in volts) Great!! So what does all that mean? Let's go through it one by one. K K is a Konstant = 10.75, just use it. I I is total MAXIMUM desired current draw, or a 5 amps above the rating of your fuse. (Choosing a fuse is a different topic entirely.) L L is total wire run length. Meaning how much wire is run from the battery through the switches to the motor AND BACK TO THE BATTERY AGAIN E E is the Voltage drop (in volts) For motor applications (& to be safe, we will assume 3% drop) So, @ 12V: E = 12*.03 = .36 @ 6V: E = 6*.03 = .18 CM CM is the "Circular Area of Conductors", basically the wire's gauge. Remember to always "round up"; so if you have CM = 3,000 USE 14AWG. 18AWG = 1,600CM 16AWG = 2,600CM 14AWG = 4,100CM 12AWG = 6,500CM 10AWG = 10,500CM 8AWG = 16,800CM 6AWG = 26,600CM 4AWG = 42,000CM Example: The motors are 2 feet from the 12V battery, and you have calculated that you need to use a 35 Amp fuse. I = 35A + 5A(tolerance) = 40A L = 2'(positive) + 2'(negative) = 4' E = 12*.3 = .36 CM =(10.75 x 40A x 4') / .36 = 4778 Therefore, for this application; use 12AWG Notes: 105C insulation rating AWG wire sizes, not SAE Conductors are not bundled Definition: Several wires bundled (like heatwrap) to make a larger wire. Solution: If 3 conductors are bundled, reduce maximum amperage by 30%. If 4-6 conductors are bundled, reduce maximum amperage by 40%. If 7-24 conductors are bundled, reduce amperage by 50%. Since we are using DC, it doesn't matter if we use stranded or single core wire. However, keep in mind, single core wire is tougher to bend & if it breaks in just one place... the circuit is broken.
Not to start another electrical argument, but why base the wire gage on stall current? Wouldn't it be also ok to base it on running current, fused for stall current, that way if you stall a motor, you don't fry it when the wires carry the load? i.e. run 14ga wire, with an 18A fuse? The fuse'll blow before the motors fry, or the wire melts
Tuggy, You right, that part should read 5Amps (tolerance) above your fuse rating. But you shouldn't use the wires to do the job of the fuse. The wires will start a fire just as easily (probably more) than a motor. It is another topic entirely to determine what that fuse rating should be.
I don't use fuses at all in my ships. I found if you mossed up or stalled your engine on something you blow a fuse and your dead. If I am mossed or stalled I don't keep applying power. That will just overheat the motors and the wires risking a meltdown. I stop the engines and then try small spurts to get out of a stalled situation. I find with the smaller ships 12 gauge works well depending on the motors current draw but mostly for med to large and superlarge I use 14 gauge and have not had a meltdown in a long long time.
