Wiring for Trolling Motor

[Mo Redd]

I have a 9 foot Sea Eagle with motor mount. I have a 36 pound trolling motor and two Interstate
DC batteries with a Perko switch that can select 1, 2, or both batteries in parallel. I'll need to run wires from the batteries
to the switch, each just a foot or two in length. Can I use 12 ga. wire (as it won't be used for a high amp
load) or should I go heavier? If I later get a fishfinder I assume I can attach it to the Perko on the same terminals that the
trolling motor clips to. Thanks in advance for any advice.

[Steve Stinson]

Use at least the same sized wire as what is already on the trolling motor leads. Larger is okay, but not smaller. It think I have some in my boat shed that will work if you need it.

- Steve Stinson

[Steve Stinson]

I may not have understood your question correctly - Use the same size or larger wire for all of the run to and from the trolling motor. If you are wiring the second battery to run a depth finder and other accessories, you can use smaller gauge wire for that run.

[onefishtwofish]

I agree. Sounds small to me. I let a un named local boat service dealer run a smaller gauge wire from my motor alternator to my battery. I KNEW it was too small but let him do it anyway. My mistake. It did not recharge the battery at all.

12 gauge sounds small unless I misunderstand. Sounds like you are running 12 gauge to the switch from the battery and one of those will run the trolling motor? Sounds like it is too small.

[charlie tuna]

I would go with standard battery cables since it is very close to your switch -- that way you have factory battery terminals on the cables and ANYTHING you add to the load side of the battery switch wouldn't require changing the wiring. In low voltage(12 volts) wiring, most of your future problems are going to be "connection problems".

[fishinfool]

A foot or two from the batteries to the trolling motor connection will not need huge wires. It will, however be a high current circuit (high amperage) circuit. You should use at the very least, #10 or larger wire to the troller connection. I would even err to the safe side and go with 8 gauge. In the long run you will have fewer heat and corrosion problems. There will be a smaller voltage drop, and you will get better performance from your trolling motor. If you use 12 gauge wire at two feet in length there will be a .26v drop (or .26 volts less at the motor than the battery). If you use 8 gauge wire, there will only be a .10v drop. That means your motor will get better performance from larger wires. Think of the wire size in comparison to water pipe diameter. Bigger pipe, more water.

[wacissaguy]

I just finished doing mine-I am a master electrician-so I have a little experiance at this. Most motors come with 10 ga wire, if you're not adding more than 100 feet the same size wire is in order 10 ga. battery to battery use the same unless you plan to hang more accessery's to its load,if so you should go to a size larger 8ga. Hope this helps.

[charlie tuna]

What we are talking about here is called "VOLTAGE DROP". We have all, probably at one time or another, operated some electrically supplied motor or string of lights that we "felt" some warmth in the wire. This "heat" is caused by the resistance to current flow. VOLTAGE DROP = I X R, or it is a direct function(up or down) by one of two things! Current(I) or Resistance(R). The power source(your boat's battery) see's this "heat" as just additional load. Because the trolling motor runs isn't the only thing you need to be concerned about, we all want to minimize the electrical load on our batteries so we can fish longer. This VOLTAGE DROP causes the trolling motor to run hotter, again, adding load on your batteries, and at the same time reducing the horse power of the motor. When electrical connections are not properly made, high resistance to current flow can be created - again causing "HEAT", which is power loss on your batteries. Bad or "poor" connections , thru expansion and contraction with applied loads, cause this connection to get "looser" -- then "hotter" -= etc.. "Rule Of Thumb" tells us when we reduce the voltage in a circuit, by ONLY ten percent, the current in that circuit doubles, making VOLTAGE DROP important. Around the house, we don't see a lot of this, maybe when the A/C compressor comes "on". That's because we are dealing with a higher voltage than our boats. On a twelve volt battery circuit, it doesn't take much VOLTAGE DROP to seriously effect both the operation, and the efficiency of our equipment. If you wired your battery's leads to accommodate "just" your trolling motor, anything added to the system will be directly effected by VOLTAGE DROP. Today's electronics can't handle much VOLTAGE DROP. And many of the new trolling motors have electronic circuit boards in them.....

[reelhandy]

The current flow itself has to be a consideration as well. A 12volt 36lb thrust motor is going to draw up to 44 amps through that wire. You need #6 wire for 50 amps of current per code. Just because it's a short length to the switch doesn't matter. Fuses are really short lengths that melt when the current rating is exceeded. I'd run #4 myself. I'd also want it fused somehow if I could. I've seen the insulation on an entire length of 12 ga wire hooked to 12 volt DC catch fire literally in 2 seconds because it was shorted and unfused.