Posts: 120
Location: Twin Cities Metro | 14 AWG wire (the typical wire used in sonar power wires) has a resistance of 2.5 Ohms per thousand feet of length. If your wire length is about 20 feet total, that would be a resistance of 0.050 Ohms. Helix 12 has a typical draw of 3.2A (according to Humminbird). With that resistance and current draw, you should be looking at a voltage drop of about 0.16 Volts from one end of the wire to the other.
A drop of more than 4 Volts along that wire, like you appear to be experiencing, indicates a poor connection or faulty wiring of some sort. Hoping it is an easy fix, I would check the connections at the battery and the sonar unit for corrosion or wear. Check the fuse for proper connectivity (sometimes the connections to the fuse will have corrosion, or the fuse itself will be faulty). [By the way, a 30 Amp in-line fuse seems like WAY too high of a rating to me if this is the in-line for the graph.] If not those things, try a load test on your battery to verify that it is as good as you think it is. When a battery is unloaded, it can still show 12+ volts on a voltmeter even though it is not able to effectively supply steady current. If this is your cranking battery and it is able to start your outboard, then the battery is almost certainly fine. If it is not any of those things, then you almost certainly have a continuity problem in the wiring. That involves running new wire which is usually annoying. That's why I suggest you check other things first that are easier to deal with.
The only reason to got to 10AWG wire is if the wire in question is feeding multiple units (eg. the "supply" wire from a battery to a fuse block). In that case, it really isn't the resistance and subsequent voltage drop that you should be worried about. It is the current limitation of the wire. 14AWG is rated to safely draw up to 15 amps. 10 AWG is rated for 30 Amps. Most modern electronics draw between 1.0 Amps and 5.0 Amps each, so if you have 3 or more units with large-ish current draws, 14 AWG starts to be "unsafe". If you are wiring just one unit directly to a battery, 10AWG is overkill. Perfectly safe, of course, but overkill.
Edited by RobertK 3/12/2024 10:17 AM
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