Anyone want to doublecheck my wiring scheme?

Cody Williams

Cody Williams

Well-known member
Hey guys, I'm figuring out a wiring schematic for a new boat project I'm starting. I'm pretty savvy with house wiring but this will be my first DC project, so I could use some advice! It will be pretty simple-I will be running nav lights, interior cockpit lights, and an LED headlight bar. All this will run to a 4-gang breaker/switch panel, with a digital voltmeter and 12v/usb socket included. All lights will be LED, and the wiring will be THHN running through liquidtight and PVC conduit. I omitted the negative runs in my drawing for clarity but all negatives will run to a negative buss bar. The motor will have its own starter battery and be seperate from the boat wiring. Thank you guys for any advice you have!
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Run all lights back to bus bar and switch. Cockpit lights, port and starboard. Bow and stern separate, but same switch.
If the boat will be left in water, bilge pump on switch and auto switch.
Running them separate will leave it easier to trouble shoot. Don't skimp, will bite you later.
 
Good advice Capt., I would put the battery in the back to eliminate the LONG run to the switches. Boat wiring is fun for me so I usually overdo it but keep circuits as easy to troubleshoot as you can, remember that Murphy of Murphys law fame is alive and well. Auto bilge is a feature that you only need once to appreciate.
 
For a 19' duck boat, I would advocate you install a 1000-1200 GPH bilge pump with a float switch in the stern sump. I would also encourage you to follow ABYC wiring standards during wiring run installation, using good tinned marine grade wire which contains a higher strand count per wire gauge to offset wiring circuit "decay" via the near continual percussion and pounding a boat hull endures while underway. One point about installing your wiring in conduit, you can't tap into a circuit very readily for an additional installations...

I like your idea of placing the battery in the bow to keep it dry, as well as aid as a counterbalance in trimming the hull. What amperage does the rectifier in your motor's alternator put out in the unit's RPM mid-range? For maximum longevity an AGM group 27 would be my choice; deep-cycle if your alternator is whimpy. Have you given any thought or consideration to wiring-in a battery charger? This would be overkill if you have a newer outboard that has an alternator that actually puts out a fair amount of "juice" while running at speeds less than WOT, particularly given your choice of LED lights for internal and external use. This would be beneficial down-the-road should you decide to add a fishfinder/plotter unit, too. I would advocate for sealed marine (red) interior LEDs since they do not impair night vision.
I would also make a point of buying a stern light with a mast long enough that it will be located well above your head when underway while seated at the helm station. Rigged this way, when you look back into the starboard stern-quarter you will not be blinded by the mast light "staring back at you".
 
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Thanks for the advice guys. Some more info-this boat will be 16' long with a 60" transom, and running a 35hp longtail mud motor. I would like to keep the battery up front to counterbalance the motor and fuel tank which will weigh about 245lbs ready to run. It will be trailered except when in use so I'm not sure if I need a bilge pump or not, I'm sure it would be a nice safety but for simplicity I'm leaning towards stowing a hand pump on board.

I was wavering between using Marine wire or just regular copper, sounds like Marine might be worth the extra money. Since all the lighting is LED, this system will have a very small amp draw, less than 10A with everything on, so according to my charts a #6 wire between the battery and buss will give less than 2% voltage drop. The biggest light, which is the 4500 lumen LED bar on the bow, draws less than 1A-I love LED's!

RL-according to the motor's website, the alt puts out 20A at 2,000RPM, which is mid throttle. Should be enough to keep the battery charged up if all I'm doing is using it as a starter. I plan to keep a power pack on board for emergencies, plus when it gets cold I won't mind the extra insurance! The light I got for my stern can extend to 48" above the deck, which should be plenty.

Thanks again you guys, I actually really enjoy wiring and boat electrical stuff......what is wrong with me?
 
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2 things to think about Cody.
Advice from my recent build, overdo the size of conduit you think you may need. Easier to pull back wires if you ever needed to. I made a late decision on a few extras and things got a bit tight on 1/2" conduit.
If you are running the mud motor you wont have a need for a large starting battery. Backwater recommended a small lawn tractor battery (after all it is the exact same as a mower engine). I bought the battery from them with a smaller marine battery box. The motor has a 1 amp alternator so running my nav and interior lights I didn't think would be a problem, I will let you know though as I have not done much lengthy testing with that.
 
Thanks for your input Andrew. I'm planning to just run the lawn tractor battery as a starter and keep the heavy deep cycle battery in the bow, but with my system drawing so little current I may be able to get away with a smaller battery-I will have to experiment! I will be running the Backwater 35 on this one-it's sitting in my garage, tempting me every time I walk by it!
 
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You know the water you hunt far better than I do. Shallow open water can get rough quickly, particularly if the fetch is right.


I think ABYC standard is a 5% voltage drop within a circuit, so with that deep-cycle battery and the LEDs you should be in good shape ( I would go down to a group 24 now, based on your description of use and draw loads.) There are some gel "pucks" you can pick-up to nest under your bow battery to lessen the impact of pounding on the plates in a standard wet-cell battery. I used this set-up when I wired my 14' TDB...they don't give AGMs away!


Have you settled on a circuit breaker size?
 
Thanks again RL. My panel has a 5A, 2 10A, and a 15A breaker in it-not sure if that's OK or not, since the most draw will be around 1.5A or so.
 
Thanks again RL. My panel has a 5A, 2 10A, and a 15A breaker in it-not sure if that's OK or not, since the most draw will be around 1.5A or so.
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I've never wired for a marine circuit breaker, just marine fuses and residential circuit breakers. You want the breaker sized to the wire, I don't know how to do that with a premade panel (that is one reason I went with a fused panel on my snowgoose, so I could fuse it as I needed).

As a side, note on wire size, even with LEDs having some decent sized wire is nice to work with even if you don't need it. Look at genuinedealz.com for wire and connectors, especially for a la carte pieces - they have great prices and service and shipping.
 
If this were my boat i would probably put a fuse between the battery and the master switch, if nothing else, for peace of mind. Without it, if the positive and negative wires ever shorted together before the breaker panel (10 ft run?) you would have no protection from the battery terminals being shorted.
 
If this were my boat i would probably put a fuse between the battery and the master switch, if nothing else, for peace of mind. Without it, if the positive and negative wires ever shorted together before the breaker panel (10 ft run?) you would have no protection from the battery terminals being shorted.
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Yes, a terminal fuse would do that, below is the one I've used.

http://www.genuinedealz.com/blue-sea-systems-5191-fuse-block-for-battery-terminal-fuse
 
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Good idea, I will work that into the design.
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Very easy, just set it on the stud and then use the stud on it. You can get fuses of any size for it. They are spendy, but they shouldn't ever blow (unless you are a doofus and size them "perfectly", but don't take into account that the converter in your camper can put out slightly more amps than expected at the same time your solar is charging). Just size it to the large traveling wire from battery to buss, that is all you need.

In thinking about your setup, I'd personally go with only one battery. A combined starting and deep cycle battery. On the deep cycle side, you don't have hardly anything for draws and the motor will keep it topped off. (as an aside, I for sure wouldn't consider two batteries if you have a pull starter on the motor that can be used as a backup.) For a low draw system like your deep cycle side, you can easily get away with a lawn mower battery size - that is what I'm using on my snowgoose to run lights, bilge pump, GPS, fish finder, etc.... I have used fancy AGMs U-1s for years and after the second one failed, I quick grabbed a lawn tractor battery, since it fit in the same box. Anyway, the lawn tractor battery has lasted and does all that I need. I don't think it is ideal (not deep cycle), but is sure works and hardly needs charging. Going with just a quality starter battery and the miniscule deep cycle use of your LEDs will be not even noticed.
 
Thanks again RL. My panel has a 5A, 2 10A, and a 15A breaker in it-not sure if that's OK or not, since the most draw will be around 1.5A or so.
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It seems like you can reconsider battery size. If your system is 1.5A max draw a Group 24-27 (ca. 90 amp hours) could run it continuously for quite some time. You have just a tiny draw there. No need for the expense of a big and heavy battery and no need to charge a deep cycle at home if the motor will do it. I'm all for redundancy and separate systems, but in this case, the simplicity of one small rear mounted battery wins for me (especially if your motor can be started with a pull start in an emergency).
 
I used lawn mower batteries with my Nissan 18 hp for years, used it as a cranking battery and to run my lights, spotlight & fish finder.
Advantages are that they are small, light and cheap.
Disadvantage; I usually got about 3 years out of one before cells started to fail.
They just don't hold up well from the pounding they get in a boat.
It would still run my lights but not always keep enough charge to crank the motor after it sat for a month or so. Luckily it was easy to pull start.
 
Thanks for the battery advice guys. I think I will go with the lawn tractor battery to power the light system, I like the idea of a small lightweight battery vs. a 75lb deep cycle! Tod, this motor doesn't have a pull start, electric only, so I kind of like the idea of having 2 batteries aboard just for insurance during the winter. I also have one of those portable power packs that I'm planning to bring along as well. Being stuck out in the marsh in sub-zero temps with a dead motor is an experience that I'm not too eager to repeat!
 
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