Wire size and number of batteries questions

A

Andrew Holley

Well-known member
1) What size of wire do I need to run from the front of the boat where I plan on storing the batteries back to the motor? Went to the local big box and they have #2 copper strand and #4 copper strand. #2 seems to thick to work through the bends, however might need the size.

2) How many batteries should I have? Original thought was 1 for the motor and one deep cycle on a seperate circuit to run the lights/bilige/radio and then being about jump start the motor battery if needed.
 
1) What size of wire do I need to run from the front of the boat where I plan on storing the batteries back to the motor? Went to the local big box and they have #2 copper strand and #4 copper strand. #2 seems to thick to work through the bends, however might need the size.

2) How many batteries should I have? Original thought was 1 for the motor and one deep cycle on a seperate circuit to run the lights/bilige/radio and then being about jump start the motor battery if needed.
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I would look it up. 12 volt bible for boats or even a west marine catalog. Big box won't have marine grade.

T
 
I don't know about the larger sizes, but a lot of the smaller marine grade wires are tinned and for some reason I think they may have a different jacketing material.

I've always used factory battery wires, but I've heard welding cable is the cats meow. Thinner/more strands and more flexible than auto grade battery wire.
 
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Andrew,

With out being an electriction, I'll say that I've used welding cables myself for longer runs and have been quite pleased. I don't know cost comparison but yes they carry a good load and are easier to run due to the extra flexability.

Marine wire is "tinned" which helps prevent corrosion and surface oxidation on the strands of wire. If you use "un-tinned" wire and in the future you need to splice or make a new connection, it can be harder to get a good clean electrical connection to the oxidized (sp) strands.

Sealing the exposed ends well (use epoxy filled marine connectors and dielectric grease) when you first wire everything up, will help to postpone the oxidizing (sp?).
 
I would go to a welding supply store. They have two different size cables. The smaller should do. It is sold in twenty five foot lengths 50 ft and 100ft. Some stores also have it in a large roll and you can have it cut to what ever length you want. They also have the connectors for the ends that should fit your battery. Airgas should have a store in Green Bay. If they are a good as Wausau they should have what you need.
 
What's the distance between the battery and starter, and how many amps does the starter draw? It's hard to find marine wire big enough to run the circuit to the starter. The jacket is more waterproof than standard wire, and the wire is tinned to resist corrosion. If you have a big enough alternator on the engine to run all you accessories, and you don't plan on running them for very long with the engine off, I'm not sure why you'd need the second battery, unless you were to separate it from the rest of the system with a battery switch and just keep it as a reserve.

You can get some pretty good deals on wire on ebay. Calculate the gauge wire you need and do a search. There's all kinds of tables and calculators on the web if you search "awg" "amps" "table".

Ed.
 
bluesea.com has a few different calculator thingies. Very helpful for this kind of thing... and I've been pretty happy with their products, too.

FWIW, having rewired a bunch of different boats over time -- I just buy a bunch of 10 ga. and 16 ga. marine tinned cable every time I do a boat -- Those too ga's. will be stout enough (or more than) for 95% of boat projects, and that way I don't have to spend a lot of time searching for just the right wire.

There's an outfit on LI called Dave's (dave's marine electronics, maybe?) that has good prices and reasonable shipping. It is very worth getting the marine stuff. The other hasn't held up in my experience.
 
If this helps...on my Lund I run the starter and accessory(bilge, lights, livewell)battery in the stern and I have the big deep cycle stowed nicely in the center near the bow-under the decking. I ran heavy duty 8 gauge(whatever that means)through the side lockers to the stern for the trolling motor plug and at the bow for the trolling motor plug in and the anchor winch. I used the fancy waterproof connectors and they seemed to have worked great. There is no noticeable corrision, as you alluded to above we don't have near the issues that saltwater applications do as far as that goes. I have a 10 amp(two 5 amp banks stacked)battery charger bolted in near the battery in front that charges the deep cycle. The stern start battery runs off the motor(40 hp Mariner). Now, when I have to jump the stern which has happened a few times...if I'm not at the ramp and can use a vehicle...I have jumped the starting battery off the deep cycle with good old jumper cables that I keep in the boat-you have to make sure they are long enough of course. If you have to run the wires and maybe even invest in a Perco switch for a back-up starting battery it may be easier/cheaper to do the jumper cable thing or even get one of those portable starter packs.
 
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Use the Blue Seas calculator to figure the wire size based on ABYC recomendations for voltage drop in your application. Welding cable has been used extensively in the past and works, but is not as flexiable as marine wire with more strands and is not tin coated so will not resist corrosion as well, but if you seal it up it will work and cost a lot less. Copper is nuts on price right now. All depends on how far you want to go with the work based on your level of comfort with the materials. Make sure you have a good crimper and do a very good job sealing the ends. Do not use ring ends with open sockets. Hard to seal. I have seen electrical tape give good service over heat shrink tube, but at work we use only tinned wire and Electro Term Hollingsworth shrink tube and Anchor battery cable lugs.
You must have an accurate AMP draw number to size the wire and the length of the run down and back.
 
Andrew,

You've got good advice here on what to do for cables. I thought I'd mention what I have in my boat (16' Starcraft jon, console steer, 40hp Merc) for a two battery setup. I have a my big group 27 deep cycle in the front compartment with 10ga marine wire running to a trolling motor receptacle. Male trolling motor plug is wired to the fuse box under the console to run all the accessories (lights, bilge, radios, gps/depth finder). Starting battery is behind the seat next to the motor, wired with a second trolling motor receptacle that can be used to plug the accessories into in event of a dead deep cycle. This way I can have run accessories without draining the starting battery and still have an emergency back-up without an expensive battery switch. If the starting battery dies I can simply pull the deep cycle and move it back. Charging the batteries is done through the receptacles so I don't have to pull battery box lids.

Jim S
 
If this is a standard duck boat with a electric+pull start motor, one full size good marine starting deep cycle should be fine for all. Unless you don't have a back up pull start on the motor, I don't see a need for a seperate battery to power accessories. If you are running a big boat with a big engine, then put in two with a "perco" switch. Wire your all the assecories into one so you can isolate it from the starting battery with the switch.
I have an 18 nissan on my boat & use a small marine deep cycle from Academy for all my power needs. It starts the boat, run the lights, spotlight and fishfinder all just fine. But an 18 is easier to pull start then a 40! :)
 
Carl, the boat is 25'6" long and 8'6" wide with an older 140 hp merc. No way I could pull start it.

Need to look into the switch you are talking about, I don't know anything about them.

Later
 
Yep, I would say you need two. Not sure boaut three. Wont hurt.
I used two standard size marine deep cycle starting batteries on my 20' center console offshore boat back when I owned it. I had them wired through a Perco switch. When we were going to be at anchor for a while, I would isolate one battery so we could run the livewell and fishfinder without worrying about draining both batteries. Works great. it also allows you to turn the batteries off when stored for a while to keep anything you left on from drainng the batteries. Here is a link to the switch at west marine:

http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/14763/377%20710/0/Perco%20battery%20switch/Primary%20Search/mode%20matchallpartial/0/0?N=377%20710&Ne=0&Ntt=Perco%20battery%20switch&Ntk=Primary%20Search&Ntx=mode%20matchallpartial&Nao=0&Ns=0&keyword=Perco%20battery%20switch&isLTokenURL=true&storeNum=5002&subdeptNum=9&classNum=297
 
But closer to the truth as to what is needed for most outboard motors. The way things have gone crazy checking with your local dealer may net you even better pricing for a 300 amp or so continuous rated switch.

By the way, excellent idea on the spare rope for launching single handed. (re Greg's post) I'll be using that one.

Eric
 
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