wire guage?

[bkft]

I recently decided to move my battery to the front of my small boat. I'm trying to figure a way to run wires from the terminals to the back of the boat where I can connect the motors/lights/electronics/etc to some kind of hub. My question is: what guage wire should I use? My first inclination is to use the largest guage of any device I'm going to attach to the battery (outboard motor). Any advice? Thanks in advance!

John

[18 inch Crappie]

I owned a stereo shop for years and we used a lot of 8gu and 10gu I would use 8, that should hold anything you are going to run.

[Kevin Turner]

How long of a run will you need to make? If you plan on using the battery in the front to start your motor, You'll need at at least 4 Ga.

[bkft]

I will be using the battery to start my outboard motor, so I should probably go with 4. Thanks guys. Would anyone have any advice about how to set up some kind of hub in the back to connect everything to?

[Graywolf]

BKFT,

Go to Boat US on Lynndale about 3 blocks S of 494. In a small mall on E side. They will be able to help you with the wiring materials needed. Or West Marine. Fuse or circuit breaker is always a good idea.

[Surface Tension]

You can get a fuse block or circut breakers for the electronics. You would run an in-line fuse between the battery and the block.

Normally the line to the starter isn't fused, since your running a #4 to the back of the boat for the starter this is something you may want consider adding a fuse to. Theres a lot of load on that line so you couldn't get by with any ordinary in-line fuse. On samll boats I know a battery in the stern can really kill the performance but if you went with a small starting battery (a lawn tractor battery would even work) dedicated to the starter and left it back there then put a big deep cycle in the bow for electronics and a bow mount electric motor.

[Moose-Hunter]

I really like Frank's idea of a "smaller" dedicated starting battery. That's the way I have my own boat set up, however on a somewhat larger scale. With a dedicated start battery, your heavy load wiring would be a much shorter run. And you'd have easier access to all the connections needed in the bow since that's where your equipment is located.

[musky hunter]

Since boats usually deal with low voltage, the bigger the wire the better. Less resistance means less power converted to heat and longer battery life on a charge. One of the best sources of heavy guage wire I found was to go to the auto parts store and purchase a set of perfectly good jumper cables, cut the battery clips off, and hook up the wire. Battery cables are quality wire with good insulation. I'd recommend some of the good neoprene cables. They can also sell you the proper cable end connectors.

[Valv]

Or go to Kvesurplus and buy a whole boat harness for $ 25.00....

[bkft]

I just talked to the guys at Boat US and they said 4 guage might not even be enough. They would like to know how much current my outboard motor ('89 25hp mariner) and trolling motor (55# minnkota maxxum) each draw from the battery. I have no idea what those numbers might be. Anyone happen to know this or where I can find out? Thanks again, guys!

John

[Whoaru99]

The current draw is sort of hard to say for the engine starter; I'm guessing that it is probably between 100 and 200 amps although it could be more, could be less.

For the trolling motor it will depend on what speed you run it. Here again, just a guess, but 20 to 30 amps (assuming 12 volts, 1/2 as much at 24 volts) running wide open is probably in the ball park. Likely not less, if anything, I think it could be more than 20 - 30 at the top speed.

The deal is though, you have an intermittent load with the engine starter so from a purely wiring standpoint to size the wire for this much continuous load is probably a bit overkill. However, by the same token, you don't want to undersize so much that the voltage drop from cranking will hinder engine starting.

My wiring table reference from the aircraft industry allows 0.5 volt drop for a 14 volt system continuous rating. So, just for the trolling motor assume 30 amps maximum, and 35 feet length (total of + and - wire length additive) the curve falls between 8 ga and 6 ga, always select the larger size.

If you size for intermittent load on 150 amps for the starter, then the chart indicates between 4 ga and 2 ga, so again go with the larger size 2 ga.

Keep in mind this all assumes the distances and loads represent your situation which is purely speculation on my part. Any use of this information is done at your risk.

[bkft]

Thanks Whoaru99, I talked to a MinnKota service dealer and they said the 55# Maxxum would draw between 42-45 amps. I've got a call into a Mercury dealer for the motor, but I'm not very hopeful he'll find out for me. It didn't sound like a question they often get!

[Whoaru99]

FWIW...

The OEM service manual for my Merc 90 says 120 amps for the 75/90hp engines and 150 amps for the 100/115/125hp engines.

I presume the 25hp has a service manual available to the dealer so it shouldn't be too hard to find. The data for mine is listed in the "General Information and Specifications" section.

So, assuming your 25hp draws less than 100 amps, I'd think 4 ga should be OK for the intermittent starter load and OK for the trolling motor continuous load.

[McGurk]

Use 4 guage and have a fuse/circuit breaker within 2 feet of the battery. Set a terminal fuse block in the back for all of your add. elec., with a fused 8 gauge lead to the trolling motor. The momentary high voltage draw for the starter motor will not be enough on a 25hp to necessitate 2 gauge or 1/0 wire, and it is a bear to run (size of a nickel or quarter w/ jacket) whereas 4 gauge (size of a dime) is a lot more flexible and easier to run. Is it necessary to move the battery in the first place, or just a convenience? I'd try to keep the battery as close to the largest drawing thing on the boat, and let the other elec. get the longer leads. bumping from 18 gauge wire to 16/12 gauge wire for all of the accessories is a lot cheaper and easier to run than trying to do what you are asking. $0.02

[Kevin Turner]

Some good ideas so far. You will need quite a large (slow blow) fuse for your starter draw. One note: Be sure nothing is grounded to your aluminum hull.