Really Dumb Question- POS/NEG Cables

[Fletch170]

On my last boat (115 yamaha 2 Stroke), I ran a 2AWG wire. My new project has a 225 Merc 2 stroke.

The 2 GA cables were really bulky and didnt bend well. For this large engine 3.0L, setup with dual batteries, Is the 2GA overkill? I'd like the 4GA as it's one hell of a lot easier to rig.

-Fletch

[Capt. Bob]

What's the total length of the cable run (from the battery to the motor)?

The main concern you need to deal with is voltage drop between the battery and the motor. The allowable percentage of this voltage drop has been discussed before on this Forum and is still a matter of opinion to some. You'll need to decide what is acceptable to you while fitting your budget and protecting your starter armature from low voltage overheating. Proper size and type cable is expensive so it is important to know that distance. Some agree that 2AWG is the biggest cable you need with the batteries located in the console. They contend voltage drop isn't a problem with this size cable. Since you own this size already, it's just a matter of length.

Good luck.

[seabob4]

Stick with the 2GA.  If your motor has one of those grommets (like Yamaha) where there is a "location" for each piece of rigging to pass through (major PITA!), cut out the center sections of the grommet, makes it MUCH easier to rig.

Anytime I have a customer that wants the batts moved to the console, I always step up to 2GA...

[Fletch170]

So, it's about 16 feet of cable run, as I measured. (From the console through the hull, through the rigging sleeve, yada yada yada. I purchased the adaptor to have this motor accept a sleeve, so there is more room, but it's only a 2 inch hole. Got 2 cables, the oil lines, a fuel line, shifting and throttle cables, and the harness. 10 pounds of ship in a 5 pound bag. As I recall, doing this last time was an EPIC  pain in the balls.

[Capt. Bob]

So, it's about 16 feet of cable run, as I measured.

Here's the calculated drop using a 170 amp load (my 200 Yamaha measured load while cranking). Yours may be higher (or lower, though I'd guess not).

2AWG
http://www.calculator.net/voltage-drop- ... &x=47&y=12

If 3% was the maximum allowable drop, you see you have exceeded that by more than double. You'll be cranking that beast of yours with just over 11 volts on a fully charged battery so you certainly can't go down to the 4AWG.

4AWG
http://www.calculator.net/voltage-drop- ... &x=61&y=12

Also remember that the bigger conductors not only allow more energy to reach the motor for starting but also carry back more voltage from the charging coils (or alternator) to your batteries while underway.

Lube up them 2AWGs

[Fletch170]

What about the cables to the main battery switch, and the jumps between the batteries, as well as the cable feeding power to the main positive bus? Is that just throwing money away rigging that all with 2Ga? Any suggestions there?

You guys really helped me last time with this, in regards to where fuses went, etc. I really do appreciate the help.

[Fletch170]

Also, the main bus ground (negative) to the battery. Last time I did everything 2ga. Greg's marine wire LOVES me:)

[seabob4]

The cables from the batts to the switch, the ground jumper between batts, must be 2 GA.  In other words, all the cables associated with engine starting must be of equal size or greater than the the main cable from the batt switch to the starter.  The main pos bus, if your talking about house power, can be 8 GA, even 10 GA.

[Fletch170]

Bob,

Makes complete sense, and your answer is as I expected. Just dropped 250 bills for the wiring. all custom cables, etc. greg does awesome work.

-Fletch

[seabob4]

Yes they do, Christian...

When I was at Stamas, we used to install Vetus bow thrusters, running off the house batt, located all the way aft...so the install required 4/0 cable.  Since the house batt was tied into the engine batts, ALL the cableing off the batts gad to be 4/0!  You talk about a royal PITA!!!

[Fletch170]

you know what else is a PITA? Catching on fire.. and having your face blown off your face.

Bob, as always, you are the man. thanks for the help brother.

[seabob4]

Christian, didn't really mean to spend YOUR money, but it is what it is.  You're welcome, Sir...