tj309

I would like to move my batteries forward about 20 feet for CG purposes. Can I do this? Should I increase the thickness of the main leads to avoid excessive voltage drop? Currently the leads are about 6' battery to outboard motor.

Thanks, TJ

Outdrive1

What gauge are they now? Probably about 4 gauge? The longer your run the more resistance, so if you have to buy new cable anyways just upgrade a size or two. You can put the battery as far away as you want as long as your wire is capable of handling the demand.

hillbilly24

It sounds excessive but for a 20 foot run I would probably run single 0 guage wire. If you stop by west marine they have a chart that tells you what guage you need based on amp draw and length of cables. The amp draw specs are in the factory manual, I don't know em off the top of my head. Also remember that the ground cable needs to be the same size as the positive or it all worthless anyway.

Wally

iTrader: (1)

You are gonna need to know how much amperage the starter draws at startup to figure this out. Assuming you want to be safe with this and lets say we allow for a max of 20% voltage drop.........if you have 500 amps being pulled for a 26' run you will need 2/0 battery cable.......actually the 1/0 is good to 24.5 feet and you could probably get away with it, with out any problems...but its better to be safe then sorry. If you have a bigger amp draw, lets say 700amps then you will need to step up to a 3/0 cable!
If you have less amps like 300, then you use a 1 gauge......if its 100 amps or les then you can use 6 gauge wire. I dont think an outboard takes all that much to start up so you should have no problems with a 4 gauge wire like BADKACHINA mentioned.....but if you are allready paying for cable that size spend the few extra dollars and get the 1 gauge and not worry about it. Make sure the wire is tinned to help prevent corrosion. And for extra measure if the cable doesnt allready have it...i put some dielectric grease and some shrink wrap over the crimp to help prevent corosion more.

Hope that helps..........i cant believe my schooling actually came in handly after 10years!!!

hillbilly24

What kinda schoolin is that wally, they don't each that krap in college.

Wally

iTrader: (1)

They sure do.....i have a EET (Electronics Engineering Technology) Degree. I am one of the lead engineers for a company that makes seal-less magnetic drive chemical transfer pumps. I actually design shaded pole motors. The kind you find in refrigerators and home humidifiers etc. I deal with wiring on a smaller scale cause we wind our motors with anything from 22-34ga wire for the coils. But the basics are all the same when it comes to voltage/resistance/amperage ......its just math!

heres a pic of the types of motors i design and make Oh and if you look in the bilge of most boats that have AC units onboard you will see one of my motors in there for cooling the AC units! Its encapsulated in some blue or red epoxy but its got a motor like the ones pictured inside it!

hillbilly24

cool stuff. I'm a proud gradute of Wyoming Tech myself, with an assotiets(sp?) in applied diesel siences. No there were no elglish classes involved

Wally

iTrader: (1)

Good deal man....i actually thought of going to Wyoming tech myself right after high school.....but during the time i was taking shop class's in high school i just couldn't stand having dirty hands and finger nails all the time. If i was guaranteed working on nothing but new clean stuff i would have done something in a heart beat.....but i still play with my truck and boat engines all the time....and now i get to tinker with the wife's jeep liberty!!

Gary Anderson

Increase the wire guage by 1 size (numerically -2) for ever doubling in length and you'll be fine.
Gary

Wally

iTrader: (1)

Gary it doesnt quite work that simply......it all depends on how much current you will be pulling through the cable. In small current applications that may hold true. But lets take for instance a BBC chevy engine....and lets say its a cold motor on a chilly morning. You may pull more then 300 amps trying to turn the engine over. Ofcourse that gets less when the engine is warm and easier to turn over. But in that case lets say there was a 10' run at 300amps and allowing a 20% drop in voltage you would need a 6ga wire.....now if you double the run to 20' you would need to step up to a 2ga wire because the 4ga wire is only good at those specs to 16'. Would it work?.....yes. But you run the risk of melting things if lets say you run into fuel problems and need to keep cranking for longer periods of time. I bet that wire would get warm or hot depending......
And the more current you need the bigger the cable will get.......lets say you for some strange reason need 900amps......on this 10' run you need a 1ga wire......if you double that to 20' you would need to go with a 3/0 cable!!!

The bigest cable i have ever worked with was 777 locomotive cable at Motorola. The stuff was mulit-strand to help us bend it around corners and such......but i swear the stuff has to weigh about 5lbs/foot and the wire part of the cable has to be about 3" in dia!!!! We had to use a hydraulic cutter/crimper cause nothing we had would go through it cleanly!!! I wish i could have taken some pics of that stuff but Cameras were a big no no in an R&D sept!