what is the point?

[js361]

hey all,<br /> really appreciate all the help i get on this site. i gotta lotta questions cuz i like to do things right! so here goes: what is the point in connecting a ground cable b/w 2 batteries? does this make a continuous circuit or is it just a safety issue?

 

[demsvmejm]

Re: what is the point?

The point depends on whether you are running the batteries in parallel (maintaining voltage level) or in series (combining voltage levels). If you are trying to achieve 24V by running two 12V batteries in series then the 'tween cable runs POS on BATT1 to NEG on BATT2, thus increasing the voltage, just like in a flashlight. But if you are runnign the batteries in parrallel to increase reserve, then the redundant cable between the batteries is for integrity of the circuit. Instead of having to travel though the ground path (frame) between the batteries, the cable is a shunt, or a secure stable connection between the two batteries.<br />If you are hooking up two batteries without increasing voltage you will be wise to use the redundant cable between the batteries. The less resistance the current has the greater the resulting effect of your setup.<br /><br />Use all of the cables, don't skimp.

 

[js361]

Re: what is the point?

the batteries are running in parallel 1 for start motor othe for troliing motor & accessories....so what you are saying is leave the cable connecting the negative terminals?

 

[amirm]

Re: what is the point?

The ground in DC systems (i.e. batteries) is not the same as your household A/C. Here the ground is a required connection as any power source has two wires: the positive and negative. We call the negative "ground".<br /><br />So yes, you mus have the ground connection or the other battery does nothing.<br /><br />I highly recommend that you get a book on boat DC (12v) system. You are dealing with seriously high current circuits and could hurt yourself or the boat if you are not experienced. The book will explain the topics far more than our quick answers here .<br /><br />Amir

 

[jtexas]

Re: what is the point?

jsscheh, <br />are you saying you have one battery for cranking and a separate battery for T/M, and no other connection between them except the ground? The positive posts aren't connected to each other at all? if so, that's not parallel, that's just two separate circuits. That's the best way to go when you only have two batteries on board. <br /><br />I believe that for saltwater operation a common ground helps alleviate corrosion problems, which I don't really understand because I run in freshwater only, in which case tieing the grounds together isn't necessary.<br /><br />If you aren't sure about it, take amir's advice; you wouldn't want to start any fires!

 

[Darren Smith]

Re: what is the point?

I have a similar set up in my boat. The difference is twin O/B's. I found out when I was messing around on it, that the power for ignition and such was pulled from one batt's positive, but didn't really run to that batt's negative. instead it ran to the other motor(trim in this case), through it's ground on the other batt, then accross the "jumper" between the two batteries negative posts.

 

[js361]

Re: what is the point?

Ah so it takes both abtteries to start the outboard, basically? Anyways can anyone tell me where I can get a book, like amir, mentioned?<br />thanks

 

[Harold Paratestis]

Re: what is the point?

Try a book store.

 

[Perfidiajoe]

Re: what is the point?

It don't take 2 batteries to start the boat ! Stop thinking ground think negitive terminal. With no battery switch, (Which I really recomend having) 1 Battery Positive will control the starting & functions of the engine, The negitive will go to the engine block or a common which connects to the engine block. 1 overly simplified circut minus switches, controls etc. The 2nd battery Positive & negitive goe to the Pos. & Neg. on the trolling motor,(Assuming it is an electric trolling motor) & a second set of leads from the second battery, both + & - go to your accessories, either through dash switches or directly. As I said over simplied, but if you start with a drawing you will see the circuts. You can get a book, " The 12 Volt Bible", if you don't want to buy it check the library, my local library has it. It seems to me this is what you asked for, but this is not the best (IMHO) way to hook it up. Good luck, Joe P.S. I say stop thinking ground because people thing it terms of a car where any place on the body or chassis of the car is connected to the neg. of the battery, (Most cars are metal, most boats are not, & even the ones that are, run in water which is a good conducter of electricity, bad for the electrical system) So unless you have a common grounding plate or common ground strip, running through a heavy wire thoughout the boat, think in terms of battery neg.

 

[18rabbit]

Re: what is the point?

Jsscheh - This is a prety good book on marine electrical that I frequently recommend. Easy to read, easy to understand, covers everything you're likely to encounter. You can ordered it right here, from iboats' MegaMall:<br /><br /> http://www.iboats.com/mall/index.cg...ectric&**********=959821961&*******=595763063

 

[js361]

Re: what is the point?

I bought this boat used.....this is not my configuration, but rather the how it was when I got it...so it's all new to me.