Converting to a 2 Battery System

[NYMINUTE]

What is involved in adding a 2nd battery to my boat? Wiring changes. Primary use is as alternate starting power. Any diagram would be helpful. This is a 5.0 Mercruiser.

 

[bayman]

Re: Converting to a 2 Battery System

It depends on how you want your batteries configured. I'm assuming you want to add a battery and not have 2 that are both connected. Do you want them on a switch so you just choose one or the other? There are few different ways to go depending on what you want. Some can get expensive too.

 

[NYMINUTE]

Re: Converting to a 2 Battery System

Switch between the two for starting and charging.<br />My boat will stored 125 miles from home during the season. Hate to drive that far and have one too weak to fire up the boat. Appears easier than hauling a spare back and forth

 

[gsbodine]

Re: Converting to a 2 Battery System

I've got a dual, swtiched battery setup using a Perko selector. It's an inexpensive setup (around $25 plus cables) and works well for doing what you are talking about. If you want to see several discussions about alternative setups, use the search feature and search for some of ThomWV's posts. 18rabbit often has interesting things to say about stuff like this too. Here's a couple of diagrams to look at anyway:<br /><br /> http://www.perko.com/diagram2.html

 

[NYMINUTE]

Re: Converting to a 2 Battery System

Thanx Ol Norse, Perko drawing is what I expected.<br />Looks like a winner.

 

[18rabbit]

Re: Converting to a 2 Battery System

Whatever battery switch you end up getting, I feel it is worth a few extra bucks to get a battery switch with AFD (alternator filed disconnect). With AFD you can flip the switch to “off” while the engine is running without frying the diodes in your alternator.

 

[islandboat]

Re: Converting to a 2 Battery System

Are you sure that you can switch the batteries "off" while the engine is running without damage? I know some battery switches have the ability to switch from one battery (1) to the other (2) or to "both" while the engine is running. It does this by not disconnecting the 12 volts from the alternator/ignition while switching. Once you switch to "off", all voltage is disconnected. (always wire the bildge pump float switch to the "hot" side of the switch so it never gets disconneted if you leave the boat in the water for any length of time)

 

[18rabbit]

Re: Converting to a 2 Battery System

Originally posted by trophy175:<br /> Are you sure that you can switch the batteries "off" while the engine is running without damage?

Yes. AFD is a switch within the battery switch that will open the field between the alternator and the regulator before disconnecting the alternator’s output from the battery(s). If you have AFD on a battery switch you get to run a couple 14 gauge wires for the alt’s field in addition to the battery cable you would normally run. If you only have battery cable going in and out of your battery switch, it does not have the AFD function. Perko, Blue Sea Systems, Guest (my personal favorite) all have battery switches either with or without AFD.

 

[islandboat]

Re: Converting to a 2 Battery System

NYMINUTE had an inboard/outboard. Now I understand. I remember seeing battery switches like that. Question; Would an outboard need something like that or is the afd not necasary on an outboard? I don't have this type of switch on my outboard and may not need it. It came from the dealer with the standard switch and no afd. I certainly would not want someone to switch the batteries "off" instead of just swapping charging from one battery to the other on my outboard when it is running (by mistake).

 

[scottb218]

Re: Converting to a 2 Battery System

If you want to charge two batteries from a single alternator you can wire in a switch as described above and also add a battery "isolator" this device will charge both batteries while you perko switch is only set to one. this only works with automotive style alternators and you can pick one up at a rv store

 

[NYMINUTE]

Re: Converting to a 2 Battery System

Thanx Scottb218, and welcome aboard.

 

[18rabbit]

Re: Converting to a 2 Battery System

Nyminute – I like the way Scottb218 is thinking. If you are going to go with a battery isolator, I recommend a marine version. But, in general, I do not recommend battery isolators. Battery combiners are marginally better, Balmar makes good stuff but expensive. The Blue Sea Systems Auto Charge Relay (ACR) is better ... basically a smart solenoid. I prefer a simple continuous-duty solenoid (cheapest!) but it is an all-manual operation, so it’s possible you can accidentally mess things up.<br /><br />Do a web search for whomever sells the Blue Sea Systems ACR the cheapest and install it. Budget about $130. Don’t know if iBoats sells it because the Mega Mall search engine remains partially dysfunctional ... kinda like me.

 

[624oldron]

Re: Converting to a 2 Battery System

I use a small solar power unit on each battery, in fact with vehicles as well, and never seem to run into battery discharge problems