want to add another battery, how to

[fourwinns170]

Greetings,

I currently have a four winns 170 horizon, love it ! I just want to add another battery, it currently sports one....im looking to have both be able to be charged by the alternator if possible...else i would just have one hooked for cranking and being charged by the battery the the other just hooked up the to lights/music etc. but that wouldn't be getting charged...is it possible to run two batteries in a series ? or no? how is this handled? thanks !

 

[Boatist]

Re: want to add another battery, how to

Two batteries in serries would be 24 volts and you alternator could only charge one.
What you propably want is two seperate batteries charged by your alternator.

This is the way My boat is wired. I charge both batteries thru a Battery isolator. Output wire from your alternator goes to the common lug on the isolator. Then hook plus side of battery one to the isolator battery 1 connection. Battery 2 plus lead goes to the isolator battery 2 connection. Use at least 10 guage wire.
Both battery ground wires connect to the Engine block.

The battery you have now I would make battery 1. This is already wired to the starter and all your gear.

Now the next question is what your want to run off the second battery. This is a personal choice you will need to make. On my boat left every thing needed to run the boat on battery one. Starter, Ingition, Blower, compass, Horn, Wipers, Navigation lights.

Battery 2 has the accesseries VHF, Loran C, GPS, Radio, Spot light, Accessories plugs/12 volt lighter plugs. At first I was going to put VHF and GPS on battery one also but after thinking about it for a while put them on battery 2. While these iteams can be needed to get help or guide Me home even if battery 2 was run down as soon as I start the boat the alternator will supply them power. Also when drift fishing in the ocean for hours the VHS, Loran C and GPS are always on. Also when night fishing at anchor the gear that is always left on is on the second battery. The gear to run the boat is on the starting battery but off until turn the Key on.

Many will also add a battery switch so can flip the switch and use battery 2 to start the boat. With an isolator to protect both battery from the other wireing get a little more detailed but if battery one should die do not have to move batteries or jump form one battery to the other to start the motor.

 

[fourwinns170]

Re: want to add another battery, how to

So this would be the correct way to wire it then? Please excuse the crudeness. This way, the alternator charges both batteries, and if one is fully charged, all the "charge" from the alternator will go to the low battery correct??? It sort of acts like a fork in the road, sending the current where it needs to go, correct? If so this is exactly what i was looking for, thanks boatist!!!

 

[--GQ--]

Re: want to add another battery, how to

 

[Boatin Bob]

Re: want to add another battery, how to

GQ's picture shows using a switch which works well but it's a manual effort, this diagram shows a simple 1 alternator, 2 battery isolator where battery one is your main/starting battery and battery 2 is for accessories.

 

[Boatist]

Re: want to add another battery, how to

The second diagram is the way mine is wired.

How the battery isolator works is alternator puts out between 13.8 and 14.4 volts. That goes to the isolator and any battery that is lower than the alternator output will be charged by the alternator. If one battery is charged and one is low then more charging current will go to the low battery.

You do not say what type motor your have but most I/O have alternator of at least 30 amps.
Most newer large outboards also have 20 to 30 amps of output and will work very well like the I/O.

Some older outboards and smaller outboards may only have 8 to 12 amps of output. With these small alternators if you have a starting battery and a Big discharged trolling motor battery then the trolling motor battery can take most or all of the charge for a long time before the starting battery gets a charge. In this case I would not recommend charging the trolling motor battery as it would take 15 hours or more anyway. A normal size acessory battery would work good with even a small alternator unless it was fully discharged like form a big high amp stereo

 

[boatingnva]

Re: want to add another battery, how to

When I did mine, I wanted to keep it simple, I wired mine with a Perco switch like GQ's diagram. I wanted to ensure I could shut off the batteries completely to prevent any parasitic drain (e.g. ignition, radio, etc) when not in use and the on-board batt charger is plugged in. Been over 2 yrs now, works great.

 

[Seafox230]

Re: want to add another battery, how to

My boat 2nd boat is a gradywhite the alternator only charges 2 batterys of four. The other two batterys only run equipment. They made mine like this for longer battery life cranking up 4 yamaha 200hp 4strokes drains the batterys life. i would recommand getting another battery and use one for equipment.

 

[bruceb58]

Re: want to add another battery, how to

The problem with the isolator is that if you don't run a remote sense from the alternator to a battery both of your batteries will be undercharged because of the voltage drop across the isolator. Even if you do use a remote sense, one of the batteries is going to have a tough time getting fully charged. Lets say the battery that has the sense on it is fully charged and the other battery is low, The alternator will believe it does not have to raise its output voltage and the low battery will get very little current directed its way

Way better to use a combiner. Bluesea makes one that you can pick up for less than $80. http://www.bluesea.com/product.asp?Product_Id=53476&d_Id=7491&l1=7459&l2=7491

http://www.bluesea.com/Article_detail.asp?Section_ID=291&id=303

 

[Boatist]

Re: want to add another battery, how to

I like the battery isolator better than a battery the battery combiner. Yes there is a small voltage drop to foward bias the diodes in the isolator and if your charging system is very weak it might have some impact.

All I know for sure is I have been useing an isolator to charge my batteries since 1980 and never had a battery that did not last at least 6 years. I have an group 24 auto battery and and group 24 deep cycle. I do hot have a trolling motor or any iteam that is know to runn down batteries.

In my opinion the things that kill batteries is not the way there charged.

Running a starting battery down more than 20 percent or a deep cycle more than 50 percent will shorten the life.

Leaving a run down battery in that condition for any length of time will really shorten it life. An example use a trolling motor all day Saturday and run it way down. Then when you get home just leave it until the next Friday when you charge it up for Saturday fishing trip. Running it this way the battery will not last one year.

Batteries need to be charged at least once a month in summer and at least every 2 months in winter. More often will not hurt them.

Battery switches kill more alternator than any other iteam in my opinion. Some models if you turn the switch with the engine running it will blow up your alternator. Even Good switches if you turn thru off with the motor running you will blow your alternator. Also with switches a loose battery cable on the battery switched in can kill the alternator. After you kill the alternator then the battery runs down and damages it.

However if you have a Battery isolator none of these things will hurt your alternator. To hurt the alternator you would have to remove the postive cable to both of your batteries at the same time with the motor running.

 

[Boatin Bob]

Re: want to add another battery, how to

Well...there you go fourwinns, 3 different approaches with the switch, isolator and combiner, all 3 will work and do what you want to do and everyone has an opinion as to which is better so now all you have to do is decide which way to go....are you having fun yet or are you just totally confused now ?

 

[bruceb58]

Re: want to add another battery, how to

If you go with a battery switch(I would) you will find that almost all of the switches have make before break contacts. This way you can switch between batteries without worrying about the alternator being disconnected from a load.

The nice thing about having the switch is that if you happen to leave the ignition on somewhere, you can easily start your boat on your second battery without having to use jumper cables. Jumper cables should not be used in a boat if at all possible.

I also have an onboard charger so that my boat is always plugged in and batteries fully charged when sitting in my driveway

 

[ricksrster]

Re: want to add another battery, how to

I disconnected the red wire at the rectifier and did this:

 

[Boatin Bob]

Re: want to add another battery, how to

Just a couple of points about the switch that I have seen happen.

If you go with a battery switch(I would) you will find that almost all of the switches have make before break contacts. This way you can switch between batteries without worrying about the alternator being disconnected from a load.

As long you or someone doesn't turn it to the off position accidently while running

The nice thing about having the switch is that if you happen to leave the ignition on somewhere, you can easily start your boat on your second battery without having to use jumper cables. Jumper cables should not be used in a boat if at all possible.

As long as you don't leave it on the both or 2 position

 

[bruceb58]

Re: want to add another battery, how to

There is no reason to leave the switch in the both position if you have a combiner or an isolator.

 

[Boatin Bob]

Re: want to add another battery, how to

There is no reason to leave the switch in the both position if you have a combiner or an isolator.

Understand that Bruce but you did not mention using an isolator or combiner with your switch post above so I thought I would throw in those two gotcha's!

 

[bruceb58]

Re: want to add another battery, how to

Bob,

Yes...that can be a problem. When I first bought my new boat, it didn't have a combiner on it but it did have the two batteries with a switch. I always would run half the day on one and switch to the second for the second half. I probably would only use the "both" position in the case where I was having problems starting with 2 low batteries.

Bruce

 

[ricksrster]

Re: want to add another battery, how to

In my diagram above, the batteries would still be connected to the charging system even with the swwitch in the off position.

 

[Boatist]

Re: want to add another battery, how to

Ricks way is the best I have seen. Isolator charges both batteries all the time. It also protects the alternator all the time even if turn switch thru off.
Switch still lets you select your starting battery.

 

[bruceb58]

Re: want to add another battery, how to

Every method has advantages and disadvantages. The isolator is best if you can tolerate an undercharged battery and the combiner is best if your sensed battery will be fully charged before your house battery is.

There is a lot of info on the web on this subject and both methods have been used a lot. RVers have the exact same application so there is probably more info from them than boaters.

I have used both methods and have found the isolator way a problem when the second/third battery powers a refer.