two battery hookup

DaverDog

Cadet
Joined
Jun 24, 2007
Messages
18
Yes im new to boating...what id like to do is have a two 12 volt battery hookup instead of running a 24 volt.do they have a cable setup that i can hook the two batterys up together? and if i can,can i run everything off them or should i not cable them together and run the motor off one and everything else(trolling motor,radio,lights etc)off the other. Or trolling motor off one battery and the motor and all else off the other?...thanx guys
 

drewpster

Commander
Joined
Oct 17, 2006
Messages
2,059
Re: two battery hookup

Just to clarify. Does your boat have a 24 volt electrical system? Or are the two batteries you mentioned used for the trolling motor only?
 

DaverDog

Cadet
Joined
Jun 24, 2007
Messages
18
Re: two battery hookup

yea sorry drewp i just got the boat and the previous owner has been running it on a 12 volt battery ...i havent gotten into the boat much yet to see whats really going on and what runs on what and from what..hope that helps ya a bit better and thanx
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: two battery hookup

You need to determine for sure what you have and to be a little more clear before we can make any recommendations. Everything on a small boat runs on 12V with the exception of some trolling motors. Some of those run on 12V, some run on 24V and some run on either 12V OR 24V. I posted three diagrams in the link below. Go there to help determine what you have.

http://forums.iboats.com/showthread.php?t=204320

If your trolling motor runs on 12 OR 24V it will have a switch either on the motor or on a separate panel at the front of the boat. If it doesn't have this switch, you have either a 12V motor or its a 24V only motor. If its a 24V ONLY motor and you are using only one battery you are getting very poor performance and roughly half the power out of the motor.

If you will run two batteries, I suggest you use one for the engine and all accessories except the troller. Use the other battery for it. If you simply parallel the two batteries and wire everything to them, you run the risk of running down both batteries and the engine won't start. Next, you need to determine how you will charge the trolling motor battery. The engine will not do that as it simply doesn't have enough output to top off a deeply discharged battery. You have to run wide open for hours. The best bet is to simply leave the engine and accessories on the start battery. Accessories don't take much power. Wire the troller to the other battery. Use a hand held charger at the dock to charge it or install an on-board charger that you leave in the boat and plug in at the dock.
 

DaverDog

Cadet
Joined
Jun 24, 2007
Messages
18
Re: two battery hookup

Silver thanx a bunch for those diagrams they were just what i was looking for!...Thanx again and safe boating to you
 

bowman316

Lieutenant Commander
Joined
Oct 21, 2008
Messages
1,822
Re: two battery hookup

Hey guys,
Can i hoop up a deep cycle battery to a starting battery in parrell? So it is still 12 v. Or would that mess up the deep cycle batt?
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: two battery hookup

You can, provided you use a dual battery switch, isolator, or VSR (voltage sensning relay). A permanent connection is not recommeded because of the very different discharge characteristics of the two batteries. This is how that system would look. With this system you use the OFF position to essentially kill everything on the boat except a bilge pump if you have an automatic type. BAT 1 is typically the start battery. BAT 2 is the accessories battery. BOTH means the accessories are drawing from both and if the engine is running, both will be charging. In the BAT 1 or BAT 2 position only that battery will charge and ALL accessories will run from whatever battery you have selected. ALL accessories would be wired to the COM terminal on the switch.

StandardBatterySwitchWiring.jpg
 

bowman316

Lieutenant Commander
Joined
Oct 21, 2008
Messages
1,822
Re: two battery hookup

so where would i hook up the positive and negative wires for the troling motor? Would i hook up the positive to the com, and negative to either battery, or would i hook them both up to one battery?
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: two battery hookup

If you have a 12 volt trolling motor you hook it directly to the deep cycle battery. Everything else gets powered from the COM terminal. You would typically have BAT 1 as the start battery and BAT 2 as the troller/accessory battery. When you run the troller set the battery switch to BAT 2. This prevents you from draining the starting battery which would happen if you had the switch set to BOTH. BOTH places both batteries in parallel which is what you want to avoid except for charging while running. An isolator or VSR does this for you automatically but they are more expensive and you lose the versatility of the switch.

I should have asked earlier, but you have a 70 HP outboard so why do you feel you need to parallel the troller and start batteries? The alternator output of the engine is not large enough to fully charge the deep cycle after a day of trolling anyway. And if you intend to parallel the two batteries for to extend trolling time, you have two different styles of batteries and you also run the risk of draining the start battery so you are stuck. I think you need to really reason this out a bit more. Most folks install an on board charger that you can plug into shore power at the dock to recharge the troller battery. The engine can take care of the start battery. Don't add things to a boat that serve no practical purpose for the use of your boat. Yes, the switch is nice if you understand how to use it and it is really necesary. In your case I don't think that's the case.
 
Top