Boat Wiring Help

[Christopher D Terpening]

I was hoping to get some feedback on my boat wiring plans (see attached diagram). I have two dual purpose group 31 batteries. These will be powering my accessories (primarily fish finders) as well as starting the motor and running the trolling motor. I want to be able to have two isolated circuits. Circuit 1: Fish finders and all other accessories. Circuit 2: Outboard and Trolling motor. Additionally, I would like to be able to switch which battery each circuit is drawing from. For example, if the trolling motor draws Battery 1 low, I would like to be able to switch it over to Battery 2, then switch the accessories over to Battery 1. The primary reason for this setup is that I want to keep the fish finders on a separate circuit from the trolling motor and outboard in order to avoid any interference. This setup also gives me full flexibility in choosing which battery powers which circuit, and also gives me the ability to run everything from both batteries simultaneously if desired.

Will the combination of switches and circuit depicted give me what I am looking for?

Are there any potential issues wiring this way? For example, what happens if both 3 position switches are positioned to Battery 1, and the Dual Selector Switch is positioned to “Combine Batteries”? Not that I plan on doing that, just want to make sure there are no dangerous combinations.

Does the common ground between negative battery terminals introduce the possibility of interference across circuits (e.g. trolling motor interfering with fish finder)?

Thanks in advance for your help!

 

[Chris1956]

First, I would not think you will want the trolling motor and OB on the same battery. They should use different kinds of batteries. Also, the trolling motor uses the most power of anything you have and will run the OB starting battery down.

Second, that three switch setup will get you what you want, but I think you could achieve the same with only 2 switches. You have 2 batteries and need two 2 position switches to power 2 circuits. Sounds like a fit.

Connect 1 battery to each switch's common post. Connect one of each switch terminal to one of the circuits. You may need a battery combiner to charge both batteries from the OB, most efficiently.

 

[Christopher D Terpening]

First, I would not think you will want the trolling motor and OB on the same battery. They should use different kinds of batteries. Also, the trolling motor uses the most power of anything you have and will run the OB starting battery down.

Second, that three switch setup will get you what you want, but I think you could achieve the same with only 2 switches. You have 2 batteries and need two 2 position switches to power 2 circuits. Sounds like a fit.

Connect 1 battery to each switch's common post. Connect one of each switch terminal to one of the circuits. You may need a battery combiner to charge both batteries from the OB, most efficiently.

Thanks for the quick reply. I am using 2 matched dual purpose deep cycle batteries, so I didn't think it mattered if the trolling motor was on the same battery as the OB. Also, my OB is a 1960s mercury and does not recharge the battery when running. I am a little confused by your recommended switch setup, but I think i see what you are getting at. I have attached an updated diagram depicting what I think you recommended. Is this correct? This does achieve the ability to switch batteries for the load sources, however, it does not provide the ability to run both batteries in parallel and run all loads. It does allow batteries to run in parallel, but only supply power to one circuit. Am I thinking about this correctly? (Note that I moved the OB to the house circuit and kept the TM on the other circuit. I'm primarily trying to keep the TM and house circuit separate. The fish finders will be on the house circuit, so I do not want to have any interference from the TM.

 

[poconojoe]

A deep cycle battery is needed for the trolling motor. They can handle the repeated discharge. They can survive severe discharging. A starting battery cannot. For longevity, you should fully recharge it as soon as possible using a good battery charger, not the outboard. Chances are that the outboard will never be run long enough to fully recharge it.

They do make dual purpose batteries, but I personally have no experience with them. Hopefully someone will chime in on that.

I would keep the deep cycle for trolling and use a start battery for the engine, but that's my opinion.

 

[dingbat]

With no charge capability, I don’t understand the need a 1/2/both battery switch, let alone two on that setup.

TM goes on one stand alone battery. The general purpose will work but not the best choice. Not good at deep cycling.

Everything else on the other battery. Install a on/off switch if anything on the circuit.

TM noise on a Sounder is a flaw in the design of the trolling motor, not a wiring issue

 

[Christopher D Terpening]

A deep cycle battery is needed for the trolling motor. They can handle the repeated discharge. They can survive severe discharging. A starting battery cannot. For longevity, you should fully recharge it as soon as possible using a good battery charger, not the outboard. Chances are that the outboard will never be run long enough to fully recharge it.

They do make dual purpose batteries, but I personally have no experience with them. Hopefully someone will chime in on that.

I would keep the deep cycle for trolling and use a start battery for the engine, but that's my opinion.

I stand corrected. What I currently have are 2 marine deep cycle group 31 batteries. (Not dual purpose). Either way, i haven't had trouble using them to start the OB. My OB is a 1960s mercury and it doesnt have an alternator, so I dont have to worry about it charging the battery. Thanks!

 

[Christopher D Terpening]

With no charge capability, I don’t understand the need a 1/2/both battery switch, let alone two on that setup.

TM goes on one stand alone battery. The general purpose will work but not the best choice. Not good at deep cycling.

Everything else on the other battery. Install a on/off switch if anything on the circuit.

TM noise on a Sounder is a flaw in the design of the trolling motor, not a wiring issue

Thanks for the reply. As you stated, my primary goal is to have two isolated circuits. One for TM and one for everything else. I'd also like to be able to switch the source battery between the two circuits which is why I introduced the two 3 position switches. I tend to run my TM all day, but only start the OB a handful of times. In the event that I run one battery down with the TM, I can switch it over to the other good battery (I have pull start on OB as backup so i dont necessarily need to worry about the OB being on the low battery). In addition to this, I thought it would be nice to also have the option of running both batteries in parallel while running everything on one circuit. This is why I introduced the Dual Position switch in my first diagram. This would be for an emergency scenario to squeeze all the amps possible out of two low batteries. Make sense?

With that said, if I forgo the option to run the batteries in parallel, will my second diagram with the two 3 position switches achieve the ability to switch over battery sources between the two isolated circuits?

Finally, does creating a common ground between the battery negative terminals create a problem? I'm just considering this to cut down on the negative leads to run.

 

[poconojoe]

With no charge capability, I don’t understand the need a 1/2/both battery switch, let alone two on that setup.

TM goes on one stand alone battery. The general purpose will work but not the best choice. Not good at deep cycling.

Everything else on the other battery. Install a on/off switch if anything on the circuit.

TM noise on a Sounder is a flaw in the design of the trolling motor, not a wiring issue

@dingbat seems to be a lot more coherent than the rest of us! Maybe we're a bit groggy from our New Year's celebrations!
All his points make perfect sense.

Leave the trolling motor battery standing alone.
Charge it when you get home. If the boat is moored/docked where there's no electricity, pull the battery and take it home for charging.

Since you said your outboard is absent of a charging circuit, you'll need to charge the starting battery at home as well.

No need for a 1-2-all-off battery switch. Like @dingbat said, there's no battery charger. (or any other onboarding charging capability)

When I had my Jon boat, I had two deep cycle batteries onboard so I could fish all day. I ran with one and I had the second on hand if it was needed.

 

[Christopher D Terpening]

@dingbat seems to be a lot more coherent than the rest of us! Maybe we're a bit groggy from our New Year's celebrations!
All his points make perfect sense.

Leave the trolling motor battery standing alone.
Charge it when you get home. If the boat is moored/docked where there's no electricity, pull the battery and take it home for charging.

Since you said your outboard is absent of a charging circuit, you'll need to charge the starting battery at home as well.

No need for a 1-2-all-off battery switch. Like @dingbat said, there's no battery charger. (or any other onboarding charging capability)

When I had my Jon boat, I had two deep cycle batteries onboard so I could fish all day. I ran with one and I had the second on hand if it was needed.

Thanks for the comments everyone! I'm going to go with the 2 switch setup I showed in the second diagram. Even if I dont use the switches to swap over battery sources, at least they will serve as cutoff switches when the boat is not in use.

 

[poconojoe]

Thanks for the comments everyone! I'm going to go with the 2 switch setup I showed in the second diagram. Even if I dont use the switches to swap over battery sources, at least they will serve as cutoff switches when the boat is not in use.

Just be careful. If drain your trolling motor battery, don't switch the other (starting) battery or you might not have enough power to start the outboard.

 

[Christopher D Terpening]

Just be careful. If drain your trolling motor battery, don't switch the other (starting) battery or you might not have enough power to start the outboard.

My OB has a pull start for backup so I'm not overly concerned about not having enough battery for the starter.

 

[bruceb58]

What I currently have are 2 marine deep cycle group 31 batteries. (Not dual purpose).

Marine deep cycle batteries are dual purpose batteries. If they have a marine cranking spec on them, they are dual purpose.

Personally, if I had a trolling motor, I would be using golf cart batteries if you wanted to go with flooded batteries.

Even if you use true deep cycle batteries(golf cart or similar), don't drain them more than 50%(around 12.0V) if you want them to last very long.

 

[poconojoe]

My OB has a pull start for backup so I'm not overly concerned about not having enough battery for the starter.

That's great!