Battery wiring question

I recently purchased a 33 Egg Harbor and drew out how the batteries are wired. If anyone can give it a look and let me know if everything looks right or if anything is wrong I would greatly appreciate it. What I'm confused about is why the Feeder from Switch 2 is connected to #2 on Switch 1. Also, #2 on Switch 1 is connected to a Guest device which I'm not too sure what it's for. I attached the pic of the device, does anyone know what that is?

Re: Battery wiring question

The Guest device is very likely a dual battery isolator. The big red cable is the feed to the isolator. The other two terminals would go to two batteries. The isolator is a one way device (a splitter of sorts). It allows the batteries to charge but you cannot draw current from the center terminal. These are used to keep one battery from discharging the other. It was probably eliminated when the switches were added. Now to the switches. If your diagram is correct, here is a table that shows the combinations of switch settings and what happens. If this were my boat I would be shaking in my boots. You cannot have alternators with no load when the engine is running and as you can see there are a bunch of those scenarios. Scenario 10 and 11 are the only two that allow charging all three and that happens from both engines simultaneoously. While this setup will work, it is certainly not my idea of a safe or efficient way to do this. Some of the multi-engine folks can provide a better scheme if you explain how you want this system to work.

Re: Battery wiring question

Thank you for the info Silvertip. I'm not an electrician but I know my way a little bit and I wasn't so warm and fuzzy when I saw all this. I would like to remove one battery and go with two bigger batteries. That's what my setup was in my last boat and I feel more comfortable with that setup. Any recommendations?

Re: Battery wiring question

On a boat that size I would retain the three batteries but with drastically different switch wiring and there would be a multitude of ways to use them. However, I subscribe to the principle that keeps things simple. Therefore switch 1 would allow charging battery battery 1 and the house battery (call it battery H). Switch 2 would control battery 2 and and the house battery as well. The house battery is what powers the cabin lights, electronics, etc. Battery 1 and 2 are then reserved for starting engine 1 and 2 respectively. You could also have this configured so you could start engine 2 from Battery 1 should Battery 2 go flat, and vice versa you could start engine one from battery 2. One thing you want to avoid is the possibility of ever allowing the alternator on either engine to run with no load as so many settings in the current setup allows. Don't hesitate to use an ACR (automatic charge relay) which is similar to the Guest device you have. An ACR take alternator output and designates one of its outputs as the priority output which is usually the start battery. When the engine is running the priority output always charges the start battery until it is charged. It then switches to the auxiliary output. As with an isolator, the ACR will not allow the two batteries to interact unless the ACR has a combine function which would be like the BOTH setting on a switch. Take your time and work with one engine and charging system at a time. Then figure out how or if you even want or need to interconnect them. If you spend a fair amount of time operating on one engine, the ACR could be very handy in charging the non-operating engines start battery.

Re: Battery wiring question

Thank you very much! I appreciate it, I'll definitely rewire it all in the spring. Do you recommend any specific ACR or are they all pretty much the same?

Re: Battery wiring question

Hi, I've installed a isolator a couple of times, except I used it in my vehicles to keep my marine battery charged while not used in the boat. Anyway, I just thought I'd mention that red lead on the isolator should be fed downward from the centre terminal and kept clear of the other two. Or perhaps the isolator can be inverted if lead-length was the reasoning behind that connection. Good luck with the rewiring project.