Isolating Batteries

[Jim Hawkins]

So, I continue to try to get my head around the workings of the (project) sailboat a friend bought. In trying to get the battery situation sorted out I found that the bank of deep cycle batteries that are charged by solar and run refrigeration and such, are wired into the starting battery for the engine.

Now everything I know about batteries and associated systems says this is wrong. It mixes two different sizes, types and uses of batteries and the only gain is to know you always have plenty of CCA's to start your motor, but at the expense of your deep cycle bank.

However, because I am sometimes wrong, I wanted to ask you folks, Am I missing something here?

 

[Davidasailor26]

You’re not wrong. Not only is the mixing of different battery types an issue, but if the two banks are really wired together then draining the house bank will leave you without any power to start the engine either.

There are a myriad of ways to have the start and house bank coexist and provide redundancy while being isolated. Check the archives here and Marine How To - DIY for Boaters - Marine How To for discussion about how that can be done.

 

[dlochner]

If there is an isolating device, such as an echo charger, or ACR, then it is OK to have the batteries connected to each other and the charging source only going to the house bank. In fact this is a good scheme as the house and start/reserve batteries are being charged. If the batteries are directly connected then this is a poor way as @Davidasailor26 points out.

There is a recent somewhat rambling discussion here on SBO that touches upon this.

Starting Battery won't hold a charge

I have a 3 battery setup on my 340. 3 Deka Deep Cycle Group 24. I use 1 as a Starting Battery and the other 2 as my House Bank. I had a friend selling his boat and he had these on his boat. They were all purchased the same day (May 2018) and were 3 months old and used only to start his...

forums.sailboatowners.com

 

[Jim Hawkins]

Thanks, I'll make short work of that problem.

 

[Head Sail]

Am I missing something here?

Yes, a wiring diagram. Your friend needs to do that first so you understand what currently exists. That being said, a Blue Seas SiACR will isolate batteries.

 

[Scott T-Bird]

To respond, or not to respond …

 

[Scott T-Bird]

Jim, I'm not making fun of your post … I'm really making fun of myself!

That said, I think your fundamental question has focused on a problem that should be corrected, so you aren't missing anything. The next step would be how the owner fundamentally wants to manage his battery and charging system. There are a lot of good options and the reading should be entertaining if not enlightening!

 

[Jim Hawkins]

The boat is a 1967 and the current owner has just taken possession and knowing little of boats and there systems, she will gladly accept whatever I recommend. I recommend, and will, simply isolate the starting battery and if it ever needs a charge a jump from the main bank or the generator will do just fine.
The boat is already a maze of wiring. Multiple VHF, GPS, radar and all manner of things have been added over the years. I am having to go through methodically and learn what is what and eliminate unneeded crap.
Thanks for the input. This really was a simple one but one thing I have learned fixing up old boats is, Don't undo anything until you understand why the PO did it in the first place.

On a side note, what brought this to my attention was that when I removed the starting battery, the bilge pump stopped working. My first instinct was to rewire it to the main bank but instead I will leave it as-is and install a second pump connected to the main bank. I like multiple pumps for redundancy.

 

[Jim Hawkins]

Oh well now, this really Is embarrassing. Good thing it weren't no snake.

 

[Davidasailor26]

Oh well now, this really Is embarrassing. Good thing it weren't no snake.View attachment 186046

Yep, better than it just being all one bank. Still wouldn’t be bad to have something like an ACR to automatically combine and isolate the banks. That might help especially if the owner might not have the interest or discipline to switch the 1-2-B switch for all the necessary starting/charging cycles.

 

[dlochner]

That switch may not be a "make before break" switch. See this article;

1/2/BOTH Switch Considerations

1/2/BOTH Battery Switch Considerations - Ever wonder how to make the 1/2/BOTH switch easier to use, let this article explain how to do that.

marinehowto.com

 

[Scott T-Bird]

Just realize that labeling it a starting battery don't necessarily make it exclusively so. On that switch, the house load and the start load is on the same post. The only thing that differs is the source between Bank 1 and Bank 2. If the switch is normally on "ALL" then they are using and charging both banks at all times. It's not the worst thing, they just don't have any reserve if they need it. Just think of it as a good opportunity to make a productive change!

 

[Jim Hawkins]

That switch may not be a "make before break" switch. See this article;

1/2/BOTH Switch Considerations

1/2/BOTH Battery Switch Considerations - Ever wonder how to make the 1/2/BOTH switch easier to use, let this article explain how to do that.

marinehowto.com

Thanks Dave, good read. I'll do it right.