So, I have a quite simple electrical set up with minimal electrical needs- I do mostly day sailing with occasional weekends or weeklong cruises. I have no refrigeration, but I do have a chart plotter and other common electronic navigational devices. I have two Group 31 deep cycle flooded batteries. I was doing some winter cleaning on the boat in the battery compartment and noticed that my batteries were linked together positive to positive and negative to negative. Disclaimer they have always been set up like that since I have owned the boat and never questioned the raision d'etre until now. I looked in past forums and don't see any batteries wired this way except to increase the total amp hours. Is there any reason I need to have it set up this way in my simple system ? Thanks in advance for your thoughts
Battery Wiring
- Thread starter nveater
- Start date
What you have is the common way of powering a 12V system. Why would you want to change the simplicity of paralleled batteries by adding switches which would separate them?
Your system appears to wired by someone who may not have a good understanding of DC systems.
Typically, 1-2-Both switches are used to isolate the two batteries so that there is always a fully charged battery. With the switch turned to Both the batteries are paralleled which allows for charging both batteries from one source.
Your schematic shows a cable connecting the two batteries at the positive and terminals. This is an unusual arrangement and renders the 1-2-Both switch basically useless. The batteries are never isolated and are always combined.
If you have a separate start battery there are advantages to having both house batteries in parallel. Deep battery discharges shorten battery life, the same amount of current drawn equally distributed between 2 batteries will result in shallower discharges for each battery. In your case, this may not be much of an issue as your current draw is fairly small.
If this was my boat, I'd remove both the negative and positive cables between the batteries and learn to use the 1-2-B switch properly. See this article for a deeper explanation:
Typically, 1-2-Both switches are used to isolate the two batteries so that there is always a fully charged battery. With the switch turned to Both the batteries are paralleled which allows for charging both batteries from one source.
Your schematic shows a cable connecting the two batteries at the positive and terminals. This is an unusual arrangement and renders the 1-2-Both switch basically useless. The batteries are never isolated and are always combined.
If you have a separate start battery there are advantages to having both house batteries in parallel. Deep battery discharges shorten battery life, the same amount of current drawn equally distributed between 2 batteries will result in shallower discharges for each battery. In your case, this may not be much of an issue as your current draw is fairly small.
If this was my boat, I'd remove both the negative and positive cables between the batteries and learn to use the 1-2-B switch properly. See this article for a deeper explanation:
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
The problem is the batteries are not paralleled correctly. Positives from both batteries are connected to the switch and the negatives are connected at the bus bar and by a cable between them. And I agree, paralleled batteries are more efficient than separate batteries, if there is a dedicated start/reserve battery.
Wow there - the point is not to remove them but rather change the location of attaching them directly at the battery posts
Here's a longer answer so you can understand the whys & wherefores:
OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams
1-2-B Considerations (New 2020 - Rodd finally got around to diagramming what I had done in the above link in 2009
)
1/2/BOTH Switch Considerations
Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams
This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings
This is a newer primer for boat system wiring design with a thorough digram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation
The Short Version of the 1-2-B Switch Stuff: Electrical Systems 101 This is a link to the Electrical Systems 101 Topic, reply #2
What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
Battery Switch Question ? and Battery isolator / voltage regulator / batteries
Making Sense of Automatic Charging Relays (2019)
Making Sense of Automatic Charging Relays - Marine How To
OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams
1-2-B Considerations (New 2020 - Rodd finally got around to diagramming what I had done in the above link in 2009
)1/2/BOTH Switch Considerations
Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams
This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings
This is a newer primer for boat system wiring design with a thorough digram: Building a Good Foundation (October 2016)
Building a DC Electrical Foundation
The Short Version of the 1-2-B Switch Stuff: Electrical Systems 101 This is a link to the Electrical Systems 101 Topic, reply #2
What are ACRs, Combiners & Echo Chargers? (by Maine Sail) [scroll to the top]
Battery Switch Question ? and Battery isolator / voltage regulator / batteries
Making Sense of Automatic Charging Relays (2019)
Making Sense of Automatic Charging Relays - Marine How To
Thanks Stu and Don- let me review the reading list from Stu and then make a more informed decision
Diagram how your charger is connected also so we get the full picture.
Mine is wired so the batts are always connected to the charger and my 'A-B-All' switch determines which group supplies power. House, Start or none(off).
Mine is wired so the batts are always connected to the charger and my 'A-B-All' switch determines which group supplies power. House, Start or none(off).
See the image below. Remove those 2 cables and you system will typical of the 1-2-Both battery set ups.
If you have a battery charger capable of charging 2 batteries, connect one positive lead to each battery positive and the negative to the bus bar.
The alternator output probably feeds to the starter and from there to the switch which will then direct the charging current to which ever battery is selected or both if the switch is on both.
This is perhaps the simplest arrangement, however, it is not without limitations. The many links @Stu Jackson provided will give all or more than all the info you need or want.
If you have a battery charger capable of charging 2 batteries, connect one positive lead to each battery positive and the negative to the bus bar.
The alternator output probably feeds to the starter and from there to the switch which will then direct the charging current to which ever battery is selected or both if the switch is on both.
This is perhaps the simplest arrangement, however, it is not without limitations. The many links @Stu Jackson provided will give all or more than all the info you need or want.
Thanks this is probably what I will do- but I will review Stu's links first- I do have a charger hooked up to both pos terminals and the neg is attached to the buss bar-Again thanks for all the feedback- that's why I like this site
It is all about options. Instead of having effectively what is a single battery you will have two batteries that you can combine or isolate as your needs determine. The combined large single battery gets accidentally discharged or some of the cells fail and you are out of power. If you have two batteries even if they are smaller and one dies the other could bring you home. A single group 31 battery is more than capable of running your electrical system in day-sailing so the smart thing to do would be to keep one battery in reserve while using the other. To maintain battery life similarity the proper way to do it would be to alternate their use, use battery "A" on one outing and use battery "B" in the next. Combine them only if the one in use seems to be weak or to charge both batteries when running the engine underway. When two batteries are connected there will always be one stronger than the other, I don't care if they have the same Build Date. The weaker battery will always be draining power from the stronger one. This difference can range from insignificant to significant. By keeping them isolated their difference will not be an issue.
Not relevant the the OP, but...
Every boat I have owned used batteries in parallel. Although there were switches to separate them on one of the boats, they were never used. Why?
The boats ran off outboards that could be pull started in an emergency, so it made better sense in terms of battery life expectancy and usable capacity to use them as one large bank. It takes little to turn over one outboard, and once one is running, the other will start. Twin outboards are common with catamarans up to 36 feet. This also can make sense for boats that charge primarily from solar, since it is easier to keep the batteries balanced.
BTW, you can always sail home. I've done it several times. Sail off the hook, and then right into the slip. Not good as a common practice, but you should at least be able to sail to your home harbor in most cases. Maybe you have a powered tender. Old school.
Every boat I have owned used batteries in parallel. Although there were switches to separate them on one of the boats, they were never used. Why?
The boats ran off outboards that could be pull started in an emergency, so it made better sense in terms of battery life expectancy and usable capacity to use them as one large bank. It takes little to turn over one outboard, and once one is running, the other will start. Twin outboards are common with catamarans up to 36 feet. This also can make sense for boats that charge primarily from solar, since it is easier to keep the batteries balanced.
BTW, you can always sail home. I've done it several times. Sail off the hook, and then right into the slip. Not good as a common practice, but you should at least be able to sail to your home harbor in most cases. Maybe you have a powered tender. Old school.
Batteries do go bad and many times they do not give any warnings. The battery warranty business thrives because the life expectancy of batteries is basically unpredictable. They say a battery is just as good as it's warranty but when you are out in the water the warranty will not do much until you get back to land. When connecting single batteries in series you end up with a much larger but still single battery. If one of the batteries goes bad it can bring down the whole single battery rather quickly. A sailboat sailing close to shore may not have a problem if their battery or engine dies but someone making an overnight passage may be in trouble if they loose communications and navigation capabilities not to mention the ability of being able to start the engine. It is unlikely that if you have two single batteries isolated that the two of them would fail at the same time but yet you retain the option of combining them if you should need to. Yes, there is a trade off in the loss of power capacity and efficiency but that tradeoff is usually irrelevant as that extra capacity is rarely if ever used or necessary. How many times did you ran the batteries down on those boats you referred to? In that tradeoff you would be getting a source of back up power to perhaps safely and conveniently get you home without it being an ordeal. I have had a battery go bad and the only problem it caused was having to head for the nearest port to purchase a quick replacement so that we could continue on our trip. Inexpensive wet cell batteries can be found every where and if you purchase them at a popular retailer like Walmart you may even get to use the warranty. I just remembered I also lost a battery in a powerboat, going across the Okeechobee Waterway, in the middle of nowhere. I went ashore and walked to what looked like mechanics shop hoping to find a replacement. The guy had none but gave me a used battery that he had laying there and told me it should get me where I was going. I used that battery for almost a year after that.