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Battery Switches

Sep 6, 2020
25
Catalina 315 74 Barrington, RI
My boat has two house batteries wired in parallel, plus a starter battery. For the house needs, I can run off either or both house batteries. For the starter need, I can run off the starter battery, or off the house batteries, or off all three batteries.

I'll mostly be day sailing, and on shore power at night (thus charging all three batteries). I'll do some overnights at anchor, but maybe only 10 nights a season.

I had been thinking to run the house needs off the house batteries, and the starter off the starter battery. But the manufacturer advised always running the house needs AND the starter needs off the house batteries only, and never using the starter battery unless, say I'm anchoring out and draw down the house batteries. This seems odd to me, but I'm a newbie. Thoughts would be appreciated.
 

ebsail

.
Nov 28, 2010
241
O day 25 Nyack. New York
when I had the same set up as you, I also used the 2 house batteries for everything. Only used the starter battery twice iin 10 years. Both times when guests managed to run down house batteries.
 
  • Like
Likes: Ward H
Jan 7, 2011
2,814
Oday 322 East Chicago, IN
If I had your set up, I would run everything off the 2 battery house bank. And keep the starter battery as reserve power in case something kills your house bank.

There is no problem switching over to the starter battery to check it, but your house bank should be able to start your motor.

I would also make sure your charging sources are set up correctly to charge your house bank as the priority.

I have 2 group 27 FLA batteries as separate banks. When I overnight on the hook, I always use one battery or the other, for the same reason...keeping something in reserve to start the engine. your setup is better because you have a bigger bank. Now, I just need to find room to add a starter battery...

Have fun and Happy New Year,


Greg
 
  • Like
Likes: FastOlson
May 17, 2004
3,420
Beneteau Oceanis 37 LE Havre de Grace
To some extent the best solution will depend on how your charging system is connected. If you have something like an ACR to charge both banks but isolate them when discharging then that would be ideal, and I wouldn’t be afraid to use the start bank for the engine in that case. if the engine only charges the active bank then that may explain your manufacturer’s caution, because starting and running on the start bank would never charge the house bank.

One risk of using the house bank for starting is that if the batteries are low, even if charged enough to start the engine, you could have a voltage drop for the other house loads. That could lead to problems like rebooting electronics and other inconveniences.

One more note on the house bank - since you have a separate start bank I would never recommend separating the house batteries and running off either of them individually. You’ll get better performance and longer battery life keeping both house batteries tied together. If either of them ever failed catastrophically you could isolate it, but until then keep them together.
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
The key is to understanding your question and giving a solid answer is knowing how the Start/reserve battery is being charged. Even if it is not used regularly, the Start/reserve battery needs maintenance charging. The shore power charger will do this when connected, however, when you are off shore power, how is the start/reserve battery being charged?

As has been mentioned, using an ACR to combine the banks when charging is a good approach. Here's an article that will explain this better than I can. In the article MaineSail also discusses ways to connect the batteries and charging sources for optimal results.

 
Feb 26, 2004
21,892
Catalina 34 224 Maple Bay, BC, Canada
Good advice.

What you might want to consider is expanding your horizons beyond what the manufacturer told you, and to find out as much as you can about how stuff works, together, in your electrical SYSTEM.
In addition to Dave's link, please feel free to wander around the collection of links I have assembled over the years, here: Electrical Systems 101 Electrical Systems 101

As far as switches and charging, I recommend you start with these: Good luck

OEM 1-2-B Switch Wiring History Alternator/Batteries & "The Basic" 1-2-B Switch BEST Wiring Diagrams

1-2-B Considerations
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 diagram: 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
 
May 24, 2004
6,765
CC 30 South Florida
It is a matter of redundancy. Conserving emergency power to start the engine. Batteries can and will go bad and a bad battery will bring down any good ones that happen to be combined to it. Also accidents do happen and someone forgets to turn off the refrigerator and turn the battery to House Only and boat is dead in the water. I would recommend that you exercise that starting battery by maybe once a month starting the engine at the dock with it and allowing it to recharge for a few minutes .
 
Oct 26, 2008
4,988
Catalina 320 Barnegat, NJ
I had been thinking to run the house needs off the house batteries, and the starter off the starter battery. But the manufacturer advised always running the house needs AND the starter needs off the house batteries only, and never using the starter battery unless, say I'm anchoring out and draw down the house batteries. This seems odd to me, but I'm a newbie. Thoughts would be appreciated.
The manufacturer makes that recommendation primarily because the manufacturer probably provided the ubiquitous 1+2+B switch (that is what is provided on my Catalina 320). In essence, the switch does not allow you to truly separate the house loads from the starter. The switch has just 3 posts, which means that house loads and start load are always combined, whether you use the switch in the 1 position, 2 position or Both position. Only the 2 source posts can be switched (or combined). There is just 1 load post and the cables lead to the house panel and the engine starter, so you really can't separate the loads.

1st step is to study your switch and learn how it should be used. There are distinct "do's and don'ts" and the @Stu Jackson references are a valuable source of information and will go into great detail. You may want to make alterations to your current basic system based on the other electrical equipment you may or may not have or want to purchase. Who knows what alterations have already been made to your electrical system? You should study every piece of equipment you have and draw a diagram to define the wiring layout.

After you have a thorough understanding about the system you currently have, you may want to make your own alterations. There is more than one good way to skin a cat and you aren't necessarily locked into anything the manufacturer provided. You mentioned separating your house loads from the start loads. You can do that by changing up your switching system, but you should/must also make sure that you can achieve battery bank isolation when one or the other bank fails and you need to combine the loads. The charging sources also enter into the picture, as @dlochner suggests, in a big way. You can do whatever you please as long as you understand the consequences and safety requirements. Again, all of the sources provided by StuJ will provide your educational needs! ;)

I always start with Blue Sea Systems equipment when I am planning my electrical equipment needs.
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
Bluesea is a good source for marine electrical supplies and generally I go with their products, however, the mounting options for their switches limit their use. The switch plates and knobs are connected to the switch body by the mounting screws. This works, but can just complicate the installation process.

Marinco makes a Pro Installer series of switches and bus bars that are easier to install. The base plate with the connections can be mounted first, then cables, and then the switch and cover. It is a cool system.


If you look through the catalog you will see some items that bear a striking resemblance to Blue Sea, that's becauase in this era of conglomerates and corporate buyouts, Marinco, Blue Sea, Pro Mariner, Ancor, and several other brands are under the same roof.

 
  • Helpful
Likes: Scott T-Bird

TomY

Alden Forum Moderator
Jun 22, 2004
2,646
Alden 38' Challenger yawl Rockport Harbor
My boat has two house batteries wired in parallel, plus a starter battery. For the house needs, I can run off either or both house batteries. For the starter need, I can run off the starter battery, or off the house batteries, or off all three batteries.

I'll mostly be day sailing, and on shore power at night (thus charging all three batteries). I'll do some overnights at anchor, but maybe only 10 nights a season.

I had been thinking to run the house needs off the house batteries, and the starter off the starter battery. But the manufacturer advised always running the house needs AND the starter needs off the house batteries only, and never using the starter battery unless, say I'm anchoring out and draw down the house batteries. This seems odd to me, but I'm a newbie. Thoughts would be appreciated.
I'd do what you propose. I run a starter battery solo for the starter (and the windlass) and have an ON OFF switch for that battery circuit.

The house, two Grp 27's are on a 1-2 Both switch. I always turn that to BOTH or OFF so that too could be an On OFF switch, but it works so why?

No combiner, no way to cross over the two circuits, nothing else. Both banks charge off a dull output alternator.

That's been working great for 20 years. The start battery is always well charged - never deeply discharged - and the circuit is always tested when starting the engine, so I know it all works. Start batteries last a long time due to this easy life. I replace house batteries in pairs. My house battery life seems to be most affected by deeply discharging them. If I don't do much of that, they last longer.
 
  • Like
Likes: LloydB
Jan 7, 2011
2,814
Oday 322 East Chicago, IN
No combiner, no way to cross over the two circuits, nothing else. Both banks charge off a dull output alternator.
Is a dual output alternator something special? It sounds like a good way to keep the starter battery topped off.

Greg
 
Jan 11, 2014
7,718
Sabre 362 113 Fair Haven, NY
Is a dual output alternator something special? It sounds like a good way to keep the starter battery topped off.

Greg
Balmar made them for a while. I don't think they are still in production. Don't know for certain, but this might have been one of those better ideas that technology left behind.
 
Oct 29, 2005
2,182
Hunter Marine 326 303 Singapore
**But the manufacturer advised always running the house needs AND the starter needs off the house batteries only, and never using the starter battery unless, say I'm anchoring out and draw down the house batteries. This seems odd to me, but I'm a newbie. Thoughts would be appreciated.**
That's how I setup mine. Everything runs on Bank1 including engine starter. Always preserving the Bank2 for emergency. Have a VSR between the Bank1 & Bank2 to keep Bank2 fully charged all the time.

Ken Y
 
Jan 7, 2011
2,814
Oday 322 East Chicago, IN
Balmar made them for a while. I don't think they are still in production. Don't know for certain, but this might have been one of those better ideas that technology left behind.
Thanks. I guess that is why an Echo Charger or something similar is needed.

Greg
 

splax

.
Nov 12, 2012
675
Hunter 34 Portsmouth
i have much the same setup as you. i had a cell go badin one of the house bank batteries which in turn ruined the other. avoid using the all position on the switch that connects all 3 to keep from having all 3 go bad and be stuck.
 

TomY

Alden Forum Moderator
Jun 22, 2004
2,646
Alden 38' Challenger yawl Rockport Harbor
Balmar made them for a while. I don't think they are still in production. Don't know for certain, but this might have been one of those better ideas that technology left behind.
I'm pretty sure they're not produced any longer. I bought this one in 2000. It's 'only' a 70 amp output, that may(?) have been why it was phased out. Not enough amps. for the power hungry sailboats today.

It has two output posts. There is a sense wire for the bigger bank. It doesn't overcharge the start battery even as the house bank is depleted to requiring full output.
 
Nov 13, 2013
629
Catalina 34 Tacoma
I have 2 grp 27s as one house bank and one grp 24 as start battery. The start battery has a seperate on/off swithch. The 1-2-B is set to battery #1 and stays that way for house loads. I use the start battery for starting and glow plugs. It's good to know that it's working before it's really needed. It also saves the engergy for the house.
 
Last edited:

CarlN

.
Jan 4, 2009
577
Ketch 55 Bristol, RI
Those aren't big batteries for house use. I'd parallel them and use the pair for everything. The batteries will be discharged a smaller percentage and last much longer. For an emergency start if you drain the batteries, something like this would work great. They say it can start an 8L diesel so it won't have any trouble with your puny sailboat engine. https://www.amazon.com/Imazing-Port...mergency+engine+starter&qid=1610075628&sr=8-4
 
Jan 22, 2008
8,050
Beneteau 323 Annapolis MD
... i have much the same setup as you. i had a cell go badin one of the house bank batteries which in turn ruined the other. avoid using the all position on the switch that connects all 3 to keep from having all 3 go bad and be stuck....
:plus: I have three on-off switches. One for each 31 battery. In the slip one stayes on. On the hook, two are on and one is off to be sure to have starting juice.