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Old 09-19-2020, 09:36 AM   #1
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I have 6, 6 volt batteries in series and one 12 v battery in my boat.? Being a newbie I’m having a hard time figuring why I have the 12 v separate battery. Is this the starter battery? I’m running a 2500 w inverter/charger To a 6-6 volt battery bank and the selector is set to all. Why the separate 12 v battery?

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Old 09-19-2020, 09:44 AM   #2
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A guess as to how your boat is wired--the 12 V is the start battery which you keep separate from the house bank (6 V) so you can't run it down to where it won't start the engine(s)

Ken Diestler
Galveston, Tx
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Old 09-19-2020, 10:30 AM   #3
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The 12 volt battery is most likely the start battery. The 6 6 volt will be the house battery bank. You need to see how the battery switch is wired. Generally you don’t want it set to both because it will combine both banks, depending on how it is wired, and if you draw down the battery bank it will also take the start battery down and you will not be able to start the engine. An ACR would be a good way to charge both banks while running but it will break the connection when you shut the engine down so you won’t discharge the start battery while using the house bank. If you are not familiar with electrical systems I would get a certified marine electrician to look the system over and make suggestions and also show you what you have and how best to operate it.
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Old 09-19-2020, 10:37 AM   #4
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Your boat is typical of the way boats are built and delivered: separate house and starting systems tied together at the 1,2,all switch. Yours is even better than some as the house bank is based on 6V golf cart batteries which are one of the best types for house use.

As ktdtx notes above you have two separate systems so you can set it not to run down your starting battery and leave you stranded if you draw both down while at anchor. To use this capability when you drop anchor and turn off the engine, turn the selector switch to the house bank. This leaves the starting bank in reserve for starting. Then when you get ready to go, turn the switch to the starting battery, start the engine and then switch back to all so the engine alternator can recharge both banks.

There are fairly easy ways to automated this process so you don't have to always remember to do it. You probably should consult with a local marine electrician if that is what you want.

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Old 09-19-2020, 10:41 AM   #5
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Thought the "all" setting may be necessary to charge the house bank when running if no other means is provided.

Mine is similar with an on/off switch between the 2 banks and is shut off when at anchor/no shore power.
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Old 09-19-2020, 10:53 AM   #6
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When you get in to larger boats the power needs of auxiliary equipment becomes greater. The wire size needed to make the long run from battery bank to auxiliary equipment become problematic. One way of solving this is to locate a smaller battery bank closer to the equipment. Then you can use a smart ACR or a DC to DC battery charger To maintain the second bank. You won’t find battery combining switches on these type of circuits.

As already mentioned the 12v battery is probably the start battery. The need to turn a switch from 1-2-all is problematic. It’s probably due to your alternator being wired to your start battery and your battery charger being wired to your house bank. The only way to charge both is to turn the switch to all. While this works, it is prone to failures. Forgetting change the switch at appropriate times will lead to shorter battery life and very possibly dead batteries when you need them the most.

As mentioned above, proper system wiring with the use of an ACR will solve this issue.
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Old 09-19-2020, 01:28 PM   #7
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Clamdigger appears to be a newbie, it sounds like he's trying to understand his battery system. No indications that he has any problems. ACR is an acronym for automatic charging relay. It is a simple way to charge all boat batteries on the fly. It's quite possible that his boat has an ACR already. If clamdigger would tell us about his boat brand model size etc (put it in your profile info) maybe we can be more helpful.
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Old 09-19-2020, 04:15 PM   #8
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If those 6 batteries are actually wired in series, you have a 36-volt system. If not, be careful not to wire them in series when you replace them. FWIW, in my experience (I am sure there are plenty of exceptions), when a boat has two different voltages the starter motors (and other high amperage equipment such as windlass and thrusters) are usually higher than 12 volts, and 12 volts is reserved for electronics, lights, etc. But a single 12 volt battery for that purpose doesn't make sense either. I suspect that your 6 volt batteries (like mine) are wired to produce 12 volts, and are dedicated to the house bank. The single 12 volt battery is probably for starting.
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Old 09-19-2020, 08:32 PM   #9
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Send a pic of your 6x6v batteries. I expect they are in a series/parallel configuration analogous to having 3x12v batteries in parallel.
Follow all the connections and draw a wiring diagram. it will help you understand how your boat is wired. Probably 12v start battery and 6x6v (3x12vFLA) house batteries. Now u need to figure out if these get charged thru an ACR or via the “off, 1, 2, both” switch”
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Old 09-20-2020, 06:39 AM   #10
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The 6V batts are all probably deep cycle construction and the 12V a true start batt internally.

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