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Old 02-22-2021, 10:29 PM   #1
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12v system question

I ordered my 6v 370 ah batteries today and got thinking,if I took my starting battery out of the loop,and had it standalone only hooked up to starter and another battery selector switch,then put a 20w solar panel just to maintain starting battery and if solar is down for a few days possibly small charger of inverter for emergency charge only,and then in its replacement in bank2 ordered 2 more 6v 370 ah batteries,and have bank 1and 2 for house at 740ah with 600w solar setup and standalone battery for starting,if anyone else tried something like that,I need a good setup for extended offshore fishing trips,planning to do a couple trips out to the edge of the continental shelf this summer
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Old 02-23-2021, 12:16 AM   #2
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Use a SmartACR to charge the starting battery. Send the alternator, solar and the charger to the bank.
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Old 02-23-2021, 01:28 AM   #3
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I second Tiltrider1's suggestion. Connect all your charging units to your house bank including your shore charger and then use an ACR between the house bank and the starter battery. The ACR will allow the start battery to be charged from the house bank but won't allow the house side to discharge the start battery. Modern ACR's will also have an option to allow the batteries to temporally be combined should your start battery become dead.
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Old 02-23-2021, 02:10 AM   #4
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Another thought was wiring first two 6v in series,then second 2 in series then parallel,it seems .maybe that would.be easier, but what's to gain doing it tbe 1st way I mentioned with the starter battery isolated,besides being able to switch out banks as needed
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Old 02-23-2021, 06:22 AM   #5
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I've never heard of doing that many batteries in series, but theoretically, it would work. That said, the batteries will not discharge equally - the ones in the middle will last significantly longer and not discharge as deeply as the outer two sets. Best practice (assume 12v) is to cable each 12v battery to a heavy bus bar instead of doing them in parallel.

An excellent article in ACR usage

https://marinehowto.com/automatic-charging-relays/Click image for larger version

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Old 02-23-2021, 07:10 AM   #6
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Keeping the banks together at all times means when 1 6v batt dies , they all get dragged down.

Probably safer to isolate the two sets from each other and use isolated.

No question the current thinking is one big batt(all combined) handles higher loads like an inverter better , but there is a risk.
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Old 02-23-2021, 08:56 AM   #7
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There is always risk but planning for the meteor strike is just plain foolish. Many boaters seem always to focus on the highly unlikely. How often does a battery fail? And, if it does, now one knows it is time to replace the entire bank because replacing just one failed battery in any bank is a no-no. Stated plainly, this risk is not a reason to wire it all into one bank.
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Keeping the banks together at all times means when 1 6v batt dies , they all get dragged down.

Probably safer to isolate the two sets from each other and use isolated.

No question the current thinking is one big batt(all combined) handles higher loads like an inverter better , but there is a risk.
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Old 02-23-2021, 01:37 PM   #8
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Personally I'd prefer to use a DC-DC charger in this type of situation. Connect all your charge sources to the house bank ( I wouldn't continue to have two house banks either, just one large one, or leave the switch on combine all the time except for troubleshooting issues) and use a DC-DC charger to maintain the start battery. The DC-DC charger will automatically maintain the start battery anytime there is charging voltage present on the house bank.

With an ACR, having issues with one bank or the other can reflect those issues to the other bank negating the feature of having a start battery in the first place. DC-DC charging keeps them isolated all the time and provides the ideal charging profile to the start battery even if it's a different chemistry.

A Victron Orion-TR is one charger that can do this job.
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Old 02-25-2021, 07:04 AM   #9
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"How often does a battery fail? And, if it does, now one knows it is time to replace the entire bank because replacing just one failed battery in any bank is a no-no. Stated plainly, this risk is not a reason to wire it all into one bank."

Here in SWFL many folks store their boats afloat for the hurricane season.There on their own 5 or 6 months till the owner returns.

With a charge coming from a single source AC charger or solar the chance that a single batt will fail and kill the rest of the string has happened, multiple times.

The worst was an owner that had almost new big buck batts , that then had to battle to get 8 replaced.

My suggestion was to have at least 2 house banks with different charging sources they could be joined for a massive inverter load only.


YRMV
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Old 02-25-2021, 08:29 AM   #10
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Quote:
Originally Posted by FF View Post
"How often does a battery fail? And, if it does, now one knows it is time to replace the entire bank because replacing just one failed battery in any bank is a no-no. Stated plainly, this risk is not a reason to wire it all into one bank."

Here in SWFL many folks store their boats afloat for the hurricane season.There on their own 5 or 6 months till the owner returns.

With a charge coming from a single source AC charger or solar the chance that a single batt will fail and kill the rest of the string has happened, multiple times.

The worst was an owner that had almost new big buck batts , that then had to battle to get 8 replaced.

My suggestion was to have at least 2 house banks with different charging sources they could be joined for a massive inverter load only.


YRMV
Sure, it happens, multiple times, but still only a tiny percentage of users. In any case, it is not anything that can be prevented, a battery going bad, that is. When it does, the entire bank must be replaced. Okay, two charging sources and separate banks joined only when high inverter loads but won't you be worrying about a battery going bad on both banks at some time on each bank? Oh, I know, what are the chances of that happening? Multiple times?? There is one benefit in that, with eight batteries, for example, a bad battery will kill only four batteries but, again, this is a rare occurrence relative to the boating population. And, then there is the fact that your house bank is being only half-utilized when not joined. Folks, stop worrying about the esoteric and go boating. My opinion and I respect the opinions of all.

By the way, my house bank is eight batteries in two banks wired through an Off-Left-Right-All switch. I keep it on "all" full-time. When at anchor overnight, our use profile requires both banks else the batteries will be depleted beyond the point at which I am comfortable. If disaster strikes while at anchor, I can always start my engines with the generator batteries. I sleep well. Bottom line, FF, I can do what you do but I see a miniscule risk and choose not to do so.

A question, though if I may. You mentioned two charging sources. How would that work? A mutually exclusive charging source for each bank? Two generators that feed each bank separately? Or, wind and/solar?

Quote:
Originally Posted by FF View Post
"How often does a battery fail? And, if it does, now one knows it is time to replace the entire bank because replacing just one failed battery in any bank is a no-no. Stated plainly, this risk is not a reason to wire it all into one bank."

Here in SWFL many folks store their boats afloat for the hurricane season.There on their own 5 or 6 months till the owner returns.

With a charge coming from a single source AC charger or solar the chance that a single batt will fail and kill the rest of the string has happened, multiple times.

The worst was an owner that had almost new big buck batts , that then had to battle to get 8 replaced.

My suggestion was to have at least 2 house banks with different charging sources they could be joined for a massive inverter load only.


YRMV
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Old 02-25-2021, 09:17 AM   #11
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For many years I had a boat where the alternator charged the starting battery alone and the battery charger charged the house battery bank alone. When running the alternator pushed all of the 12 volt plus charged the starter. When I dropped anchor or picked up a mooring, I switched to the house bank and charged that with a generator. As long as starting is the only draw on the starting battery, it would be theoretically fine.

Think about it, how often do you need to hook you car up to a battery charger??

The better solution would be an ACR as described above. It will dynamically switch between starting and house banks based on load, so when starting it pulls from the starting bank. Once you power down, it automatically starts drawing from the house bank. It will charge both the starting and house banks off of the alternator.
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Old 02-25-2021, 09:23 AM   #12
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Quote:
Originally Posted by catalinajack View Post
Sure, it happens, multiple times, but still only a tiny percentage of users. In any case, it is not anything that can be prevented, a battery going bad, that is. When it does, the entire bank must be replaced. Okay, two charging sources and separate banks joined only when high inverter loads but won't you be worrying about a battery going bad on both banks at some time on each bank? Oh, I know, what are the chances of that happening? Multiple times?? There is one benefit in that, with eight batteries, for example, a bad battery will kill only four batteries but, again, this is a rare occurrence relative to the boating population. And, then there is the fact that your house bank is being only half-utilized when not joined. Folks, stop worrying about the esoteric and go boating. My opinion and I respect the opinions of all.

By the way, my house bank is eight batteries in two banks wired through an Off-Left-Right-All switch. I keep it on "all" full-time. When at anchor overnight, our use profile requires both banks else the batteries will be depleted beyond the point at which I am comfortable. If disaster strikes while at anchor, I can always start my engines with the generator batteries. I sleep well. Bottom line, FF, I can do what you do but I see a miniscule risk and choose not to do so.

A question, though if I may. You mentioned two charging sources. How would that work? A mutually exclusive charging source for each bank? Two generators that feed each bank separately? Or, wind and/solar?
There are many applications where a single large bank is preferred. Electric car or off grid house come immediately to mind.

How do they manage the risk? Talking serious money for a tesla battery.

Peter
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Old 02-25-2021, 11:56 AM   #13
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I have all my charge sources (Stbd 120A alternator, charger, generator, solar) going to my 6xGC house bank. Those charges can be shared with the port 60A alternator charged start battery with a helm switch-selectable Yandina 160A Combiner as needed. All banks are monitored with a State-of-Charge (SOC) meter, separate voltmeters and the house bank has solar controller Bluetooth data on my tablet or phone.

It's important to remember that the bigger the bank, the bigger your charge needs for healthy batteries. This means bigger cables and fuses for efficiency and safety.
The entire system needs to be considered when piece-mealing the parts over time. Study the information put out there by the experts like Compass Marine/Rod Collins/CMS/Marine-how-to (that guy's got a lot of names!!) and Nidel Calder. It's all out there and all relevant and can help immensely before starting the first upgrade.
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Old 02-26-2021, 02:34 AM   #14
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I have a big battery bank. I have 150a battery charger. I needed 0000 battery cable to prevent voltage drop. Just a little bit of voltage drop can double the time it takes to recharge a large battery bank. I spent $500 just on the battery cables between my charger and my bank.

As Flyright said, this is often overlooked.
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Old 02-26-2021, 06:41 AM   #15
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"A mutually exclusive charging source for each bank?"

Two 120v chargers for power pole or noisemaker will cost little extra compared to a similar charger of 2x the amps.

The same solar group can also be split to charge with 2 controllers.

Little extra cost or complexity for basic insurance.

What has happened in the past should serve as instruction , one 1/2 size bank going dead is a PIA , but wont ruin a cruise.
Everything dead although rare , can be avoided.

The multiple choices are why there are dozens of flavors of ice cream, choose what you can sleep best with.
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Old 02-26-2021, 08:42 AM   #16
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And that is my point, FF, rare. Adding complexity to insure against the rare is, for me, not something I choose to chase.
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"A mutually exclusive charging source for each bank?"

Two 120v chargers for power pole or noisemaker will cost little extra compared to a similar charger of 2x the amps.

The same solar group can also be split to charge with 2 controllers.

Little extra cost or complexity for basic insurance.

What has happened in the past should serve as instruction , one 1/2 size bank going dead is a PIA , but wont ruin a cruise.
Everything dead although rare , can be avoided.

The multiple choices are why there are dozens of flavors of ice cream, choose what you can sleep best with.
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Old 02-26-2021, 08:48 AM   #17
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Yes. My charger puts out 125 amps and feeds the batteries through a short-run (two feet) 4/0 cable.
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I have a big battery bank. I have 150a battery charger. I needed 0000 battery cable to prevent voltage drop. Just a little bit of voltage drop can double the time it takes to recharge a large battery bank. I spent $500 just on the battery cables between my charger and my bank.

As Flyright said, this is often overlooked.
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Old 02-26-2021, 12:25 PM   #18
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I have a 1000 amp hour LiFePO4 bank and have all of my primary charging sources pointed at that bank - alternators, battery chargers, inverters, solar, etc.

I am a big fan, and have been for years, of the DC to DC charger setup for any other banks. I have two currently on Rendezvous - one for the starting batteries for the main engines, and one for the generator start battery.

I like how bulletproof they are compared to a combiner, how you can program different charge profiles (my start/gen batteries are AGM and need a different one) and how they are one way. There's no way I can accidentally discharge either the start or generator batteries through some stupid mistake or failure in the technology.

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Old 02-26-2021, 12:48 PM   #19
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Smart ACR’s are just another name for a DC to DC charger. Not to be confused with an ACR.

ACR’s combine banks. Smart ACR’s and DC to DC chargers charge the second bank with the appropriate profile for the second bank.

Much like Steve Mitchell I have a several secondary banks, start battery, crane battery, thruster battery. These secondary banks are charged via a SmartACR or DC to DC charger. It is impractical to run 40’ cable from the house bank to the front and back of the boat. Maintaining a secondary bank in the front and one in the back using a SmartACR means I only need to run 10gauge wire.
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Old 02-27-2021, 07:29 AM   #20
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+1 for the dc to dc chargers. Sterling or victron.
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