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Old 01-09-2019, 10:30 AM   #1
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Question about survey regarding batteries

The survey I got describes the batteries thus:


BATTERIES:
One (1) HD super duty 12 volt starting battery for both engines. Four(4) 12 volt house batteries. Two(2) Aux
batteries
BANKS:
Number: Two (2) banks . House and engines appeared to be paralleled



Is that normal to have one starting battery for two 3208s? What is the purpose of the aux batteries? I'm thinking one may be for the windlass, one may be for the genset. If anyone happens to know, please share.
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Old 01-09-2019, 11:41 AM   #2
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Overall not very descriptive. Wire following and maybe updating to your own preferences may be in order.


That said, I personally would want separate batteries for each engine.


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Old 01-09-2019, 11:53 AM   #3
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You are going to have to do some investigating and trace the wiring to figure it out. If the start battery and house bank are in fact wired in parallel with no relay or isolator between them, then they are really just one battery bank. The second bank could be for windlass, generator starting, electronics, bow thruster.....
A lot of people like having a separate start battery for each engine, usually with a switch between them to combine them if necessary. Some of the boats in our fleet are set up with a start bank for every two engines. Start one and the output from the alternator helps start the other one. There are options to tie in other power sources if the bank goes dead, but overall it works fine with just one bank.
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Old 01-09-2019, 12:12 PM   #4
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I'm a fan of the single starting battery.
We have one that does each engine and the generator.
Works great.
Honestly you only have to start one of the three, I see no reason to have multiple start batteries. Once you started one engine it also helps start the others, so I never understood the logic of having multiple batts for that. I'm sure somebody will jump in here.
Either way, it's definitely not something to worry about in the survey.

The wording of that description is freaking confusing. If it's paralleled with the house batteries then it's not a starting battery, unless there's a switch in there separating it... And what are the 'aux' batteries for?
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Old 01-09-2019, 02:48 PM   #5
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One start battery makes sense if the house bank could start an engine if the start battery died and there is a separate genset battery.
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Old 01-09-2019, 03:16 PM   #6
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I have 1 8D start battery for both Hino diesels. I also have a combiner switch to connect the start battery and the 8D house battery. The generator has a dedicated grp 27 start battery.
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Old 01-09-2019, 03:29 PM   #7
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Quote:
Originally Posted by psneeld View Post
One start battery makes sense if the house bank could start an engine if the start battery died and there is a separate genset battery.
Can you explain the separate genset battery?
I mean, the reason why you would need one if you have a separate starter battery.
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Old 01-09-2019, 04:13 PM   #8
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Can you explain the separate genset battery?
I mean, the reason why you would need one if you have a separate starter battery.

People usually want a separate genset start battery in case everything else goes dead. That way you can get the generator going and use the AC battery charger(s) to charge the other batteries. Kind of a worst case solution thing.
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Old 01-09-2019, 06:52 PM   #9
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Old 01-09-2019, 07:10 PM   #10
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If you don’t understand batteries and you only replace them when they won’t start your engine, then each engine should have its own battery. On the other hand if you understand batteries and do your maintenance (this would include an annual CCA test) then there would be no reason for each engine to have its own battery. Now just because I have two 8D’s in parallel to start my two CAT3208’s, doesn’t mean that it’s necessary. At some point it’s over kill. Just because you can start two CAT 3208’s with one group 31 battery, doesn’t mean it’s adequate. Some were between one group 31 battery for 2 CAT 3208’s and 2 8d’s is the sweet spot. I’ll let each one of you decide just we’re you want to error at.
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Old 01-10-2019, 06:39 AM   #11
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Thanks for the replies. I will be doing quite a lot of investigation to figure out how it's all wired.
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Old 01-10-2019, 08:03 AM   #12
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What is the charging scheme for one start battery?
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Old 01-10-2019, 08:26 AM   #13
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What is the charging scheme for one start battery?
Paralleled with the house batteries via an automatic charging relay.
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Old 01-10-2019, 08:58 AM   #14
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Originally Posted by Stripper View Post
People usually want a separate genset start battery in case everything else goes dead. That way you can get the generator going and use the AC battery charger(s) to charge the other batteries. Kind of a worst case solution thing.
...which actually happened to me. Was moving a buddy's boat from the yard back to his marina after having a bottom job done. Both engine start batteries were dead but the generator fired up. Ten minutes later, both engines started. I'm a big believer in having a separate generator start battery but one 8D should work fine for starting both engines.
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