Battery layout on my NSC

[yhc]

Good evening,

While out on the water last weekend I have noticed the battery meter was reading as low as 10.5v after having the anchor light on overnight, etc. Since there is a generator aboard I wasn't particularly concerned. However, for a good measure, I purchased new 8D batteries yesterday and drove down to the marina. I have 2 8D batteries in the aft of engine room and 2 8D batteries in the engine room bilge. There is one additional 8D battery dedicated for the generator in the lazarette. With the exception of the latter all 4 batteries in the engine room are original batteries from 2006 (or as early as 2005) so they are due for change out.

I was expecting one set of those 2 8Ds to be house batteries and the other set to be dedicated engine w/ higher CCA. However when I opened up the battery boxes and panels I was surprised to find all those batteries interconnected. They are configured as shown on the attachment as "method 4".

Now the kicker is one set of batteries were reading 11.9v and the other set showing 13.7v. These measurements were taken while the battery charger was on w/ shore power so I understand these are not true reflection of their voltage.

My questions are:

1. Shouldn't all 4 batteries show the same voltage when they are interconnected? If so what would explain this discrepancy?

2. Should I leave them as they are configured or should I try to re-wire them so that I have 2 dedicated house and 2 dedicated engine batteries?

3. If I were to leave them as they are should I change them out w/ higher CCA batteries or house batteries?

Thanks much for your input.

BatteryBankConnections.pdf

[crowra]

yhc,

That's interesting that you have a dedicated gen starter battery but combined engine and house batteries. Personally, I would separate them for a couple of reasons. 1) So you can dedicate a starting battery and not worry about draining it in 'house' mode and 2) because starting batteries are different than deep cycle batteries. Simply put, a starting battery is designed to provide a very large amount of current for a short period of time. Whereas a deep cycle battery is designed to provide a steady amount of current for a long period of time.

Our boat has two separate dedicated engine and gen starter batteries plus a separate house bank. The house batteries consist of four 6-volt "golf cart" batteries that are cheaper AND ligther than 12-volt batteries. The two 6-volt batteries are wired in series providing a 12-volt 330 Ahr battery (x2). The two '12-volt' batteries are wired in parallel giving us a 'virtual' 12-volt 660 Ahr battery.

We bought the boat from an AOG member. Here is the link to an article he posted complete with photo. viewtopic.php?f=20&t=3146&p=18860&hilit ... ies#p18860

Please note: I learned something from the PDF you attached. I should re-wire to Method #2. Thanks!

[DougSea]

Simply put, a starting battery is designed to provide a very large amount of current for a short period of time. Whereas a deep cycle battery is designed to provide a steady amount of current for a long period of time.

There's also the issue of charging, as each type of battery takes a charge differently and the charger cannot properly adjust when they are tied together.

(That PDF smackdown of "Method 1" was a bit of a surprise, wasn't it?! The current differences per battery were way bigger than I'd ever have guessed...)

[tbnolin]

Hey there Yong,
Just posted a note under "battery chargers" thread. If I understood my mechanic correctly, all my batteries were reading around 11v . Cranked the engine and they would drop to between 3 and 4v. After spending a couple of hours going through the whole system, we came to the conclusion that my batteries had expired, no longer able to take a charge. My understanding is if 8D deep cycle batteries last 3 years, you're doing well....after that you're on borrowed time. Our boats being 2006 model, a good chance the batteries were made in 2005 or maybe even earlier, so I guess I can't complain.
I have two batteries for each engine and they are interconnected and that's the way we ended up doing with the new ones. I hope it wasn't a mistake. As far as the 8D for your genny, I wouldn't think you would need a separate battery that strong to get that going. I'll check to see the size that I have for the genny, but it doesn't look like anything special, it's just something to get it started...about the size of a car battery.
Hope all is well,
Tom

[yhc]

Thanks for the replies everyone. Just returned from a weekend trip on the water thus the late reply.

While checking the batteries I noticed one of the positive posts was slightly corroded. After cleaning the post the voltage read 12.4 v which is an improvement from the original reading of 11.9 v. The latest reading was done after the batteries were disconnected from the charger overnight. Anyhow I checked all 4 batteries w/ hydrometer and 3 out of 4 batteries had couple of cells that were "dead". Once I figure out the wiring of the system then I will be replacing them.

The following attachment is the wiring diagram for the boat. It appears there are 2 batteries connecting to starboard and port engine each. I haven't figured out DK1, DK2 and CDQ, etc that are shown on the diagram. If there are folks who are familiar w/ these please give me a shout.

Wiring diagram.pdf

Tom,

Did you end up changing yours w/ all house batteries or cranking batteries?