Battery layout

[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 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".

BatteryBankConnections.pdf

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.

[akfishonguy]

I used to manufacture batteries....my advice would be to dedicate 2 to use in house power and 2 for starting.....Depends on what size engine...engines you have.....you can also install a transfer switch if you need to "jump" your starting batteries.

[NRick]

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.

Is there an isolator between the pairs? That would be one way of having different voltages. Another is if you have a loose or badly corroded connection.

11.9v is nearly dead (assuming no load) and if you had the situtation where a bank at 11.9v where straight connected to a bank at 13.7v the more depleted bank would suck the juice out of the good bank fairly quickly.

Separating the banks is the way to go. Deep cycle batteries for the cabin and starting batteries for the engine.

[MacGyver]

[QUOTE=yhc;958453]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?


#1
Yes all batteries wire in parallel will read the same voltage; there is a 1.8V difference between the batteries. They are NOT wires in parallel OR there is a high resistance (bad connection) problem OR there is a switch that is turn off.


#2
I would not rewire until you know what is going on. It may already be wire that way. Can you get a schematic of the boat?

#3
Not having a complete schematic or knowing more information it to early to give you an answer.
Adding more or bigger batteries can cause more problems.

Side note.
Your shore power charger is only putting out 13.7v does not sound good. Yes it is charging the question how much is it putting out? Is this a GC boat?

[Alaskanmutt]

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

No, you can have batteries with different voltages.

Think of a line of linked trains. 3 big ones and one little one. The little one just basically drians power from the three. This is part of the reason they recommend replacing all batteries at the same time, chances for common voltage are better as is the service life.

[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

[MacGyver]

The DK( ) could be feed through connector or a power post connectors and the CDQ could be a DC power terminal strip. It just don’t make sense, with more information, is the builder still around, if so ask him or have someone take a look at it.

[.338WM]

Sent you a PM, yhc .