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Daniel - Norsea 27
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Discussion Starter #1 (Edited)
I hauled my boat out for a number of reasons recently so starting a refit period. Looking at adding some battery capacity. Currently, the boat has a Group 34 for starting and a Group 31 for the house bank (Both AGM). The battery box that was present didn't allow me to just turn the battery and add another one so I want to build a new box for two Group 31 batteries. The batteries are located under each quarterberth. While thinking about the battery box, I thought of possibly adding a larger box under the other quarterberth and having 4 Group 31s and may move the starting battery elsewhere.

If I add more batteries under the port side quarterberth, I'd have to first remove and patch a thru-hull, which is planned anyway since the removal of the old head in place of an Airhead.

<a href="http://3.bp.blogspot.com/-vVHGHtkxIvM/T4TH5eNjLdI/AAAAAAAAAMY/OKV26dsKiyw/s1600/100_1840.JPG"><IMG src="http://3.bp.blogspot.com/-vVHGHtkxIvM/T4TH5eNjLdI/AAAAAAAAAMY/OKV26dsKiyw/s1600/100_1840.JPG" height="20%" width="20%" border="0"></a></IMG>
Click for larger image.

With the possible increase of battery power, and on opposite sides of the boat, I'm trying to think of likely ways to wire things together.

On the left side of the picture below, I have each battery bank hooked up to a switch where one side could be used or both. With that, the starting battery would be relocated, but still wired in. Looking to see if this could work in keeping the starting battery and house bank charged using the alternator when the engine is running. Another idea I have is to isolate the starting battery with its own charging method so the alternator only charges the house bank. If the starting battery is wired in with the rest of the system, would a switch be required or recommended to prevent it from being over charged when the alternator is charging the house bank?

On the right side of the picture, it's wired pretty much as it is now with the house bank on one side of the switch and the starting battery on the other.

<a href="http://2.bp.blogspot.com/-p_cWvVIQPvE/U9he_J9zJwI/AAAAAAAAB4E/tzXOM35YIo8/s1600/Battery+Banks.jpg"><IMG src="http://2.bp.blogspot.com/-p_cWvVIQPvE/U9he_J9zJwI/AAAAAAAAB4E/tzXOM35YIo8/s1600/Battery+Banks.jpg" height="30%" width="30%" border="0"></a></IMG>
Click for larger image.


I wanted to see what recommendations others say about these options and what considerations should be taken into account.

One consideration I already have is the likelihood of replacing the alternator. The engine is a Yanmar 2GM and I believe the alternator is original, so maybe 35Amp. (Haven't seen anything on it yet to say what its rating is) I looked into alternators and those things are pretty expensive. I'm thinking maybe a 100Amp or so would be good.

Anything else?
 

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There is no such battery as a group 34. 24 possibly?

House banks are better as one large bank, not divided in two. Batteries last longer, charging is more efficient, and wiring is simpler.

Best solution is too wire all charging sources to the house bank - the bank most in need. Charge the start battery with an Echo Charge or ACR. Wiring alternator (and other charge sources) direct to the house bank as above makes charging automatic - no input is required to get a full charge on any battery.

Have you given any thought to 6 volt golf cart batteries - the best cycling batteries available in lead acid.
 

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Daniel - Norsea 27
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Discussion Starter #3

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After a search I agree there is a size 34 battery. It is the same size as a group 24 battery - the smallest battery commonly used on a boat. It's number would suggest it is larger than a group 31 which it is not.

Good reserve/starting battery though.

An ACR automatically combines the battery banks for charging and separates them when not charging. An Echo Charge passes up to 15 amps to the auxiliary/start battery when charging but does not combine the batteries like an ACR does.

If you are going to get a battery monitor - as you should so you know the charge state of your house bank - the 2 pairs of group 31 batteries should be paralleled in one bank in addition to the reasons I posted above.
 

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im wiring my batteries like your setup in the diagram on the right except the starting battery and house bateries have their own on and off switch where its just one pole to go on and off. I have added a 40AMP/H battery charger that can charge 3 banks while on shore and then the altenator and solar while cruising or anchoridge.
 

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I hauled my boat out for a number of reasons recently so starting a refit period. Looking at adding some battery capacity. Currently, the boat has a Group 34 for starting and a Group 31 for the house bank (Both AGM). The battery box that was present didn't allow me to just turn the battery and add another one so I want to build a new box for two Group 31 batteries. The batteries are located under each quarterberth. While thinking about the battery box, I thought of possibly adding a larger box under the other quarterberth and having 4 Group 31s and may move the starting battery elsewhere.

If I add more batteries under the port side quarterberth, I'd have to first remove and patch a thru-hull, which is planned anyway since the removal of the old head in place of an Airhead.

<a href="http://3.bp.blogspot.com/-vVHGHtkxIvM/T4TH5eNjLdI/AAAAAAAAAMY/OKV26dsKiyw/s1600/100_1840.JPG"><IMG src="http://3.bp.blogspot.com/-vVHGHtkxIvM/T4TH5eNjLdI/AAAAAAAAAMY/OKV26dsKiyw/s1600/100_1840.JPG" height="20%" width="20%" border="0"></a></IMG>
Click for larger image.

With the possible increase of battery power, and on opposite sides of the boat, I'm trying to think of likely ways to wire things together.

On the left side of the picture below, I have each battery bank hooked up to a switch where one side could be used or both. With that, the starting battery would be relocated, but still wired in. Looking to see if this could work in keeping the starting battery and house bank charged using the alternator when the engine is running. Another idea I have is to isolate the starting battery with its own charging method so the alternator only charges the house bank. If the starting battery is wired in with the rest of the system, would a switch be required or recommended to prevent it from being over charged when the alternator is charging the house bank?

On the right side of the picture, it's wired pretty much as it is now with the house bank on one side of the switch and the starting battery on the other.

<a href="http://2.bp.blogspot.com/-p_cWvVIQPvE/U9he_J9zJwI/AAAAAAAAB4E/tzXOM35YIo8/s1600/Battery+Banks.jpg"><IMG src="http://2.bp.blogspot.com/-p_cWvVIQPvE/U9he_J9zJwI/AAAAAAAAB4E/tzXOM35YIo8/s1600/Battery+Banks.jpg" height="30%" width="30%" border="0"></a></IMG>
Click for larger image.


I wanted to see what recommendations others say about these options and what considerations should be taken into account.

One consideration I already have is the likelihood of replacing the alternator. The engine is a Yanmar 2GM and I believe the alternator is original, so maybe 35Amp. (Haven't seen anything on it yet to say what its rating is) I looked into alternators and those things are pretty expensive. I'm thinking maybe a 100Amp or so would be good.

Anything else?
If you can fit them, height wise, I would strongly urge 6V batteries not group 31 12V or any "marine" 12V...

That said no matter what you do if the batts are on opposite sides of the boat the best practice is positive up one side and negative off the other or positive on port negative on starboard.

They should ideally be wired as one contiguous bank not "switched" or alternated.


Just make the parallel jumpers between the two middle batteries longer and this is how you will want to wire it. It helps keep the batteries equally used and they will stay better balanced than pulling all loads off one end of the string...
 

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I'm surprised you need this much battery capacity. Are you Microwaving dinner? I also have yanmar diesels (twin engines) with the 35 amp alternator, and also thought I needed more batteries as my group 27s didn't seem to last very long. A friend recommended I test the alternator. Using the circuit in the service manual I quickly determined the alternators wee topping out at considerably less than 14 volts. I replaced them at $89.00 apiece... problem solved. Batteries were fine.

Seems the alternators never recovered from a lightning hit.

Imagine that :D
 

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Daniel - Norsea 27
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1,258 Posts
Discussion Starter #8
If you can fit them, height wise, I would strongly urge 6V batteries not group 31 12V or any "marine" 12V...

That said no matter what you do if the batts are on opposite sides of the boat the best practice is positive up one side and negative off the other or positive on port negative on starboard.

They should ideally be wired as one contiguous bank not "switched" or alternated.

Just make the parallel jumpers between the two middle batteries longer and this is how you will want to wire it. It helps keep the batteries equally used and they will stay better balanced than pulling all loads off one end of the string...
I've looked at 6V batteries but they stand a little too tall for the space. Still not sure if I would go up to 4 G31s but I guess if I did, I'd have to have a long run of wire from one side to the other.

I'm surprised you need this much battery capacity. Are you Microwaving dinner? I also have yanmar diesels (twin engines) with the 35 amp alternator, and also thought I needed more batteries as my group 27s didn't seem to last very long. A friend recommended I test the alternator. Using the circuit in the service manual I quickly determined the alternators wee topping out at considerably less than 14 volts. I replaced them at $89.00 apiece... problem solved. Batteries were fine.

Seems the alternators never recovered from a lightning hit.

Imagine that :D
I wouldn't say I NEED that much battery capacity but looking at the possibility of adding more than I have now. The biggest current draw is a ColdMachine unit for the icebox. I've been looking at increasing the alternator if I get a bigger bank. Did you stay with the 35A alternator or did you go up in size?


Thanks guys for the comments. Gives me more to think about. :)
 

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Mermaid Hunter
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Add me to the group supporting the use of a single house bank. As is to be expected by those who read Internet forums regularly Maine Sail has the relative subtlety of wiring spot on.

I'm surprised you need this much battery capacity.
I've never met anyone that decided they have too much battery capacity. I'm building a secondary battery box for the start batteries (one main engine, one generator) so I can increase my house bank capacity from 675 Ah to 900 Ah. In the case of battery capacity more IS better.
 

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Just because you have more battery capacity doesn't mean that you use more AH. It is not any tougher to put 100 AH into a 900 AH bank than a bank half the size. The larger the battery bank the higher the SOC they go down to with a given load. Because of this they will last longer. Due to Puekert there are gains in bank size beyond the 20 hour rating as well with a given load.

A 100 AH battery with a 5 amp load is 100 AH. A 200 AH bank with the same load is somewhat more than 200 AH.
 
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