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Discussion Starter · #1 ·
Hi All,

I want to keep this simple so as not to tax the patience of my fellow Sailnetters. I currently have (2) group 27's on board. I have a battery selector switch and an on board (West marine) battery charger. Am I correct to assume I have 2 group 27 banks (1 battery each)? When I put the selector switch to BOTH, I'm using them both as if they were (1) bank?

I was considdering adding another battery and putting the (2) existing ones together as one bank, maybe keep the other for dedicated starting? I know the options are many. I really don't want to get too complicated.

Dave
 

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If you need more power, the idea of adding another battery so you have a house bank with two 27s, and a starting battery, seems eminently sensible to me. That is what I have done.

It's considered a good idea not to combine banks with the switch set to BOTH, unless in an emergency for starting.
 

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It's a good idea.

Here's what I'd do to provide flexibility and more overall AH:

1. Leave the batteries connected as they are now, but do leave the switch in the BOTH position. Use this for your house bank.

2. Add a start battery and connect it with it's own ON-OFF switch (like a Blue Sea Systems #6006).

3. Be sure the alternator and ALL charging systems -- solar, battery charger, wind, etc. -- lead directly to the HOUSE bank.

4. Install a simple voltage-follower device like the Xantrex EchoCharge between the house bank and the new start battery. This device will keep the start battery charged automatically, with NO switching required.

5. If you ever need to start the engine and the start battery is dead, you could either: (a) move the positive battery cable from the start battery to one of the house batteries; or (b) install another simple ON-OFF switch to use as an emergency combiner switch.

Bill
 

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Hi All,

I want to keep this simple so as not to tax the patience of my fellow Sailnetters. I currently have (2) group 27's on board. I have a battery selector switch and an on board (West marine) battery charger. Am I correct to assume I have 2 group 27 banks (1 battery each)? When I put the selector switch to BOTH, I'm using them both as if they were (1) bank?

I was considdering adding another battery and putting the (2) existing ones together as one bank, maybe keep the other for dedicated starting? I know the options are many. I really don't want to get too complicated.

Dave
To DIRECTLY answer your questions; you currently have 2 banks. each bank is comprised of a single group 27 (90 AH) battery. When you put the selector to BOTH, you are combining the two banks into a single (180 AH) bank, which has a 90 usable AH capacity.

You *could* connect the two batteries together into a single bank, but if one of them has been used differently than the other, then they will have different charge "profiles." By combining the two, you will get the worst attributes of both of the batteries. It is USUALLY preferred to create a single new bank from (in this case) two new, fresh, identical batteries.

I would not do this unless I was sure that the two batteries had been treated similarly.

I am currently in the same boat as you, so to speak. I have two group 29 batteries (105 AH each). I have been careful to treat them both the same in terms of charging, and discharging. I plug in to shore power, and keep them at 100% SOC.

This year I may build a platform, and buy another battery box to store them and a third (group 24 starting) battery on. This will give me a 100 AH usable capacity, and a dedicated start battery.
 

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Discussion Starter · #7 ·
Thanks for the replies All. I have dug in and done some reading. I am going to add a third battery and it will be a starting/backup battery. The 2 existing batteries will become the "house". They're 100 amperes, so that will be a 200A house bank. My biggest question is can I connect all the negatives from seperate banks there at the batteries?

It's a start. I eventually see me with solar cells as well. At this moment in time, the wife is not ready to go big water or crusing using the hook. We're pretty much marina guests so far, (which is OK for now).
 

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Thanks for the replies All. I have dug in and done some reading. I am going to add a third battery and it will be a starting/backup battery. The 2 existing batteries will become the "house". They're 100 amperes, so that will be a 200A house bank. My biggest question is can I connect all the negatives from seperate banks there at the batteries?

It's a start. I eventually see me with solar cells as well. At this moment in time, the wife is not ready to go big water or crusing using the hook. We're pretty much marina guests so far, (which is OK for now).
Yes, as all negative conductors are grounded/bonded to the engine at a common point and are same polarity, ensure you size them correctly. If unsure hire a qualified marine electrician.
 

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Hi All,

I want to keep this simple so as not to tax the patience of my fellow Sailnetters. I currently have (2) group 27's on board. I have a battery selector switch and an on board (West marine) battery charger. Am I correct to assume I have 2 group 27 banks (1 battery each)? When I put the selector switch to BOTH, I'm using them both as if they were (1) bank?

I was considdering adding another battery and putting the (2) existing ones together as one bank, maybe keep the other for dedicated starting? I know the options are many. I really don't want to get too complicated.

Dave
Dave-
Having previously owned an Allmand 31 I recall putting (2)Groups of Group 27's ...two each for a total (4) batteries under that rear quarter berth. A tight squeeze but they all fitted.
 
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