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connecting fridge between 2 batteries (switchable)

Old 07-15-2013, 05:52 PM
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Default connecting fridge between 2 batteries (switchable)

My Stb side battery runs my galley fridge and after about 15 hours the battery indicator is at 50%. My port battery goes virtually unused or at least not enough to indicate less than full charge. When I get back to the slip, the port battery hardly needs a charge. Each of these batteries serve as my respective engine start batteries and the boat does not have battery switches.

I just installed a 450ah battery bank which runs my newly installed inverter and aft wet bar. I could easily move this fridge over to this bank but I would rather save the amp hours for the inverter. My start batts are 100ah group 31 start/deep cycle.

I rarely, if ever go more than two nights on the hook. So, if I could manually split the fridge load between the two group 31's I would be set. Maybe switch over at 10-12 hours which I don't mind doing. I can just pull the 12v feed to the fridge back to the battery box and install it right there if it's small enough. Since the amperage draw is pretty low (3 amps I believe), what kind of switch would you use?

Or, is there something that will run one device and draw off both batteries?

thanks,
Bob
Old 07-15-2013, 07:41 PM
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You should be running the fridge off the dedicated house bank. You should have VSR to charge the house bank from the engines. You should save the group 31 for engine start--and have a switch so you can start both engines from either battery. The group 31 would have about 120 amp hours, and in 15 hours it would have lost 60 amp hours from the fridge.

What batteries do you have in this 450 amp hour bank? What are your running off the inverter, and what is the projected amperage draw? You can discharge that 450 amp hour by 225 amp hours (This suggests that you have two group 8D or 8 Golf Cart batteries for the inverter bank. There should be enough reserve in this bank to allow the 60 amps for the fridge.
Old 07-16-2013, 04:39 AM
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Bob,

I do have factory emergency switch at the helm which connects the two start batteries. I've never needed it but have tested it and does work.

The factory setup splits the "house" loads between port/starboard and the respective engine start batts. I can't completely isolate either of these batteries without some major reworking because there is some draw on both for lights, vacuflush, etc. The port side has very little and essentially stays at full charge, starboard is the issue with the fridge. My 450ah bank is comprised of 4 Trojan 6v batteries which are dedicated to my aft fridge and inverter. All three banks get charged underway and in the slip. I changed both alternators and slightly up sized from 50 to 55 amps in the process. I've only run the inverter once, just installed last week but it made 3 cups of coffee and 2 cups of tea. We didn't run a hair dryer for about 5-7 mins which would be the other load. The meter didn't move off of full charge with this usage.

I'm never on the hook more than two consecutive nights and that's maybe 2x a season. If I can take some of the load off the Stb start battery, I'll be set. I can't imagine running both start batts to dead but I could always manually jump start one engine off the 450ah bank with cables I have onboard.

Bob

Last edited by BobCT; 07-16-2013 at 04:57 AM.
Old 07-16-2013, 10:39 PM
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What I understand:
1. You have 3 Battery banks:
100AH (G31) Stbd Battery for stbd engine,
100AH (G31) Port Battery for port engine
450AH battery bank used by inverter

2. STBD battery runs the Galley Fridge

What Battery bank powers the house electronics, lights, chartplotters?

For safety precaution, it would be wise to never touch the engine batteries for non-engine load. Since you already have a hefty 450AH Battery bank, it is advised to hook up the galley battery to this battery bank in the first place. If this 450AH bank is not enough, you might want getting a portable generator/charger or much larger battery bank.

I'm never on the hook more than two consecutive nights and that's maybe 2x a season. If I can take some of the load off the Stb start battery, I'll be set. I can't imagine running both start batts to dead but I could always manually jump start one engine off the 450ah bank with cables I have onboard.
Since you are ready to manually jump the start batteries to the 450AH bank, might as well permanently hook up the galley fridge to the 450AH bank in the first place and never worry about said fridge sucking the start batts dry.
Old 07-17-2013, 01:11 AM
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Originally Posted by BobCT View Post
The factory setup splits the "house" loads between port/starboard and the respective engine start batts. I can't completely isolate either of these batteries without some major reworking because there is some draw on both for lights, vacuflush, etc.
do it properly and move all the house loads onto the house / inverter battery. yes it's work / money. but it's correct and better. sometimes it's really easy. depends on how the boat is wired.

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