Battery combiner, is this best?

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bob45

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Nov 14, 2023
38
islander 34-2 lake michigan
Hi all,

it’s time for me to replace my batteries on my boat. I bought the boat 2 years ago and it has the the batteries that came with it. I have noticed some intermittent shortages in some of my electronics. I figure I’ll get some fresh batteries and start there.

it’s set up with 2 deep cycle batteries connected through a battery combiner (I have a 2 battery switch as well). Is this best practice? Should I have 1 starter and one house and avoid the combiner?

also, my charger looks pretty dated. Do these go bad over time?
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dlochner

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Jan 11, 2014
12,796
Sabre 362 113 Fair Haven, NY
HThere have been lots of advances in battery technology and charging technology since your boat was built!

The charger you have should be doing time for murdering batteries. It definitely should be replaced. Again there are several options. Likewise, the battery combiner is archaic and should be replaced and there are several options.

The place to start is to consider how you intend to use the boat. Day sailing, weekending, a week cruise in the summer, extended cruising etc. And to consider where the boat is moored, at a dock with shore power or on a mooring. The answer to these questions will determine the parameters of the system upgrade. What's best, depends on how its used.

The battery charger currently installed is not very smart, it just keeps pumping current into the battery until it can't take any more. Modern chargers are 3 stage, Constant Current (Bulk), Constant Voltage (absorption), and Float. A smart charger will extend the battery's life. Victron, MasterVolt, Sterling/ProMariner all make good 3 stage chargers. Oh, and be careful when you remove the old charger, it weighs about 35 lbs. The new one will weigh about 5 lbs.

A battery combiner allows all the charging current to go to one battery. The combiner connects the two batteries when there is a charging current and disconnects when the charging current is not present. This is different from using the Both position on the battery switch because the batteries are not placed in parallel with the charging relay whereas the Both position does put the batteries in parallel. The Blue Sea ACR (Automatic Charging Relay) is a good example. There are other approaches using FETs and Battery to Battery chargers, whether those are appropriate for you intended use, depends on your intended use.

That's the broad outline to your questions answer. To dive in more deeply read the articles on the MarineHowTo.com website. There is wealth of information on that site and specific articles on the how to use the 1-2-All battery switch and on the ACR.

www.marinehowto.com

Marine How To - DIY for Boaters - Marine How To

For DIY boaters in an attempt to try and keep the sport as affordable & safe as possible. How To articles for sailboats and powerboats.
www.marinehowto.com
 
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B

bob45

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Nov 14, 2023
38
islander 34-2 lake michigan
Great info! Thanks. A bit to unpack here. I daysail 90% of the time and am at a dock with shore power 99% of the time.


I will start with new batteries (leave the set-up the same) but get a new charger asap. Is combiner fine for a while? New chargers pretty easy to install?

After that, I can dive in, read up and come up with a grander plan.
Thanks again
 
dLj

dLj

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Mar 23, 2017
4,306
Belliure 41 Back in the Chesapeake
Ok, here comes a stupid question - what does a battery combiner do? What does it give you in you battery circuit? Sorry, I'm just not familiar with these, never had one and currently don't have one....

dj
 
dLj

dLj

.
Mar 23, 2017
4,306
Belliure 41 Back in the Chesapeake
dlochner said:
Modern chargers are 3 stage, Constant Current (Bulk), Constant Voltage (absorption), and Float. A smart charger will extend the battery's life. Victron, MasterVolt, Sterling/ProMariner all make good 3 stage chargers.
Click to expand
There is also another function called equalization that a number of the modern chargers have.

Although to be honest, I've never seen a modern charger with that function that has an equalization function that I personally find adequate. However, for sure what they do in that cycle is far better than not having it.

dj
 
D

dlochner

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Jan 11, 2014
12,796
Sabre 362 113 Fair Haven, NY
dLj said:
Ok, here comes a stupid question - what does a battery combiner do? What does it give you in you battery circuit? Sorry, I'm just not familiar with these, never had one and currently don't have one....

dj
Click to expand
A combiner is now a generic term for a device that allows 2 batteries to be charged from one charging source without being in parallel. In the past they were diode based, which was a poor solution because it dropped the voltage across the combiner leading to poor charging. The most familiar one today is the ACR, Automatic Charging Relay. When there is a charging voltage present, the relay closes and allows the current to charge batteries on both sides of the relay.

ACRs and other combiners are most useful when the start/reserve battery and house battery are isolated from each other. This allows all the charging current to go to the house battery and when the relay closes (or allows current to flow through) to charge the other battery. When there is no charging voltage the batteries are isolated.

In the OPs case with a 1-2-All battery switch the switch can remain in the 1 or 2 position and both batteries will be charged with out the risk of leaving the switch in the ALL position and draining both batteries.
 
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dLj

dLj

.
Mar 23, 2017
4,306
Belliure 41 Back in the Chesapeake
dlochner said:
In the OPs case with a 1-2-All battery switch the switch can remain in the 1 or 2 position and both batteries will be charged with out the risk of leaving the switch in the ALL position and draining both batteries.
Click to expand
Thank you for the explanation. I've always had the 1-2-Both switch. The article by Mainsail on how to wire that switch correctly is superb!

For @bob45 - I'd definitely get rid of that combiner and go to a properly wired 1-2-Both switch as a first pass, along with upgrading/getting rid of that really destructive battery charger...

See how good we are at spending your money and giving you projects? Hey, but you asked!

dj
 
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bob45

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Nov 14, 2023
38
islander 34-2 lake michigan
You guys are great, thanks.
Just to make sure I’m reading right:

Lose the combiner and make sure my switch is wired properly? Would new charger then go to each battery separately?


I posted pics of my current batteries, will two more like these to the trick?
 
D

dlochner

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Jan 11, 2014
12,796
Sabre 362 113 Fair Haven, NY
bob45 said:
Lose the combiner and make sure my switch is wired properly? Would new charger then go to each battery separately?
Click to expand
Yes. If the battery charger has 2 outputs, then yes you can have each battery on a separate cable. Keeping the 2 Group 27 batteries, you will need a 20 a smart charger.

Don't waste money on a Marine Start battery. Just get a deep cycle battery, it will start your engine. There is a good article on Deep Cycle batteries on MarinehowTo.com
 
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dLj

dLj

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Mar 23, 2017
4,306
Belliure 41 Back in the Chesapeake
bob45 said:
I posted pics of my current batteries, will two more like these to the trick?
Click to expand
Your pic showed Interstate batteries, while not aimed at the marine market, I've had very good luck with that specific brand battery. There are others here that know who really makes that battery, but I've forgotten.

FLA's ( flooded lead acid) batteries for how you say you are sailing are a great option.

dj
 
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dlochner

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Jan 11, 2014
12,796
Sabre 362 113 Fair Haven, NY
The Interstate Battery in the photo is made by East Penn. Their batteries are among the better affordable batteries. Their marine line is Deka. East Penn makes batteries for a number of labels, all the same battery, just different colors with different stickers. If the manufacturer isn't on the label, you can tell by looking at the handle and cell caps. If they match the ones you have, most likely they were made by East Penn.

 
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Maine Sail

Maine Sail

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Feb 6, 1998
11,702
Canadian Sailcraft 36T Casco Bay, ME
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