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post #1 of 19 Old 04-20-2012 Thread Starter
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Two Batteries in Parallel

I am thinking about hooking up two 12 volt dual purpose batteries in parallel. That way both my alternator and battery charger charges both. And I'll have more endurance.

Any thoughts on this?
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post #2 of 19 Old 04-20-2012
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Re: Two Batteries in Parallel

Sure, good idea.

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams [added 9/21/11]

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
http://forums.catalina.sailboatowner...d.php?t=137615

Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)
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Re: Two Batteries in Parallel

I like hearing that!

Anyone ever try this? I would like to hear about some results.
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Re: Two Batteries in Parallel

Also remember to make sure that the capacity of the bank matches the output of your alternator.

Alternators are rated for peak output, but they will burn out and meltdown if they run at peak output for extended period of time. So, if you're thinking of wiring a couple of huge batteries together to have a massive bank, but have a rinky dink 30 amp alternator...you're setting yourself up for a burned out alternator and more expense down the line.

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Re: Two Batteries in Parallel

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Originally Posted by night0wl View Post
Also remember to make sure that the capacity of the bank matches the output of your alternator.

Alternators are rated for peak output, but they will burn out and meltdown if they run at peak output for extended period of time. So, if you're thinking of wiring a couple of huge batteries together to have a massive bank, but have a rinky dink 30 amp alternator...you're setting yourself up for a burned out alternator and more expense down the line.

How many amps should one dual purpose 12 volt battery pull?
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Re: Two Batteries in Parallel

Batteries come in all sizes. If you choose 2 group 31 flooded batteries they range from 95 to 125 AH each. The most they will accept in bulk charging mode is 25% of capacity so even if you have 2 of the largest in parallel they will accept only accept about 60 amps of current. If you don't draw the batteries down past 50% which is recommended for long battery life they will only need 75 AH before the charge starts to taper off due to the increasing resistance in the battery.

Now if you have agm batteries things will change due to their high acceptance.

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post #7 of 19 Old 04-21-2012
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Re: Two Batteries in Parallel

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Originally Posted by jrophoff View Post
I like hearing that!

Anyone ever try this? I would like to hear about some results.
It's very common. Most house banks are comprised of more than one 12v battery, connected in parallel. We have four.

As mentioned above, you must be careful with the type of batteries you have and the capacity of your charging system. This stuff give me a headache. It's not hard to get your head around what you should have. It's hard to figure out what you do have and whether it will be good enough for the upgrade you want to make. Do you know the amp output of your alternator? I didn't and still question it. Do you know if you have a voltage regulator, other than the alternators internal regulator and what it is set for?

You run two risks: you could burn out your alternator or you could ruin your batteries in under one season. I just went through this trying to upgrade to a different battery type.

For starters, you can only parallel identical battery types, ie flooded, gel or AGM.


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Re: Two Batteries in Parallel

And you should parallel like battery condition, same year one will be weak link otherwise. You should equalize (desulfate) at regular intervals. Getting a good 3/4 stage charger is a wise investment.

We have 6- 6 volt batteries, first put in series to make 3 12 volt batteries, then put in
Parallel. Suggest you figure what your diet, usage is before buying the batteries.

Read up on this as you can spend money uselessly or not match you system to batteries to charge.that will result in a shorter battery life and waste of money. Lots of posts on here.

Dave


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Re: Two Batteries in Parallel

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Originally Posted by chef2sail View Post
.....You should equalize (desulfate) at regular intervals.....
Careful, I don't think we know what battery type the OP has.

As you know, I thought I had AGMs until just recently. Only some of those manufacturers would recommend equalizing. As my banks were getting weaker, I nearly pressed the button several times, but didn't until I researched the brand.

Then I learn they are actually Gels and recall the times I sat at the nav station poised to equalize. Had I pressed the button, I would have fried them.


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Re: Two Batteries in Parallel

Ample Power Company Home Page tech tab Ample Power Primer

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