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Old 12-16-2015, 05:30 PM   #1
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wiring (3) 6V Batteries to 12 V system

I would like to upgrade my house bank to (3) 6V batteries. I would love to do (4) batteries, but 3 is all I can fit. Can I wire 2 batteries in series and add a 3rd in parallel? I this Practical?
If this is possible, I'd really appreciate any advice on how to correctly wire this setup.
Thanks!
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Old 12-16-2015, 05:37 PM   #2
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Do two parallel (one big 6 volt) and then series that duo to the third.
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Old 12-16-2015, 05:44 PM   #3
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Nope. Won't work. Can series two and parallel to another series pair. The third is useless.

If you parallel two then series to the third, the third will not match the charge/drain rates needed for the others. Short life results.

Use two or four. Or six. Need even number.
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Old 12-16-2015, 06:00 PM   #4
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Yup, that third battery will be completely useless. A series parallel setup will always be limited by the single battery in series.

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Old 12-16-2015, 06:45 PM   #5
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I agree with the above comments. But there is one way that will work with three batteries:


Hook two 6v batteries in series and then hook a 12V battery in parallel. Not the best situation due to the mixed battery/connections situation, but in practice, ok. The problem will be finding a true deep cycle 12V battery.


It will be easier with AGMs as there is little difference between an AGM starting battery and a deep cycle one. But in that case you are probably better off just hooking three 12V Group 31s in parallel.


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Old 12-16-2015, 08:13 PM   #6
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Sounds like you're trying to fit 6V golf cart batteries in an 8D battery box. A battery bank should have same size batteries of similar age and condition. If you're trying to pull 12V out of 6V batteries, it needs to be done in pairs as some have stated above. Each pair provides 12V in series, then each pair is paralleled with another matching pair. Anything else will result in wasted capacity and/or early demise of the bank.
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Old 12-16-2015, 09:16 PM   #7
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Quote:
Originally Posted by Ski in NC View Post
Nope. Won't work. Can series two and parallel to another series pair. The third is useless.

If you parallel two then series to the third, the third will not match the charge/drain rates needed for the others. Short life results.

Use two or four. Or six. Need even number.
I stand corrected (and most certainly acknowledge Ski's expertise in the matter).
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Old 12-16-2015, 09:27 PM   #8
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Originally Posted by FlyWright View Post
Sounds like you're trying to fit 6V golf cart batteries in an 8D battery box.
I have that exact problem starting tomorrow. I think I am going to parallel two small 12V GC batteries in there. Is there a better option? Local repair guy insists he is right by saying I should NOT put deep cycles in and plop another 8D back in there. (there are two others in there too) Since I think it is important to have a proper house bank of deep cycle batts, I feel I am right. Am I? Are there any other options that I am missing?
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Old 12-16-2015, 10:58 PM   #9
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Not sure what size space you're working with but these 6-V US AGM 305 floor machine batteries are the same width as a T105 golf cart battery, 1.3" longer and 3" taller. They deliver 312AH per pair. I'm installing 8 of them in my house bank for a total of 1248 AH. They have non-AGM FLA models as well up to 340 AH per pair. No affiliation.

U.S. Battery | Leader in Deep Cycle Batteries | US AGM 305 - U.S. Battery | Leader in Deep Cycle Batteries

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Old 12-17-2015, 01:28 AM   #10
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Here was my adventure in golf cart batteries:


6VDC Golf Cart Battery Question
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Old 12-17-2015, 06:24 AM   #11
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When purchasing batts you get service life from the weight of lead.

You might find the 12v 8D (in deep cycle ) does weigh more than 2 golf carts , and would make the best choice.

Getting it down the dock, is why they make kids.
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Old 12-17-2015, 07:47 AM   #12
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Angus99, I had great service out of a set of 4 traditional flooded US Battery L16s, a bit taller than those delivering 425AH each. Look forward to seeing how your AGMs do.

Tom B "throw in" where? House bank, starter bank? If the latter, I'd stick with an 8D; a good one will have about the same or better AH as the GCs and better cranking characteristics and fewer connections, which is likely why the mechanic recommends that route.
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Old 12-17-2015, 07:51 AM   #13
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Mike, you might examine whether non-traditional mounting orientation is possible.


AGMs, for instance, can be mounted sideways... so maybe there's a way to stuff 4 6Vs in there if you experiment with that.


Or... if you're mostly constrained by the horizontal size of an existing battery box (for an 8D, for example)... maybe there's just slightly enough room around that box so that a new and slightly larger box could handle 4 6Vs.


And then as Angus also mentioned, there are about 3 different sizes of 6V batteries... The "standard" (like a Trojan T-105) usually gives about 220 Ah/pair, and the two larger sizes go up from there. Of the two larger sizes, one is same footprint but taller, the other (L16) is physically larger all over. (All this from memory, check the Lifeline and Trojan sites for typical specs.)


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Old 12-17-2015, 07:59 AM   #14
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Quote:
Originally Posted by Tom.B View Post

I have that exact problem starting tomorrow. I think I am going to parallel two small 12V GC batteries in there. Is there a better option?
Two 6v in series is preferable to two 12v in parallel.
Benefit is in ability to charge fully \ consistently.
Should be lots of articles out there w a Google search
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Old 12-17-2015, 08:29 AM   #15
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Hook two 6v batteries in series and then hook a 12V battery in parallel. Not the best situation due to the mixed battery/connections situation, but in practice, ok.
That will work.
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Old 12-17-2015, 09:12 AM   #16
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Make sure you get real deep cycle 8D battery's, it seems only two company's make real ones, the rest are just labeled as such but are not.

What Is A "Deep Cycle" Battery? Photo Gallery by Compass Marine How To at pbase.com


Quote:
Originally Posted by FF View Post
When purchasing batts you get service life from the weight of lead.

You might find the 12v 8D (in deep cycle ) does weigh more than 2 golf carts , and would make the best choice.

Getting it down the dock, is why they make kids.
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Old 12-17-2015, 10:50 AM   #17
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"Not sure what size space you're working with but these 6-V US AGM 305 floor machine batteries are the same width as a T105 golf cart battery, 1.3" longer and 3" taller. They deliver 312AH per pair. I'm installing 8 of them in my house bank for a total of 1248 AH. They have non-AGM FLA models as well up to 340 AH per pair. No affiliation."

Angus

Good addition for those wanting AGMs.

When not at the dock how will the new AGM batteries get recharged - size and model of alternators or genset via inverter or both or ??

Also where in your ER will these be mounted?
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Old 12-17-2015, 10:59 AM   #18
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Of the two larger sizes, one is same footprint but taller, the other (L16) is physically larger all over.
The largest Trojan L16 is an 1 1/4" longer than their GC2, 1/8" narrower and almost 6" taller. The 305 are the same footprint as an L16, but shorter. Since height wasn't an issue for my inverter bank, I really liked the L16 format. I got a nice purpose built box that holds 4 from Dyno Battery in Seattle, via Fishery Supply.
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Old 12-17-2015, 12:47 PM   #19
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I bought my "wet" (lead acid) 6Vdc deep cycle batteries at Costco. They are just as good as the Trojans but for less cost. I paid $83 each and I have 8. AGMs are much more $$$ and really don't last any longer than the lead acid batteries, so long as you maintain them on a regular basis.
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Old 12-17-2015, 01:18 PM   #20
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I bought my "wet" (lead acid) 6Vdc deep cycle batteries at Costco. They are just as good as the Trojans but for less cost. I paid $83 each and I have 8. AGMs are much more $$$ and really don't last any longer than the lead acid batteries, so long as you maintain them on a regular basis.
In my experience, the Costco GC2 batteries are nowhere near as robust as the Trojans. The Trojans will take abuse that has the Costco (which I believe are Johnson Control) batteries crying uncle. Just look at the weight difference. Lead is everything.

That being said, I replaced the Trojans that came on my sailboat with Costco batteries this time. While the Trojans are undeniably better, the difference (in my probably deficient math) doesn't justify the price premium.

Where the difference really manifests is out on the hook, where it isn't (wasn't) practical to fully recharge. Most cruisers were running between 50%-85% SOC on a daily cycle. Now, however, solar panels have come down in price and up in efficiency enough that most modern cruising sailboats are able to fully charge daily. That's significantly less wear and tear on the batteries, so it isn't as vital to have the thickest plates available.

I could buy the Costco batteries and more solar for the same dollars as the Trojans, and use less charging fuel. Seemed like a pretty easy decision.
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