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  #71  
Old 11-28-2012
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Re: Battery Sizing - am I crazy?

Reasonable? Dunno about Cali but in most states the "mandatory" surrender fee is about $9 when you turn in old batteries while buying new. And then you've got to drag them in. to find someone willing to come fetch? Priceless.

Heck, Cali is the state that made lead wheel weights illegal, be glad they don't send the Lead Police out to supervise you while you've got excess batteries on your premises.
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Old 12-16-2012
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Re: Battery Sizing - am I crazy?

I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt, but at twice the cost is the benefit twice as much. At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??
I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
sailor0516
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Old 12-16-2012
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Re: Battery Sizing - am I crazy?

"but at twice the cost is the benefit twice as much"

I think you may be misunderstanding the numbers. 6 volt batteries will have twice the amp-hour capacity of a similar size and cost 12V. When you wire two 6V's in series you get a bank that's very similar to two 12V's in parallel in every aspect including size, cost and weight.

Where the advantages come in are mostly in overall lifetime. Golf Cart batteries are designed to be truly deep cycled and last longer than "Marine Deep Cycles" in this application. Marine batteries, even good "Deep Cycle" ones still compromise lifetime for cranking amps. This is unfortunate and leads to lots of confusion over this issue (see my posts earlier on in this thread..)

Just to be clear, the advantages of the GC batteries have little or nothing to do with the fact that they are 6V. It's that they are one of the easiest to find suitable true deep cycle batteries and the fact that they are 6V is a coincidence. As Mainsail has pointed out, full deep cycle 12V's exist but are harder to come by. By itself 6V is actually a small disadvantage because of the added wiring complexity. But the longer life, increased capacity, low cost and often better form factor (taller and narrower) of GC's often make up for this.
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Old 12-16-2012
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by hj0516 View Post
I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt,
Two 6V batteries in PARALLEL make a 6V bank. Two 6V batteries in SERIES makes a 12V bank..



Quote:
Originally Posted by hj0516 View Post
but at twice the cost is the benefit twice as much.
Actually $$$ to Ah's 6V batteries are less costly. The typical GC2 6V golf cart batteries will yield about 225 - 240 Ah's and almost always for less money than 12V batteries. To equal that capacity in 12V would run you more $ for two 12V batts and take up a larger footprint.

Here's an example from the same retailer:

Group 24 12V Deep Cycle 75Ah = $69.76 X 2 = 150Ah's = $139.52 = 93˘ Ah
Group 27 12V Dep Cycle 90Ah = $77.76 X 2 = 180Ah's = $155.52 = 86˘ Ah
Group 31 12V Deep Cycle 105Ah = $84.67 X 2 = 210Ah's = $169.34= 81˘ Ah
GC2 6V Deep Cycle 215Ah = $78.83 X 2 = 215Ah's = $157.66 = 73˘ Ah
EGC2 6V Deep Cycle 230Ah = $88.74 X 2 = 230Ah's / $177.48 / 77˘Ah


Quote:
Originally Posted by hj0516 View Post
At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??

No, it would not be better in terms of either cost or longevity.. One thing the above cost example leaves out is that 6V golf cart batteries will survive many, many, many more "cycles" than a deep cycle 12V battery. Trojan for example says up to 50% more cycles that their 12V brethren. So not only are they cheaper on a $$ to Ah scale but they will also outlast a 12V battery too making the $$ to Ah conversion but a small piece of the cost analysis....


Quote:
Originally Posted by hj0516 View Post
I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
sailor0516
Stick with what you have. You have a series parallel bank that will outlast just about any12V configuration that would fit in that foot print and you have it for less money..
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Last edited by Maine Sail; 12-16-2012 at 12:47 PM.
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Re: Battery Sizing - am I crazy?

The one virtue of the 12 volt battery is voltage. You are getting twice the voltage for half the weight. Two 6 volt GC's weigh about 120# for 12 volts while the 12 volt battery is 60#. If you want 24 volts two 12 volt batteries weigh 120 # but you need four GC's at 240# to get 24 volts. Usually sailors worry about weight. Unless you absolutely need the extra capacity from the GC's, 12 volt batteries have the weight advantage. Thanks. Steve S.
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Re: Battery Sizing - am I crazy?

down sizing for your needs is a great option , I would put in qtty 2 f27 deep cycle 750 cranking amps batteries maintenance free and then put on a Sunforce 5w solar panel
for your needs this would more than meet your goals
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by sstuller View Post
The one virtue of the 12 volt battery is voltage. You are getting twice the voltage for half the weight. Two 6 volt GC's weigh about 120# for 12 volts while the 12 volt battery is 60#. If you want 24 volts two 12 volt batteries weigh 120 # but you need four GC's at 240# to get 24 volts. Usually sailors worry about weight. Unless you absolutely need the extra capacity from the GC's, 12 volt batteries have the weight advantage. Thanks. Steve S.
Steve,

For sailboats there is no weight advantage when you are talking 12V batteries, unless the ONLY factor you include in the equation is the weight. You don't buy batteries by weight however, you by them by your consumption needs or Ah capacity for your planned use.

The the 120 pounds of 6V will be giving you 225 - 240 Ah's and the 60 pounds of 12V will be giving you just 105Ah's... That is less than half the capacity and roughly half the cycles. When you cut the capacity you also cycle the batteries deeper thus also shorten battery bank life.

When comparing weight it is best to compare Ah's to pounds based on price, consumption needs, cost, charging capacity and life cycles...

6V batteries are heavier because they have thicker lead plates. Because of this, they last longer. They also very often have more Ah capacity per pound than 12V making 12V batteries heavier for the same Ah capacity.. When you get to equal Ah's capcity a 12V battery the weight differences are negligible but the life span is not.

So for a 450Ah bank there may be 10 pounds difference, either way, but multiple years & cycles difference in battery bank longevity..

If you look at "foot print" a group 24 is roughly the same as a GC2 6V in the floor space it requires..

Four 6V GC2 batteries will give you 450Ah's and weigh roughly 260 pounds.

It takes SIX group 24 12V batteries to equal the Ah capacity of 4 6V batteries.

Those SIX group 24 batteries weigh 270 pounds or 10 pounds MORE for the same Ah capacity. You weigh more yet you will have a LOT shorter battery bank life with this ten pound heavier 12V bank than you would with 4 6V GC2's..

Weight to Ah's..

450 Ah's GC2 6V = 260 Pounds (4 batteries)
450 Ah's G-27 12V = 265 Pounds (5 batteries)
450 Ah's G-24 12V = 270 Pounds (6 batteries)



There are very few boats today over 30 feet that can get away with a single 60 pound/100Ah battery, (35 usable Ah's when cruising), and not be replacing it every other year or sooner. People are simply using a lot more power today than they did even 10 years ago..
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  #78  
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Re: Battery Sizing - am I crazy?

Well Steve does hava a point. If all you care about is volts and weight, you buy a #23A twelve volt alkaline remote control battery. Twelve volts, that's all that's important. Doesn't need any of that charging equipment, and weighs only about a half ounce, too. Much lighter and smaller and cheaper than those expensive lithium-whatever batteries too.

Best of all you can carry a spare one in the remote control on your key chain! About a buck and a half at most drug and hardware stores.

He's got a point, Maine.
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by hj0516 View Post
I have read that it is better to have two 6 volt batteries in parallel rather than one 12 volt, but at twice the cost is the benefit twice as much. At about the same cost you could have two 12 volt batteries and would that be better that two 6 volt??
I am talking about deep cycle for house bank needs, I have 4 golf cart batteries now and cruise every weekend and in the marina it is on charger. I also have twin solar panels and a wind charger. Plan next year to cruise and anchor out a week or two at a time.
Any suggestions on which way is better?? Also have separate starting bank. Thanks for any help.
sailor0516
2 6 volt batteries = 220 ah at 12 volts

2 12 volt group 31 batteries have 220 ah at 12 volts

2 6 volt batteries ahs the footprint basically as 1 group 31

2 6 volts = same ah for 1/2 the space
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Old 12-17-2012
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Re: Battery Sizing - am I crazy?

Most boats on the water are less than thirty feet. Relative to displacement the difference between 60# and 120# is not significant for a thirty footer. As the boat gets smaller the battery weight is still the same and their weight does make a difference. Thanks. Steve S.
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