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  #31  
Old 11-20-2012
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Re: Battery Sizing - am I crazy?

I just like to understand things well. And what I'm still missing is what's the downside to the GC's? We've established they have have longer life and more energy per volume...but what are they missing? It's got to be something otherwise these companies are just selling second rate products with "Marine" stamped on them...

They must think thinner plates have some advantage in the marine environment, is it still cranking amps? Are our Duracell Deka deep cycles still designed to provide cranking amps? They are rated for that while the GC's arn't.
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Old 11-20-2012
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by hellosailor View Post
"I know Deep Cycle batteries are not supposed to be starting batteries"
A common mistake. Deep cycle batteries are supposed to be deep cycle batteries. Starting (SLI) batteries are designed to be CHEAPER batteries with a MORE LIMITED PURPOSE and one special trick, high impulse discharges.
When you build a battery with thick plates, that physically limits how much impulse power those plates can put out, probably due to internal resistanace and heating. When you build lots of thin plates, you can put out lots of impulse power--as an SLI battery does. The problem with thin plates is that traditionally that compromises their physical strength, so they tend to fall apart and break down faster IF they are allowed to weaken (by discharging) in any significant way.
So regular automotive batteries are sprinters and deep cycle batteries are marathon runners?
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Old 11-20-2012
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by asdf38 View Post
I just like to understand things well. And what I'm still missing is what's the downside to the GC's? We've established they have have longer life and more energy per volume...but what are they missing? It's got to be something otherwise these companies are just selling second rate products with "Marine" stamped on them...

They must think thinner plates have some advantage in the marine environment, is it still cranking amps? Are our Duracell Deka deep cycles still designed to provide cranking amps? They are rated for that while the GC's arn't.
The golf cart battery is the most widely sold size of battery if I recall correctly. They're mainly used in forklifts. One downside is that they require twice as many connections and thus have twice as many cables and potential rust points. More places to maintain.

For deep cycle applications they generally ARE considered better by the likes of us. On the other hand, if you want a deep cycle for your 14ft fishing boat's trawling motor, you don't want to disconnect 2 golf carts and lift the two of them out daily as you charge them. The other batteries have their uses and for many the need for deep repeated cycles isn't crucial.

As in your case, where you'd be just fine with any size deep cycle for your house battery and any size deep cycle or starter for your starting bank.

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  #34  
Old 11-21-2012
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Re: Battery Sizing - am I crazy?

Ok well the answer is in. According to Trojan, as Mainsail said, Golf Carts will have almost 50% longer life. The tradeoff, as I suspected, is in cranking amps - apparently even the deepest "Marine Deep Cycle" battery is still designed with cranking performance in mind.

This comes directly from Trojan tech support when I asked them specifically about the differences between their SCS200 G27 and T-105 Golf Cart batteries. Credit to Trojan for the quick response.

I'll say that I find it disappointing, and counter-productive that manufactuers don't make these tradeoffs clear. There are a ton of marine buyers who want nothing but the very best deep cycle performance and published literature makes no note of these lifetime tradeoffs.

Anyway, as far as I'm concerned the verdict is in. I have little doubt that a normally sized golf cart house bank can start any engine in it's sailboat. So...

Never buy a marine battery for your boat unless you absolutely can't fit a GC.
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Old 11-21-2012
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Re: Battery Sizing - am I crazy?

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Originally Posted by asdf38 View Post
.....Never buy a marine battery for your boat unless you absolutely can't fit a GC.
Not so fast. I have nearly 20 batteries aboard and can't either take them off or keep them routinely charged over the winter. AGM or Gel are the only way for me. I have the later for my house bank, as the charging system was spec'd that way from the factory. All others are AGM, expect one. The dinghy start battery is a plane old maintenance free tractor battery. It was $30 and I'm happy to buy a new one every year, compared to the cost of a marine battery. This winter is the first experiment with it. One season is breakeven, two seasons is a winner. For $30 and breakeven chances, I'm willing to go for it. Not on a house of golf carts.
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Old 11-21-2012
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Re: Battery Sizing - am I crazy?

Quote:
Originally Posted by asdf38 View Post
Ok well the answer is in. According to Trojan, as Mainsail said, Golf Carts will have almost 50% longer life. The tradeoff, as I suspected, is in cranking amps - apparently even the deepest "Marine Deep Cycle" battery is still designed with cranking performance in mind.

This comes directly from Trojan tech support when I asked them specifically about the differences between their SCS200 G27 and T-105 Golf Cart batteries. Credit to Trojan for the quick response.

I'll say that I find it disappointing, and counter-productive that manufactuers don't make these tradeoffs clear. There are a ton of marine buyers who want nothing but the very best deep cycle performance and published literature makes no note of these lifetime tradeoffs.

Anyway, as far as I'm concerned the verdict is in. I have little doubt that a normally sized golf cart house bank can start any engine in it's sailboat. So...

Never buy a marine battery for your boat unless you absolutely can't fit a GC.
And even two T105's or similar will still start a large Cummins even on the coldest winter days. We had a 300HP Cummins in our old power boat. Started easily with two T105's...


This is one of my power boat customers who is also a sailboat customer. He takes his batteries and charging as seriously on his twin screw power boat as he does on his blue water cruiser that has been across the Atlantic and beyond about 6 times..


These 4 6V batts start the twin screw/engine 6 cylinder turbo Volvo's @ 260HP each, with zero effort. The engines start in 0.75 seconds as measured with my Midtronics analyzer.... He starts both motors off the house bank down to 50% SOC easily....

So yes, as I have been saying, unless you can't fit the height of 6V batteries they are the best bang for the buck..
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Re: Battery Sizing - am I crazy?

[QUOTE=Maine Sail;951592]/QUOTE]

Wow!
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Re: Battery Sizing - am I crazy?

Most manufactures will state that some Deep cycle lead 6V batteries will get about twice the discharges etc vs and equal sized 12V be it lead, agm or gel. At the end of the day, it really depends upon how much you want to spend, what your charging system has to charge the batteries. Does not do any good to put in AGM's if you have a smallish alternator as and example, as the batteries may take more than the alternator can produce, and blow it up!

Then one has to decide how much and often the batteries will be discharged, rate etc, as to what amount of house bank one needs. I've frankly done well with a single size 24 for the last 6 yrs. But, I mostly day sail, rarely anchor out and need upwards of 24 hrs of power, for a fridge (I have an ice chest), few lights, running lights, st60+ guages, and radio. Very little power useage! Hence why I could see the OP using a single 24 as a starting battery, and another 24 in a DC style for the house battery! If he needs a bit more, there are some 24's with up to 90ahr vs the typical 70-75. Or go to a 27 with around 85-90, and some of the higher led content to 105!

This battery what you should have or not is almost as bad as anchor option!.....well, maybe on par with sailcloth options or a bit worst.......

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Old 11-22-2012
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Re: Battery Sizing - am I crazy?

My boat has two 6V GC batteries (got them at Costco; they have similar specs to T-105s, but I'm under no illusions about them being "as good as" T-105s) as the "main" bank, and a 50 ah "wheelchair" AGM battery (got it at Sears) as the "reserve" bank. Either bank will start the 2gm20, no problem. I normally use the main bank for everything (starting and deep-cycle usage), with the AGM being there "just in case" (but I never really needed it, yet). All the charging inputs (alternator, solar, shore power) are connected to the "main" bank with a battery combiner, that has a AGM setting for the reserve bank, interconnecting the two banks. The access to the batteries on my Cal 2-27 is rather insane, so muscling anything bigger than the golf cart batteries into place would have been out of the question. The capacity of the GC batteries is probably over-kill for my boat. But I NEVER have to seriously worry about draining the batteries too much.
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Re: Battery Sizing - am I crazy?

Maine Sail.

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